# Wiring cabin lights in Serial



## maccauley123 (Sep 2, 2004)

I am starting a project to rewire my boat. I understand the ideal is to wire everything in parallel. Is there a reason I should not wire my cabin lights in parallel?

I would have two runs down each side of the boat. I would use wire for each rated for the max amp draw for all lights at the full distance.

Other components like VHF and GPS would all be wired in parallel with their own fuses etc. through a fuse block.

Is there any reason I should not do the lights in parallel? It just seems to make more sense rather than having bundles of 3-4 duplex wires starting out from the beginning on each side.

Thanks.


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## sailingdog (Mar 19, 2006)

Maccauley-

Unless you're planning on wiring a separate circuit for each and every light, you have to run them in parallel. If you run them in series, you couldn't turn on one fixture without having them all on, and the voltage requirements would be added, so five fixtures would require 60 VDC, rather than the 12 VDC you're supplying and five times the current.

It really depends on how much control over the lighting you want, and whether you want to be able to add to the system down the road or not. By ganging all the lights in to a single parallel circuit now, you make it much less likely that you'll be able to tap in to a light fixture for power at the different locations on the boat later, since you'll run a risk of overloading the circuit. If you ran separate wires for each light fixture, then you can always tap into one in the future for small accessories, like cabin fans and such.

Personally, the way I would probably wire the boat, if I were doing it, is to wire the light fixtures independently, and then run the wire back to the electrical panel, but put them into a fused switch block, like the one shown below, and then have the switch block connected to the circuit breaker on the panel. This is especially true if I were going with LED-based lighting. Then I would match the individual switch fuses to that of the load that circuit would generally use. This way, you can also upgrade the fusing on the circuit or split the circuits to separate breakers in the future relatively easily. Having multiple small loads on a single large breaker can be somewhat dangerous from a safety standpoint.


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## TSOJOURNER (Dec 16, 1999)

Just make sure the lead wires to the individual fixtures are rated for the max current from the breaker or fuse. Use terminal blocks to branch off of (not those silly three way butt connectors). A port & stbd DC bus reminds me of how a submarine is setup. There shouldn't be anything wrong with little things like lights (esp if you use LED).. just don't start hooking up pumps, fans, DC outlets and stuff.. those sort of things need their own leads from the panel. Both side should have their own breaker/fuse.


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## xtatico1404 (Jan 20, 2008)

mccauley, the reason behind wiring in parallel is that you will have the same voltage across all fixtures. If you were to wire in series, the first fixture will have the proper voltage, say 12V, then the voltage will start dropping with each additional fixture on the circuit. In other words, the 1st fixture will have 12V, the second might have 11V, then the next one 10V, and so on. This means that your fixtures will be dimmer that the previous one on the circuit, with the last one on the circuit being the dimmest.

Sailingdog comment is based on wanting 12V at the very last fixture, so you would have to raise the voltage at the begining and have some blindingly bright & hot lamps  . As he said, this will also consume more amps.

When wiring in parallel, you take the positive wire and connect it to the positive terminals of ALL fixtures on the circuit. The you take the negative wire and connect it to the negative terminals of ALL fixtures. In the end, you will have one positive and one negative wire going to your fuse, for each circuit.



This would be a series circuit, and like I said, voltage would go down from 12V at the first fixture, and go down with each additional fixture.


Also, in series, depending on the fixture itself, if you turn off a fixture (you are opening the circuit), the rest of the fixtures on the circuit will go off. Sort of like the older Christmas lights, that once one goes bad, the rest also turn off. However, there are ways around that with fixtures designed specifically for series connection.

I agree with sailboy, I would go with one stardboard and one port circuit


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## tomaz_423 (Feb 5, 2006)

xtatico1404 !
Not quite.
If you wire in series as you described then the first light will not have 12V. It will only have 6V if both ligths are the same. The second will also have 6V.
So it will not work at all unless you use 6V bulbs.


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## maccauley123 (Sep 2, 2004)

SD, to control each of the lights I have fixtures that each have a switch. The switch on the main panel would be used to energize the cabin light circuit and I can then turn each one on/off at the fixture.

Forgive my ignorance but why does it work for my house to be wired in series?. My living room for example, all lights and fixtures, are on a single circuit, wired back to a single switch on the main breaker panel. That circuit is a single wire run first to one outlet, then to another, and so on terminating on one of those. The single breaker switch energizes that whole circuilt and I turn on those I want. I would think for the boat it should work to do it the same way.

My cabin lights are all 10 watts which I think draws about an amp. If I wire the port circuit assuming 5 amps of power draw for 5 lights shouldn't I have enough for each one to work?


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## xtatico1404 (Jan 20, 2008)

tomaz_423 said:


> xtatico1404 !
> Not quite.
> If you wire in series as you described then the first light will not have 12V. It will only have 6V if both ligths are the same. The second will also have 6V.
> So it will not work at all unless you use 6V bulbs.


Tomaz, you are right, there will be 12V from the begining to the end of the circuit, so with two fixtures of the same wattage, each will have 6V, and if you add more fixtures, the votlage will keep going down. Thanks for the correction, for some stupid reason I was not assuming the same resistance per fixture


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## sailingdog (Mar 19, 2006)

If your house is wired in series, you're in deep ****... the electrical system in a house is wired in parallel... never in series, so I hope you didn't do any of the wiring if you can't tell the difference.

Yes, if each fixture draws an amp, and you have the wiring and breaker heavy enough to support the load, you should be fine. BTW, if the light fixtures draw 1 amp each, and you have five of them, you don't want to use a 5 amp breaker, but something like a 7.5 amp breaker. This is because most fuses and breakers are designed to operate at about 80% of their rated capacity full-time. In other words, you don't want to run a five amp load on a five amp breaker... it isn't a good idea.

The main reason for the switch panel, in my case, is that some of the light fixtures I have are custom made by a friend of mine and didn't include light switches on them... but they're far too useful to not have aboard. 


maccauley123 said:


> SD, to control each of the lights I have fixtures that each have a switch. The switch on the main panel would be used to energize the cabin light circuit and I can then turn each one on/off at the fixture.
> 
> Forgive my ignorance but why does it work for my house to be wired in series?. My living room for example, all lights and fixtures, are on a single circuit, wired back to a single switch on the main breaker panel. That circuit is a single wire run first to one outlet, then to another, and so on terminating on one of those. The single breaker switch energizes that whole circuilt and I turn on those I want. I would think for the boat it should work to do it the same way.
> 
> My cabin lights are all 10 watts which I think draws about an amp. If I wire the port circuit assuming 5 amps of power draw for 5 lights shouldn't I have enough for each one to work?


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## xtatico1404 (Jan 20, 2008)

maccauley123 said:


> Forgive my ignorance but why does it work for my house to be wired in series?. My living room for example, all lights and fixtures, are on a single circuit, wired back to a single switch on the main breaker panel. That circuit is a single wire run first to one outlet, then to another, and so on terminating on one of those. The single breaker switch energizes that whole circuilt and I turn on those I want. I would think for the boat it should work to do it the same way.


macauley, that is a common misconception, but your whole house is wired in parallel. Hopefully this will clear things up

As I said, the hot wire from your panel goes to the positive terminal of ALL fixtures in the circuit, and the negative wire goes to the negative of all fixtures and you only have one positive and one negative going back to your panel or fuse.

This is the only diagram that I found and it shows just two "fixtures" on the circuit. *If you were to put 5 in the same manner, you would still only have one positive and one negative going back to the panel (battery).* That is the reason why a lot of people tend to think that the house is wired in series, rather than in parallel, but the truth is that all fixtures share the same positive and the same negative wire.


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## xtatico1404 (Jan 20, 2008)

sailingdog said:


> so I hope you didn't do any of the wiring if you can't tell the difference.


maccauley, take that recommendation seriously. Not trying to put you down or anything, but even though we are probably talking 12V, electricity is serious business and without the proper knowledge, you can get hurt, damage a lot of equipment, etc. Again, based on the conversation so far, hire an electrician....just my 2 cents.


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## sailingdog (Mar 19, 2006)

Actually, in any circuit, series or parallel.. you've only got one hot and ground leading back to the panel. In the case of 120 VAC, you've got a hot, ground and neutral.


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## maccauley123 (Sep 2, 2004)

So, if I:
1. Run a single wire, rated for the full amps expected, from a single cabin lights switch to a 5 gang fuse block.
2. From one of those set of posts run a single duplex wire to the first fixture both pos and neg. 
3. From this same fixture run another wire to the next fixture and so on. This would essentially be a 3 wire splice, right?
4. Keep doing this until I reach the end of the port circuit.
5. Repeat for starboard circuit.


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## duffer1960 (Aug 11, 2000)

You are using the term series and parallel incorrectly. Reading your post, it sounds like you want to run one positive wire, and one negative wire through your boat for the lighting, and then connecting each light between the positive and negative wire. Yes, you could then say the lights are in "Series" the way they are physically located in the boat, from front to back, but they are actually electrically connected in parallel. This is how boats are already wired. I have one switch on my panel for the cabin lights. I turn on that switch and there is power delivered to each light fixture. Each fixture then has it's own switch. All of these lights are in parallel on the electrical circuit. There isn't one seperate pair of wires running to each light, that would be a boat-load (sorry for the pun, I couldn't resist) of wires! Your house is the same way, the lights may be considered as physically located in series throughout the house, put they are electrically connected to the wire in parallel, each light going from the hot wire to the ground.


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## sailingdog (Mar 19, 2006)

Here... this should make things a bit clearer:

Both of these circuits are equivalent, but the lower one represents using a bus bar, represented by the heavier lines, and the red represents the positive wire and the yellow the ground...as per current ABYC IIRC.  Black is no longer recommended for ground since the hot wire of an 110 VAC circuit is generally black, and mistaking the two could be very bad for you.


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## duffer1960 (Aug 11, 2000)

Sailingdog, great diagram. It shows how the circuits are identical, but look different. Maccauley123, imagine the resistor symbols as light bulbs, and you have your circuit.


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## sailingdog (Mar 19, 2006)

Duffer-

It really depends on how the boat is wired... you can have the boat wired in series or parallel and have a single set of wires going to each fixture or in the case of a buss bar setup, a set of wires for each fixture. The top part of my crude drawing shows five lights in parallel using a single duplex wire... the bottom shows five sets of lights, *also in parallel*, but using five separate duplex wires.

The switch icon I'm using is for the circuit breaker for his "cabin lights' circuit... and doesn't indicate whether the lights are individually switched or not...

BTW, thanks.. it was a rough diagram I just did just now. 



duffer1960 said:


> You are using the term series and parallel incorrectly. Reading your post, it sounds like you want to run one positive wire, and one negative wire through your boat for the lighting, and then connecting each light between the positive and negative wire. Yes, you could then say the lights are in "Series" the way they are physically located in the boat, from front to back, but they are actually electrically connected in parallel. This is how boats are already wired. I have one switch on my panel for the cabin lights. I turn on that switch and there is power delivered to each light fixture. Each fixture then has it's own switch. All of these lights are in parallel on the electrical circuit. There isn't one seperate pair of wires running to each light, that would be a boat-load (sorry for the pun, I couldn't resist) of wires! Your house is the same way, the lights may be considered as physically located in series throughout the house, put they are electrically connected to the wire in parallel, each light going from the hot wire to the ground.


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## maccauley123 (Sep 2, 2004)

That was the way initially I thought to wire it. I then started reading and must have misunderstood, thinking that was serial. Trying to do it right I planned on using bus bars with a separate wire going to each light. That would be a boat load of wire which prompted my question, seemed like overkill.

Looks like I had the right idea to begin with. All other gear like VHF, GPS, Radio etc will be wired to separate circuits.


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## duffer1960 (Aug 11, 2000)

Good point you made about not showing the switches for each individual light. Therefore, maccauley123, imagine each resistor symbol as the whole light fixture, bulb and switch included. The switch shown in the diagram is then your main circuitbreaker.

Sailingdog, I didn't think lights would be wired in series, there would be too much of a voltage drop across each light, and they would be too dim; but I guess there may be an application for that. Also, if there was a switch in any fixture in the series application, opening that switch would shut off every light in the circuit.


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## maccauley123 (Sep 2, 2004)

Duffer and Sailingdog, thank you very much for your help, greatly helped my understanding of this.


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## sailingdog (Mar 19, 2006)

Duffer-

I was specifically responding to when you said


> There isn't one seperate pair of wires running to each light, that would be a boat-load (sorry for the pun, I couldn't resist) of wires!


 in a previous post. If you used a buss bar, fuse box, or switch panel setup, like I did, you would have separate pairs running to each light.



duffer1960 said:


> Sailingdog, I didn't think lights would be wired in series, there would be too much of a voltage drop across each light, and they would be too dim; but I guess there may be an application for that. Also, if there was a switch in any fixture in the series application, opening that switch would shut off every light in the circuit.


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## Omatako (Sep 14, 2003)

maccauley123 said:


> SD, to control each of the lights I have fixtures that each have a switch. The switch on the main panel would be used to energize the cabin light circuit and I can then turn each one on/off at the fixture


Notwithstanding all of the danger warnings that have gone before, look again at the series circuit shown above. The electricity in a series circuit has to be able to pass through one appliance to get to the next one. If your lights each have a switch on them and you switch any one of them off, you switch the whole circuit off.

To put it in more understandable terms - imagine a hose pipe with ten ball valves along it. Turn any one of the valves off and visualise how much water will come out of the end of the hose.

(I think I got that right?? )

Andre


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## Classic30 (Aug 29, 2007)

Omatako said:


> Notwithstanding all of the danger warnings that have gone before, look again at the series circuit shown above. The electricity in a series circuit has to be able to pass through one appliance to get to the next one. If your lights each have a switch on them and you switch any one of them off, you switch the whole circuit off.
> 
> To put it in more understandable terms - imagine a hose pipe with ten ball valves along it. Turn any one of the valves off and visualise how much water will come out of the end of the hose.
> 
> ...


Andre, in this case, I don't think you did..  

Cabin lights typically have a switch on them which is wired *internally* as part of the fitting. Connections are made to terminals **before** the internal switch.

If maccauley123 wires them up the way he said he was going to, then he will be able to turn each one off individually or turn them all off together at the main panel.


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## sailingdog (Mar 19, 2006)

Actually, you've missed the point... *Andre is talking about what happens if you have a set of lights hooked up in SERIES*, and you turn one of them off... they all go dark. 


Hartley18 said:


> Andre, in this case, I don't think you did..
> 
> Cabin lights typically have a switch on them which is wired *internally* as part of the fitting. Connections are made to terminals **before** the internal switch.
> 
> If maccauley123 wires them up the way he said he was going to, then he will be able to turn each one off individually or turn them all off together at the main panel.


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## Classic30 (Aug 29, 2007)

Wow, you've got me confused now!!.. and I actually *read* this thread (now, now, don't act so stunned!) and mostly agree with what you and Duffer have posted. 

..unfortunately, your circuit (as good as it is) doesn't show the fixture light switches.


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## artbyjody (Jan 4, 2008)

Hartley18 said:


> Wow, you've got me confused now!!.. and I actually *read* this thread (now, now, don't act so stunned!) and mostly agree with what you and Duffer have posted.
> 
> ..unfortunately, your circuit (as good as it is) doesn't show the fixture light switches.


At least the thread is not how to run composite LPG tanks together and what kind of connectors to use (thread coming up shortly as I discovered that Britain, US, and Norway all use different connections....) Talk about standards mismatch (and feel the pain for cruisers that go somewhere)...

None the less back on topic... Original poster you should by all means avoid doing anything in series for the before stated reasons... a DC circuit breaker providing the input for the parallel connections to each of the lights will do fine as it is a single source to cut them off and turn whatever ones on - that were left on... It really is not that confusing ...But if it is hire someone to come out for an hour to explain and walk you through- will be money well spent... I do that all the time on systems I am not totally confident on and most good consultants will gladly share knowledge plus their hourly rate and tell more sharing a liquid beverage of some said alcohol content...

This thread I agree has made wiring lights more complicated than need be... but then I am still trying to figure out the gizmodo that another thread posted and have not yet won the 1858 Scotch Whisky Label Scotto de Bellegario so there ya go....

It is a DIY job..here is yet another obscure link on wiring: http://www.screamandfly.com/home/hull_tech/wiring_6.6.2004/wiring_1.htm


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## sailingdog (Mar 19, 2006)

The reason I didn't show the individual fixture light switches is because they are integral to the light fixture, and not wired separately... if you've bought a marine light fixture and the switch wasn't built into the fixture, you've done something very strange.  When you're wiring up a marine light fixture, you're only attaching wires to the fixture... so I showed just the fixture as a unit. Besides, overly complicating a drawing when you're trying to explain a very basic electrical principle is a bad idea. Sorry to confuse you with all the three-syllable words...   



Hartley18 said:


> Wow, you've got me confused now!!.. and I actually *read* this thread (now, now, don't act so stunned!) and mostly agree with what you and Duffer have posted.
> 
> ..unfortunately, your circuit (as good as it is) doesn't show the fixture light switches.


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## mjrogers (Oct 31, 2007)

I've seen a couple of references to breaker / fuse size in this thread which concern me. The reality is that the breaker size is determined by the wire size. Too big a breaker and the wire becomes the weak link in the system and will burn in an overload situation. The breaker size (ampeage) is determined by the wire size (gauge) which is determined by the sum of the load and a safety factor (amps). Failure to do this properly equals fire.

The voltage isn't as much of an issue to safety, amperage is. Wattage = volts X amps, so if the voltage is less for a given wattage, the amps will increase accordingly. In the case of 12 volts vs 120 volts the amperage with be 10 times as much for a given wattage.

Than being said, with all due respect to all concerned, I've seen references ranging from correct to frightening in this thread. If someone doesn't know what they are doing they could wind up at the minimum doing damage, if not killing someone.

If you don't know what you are doing *HIRE AN ELECTRICIAN*.


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## xtatico1404 (Jan 20, 2008)

mjrogers said:


> The reality is that the breaker size is determined by the wire size. Too big a breaker and the wire becomes the weak link in the system and will burn in an overload situation. The breaker size (ampeage) is determined by the wire size (gauge) which is determined by the sum of the load and a safety factor (amps). Failure to do this properly equals fire.


mj, you are correct that wire is sized depending on the load and a safety factor. However, the breaker/fuse is sized either to the wire or to the load, depending on the location on the electrical system. A very simple system will have a 12V battery, a DC Main Panel and branch circuits.

The 12V battery has a fuse protecting it, and that one is sized to the battery wire. The Main Breaker of the DC Panel is sized to the total load on the panel (sum of all circuit currents). However, on the individual branch circuits is where things change.

One of the branch circuits has a Rule 360 bilge pump, which draws 2.1 amps and will probably be wired with a #18 gauge (not taking into account voltage drop, wire length, bundling or any other de-rating issue). Outside of engine space, a #18 will give you 20A according to industry tables. The fuse or the breaker is a 2.5 Amp. The reason behind it being fused to the load on the branch circuit is that if you have a short circuit of say 18 Amps, and your breaker/fuse was 20Amp, the breaker will not protect the load. However, if you fuse to the load, with a 2.5Amp fuse, you will be protecting BOTH the load and the wire.

So, in branch circuits, you size the fuse/breaker to the load.


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## sailingdog (Mar 19, 2006)

This is only true if you've wired the circuit with wire of a heavier gauge than necessary for the load and run length. Generally, I prefer to oversize the wiring on my boat by a bit...going up a size in wire gauge, since oversized wiring is generally not the problem undersized wiring is, and it reduces the voltage drop at the terminal end as a bonus.



xtatico1404 said:


> One of the branch circuits has a Rule 360 bilge pump, which draws 2.1 amps and will probably be wired with a #18 gauge (not taking into account voltage drop, wire length, bundling or any other de-rating issue). Outside of engine space, a #18 will give you 20A according to industry tables. The fuse or the breaker is a 2.5 Amp. The reason behind it being fused to the load on the branch circuit is that if you have a short circuit of say 18 Amps, and your breaker/fuse was 20Amp, the breaker will not protect the load. However, if you fuse to the load, with a 2.5Amp fuse, you will be protecting BOTH the load and the wire.
> 
> So, in branch circuits, you size the fuse/breaker to the load.


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## duffer1960 (Aug 11, 2000)

Sailingdog,
I made the series comment again because you hade posted:

"It really depends on how the boat is wired... you can have the boat wired in series or parallel...." 

and I was looking for some clarification on the series comment you made.


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## sailingdog (Mar 19, 2006)

Duffer-

I was just trying to clarify that having a single set of wires going to the lights doesn't necessarily indicate whether the lights are in parallel or series... that it could be either... you actually have to look at the wiring to see whether they're hooked up in parallel, which is the correct way, or series, which is usually incorrect. Mind you, there are probably some strange little exceptions to this, but they're exactly that...strange little exceptions.

BTW, I never said it made sense to wire the boat with the lighting fixtures in series... which is a bad idea, just that the boat could be wired in either series or parallel...and only looking at the way the wiring is setup will tell you which it is. The number of wires running to the fixtures tells you nothing.


duffer1960 said:


> Sailingdog,
> I made the series comment again because you hade posted:
> 
> "It really depends on how the boat is wired... you can have the boat wired in series or parallel...."
> ...


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## duffer1960 (Aug 11, 2000)

Now your comment makes sense. Thanks.


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## xtatico1404 (Jan 20, 2008)

sailingdog said:


> This is only true if you've wired the circuit with wire of a heavier gauge than necessary for the load and run length. Generally, I prefer to oversize the wiring on my boat by a bit...going up a size in wire gauge, since oversized wiring is generally not the problem undersized wiring is, and it reduces the voltage drop at the terminal end as a bonus.


SD, this is where real "know how" is important on electrical systems and unfortunately where people make mistakes. Please *don't* take that as me saying that your statement is incorrect. BTW, I totally agree with you on oversizing & the 80% factor.

People need to properly fuse and protect equipment. Saying that fusing is done accroding to wire size, is incorrect. Fusing depends on the location as well as the situation. A circuit with a single load might be fused differently than a circuit with multiple loads. Further more, circuits with electric motors on them are fused completely different. I always recommend, when installing a single load on a circuit, *read the manufacturer's recommendation* regarding fusing. It is much better to take the time to get really informed or pay some one to do the job, since electricity is serious business and an improper installation can lead to problems, including fire.


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## svbeatrix (Aug 26, 2007)

Interesting thread. I believe the purpose of a breaker is to protect the wire, not the load. Individual fuses, or sub-panels, can protect the device. There are a lot of nice ATC (automotive type) fuse blocks available and they come in sizes from 1A to 30A and are available worldwide. I have very few of the old glass fuses on my boat.


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## mjrogers (Oct 31, 2007)

Xtatico, You are correct. But saying that the breaker is sized in consideration of the load only is also an incomplete statement. If the breaker amperage exceeds the current carrying capacity of the wire the wire could overheat and burn. So, I will still modify my statement.

As we know all electrical devices run on magic smoke. If the magic smoke escapes bad things happen. Unless someone is able to adhere to the magic smoke containment codes, ABYC electrical wiring standards in this instance, magic smoke could escape and rain down bad Juju. Therefore, *HIRE AN ELECTRICIAN.*


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## xtatico1404 (Jan 20, 2008)

svbeatrix, yes the primary function of a fuse/breaker is to protect the wires, but it also offers some protection to the device that is connected to it. However, as you correctly stated, the main function is to protect the wire.

mjrogers, you got it. There is no single rule for fuse selection/application. That's why I said that selection depends on the wire it protects, the location on the system as well as the connected loads, hence the need to have the proper knoledge. As you said, bad Juju can happen.


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## sailingdog (Mar 19, 2006)

No, in a house that might be the case... on a a boat, where there are often no switches for a circuit, other than the breaker, the breaker really has to be designed to protect both the wire and the load. That isn't always true, since I do have a few fused switch panels on my boat, to separate out the individual lighting fixtures from a single circuit breaker, but this is not generally the case on a boat.



svbeatrix said:


> Interesting thread. I believe the purpose of a breaker is to protect the wire, not the load. Individual fuses, or sub-panels, can protect the device. There are a lot of nice ATC (automotive type) fuse blocks available and they come in sizes from 1A to 30A and are available worldwide. I have very few of the old glass fuses on my boat.


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## artbyjody (Jan 4, 2008)

Oversizing wire however actually generates more load resistance to begin with and should not be overly done or practiced as you decrease the overall cpacity of your storage system...which is the making the batteries work harder and deplete faster...
Oversizing you have to consider also distance and gauge ensure sure you do not see more than a 3% drop in voltage over the run... (if you can make sense of it - the charts http://www.powerstream.com/Wire_Size.htm)

A checklist however somewhat related:

http://www.islandnet.com/robb/marine.html#WiresCables (good site in general)

Not that it is an evil practice -however....really should be avoided...

VD= 2*K*I*L/ CSA

WHERE:

VD= VOLTAGE DROP
I= CURRENT
L= DISTANCE OF THE LOAD FROM THE OUTLET (IN FT)
K= 12 FOR COPPER AND 19 ALUMINUM (FOR MAXIMUM TEMP OF 75 DC)
CSA= CONDUCTOR CROSS SECTIONAL AREA IN CIRCULAR MILS.


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## sailingdog (Mar 19, 2006)

Jody-

I'm not talking about going with 0 AWG wire for everything...just using 12 AWG instead of 14 AWG and such...


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## artbyjody (Jan 4, 2008)

sailingdog said:


> Jody-
> 
> I'm not talking about going with 0 AWG wire for everything...just using 12 AWG instead of 14 AWG and such...


Yeah but we have to be careful around here after all, Cam supports using SPAM instead of proper materials for patching things


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## TSOJOURNER (Dec 16, 1999)

sailingdog said:


> No, in a house that might be the case... on a a boat, where there are often no switches for a circuit, other than the breaker, the breaker really has to be designed to protect both the wire and the load. That isn't always true, since I do have a few fused switch panels on my boat, to separate out the individual lighting fixtures from a single circuit breaker, but this is not generally the case on a boat.


Yeah.. maybe for lights and pumps but anyone trusting a generically sized (5, 10 15 etc) mechanical breakers for radios, chart plotters, radar, GPS etc is asking for it.. these devices need fuses. I never understood those HUGE breaker panels with an _expensive _breaker for EVERYTHING.. No shame in using a 15 amp breaker for "electronics"


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## artbyjody (Jan 4, 2008)

sailboy21 said:


> Yeah.. maybe for lights and pumps but anyone trusting a generically sized (5, 10 15 etc) mechanical breakers for radios, chart plotters, radar, GPS etc is asking for it.. these devices need fuses. I never understood those HUGE breaker panels with an _expensive _breaker for EVERYTHING.. No shame in using a 15 amp breaker for "electronics"


I agree - they should be judicially broken up and I actually prefer having a backup to a backup...there is nothing wrong in my book having inline fuses close to the source that further protect.. odds are the main breaker will go - but in the rare case - nice knowing you are providing that additional eh... birth control measure in case the main breaks...


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## Classic30 (Aug 29, 2007)

artbyjody said:


> Oversizing wire however actually generates more load resistance to begin with and should not be overly done or practiced as you decrease the overall cpacity of your storage system...which is the making the batteries work harder and deplete faster...


For a 12VDC power system, Jody, that statement is complete hogwash!! 

You can oversize the wire to blazes and the only thing it will hurt is your wallet (what, with the price of copper these days) - and increase the size of any potential fault current, meaning a bigger bang if something shorts out. Heck, there's nothing stopping you wiring your entire boat in 1" copper bus-bar should you ever feel so inclined. Will it work better than a correctly-sized cable? No. Will it cost more?. Yes. Is the boat more likely to sink due to excess weight or be raided by copper-recyclers because there's more copper on board?.. Yes. Are my batteries more likely to explode if something goes wrong?... Yes.

.. hence, there's no practical reason to do it - but that doesn't mean it won't work just fine and dandy.   



artbyjody said:


> CSA= CONDUCTOR CROSS SECTIONAL AREA IN CIRCULAR MILS.


Interesting link. I've been around a while but I've never come across a "circular mil" before. If I didn't know better I'd have thought it might be something you grind flour on!! We'd call it "square millimeters" over here. It's amazing what you learn on Sailnet...


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## artbyjody (Jan 4, 2008)

Hartley18 said:


> For a 12VDC power system, Jody, that statement is complete hogwash!!
> 
> You can oversize the wire to blazes and the only thing it will hurt is your wallet (what, with the price of copper these days) - and increase the size of any potential fault current, meaning a bigger bang if something shorts out. Heck, there's nothing stopping you wiring your entire boat in 1" copper bus-bar should you ever feel so inclined. Will it work better than a correctly-sized cable? No. Will it cost more?. Yes. Is the boat more likely to sink due to excess weight or be raided by copper-recyclers because there's more copper on board?.. Yes. Are my batteries more likely to explode if something goes wrong?... Yes.
> 
> ...


Nice post - like the humor but you are wrong in your basis... "and increase the size of any potential fault current, meaning a bigger bang if something shorts out." you actually want that event to be with the thinnest gauge wire you can - why - the bigger it is the bigger the threat in terms of fire... a smaller diameter wire if it gets overloaded melts , burns etc - has less fuel so to say... minimizing your risk...

Just because it is 12 VDC - trust me - I had a car catch on fire due to the wiring ... proper specs yield proper damage control situations and appropriately more manageable situations...

But sure if you are lax (and eat lucky charms for breakfast) or you perform the wiring in somewhat professional manner odds are that will not happen - but when it comes to recommendations over the internet - or in general - I prefer to err on the side of least is more...


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## sailingdog (Mar 19, 2006)

Most of the equipment you mention has in-line fuses in their power leads.



sailboy21 said:


> Yeah.. maybe for lights and pumps but anyone trusting a generically sized (5, 10 15 etc) mechanical breakers for radios, chart plotters, radar, GPS etc is asking for it.. these devices need fuses. I never understood those HUGE breaker panels with an _expensive _breaker for EVERYTHING.. No shame in using a 15 amp breaker for "electronics"


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## xtatico1404 (Jan 20, 2008)

Hartley18 said:


> Interesting link. I've been around a while but I've never come across a "circular mil" before. If I didn't know better I'd have thought it might be something you grind flour on!! We'd call it "square millimeters" over here. It's amazing what you learn on Sailnet...


LOL about the flour grind!!! While all wires have a "circular mil" (unit of area)it is mainly used on the US system for the larger gauge wires. Starting at 250 MCM, it is a direct relation to the circular mil size, which for 250MCM is 250,000 circular mils.


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## maccauley123 (Sep 2, 2004)

Wow, I had no idea what I started. Great thread and I have learned a lot.

The last discussion about cautions on oversizing wire has me scratching my head though. I have reviewed both Nigel Calder's and Don Casey's books and all I find there is to make sure the wire is big enough for the anticipated load. I don't see anything that says to make sure the wire is not too big. In fact I think both say oversizing is good.

For my rewire project the tables say for a 5 amp draw with a 40 foot round trip run 10awg is the wire to use. For my run of lights through the boat on either side this is what I need and will be my longest run. I was going to use this gauge for much of my wiring and then a smaller gauge say 14awg for the running lights which are a long run but will only have a 1 or 2 amp draw.

I don't see anything that says don't use wire that is too big? I know I am probably paying a little more than I need to but felt it easier to just have two spools of wire and pick the one that is larger than needed for each run.


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## sailingdog (Mar 19, 2006)

Maccauley-

You don't want to go too large on the wiring since that costs money and adds a good bit of weight.  Sometimes, the fact that you can buy more wire of a given size means you'll save money on that wire, over buying several different gauges of wire in shorter lengths, and the cost difference becomes fairly minimal.


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## rhaley (Jun 18, 2007)

artbyjody said:


> Oversizing wire however actually generates more load resistance to begin with and should not be overly done or practiced as you decrease the overall cpacity of your storage system...which is the making the batteries work harder and deplete faster...
> Oversizing you have to consider also distance and gauge ensure sure you do not see more than a 3% drop in voltage over the run... (if you can make sense of it - the charts American Wire Gauge table and AWG Electrical Current Load Limits)
> 
> A checklist however somewhat related:
> ...


Over sizing the wire will DECREASE load resistance as the wiring runs will add less resistance to the circuit as a whole. The equation you posted says exactly that. For a given load, the larger the CSA, the less inherent resistance the wire adds to the circuit, hence the lower the voltage drop.

Oversized wire does not increase the available fault current of a circuit, a protective deveice with a larger rating does. If you size the breaker (or fuse) for the wire, which you should, then the breaker (or fuse) should trip LONG before the wire melts and burns. If it doesn't, there was no point in the protective device in the first place. Minimizing your "risk" by using a small wire that won't burn as long is the definition of false security. How about preventing the wire from burning in the first place? As far as I'm concerened, I don't want any fire on my boat, no matter what size.

As Hartley18 stated, oversizing your wiring, as SD has done (as well as myself) will hurt nothing but your wallet.

Now I certainley agree that if you use grossly oversized wire, and size the breaker or fuse to protect that wire, you have created a situation that will produce more fault current before the protective deveice activates. It does not, however, increase the risk of the wire burning because the wire and breaker are sized to match each other and the breaker will trip long before the wire reaches its burning point.


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## Rockter (Sep 11, 2006)

I have a Russian motorcycle, and I wish the wires worked evey now and again. 

Right now they work every once in a while and blow fuses nearly all the time.

Thicker wire would just tempt me to hang myself with it.


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## Classic30 (Aug 29, 2007)

Rockter said:


> I have a Russian motorcycle, and I wish the wires worked evey now and again.
> 
> Right now they work every once in a while and blow fuses nearly all the time.
> 
> Thicker wire would just tempt me to hang myself with it.


A Russian motorcycle, huh?? Hmm... You sure they actually used wire? 

I thought that russians often used whatever they could find nearby!


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## sailaway21 (Sep 4, 2006)

I hate in-line fuses as a practical matter; they're a pain to secure properly with the wire and then easily access their contents. I much preferred it when most components came with the fuse incased in the back panel of the component,

That being said, it should be emphasized that they, or a suitable replacement for them are necessary. You can install a breaker or fuse for each circuit not to exceed that required by the wire and thus protect the wire, while doing nothing to protect the component. If you have a seperate circuit for each component, there is nothing wrong with having 12 gg wire with a 1 amp fuse reflective of the component's requirements. If, as is common, you're to have multiple components coming off the same circuit, the fuse should be of a size reflecting that of the lowest rated component. Since that practise results in the lowering of the utility of that circuit, ie..how many things you can place on it, it's perhaps best to fuse or size the breaker for the wire and fuse each component seperately at the component.

Anotherwords, Don't cut off those in-line fuses and throw them away without planning for adding similar fusing capability elsewise in their replacement! Remember that the tendency will be, when confronted with a single fused circuit, to apply a larger fuse at some future date, thus jeopardizing all unfused componnents down line.


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## sailingdog (Mar 19, 2006)

One other thing you should do... if you're going to use in-line fuse holders, you really should make all the in-line fuse holders use the same type of fuse so that you don't have to carry different types of fuses on-board. I prefer to use the ATO/ATG type mini-blade fuses.



> Anotherwords, Don't cut off those in-line fuses and throw them away without planning for adding similar fusing capability elsewise in their replacement! Remember that the tendency will be, when confronted with a single fused circuit, to apply a larger fuse at some future date, thus jeopardizing all unfused componnents down line.


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## TrueBlue (Oct 11, 2004)

If installing new circuit overload interupters in your boat's DC system - why use fuses? Most modern boats are equipped with circuit breakers - even my 20 year old Nauticat had them - not one fuse onboard.


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## Classic30 (Aug 29, 2007)

Another thing to bear in mind (and something most people forget) when dealing with 12V circuits on a boat is that batteries can deliver *large* amounts of current under short-circuit conditions - many hundreds of amps for a very short time. This is far more than you'll ever get out of a shore power connection without tripping something on-shore first.

Apart from the risk of fire on board from melting wire insulation (the obvious one), a more insidious problem is that high DC currents cause magnetic fields that will tend to push +ve and -ve wires apart (usually seen as "wire jump"). These forces are pretty impressive and can crack bulkheads wires pass through, force wires partly out of terminal blocks and damage the batteries themselves, so it's wise to check the entire run back to the battery if ever you accidentally short something out.

To stop this, a good practice is to fit a fuse or circuit breaker to the battery itself (like those fitted to cars for the same reason). These fit on one of the battery terminals and, rated to the maximum current of your house power, will limit the amount of accidental welding you'll do whilst fiddling with the wiring with the power switched on...


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## Freesail99 (Feb 13, 2006)

> To stop this, a good practice is to fit a fuse or circuit breaker to the battery itself (like those fitted to cars for the same reason). These fit on one of the battery terminals and, rated to the maximum current of your house power, will limit the amount of accidental welding you'll do whilst fiddling with the wiring with the power switched on...


Do you have a link to show what it looks like ?


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## Classic30 (Aug 29, 2007)

Freesail99 said:


> Do you have a link to show what it looks like ?


They look like this, but this one is some bizzaro 3-way thingy. For this type, you specify what fuse rating you want from about 50 amps up.

I know I've seen single resettable circuit-breaker ones around someplace (I thought Whitworths used to sell them) but in this case Google has failed me.


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## sailingdog (Mar 19, 2006)

TB-

This only works if you've got enough space to have individual circuits for each piece of equipment. If you have to gang multiple pieces of equipment on a single breaker, which is often the case... you really want to have fuses in-line for each piece of equipment.


TrueBlue said:


> If installing new circuit overload interupters in your boat's DC system - why use fuses? Most modern boats are equipped with circuit breakers - even my 20 year old Nauticat had them - not one fuse onboard.


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## Classic30 (Aug 29, 2007)

sailingdog said:


> TB-
> 
> This only works if you've got enough space to have individual circuits for each piece of equipment. If you have to gang multiple pieces of equipment on a single breaker, which is often the case... you really want to have fuses in-line for each piece of equipment.


SD, you can get some pretty small 'in-line style' circuit breakers these days so size is not really an issue. Circuit-breakers also inherently tend to be more reliable than fuses - because there's no fuse wire to go high resistance on you! (yes, I've had it happen). And it doesn't matter how many times they trip (within reason) they can be reset very quickly... but once they fail, if you're well out of sight of land on a dark night, you're stuffed - unlike a fuse where you can just pop another one in.

The above notwithstanding, fuses are simpler, way cheaper and far less bother for most people so they do still have their place on anything other than some luxury cruiser. Each to their own. 

A Point of Trivia of No Relevance To This Thread: Most fuses (all that I've ever known, anyways) are *not* designed to blow at their fuse rating but at some figure above it instead. eg. a 2A fuse will hold 2 Amps forever, but will blow quite happily at 3... but a 2A circuit breaker OTOH will trip just above 2 amps.


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## Rockter (Sep 11, 2006)

The Russky bike does not have circuit breakers. 
It behaves like it does though.
They are breaking all the time.


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