Wire sizing to Breaker Panel

[Swift Drift]

I'm in the process of rewiring my boat and am planning on using a blue sea systems 8 position 12 volt breaker panel as my sole distribution center: https://www.bluesea.com/products/437...ay_8_Positions

My confusion starts with the individual breakers on the aforementioned product being rated at 15 amps. If I want to avoid any additional over current protection devices (fuses) will I be forced to use wiring that is rated at 15 amps or more for all of the wiring downstream of the breakers? Seems silly to use such "over sized wire" for items such as LED lighting, instrumentation, etc. However, if that is the price I must pay to have a simple system with fewer variables then so be it. Appears that most runs would require 10 or 12 gauge.
Just wanted to see if I could get the insight of those wiser than I before I make a final decision.

FWIW the boat is a Merit 25 and there will be no other switches, breakers, fuses, etc (with the exception of a main breaker at the positive cable coming from battery and any fuses/switches that are integral to an accessory).

[smac999]

Just replace with smaller breakers.
15a is 14awg wire which is normal size wire

[Swift Drift]

That's too simple! Just looked into and it appears the blue sea panel is serviceable to accept other sized breakers. Great idea. Originally I was assuming that I'd be stuck with the original breakers supplied with panel.

[deblen]

The specs for the panel states 45amp cumulative rating(total max panel draw)
45amps calls for #6 ga. wire for a "short" to & from panel & Bat. source.
This #6 feed must be fused at the bat.+ with a 40-45amp fuse/brkr.

Use all 15amp brkrs & 14-2 distribution wire. You are fusing the 14-2 distribution wire at the panel & 14 ga calls for 15amp brkr. You could use 16-2 dist. wire & reduce the brkr to 10amp,but there is no need.
Ensure that you use only marine grade dist. cable

NOW-at the individual loads,you use individual smaller fuses(normally provided with decent eqpt). The use of small fuses is as much to do with protecting the small ga eqpt power leads from burning as it does with overcurrent protection of the internal electronics/circuitry.

The main purpose of breakers/fuses is to prevent wiring from catching fire & burning the boat.Therefore,if you fuse/breaker the wire properly,you have made things as safe as possible.As the wire gets smaller,so must the fusing
/ Len

[mitiempo]

Originally Posted by deblen

The specs for the panel states 45amp cumulative rating(total max panel draw)
45amps calls for #6 ga. wire for a "short" to & from panel & Bat. source.
This #6 feed must be fused at the bat.+ with a 40-45amp fuse/brkr.

Use all 15amp brkrs & 14-2 distribution wire. You are fusing the 14-2 distribution wire at the panel & 14 ga calls for 15amp brkr. You could use 16-2 dist. wire & reduce the brkr to 10amp,but there is no need.
Ensure that you use only marine grade dist. cable

NOW-at the individual loads,you use individual smaller fuses(normally provided with decent eqpt). The use of small fuses is as much to do with protecting the small ga eqpt power leads from burning as it does with overcurrent protection of the internal electronics/circuitry.

The main purpose of breakers/fuses is to prevent wiring from catching fire & burning the boat.Therefore,if you fuse/breaker the wire properly,you have made things as safe as possible.As the wire gets smaller,so must the fusing
/ Len

I agree with Len for the most part. The feed to the panel I assume comes from the main switch - 1/2/both or similar. That is where the fuse should go. It should be somewhere between the expected load - 45 amps - and the wire ampacity, which for 6 awg is over 100 amps. A fuse of 50 or 60 amps is a good choice and there is no chance of a nuisance blow.

I wouldn't bother fusing the last 6 or 8"of smaller wire to each load. There is no reason as a short in these wires will blow the breaker on the panel. A short on small wire will easily blow a large fuse of pop a large breaker.

On a 25' boat there is no reason to use 10 or 12 gauge wire for simple loads. 14 awg is the best choice.

[rwidman]

It's pretty clear to me that you don't know enough about electricity or boat wiring practices to be wiring a boat so I'm not going to answer your question. I don't want to encourage you to do something you're not qualified to do and something that could endanger your boat and passengers.


If you are unable to bring in a qualified professional marine electrician, then my suggestion to you is to buy some books on electricity and boat wiring and study them until you think you understand what they are saying. If you understand boat wiring, you won't have to ask people who may or may not know what wire size to use for a particular circuit.

[Swift Drift]

Originally Posted by mitiempo

I agree with Len for the most part. The feed to the panel I assume comes from the main switch - 1/2/both or similar. That is where the fuse should go. It should be somewhere between the expected load - 45 amps - and the wire ampacity, which for 6 awg is over 100 amps. A fuse of 50 or 60 amps is a good choice and there is no chance of a nuisance blow.

I wouldn't bother fusing the last 6 or 8"of smaller wire to each load. There is no reason as a short in these wires will blow the breaker on the panel. A short on small wire will easily blow a large fuse of pop a large breaker.

On a 25' boat there is no reason to use 10 or 12 gauge wire for simple loads. 14 awg is the best choice.

Thanks for the thorough responses Len & mitiempo.

Regarding my fusing coming off of the battery bank, I will be installing a breaker within 8" of the battery terminal that is rated at less capacity than the wire it is protecting which leads to the panel....that's always been part of the plan.

Regarding fusing the individual loads, all loads (with the exception of my LED lighting) already have integrated blade style fuses on the respective devices so I should be good as it relates to protecting my devices.

mitiempo's mention of small wire shorts not having issue tripping 15a breakers confirms my comfortability using 14 gauge wire from panel to loads (in addition of course to 14 gauge wire being rated to handle 15 amps at my specific run distances).

[Swift Drift]

Originally Posted by rwidman

It's pretty clear to me that you don't know enough about electricity or boat wiring practices to be wiring a boat so I'm not going to answer your question. I don't want to encourage you to do something you're not qualified to do and something that could endanger your boat and passengers.


If you are unable to bring in a qualified professional marine electrician, then my suggestion to you is to buy some books on electricity and boat wiring and study them until you think you understand what they are saying. If you understand boat wiring, you won't have to ask people who may or may not know what wire size to use for a particular circuit.

I appreciate your concern and assessment that I am unhampered by knowledge. I disagree. That said, I will not be hiring a marine electrician. My boat will be wired above minimum standards and you are more than welcome to come sailing with me. Cheers.

[Colin A]

As mentioned you won't have an issue with 14AWG 105C rated wire and the 15A breakers. If you did want to downsize you can get lower amp breakers and swap them in.

[KP44]

Originally Posted by Swift Drift

That's too simple! Just looked into and it appears the blue sea panel is serviceable to accept other sized breakers. Great idea. Originally I was assuming that I'd be stuck with the original breakers supplied with panel.

The panel comes with five 15 amp breakers and three empty slots.

[KP44]

How is it that most runs require 10 or 12 ga?

[captstu]

There are two separate issues at work here. Circuit breakers or fuses are intended to protect the wiring and downstream load from damage should there be a short of some kind.

14 gauge wire will generally handle 15 Amps without much heating or chance of damage unless the wire is coiled or run in a very tight space. Then the load capability must be derated because less heat can be lost.

But, the size ratings generally assume higher voltage circuits. The loss of a volt or two in a 120 volt circuit is in the range of 1%. The same size wire carrying the same current will lose approximate the same volt or two, but that is in the 10% range on a boat and is intolerable for most boat devices.

So, even though your load is within 15 amps and you could use 12 gauge wire, at about 50' (round trip length), you lose about 1/2 your voltage according to:

https://www.westmarine.com/WestAdvis...e-And-Ampacity

So, you have to calculate your round trip wire length, the expected load, the permissible voltage drop and choose the larger of the required size to produce an acceptable voltage drop or the size required by the protection you intend to install (14 gauge for 15 Amp breakers).

[Rorzech]

Fuse or breaker everything according to amperage and all electronics should be protected with small fuses rated by their manufactures. Fuses must be the weakest link in any circuit or you got trouble. Running 14 AWG to a string of LED's that draws 10 watts is foolish IMHO. Keep in mind that you want your fuses to pop at what ever is considered over current for any circuit.

[boatbod]

Originally Posted by Swift Drift

I appreciate your concern and assessment that I am unhampered by knowledge. I disagree. That said, I will not be hiring a marine electrician. My boat will be wired above minimum standards and you are more than welcome to come sailing with me. Cheers.

How will you know if you meet the minimum standards if you don't know what the standards are? For example, if you knew the standards, you would know how to size the cables to support the expected loads. You would also know that the standards say 16awg is the minimum gauge wire except for pigtails, and that overcurrent protection should be sized according to the wire gauge.

Sure, if you stick with big cable you will likely be safe, but it won't necessarily meet any particular standards.

[Wotname]

Originally Posted by rwidman

......
If you are unable to bring in a qualified professional marine electrician, .....

you won't have to ask people who may or may not know what wire size to use for a particular circuit.....

Originally Posted by Swift Drift

...... I will not be hiring a marine electrician. ......

No need to hire a qualified marine electrician.... as a qualified marine, aviation and communications technician I'm happy to answer your questions and point you in the right direction .

Being as you have only 8 (max) circuits and a 25' boat, it is not difficult to sort it out (remotely). We just need to know the actual equipment connected to each circuit and approximate wire run length.

If it was me (and I realise it isn't), I would replace the 15 amp breakers with smaller ones most suited to the loads and wire sizing to suit. e.g. most of my 31' circuits have 5 amp circuit protection and 16 AWG wire to supply non critical low current loads (~1 amp or less). Clearly not suited to higher current and voltage critical loads but then such loads are wired accordingly.