Outlet wire runs 14/3 vs 12/3

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winty

Senior Member
Joined
May 26, 2014
Messages
107
Location
CA
Vessel Make
'81 CHB34
34' boat with a 30A shore power service. Several AC outlet runs are solid core romex style residential wire. I'm going to replace with tinned marine wire.

For outlets, am I supposed to use 12/3 or is 14/3 AWG ok? The 14/3 will be much easier to run. I'm not sure if the outlet breaker is 15 or 20A, but the supply run from the generator to the panel is 14/3.

Main breaker on generator is 15A, single phase. Currently only one hot leg is in use, which is a topic for a future thread.

Trying to get as close to ABYC as possible, while DIY when within my ability.

Thanks
 
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Go back and check the breaker. 15 amp means 14/3 is OK. 20 amp calls for 12/3. 12/3 isn't really that much harder to run than 14/3.


The breaker for the genset is irrelevant.
 
WesK is correct. But separately you should look at how your genset is wired. If you only need 120V then both legs can usually be wired in parallel to give you 30 amps. You will need to upgrade the 15A breaker to 30A if you do this.


Both the way the genset is set up and the use of Romex type solid wire is weird. Must be some PO installed crap. CHB wouldn't do this at the factory.


David
 
Nobody ever said, "I wish I had run smaller gauge wire".

The power to the outlet on the end of the cable runs through a power pedestal breaker, a crappy receptacle, a shore power cord (with crappy ends), a crappy boat receptacle, a shore power / generator selector switch, a breaker panel, and finally your new cable. There are more than enough places for voltage loss; don't add you new cable to the equation.

Just my $ .02

Ted
 
I only use 14/3 for lighting runs. I would not use 14/3 to power a plug/receptacle. 12/3 being my self imposed minimum. Because, in the future you may need to operate a device (heater?) that pulls a good amount of amperage. OC is right, nobody regrets running wire thats larger than needed.
 
If the existing breaker is 15 amp and you are replacing all the wire, it's only the cost of a new breaker ($15) and the slight additional cost of 12/3 over 14/3 to "upgrade". That way, you can use the toaster and the coffee maker at the same time.
 
winty said:
34' boat with a 30A shore power service. Several AC outlet runs are solid core romex style residential wire. I'm going to replace with tinned marine wire.

For outlets, am I supposed to use 12/3 or is 14/3 AWG ok? The 14/3 will be much easier to run. I'm not sure if the outlet breaker is 15 or 20A, but the supply run from the generator to the panel is 14/3.

Main breaker on generator is 15A, single phase. Currently only one hot leg is in use, which is a topic for a future thread.

Trying to get as close to ABYC as possible, while DIY when within my ability.

Thanks
Click to expand...

The solid copper conductor romex really needs to go.

Does household Romex, even stranded, meet ABYC would be my question?

My Californian is wired with 12/2 marine grade cable throughout. It's round yellow sheathed cable, much like dock power cord, with three insulated conductors (Hot Black, Common White and Ground green). Common residential Romex 12/2 or 14/2 is going to have an insulated black and white conductor and an "uninsulated" Ground conductor. Is this an issue?

That's a question for all you ABYC Guru's. . . . . .
 
QUOTE=Edelweiss;439364]The solid copper conductor romex really needs to go.

Does household Romex, even stranded, meet ABYC would be my question?
NO. Not Marine Grade, no USCG or ABYC approvals. No bare conductor grounding conductors.

My Californian is wired with 12/2 marine grade cable throughout. It's round yellow sheathed cable, much like dock power cord, with three insulated conductors (Hot Black, Common White and Ground green).
This should be labeled 12/3.

Common residential Romex 12/2 or 14/2 is going to have an insulated black and white conductor and an "uninsulated" Ground conductor. Is this an issue?
It is still going to be solid, not Marine Grade, and the ground wire needs to be insulated green.

That's a question for all you ABYC Guru's. . . . . .[/QUOTE
 
Thanks for all the suggestions.

I'm sitting in front of the ABYC tech standards book... Based on my findings, planning to run 14/3 105deg C marine wire to specific outlets, which do not require runs though the engine space. New runs are replacing solid core AC wire which appears to have been installed by PO, not the factory. Locations are, transom outlet, flybridge outlet, additional aft cabin outlet, dedicated inverter to galley outlet. Also adding GFCI to all outlets on board, in series wherever possible.
 
High Wire said:
QUOTE=Edelweiss;439364]The solid copper conductor romex really needs to go.

Does household Romex, even stranded, meet ABYC would be my question?
NO. Not Marine Grade, no USCG or ABYC approvals. No bare conductor grounding conductors.

My Californian is wired with 12/2 marine grade cable throughout. It's round yellow sheathed cable, much like dock power cord, with three insulated conductors (Hot Black, Common White and Ground green).
This should be labeled 12/3.

Common residential Romex 12/2 or 14/2 is going to have an insulated black and white conductor and an "uninsulated" Ground conductor. Is this an issue?
It is still going to be solid, not Marine Grade, and the ground wire needs to be insulated green.

That's a question for all you ABYC Guru's. . . . . .[/QUOTE
Click to expand...

Ahha :rolleyes: Some of it is just common sense.

Interesting, In residential wiring, only the "non-grounded" conductors are counted. So 12/3 would be 2 hots black and red, white neutral and the bare ground conductor.

My boat wiring is 38 years old, so probably out of date with modern cable, but it's branded, 3 conductor - marine grade -12 awg.

Thanks for the info :thumb:
 
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Must be a little gennie to have a 15a breaker and 14/3 output cable. A typical little marine gennie is 5kW, breaker 40A and cable 10/3.
 
what_barnacles said:
example 2 on page 51 is a good example for you.

http://uscgboating.org/regulations/assets/builders-handbook/ELECTRICAL.pdf

the mothership...

http://uscgboating.org/regulations/assets/builders-handbook/ELECTRICAL.pdf
Click to expand...

Thank you for the link, this is consistent with the ABYC standards book I'm reviewing. Based on the above link, why is 14/3 AWG not large enough to feed a duplex outlet? Breakdown as follows.

•*My shorepower service is 120v 30A one leg. Generator is 3600w single phase, but only one leg is feeding selector switch on panel. However, ignore the generator for now.

• Outlet circuit breaker is either 15A or 20A, TBD, but lets assume 20A.

• Page 41, Table 5A "Allowable Amperage of Conductors of 50 Volts or
More When No More Than 2 Conductors are Bundled"

2 conductors table selected based on this statement, page 50, #4 "If the electrical system is 50 volts or more, determine the number of current carrying conductors
(grounding conductors are not normally current carrying) that will be bundled together. "

Table 5A
14 AWG 105 temp rated = 29.8amp for inside engine space

Unless I'm missing a variable here, 14AWG is 1/3rd more capacity than I need for a 20A max load on the outlets. Yes?

EDIT - less than 1V volt loss from pedestal to end of longest run, outlet at transom. I will meter again tomorrow, but it was so small, that I don't consider increasing cable gauge to compensate for voltage drop as an issue.

I'm not against 12/3 vs 14/3. However, based on all the documentation it doesn't appear necessary.
 
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While I only glanced over the table, I didn't see the compensation for length of the cable. Normally 120 vac wiring charts specify a wire size or amperage limit based on the length of the cable. As an example: you can use 10 gauge wire for 30 amps, but not if the length is over 30' (depending on the wire size table).

Ted
 
In order to use the 105c rating for the wire you will also need to use a 105c rated breaker. Best practices are to use #14 wire for a 15a circuit, #12 for a 20a circuit.
 
Irrespective of what the ampacity calculators or charts say, NEC specifies a minimum of 14 gauge wire for a 15 amp breaker and 12 gauge wire for a 20 amp breaker.


David
 
Many dock power supplies are really sad.

When everyone has air cond on the dock voltage may only be 105 or less.

When a few AC start at once it gets really low.

Treat your appliances to the best juice and have bigger wire in the boat than required.

The downside is cost and a harder install, a one time hit.
 
Capt.Bill11 said:
Don't be so sure. I've seen it before in older boats.
Click to expand...

Damn right. :eek: I've removed romex from my boat along with cloth insulated wire. Crazy I say. I also removed a type of wire that I've seen in houses from the '20s & '30s. I have one left to remove. Not done it yet, needed a break from the electrical stuff. Holly Molly.
 
O C Diver said:
While I only glanced over the table, I didn't see the compensation for length of the cable. Normally 120 vac wiring charts specify a wire size or amperage limit based on the length of the cable. As an example: you can use 10 gauge wire for 30 amps, but not if the length is over 30' (depending on the wire size table).

Ted
Click to expand...
I'm not saying you're wrong, but I don't believe you are right. In residential wiring, the length of a run is generally based only on the current, not the length. All the conductors feeding receptacles will be #12 regardless of the length. We're not talking about docks or outbuildings, but a house, for example. The run to an outlet on the far side of a house from the panel could easily exceed 100'. The concern for voltage drop is much less at 120 volts than at 12 volts.

That said, like so often happens, much more is being made of this project than needs to be made. #14 for 15 amp, #12 for 20 amp. 20 amp is better. That's all he needs to know.
 
djmarchand said:
Irrespective of what the ampacity calculators or charts say, NEC specifies a minimum of 14 gauge wire for a 15 amp breaker and 12 gauge wire for a 20 amp breaker.


David
Click to expand...

:thumb:
 
Use 12/3 throughout for 20amp or 15amp loads. It's just not that difficult. So, same awful labor; some extra cost.

Get a load of the receptacles on Revel. No doubt original 1984 install. Wire is stranded. Part of me wants to keep 'em for the conversation value; I've never even heard of such devices!
 

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WesK said:
I'm not saying you're wrong, but I don't believe you are right. In residential wiring, the length of a run is generally based only on the current, not the length. All the conductors feeding receptacles will be #12 regardless of the length. We're not talking about docks or outbuildings, but a house, for example. The run to an outlet on the far side of a house from the panel could easily exceed 100'. The concern for voltage drop is much less at 120 volts than at 12 volts.

That said, like so often happens, much more is being made of this project than needs to be made. #14 for 15 amp, #12 for 20 amp. 20 amp is better. That's all he needs to know.
Click to expand...
Wire Loss Table

The above table is for:
120 volts
5% voltage drop
75 degrees C temperature

Clearly there is a length limit without significant voltage drop.

According to the table, #14 should be fine.....as long as you're ok with up to a 5% voltage drop.

Not on my boat.

Ted
 
AC wiring on boats is very similar to house wiring. The NEC covers house wiring and should also apply to the AC system on boats. ABYC goes beyond NEC for marine issues, like tinned wire for corrosion protection.

The NEC doesn't even consider voltage drop for branch circuits like 15 or 20 amp home outlets. 14 gauge only hits a 5% voltage drop (which isn't going to hurt anything, but is a good limit) until the one way run length gets beyond 75'. That may happen in houses but it ain't going to happen in 99.9% of the boats that TF members own.

So just remember the NEC rule: 15 amp breaker = 14 gauge and 20 amp breaker = 12 gauge and quit worrying about ampacity and voltage drop calculators. Those are fine for 12 V where a 1 volt drop matters, but 1 volt is peanuts for 120 V.

David
 
djmarchand said:
The NEC doesn't even consider voltage drop for branch circuits like 15 or 20 amp home outlets. 14 gauge only hits a 5% voltage drop (which isn't going to hurt anything, but is a good limit) until the one way run length gets beyond 75'. That may happen in houses but it ain't going to happen in 99.9% of the boats that TF members own.
David
Click to expand...

In theory yes; in reality no.

You're assuming 120 volts at the pedestal. Reality is that often during peak season, at the end of the dock, voltage is already down significantly. On a hot summer day, you might be surprised at how much of a voltage drop there is with all the boat AC units running.

Ted
 
winty said:
Thank you for the link, this is consistent with the ABYC standards book I'm reviewing. Based on the above link, why is 14/3 AWG not large enough to feed a duplex outlet? Breakdown as follows.

•*My shorepower service is 120v 30A one leg. Generator is 3600w single phase, but only one leg is feeding selector switch on panel. However, ignore the generator for now.

• Outlet circuit breaker is either 15A or 20A, TBD, but lets assume 20A.

• Page 41, Table 5A "Allowable Amperage of Conductors of 50 Volts or
More When No More Than 2 Conductors are Bundled"

2 conductors table selected based on this statement, page 50, #4 "If the electrical system is 50 volts or more, determine the number of current carrying conductors
(grounding conductors are not normally current carrying) that will be bundled together. "

Table 5A
14 AWG 105 temp rated = 29.8amp for inside engine space

Unless I'm missing a variable here, 14AWG is 1/3rd more capacity than I need for a 20A max load on the outlets. Yes?

EDIT - less than 1V volt loss from pedestal to end of longest run, outlet at transom. I will meter again tomorrow, but it was so small, that I don't consider increasing cable gauge to compensate for voltage drop as an issue.

I'm not against 12/3 vs 14/3. However, based on all the documentation it doesn't appear necessary.
Click to expand...

The appropriate table for 12/3 -- 14/3 is 5B on pg. 41,
3 wires bundled (3 in a flat sheath qualify for that)
14g. max current for 105 degree wire: 24.5 OE, and 20.8 IE
12g. max current for 105 degree wire: 31.5 OE, and 26.8 IE

As you can see the allowable current for the x/3 flat cable is a lot lower than single wire ratings. It is really really rare to have a wire bundle of just 1 - 14/3 flat cable in it coming from the distribution panel. A lot of wires (single and cables) running along with each other is considered bundled for worst case temperature rise consideration. That is the typical situation near the panel.

While it's probably safe to assume no builder designs for the conditions O C Diver described in the preceding post (unfortunately), that is a very realistic condition that can occur. Throw in terminal corrosion of 10 year old pedastals and you can dip below 90 VAC easily.
 
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In dirt houses the power company broadcasts when a brownout will happen.

At most marinas mid summer and mid winter are almost always low voltage times.

An electric toaster wire heater mid winter will simply put out less heat , no big loss.

Most large motors today do not have brushes so the power consumption is measured in watts.

a 10A motor on a 120V source is 1200W

That same 1200w motor on 100V is going to use 12Amps running.

With a low dock voltage providing that extra 20% may tax the boats breakers and wiring.

Size does matter .
 
djmarchand said:
AC wiring on boats is very similar to house wiring. The NEC covers house wiring and should also apply to the AC system on boats. ABYC goes beyond NEC for marine issues, like tinned wire for corrosion protection.

The NEC doesn't even consider voltage drop for branch circuits like 15 or 20 amp home outlets. 14 gauge only hits a 5% voltage drop (which isn't going to hurt anything, but is a good limit) until the one way run length gets beyond 75'. That may happen in houses but it ain't going to happen in 99.9% of the boats that TF members own.

So just remember the NEC rule: 15 amp breaker = 14 gauge and 20 amp breaker = 12 gauge and quit worrying about ampacity and voltage drop calculators. Those are fine for 12 V where a 1 volt drop matters, but 1 volt is peanuts for 120 V.

David
Click to expand...

:thumb::thumb::thumb:

Yes, you may have lower voltage at the last slip in a marina but you can't raise it up by using larger wire in your boat.
 
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