AC 110V wiring - AWG wire recommendations

[ArkadiyS]

We have a 1987 35 Hunter, and I am installing an additional AC power outlet. It is being branched off of an existing 110V AC outlet (non-GFCI), and the one that I am installing is a marine grade GFCI receptacle. I am planning on using 12 AWG marine wire for it, should I go with a 10 AWG wire instead? Thanks!

 

[JohnShannon]

well here is a resource http://www.usawire-cable.com/pdfs/nec ampacities.pdf

10 AWG is depending 30-40 amps (depending on temp rating of the insulation)
14 AWG is 20A your plug is rated likely at 15A so I suspect you can get away with 14 AWG (which is I think what houses are wired with)

The other item is I think the GFCI outlet should be the first outlet in the boat and all the others daisy chain off that. This should confer GFCI protection on all downstream outlets. Boats being damp should have that.

 

[ArkadiyS]

Although I am a big believer in physics, I am not able to tell which is the first AC outlet. We have separate port/starboard circuit breakers for AC receptacles as well, creating 2 separate loops. I have just upgraded the head receptacle with a GFCI (starboard side) and will have this new one GFCI on the port side. Not looking for the cheapest solution, but the best possible. Thinking of using 12 AWG, but wonder if I should go with 10?

 

[LeoLambert310]

to be on the safe side I would go with 10 awg as if you have a high load on your plug ie. shore power with hair dryer and microwave on you have to think about the amps and heat.

 

[jssailem]

In your house you use 12awg for 20 amp circuits like kitchen circuits.

Most of your lamp circuits are 15 amp circuits where 14awg is acceptable.

Add up your expected amps to be used and decide on the wiring to support this use. note AC is not the same as DC. You use larger awg to reduce voltage loss in DC circuits. Not applicable to AC circuits.

 

[JohnShannon]

Can you connect 10 AWG to the socket? It is likely designed for 12-14. I think (@Maine Sail) ABYC wants you to have GFCI on all the sockets in the boat. So if you can't figure out which one is first and do that one with a GFCI then maybe you change them all to GFCI types.

 

[jssailem]

The electricians use a tone producer to identify systems. You should be able to follow the lines from the panel to the first circuit plug. It will be the one closest to the panel. Open it and. You should see 2 sets of wires. Disconnect the ones going away from the panel leads. Then energize the circuit and see if there is any power to the additional plugs on that side of the boat. No power means you have the first in the circuit. In stall the GFIC there.

 

[dlochner]

The wire size should match the circuit breaker. The main 30 Amp service should have 10 ga. Branch circuits will either be 15 Amp or 20 Amp. 14 gauge should be fine for 15 Amp circuits, 12 gauge for 20 Amp.

 

[Ron20324]

No way you need 10 wire. Is your new GFCI 15 or 20 amp rated? Is the outlet you are tapping of off 15 amp/14 wire, or 20/12 ? What size breaker on the panel? While you have the present outlet exposed, put the new GFCI there, then tap the new wire and outlet off of that one. GFCIs can go bad, and you'd not want ALL of you outlets working though the same GFCI.

 

[LeslieTroyer]

12 gauge max. 10 is much harder to deal with and you are likely going to exceed the bending radius while fishing and installing it in the boat. Going to smaller sizes allows you to make tighter corners.

Your perceived safety factor is lost if you damage the wire by too tight bends

Les

 

[kloudie1]

I think the early 35's were wired like the 34's of the same time period.. if so, the first outlet from the panel going forward on port side feeds the one in the head and the aft one is fed from the port breaker by itself.. The feed for the stbd side goes forward and then across the boat in the transverse beam under the mast, then turns aft and first feeds the forwardmost outlet on that side.. then the aftmost one on stbd is fed by that outlet.. The factory put in 14 ga wire in both the 110V outlet circuits. Your original thought of 12ga is probably fine
the wiring from the shore inlet to the fuse panel is 10 ga.

 

[uncledom]

The wire size should match the circuit breaker. The main 30 Amp service should have 10 ga. Branch circuits will either be 15 Amp or 20 Amp. 14 gauge should be fine for 15 Amp circuits, 12 gauge for 20 Amp.

dlochner
This is electrically correct.

 

[Maine Sail]

The wire size should match the circuit breaker. The main 30 Amp service should have 10 ga. Branch circuits will either be 15 Amp or 20 Amp. 14 gauge should be fine for 15 Amp circuits, 12 gauge for 20 Amp.

^^^Bingo we have a winner!^^^^

 

[ArkadiyS]

Thanks for all of the feedback! More homework when I get back to the boat... I will continue to replace receptacles with GFCIs whenever possible as well. All of the GFCIs that I am installing have test lights on them, is that how you can tell that the outlet is working properly, or is there a different GFCI test?

 

[JohnShannon]

There should be two buttons on the GFCI one of them says "TEST" When you push that one there should be a click and the outlet should go dead.

The second button is called "RESET" push that one and the outlet will work again. Supposed to test quarterly?

 

[Ron20324]

Read the spec sheet that should have come with the GFCIs.

 

[dlochner]

There should be two buttons on the GFCI one of them says "TEST" When you push that one there should be a click and the outlet should go dead.

The second button is called "RESET" push that one and the outlet will work again. Supposed to test quarterly?

It takes no time to test them and in a boat, especially in salt water, they should be tested frequently. The guts are metal and mechanical, a little corrosion and they won't trip.

 

[Benny17441]

If you are picking power from an existing circuit wired with 14 AWG, there is no significant benefit to extend it with 10 AWG. " A chain is only as strong as the weakest link." How do you match a 20A breaker to a 10/12 gauge wire with a circuit section of 14 AWG in between?

 

[Seahorse24]

Length of wire as well as gauge matter. Houses typically require longer runs than a boat.

Add up the total wattage that wire must supply when every load us turned on at the same time. Divide the total wattage number by 110 to get the total maximum amperes the wire will have to carry. Then Google wire gauge required for that amperage.

Wire has a certain amount of resistance per foot. That resistance times the maximum current is the wattage lost through heating the wire. Heavier gauge wire offers less resistance, therefore less heat loss.

Example: total length in feet times resistance per foot times total amperes equals total voltage drop.

20 feet times .001 ohm per foot times 30 amperes = 0.6 volts

Volts = Resistance times Amperes

Watts = Amperes times Volts

30 amperes x 0.6 volts = 1.8 watts of energy lost in the wire.

Use this chart to determine your total resistance. https://www.cirris.com/learning-center/calculators/133-wire-resistance-calculator-table

 

[uncledom]

Thanks for all of the feedback! More homework when I get back to the boat... I will continue to replace receptacles with GFCIs whenever possible as well. All of the GFCIs that I am installing have test lights on them, is that how you can tell that the outlet is working properly, or is there a different GFCI test?

You do not need to keep buying those expensive GFCI outlets. You can chain them. The top screw set is marked line and there is a lower screw set marked load. If you attach all the other outlets in a string off the load side of the GFCI outlet which should be the first one after the breaker all outlets will be protected.