Wire size question, AC side

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sndog

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Nov 15, 2022
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I am about to start running wire in my boat, from my refit, and did the calculations, and wire size calculated was 14awg. I went to start to pulling it in my conduit and it seems rather small.

So my question, is what would you recommend for wire size for outlets? Each room, and area(e.g. midship hallway) has it's own breaker. So I have 3 bedrooms, each would have its own dedicated circuit. Kitchen has 9 dedicated circuits(refrigerator, dishwasher, Anova precision oven, Breville espresso maker, stove(gas), over-the-range microwave, 3 sets of receptacles; one receptacle per breaker). There are about 60 breakers in total for AC. The longest run from the distribution panel is about 40ft. Kitchen outlets are about 10~20ft from the distribution panel.

Heavy loads such as the electric dryer, water maker, dive compressor, are are 10awg wire, as the calcs show for the runs.

Would love the input.

Thank you in advance.
 
14 gauge is generally good for 15 amps AC. So it depends on your individual circuit load what size breaker to use and therefore what size wire. 12 gauge is generally for 20 amps AC.
 
Comodave said:
14 gauge is generally good for 15 amps AC. So it depends on your individual circuit load what size breaker to use and therefore what size wire. 12 gauge is generally for 20 amps AC.
Click to expand...
This is what I have read. And I used several online tools to calculate the wire size. And everything says 14awg is perfectly fine, but it just feels so small
 
Unless you know the amperage of the loads being connected, the question of wire size is unanswerable.
 
Into which you could plug a heater drawing 20 amps. If the circuit has other outlets, and they usually do, then add those loads. Doesn't take long to use 15 amps.
 
sndog said:
This is what I have read. And I used several online tools to calculate the wire size. And everything says 14awg is perfectly fine, but it just feels so small
Click to expand...
Remember this is 120 volts not 12 volts. For routine 15 amp outlets 14 gauge is fine. Just make sure you don’t use a breaker larger than 15 amps.
 
The wire size must match the breaker size. 14 gage for 15amp breaker protected circuit is OK so long as the run is not very long and so long as the wire is not run inside a conduit together with a number of other load carrying wires. There are tables for these situations.
 
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From your posted info it sounds like 14 GA & 15A receptacles & breakers will be adequate. The cost to increase to 12 GA and 20A receptacles and breakers is likely rather small in comparison to the refit. The added capacity may only provide a safety factor but if low cost the peace of mind may be worth it.
Are you using stranded & tinned conductors vs solid copper?
 
Wire sizes for home and by extension boat AC circuits generally are not calculated. Y the installer. They match the rating of the fixture or device they are connected to.

14 gauge for 15A, 12 gauge for 12A, 10 gauge for 30A, etc. Since the distance of the circuit runs are much shorter in boats, this should be a conservative approach for voltage drop.

High current, hard wired appliances like A/Cs usually have wire size vs circuit length specified in the installation instructions. If not, size the wire based on its maximum current draw and circuit distance.

David
 
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I always run 12 gauge and 20 amp breakers for outlet circuits. The cost to upsize is worth it to me. You never know what sort of turbo hair dryer someone will plug in somewhere.
 
When I did my boat, I ran both 12ga and 14 ga. 14 where it was to an appliance that required a dedicated line or just a single outlet and 12ga where it was a string of outlets or an appliance that was right at 15A draw or higher. The 12ga wire got the 20A CBs.

Essentially the concept of just using 12ga and 20A breakers is not a bad idea as living aboard it was easy to fill every outlet up with plugs and still wish you had more at times.
 
Bacchus said:
From your posted info it sounds like 14 GA & 15A receptacles & breakers will be adequate. The cost to increase to 12 GA and 20A receptacles and breakers is likely rather small in comparison to the refit. The added capacity may only provide a safety factor but if low cost the peace of mind may be worth it.
Are you using stranded & tinned conductors vs solid copper?
Click to expand...
Using stranded. In conduit
 
14 gauge for 15A, 12 gauge for 12A, 10 gauge for 30A
Click to expand...
I am sure you meant 20A for 12 gauge.
Into which you could plug a heater drawing 20 amps
Click to expand...
While I know you can wire a 12G wire with 20A breaker to a regular 15A wall outlet, I did not know 20A appliances were wired with 15A plugs, but rather with one of these to fit a 20A outlet.
1725288313112.png
 
DavidM said:
Wire sizes for home and by extension boat AC circuits generally are not calculated. Y the installer. They match the rating of the fixture or device they are connected to.

14 gauge for 15A, 12 gauge for 12A, 10 gauge for 30A, etc. Since the distance of the circuit runs are much shorter in boats, this should be a conservative approach for voltage drop.

High current, hard wired appliances like A/Cs usually have wire size vs circuit length specified in the installation instructions. If not, size the wire based on its maximum current draw and circuit distance.

David
Click to expand...
Essentially, I am doing load calcs for specific areas, and anything dedicated. Places like the bathrooms, I have hairdryers I am putting there for usage.
 
Essentially the concept of just using 12ga and 20A breakers is not a bad idea as living aboard it was easy to fill every outlet up with plugs and still wish you had more at times.
Click to expand...
Multiple outlets by design do not expect that each outlet will ask for the max rating of the breaker but rather added up to the rating of the breaker.
The 12G with 20A breaker then serves a purpose to allow multiple 15A outlets to be used as long as the total load is not greater than 20A.
 
Use stranded and tinned wire. Put ring connectors on the wire, don’t insert the stranded wire directly into the outlet.
 
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