amp/ wire size noob ?

[-Hube-]

when wiring a 240v 50 amp breaker, for example, does each hot wire have to be rated for 50 amps or 25 amps per wire? 100 amp breaker, 50 amps per wire or 100 per wire. I think I know the answer but not sure. thx.

 

[brianmoooore]

AFAIK, US 240v is similar to UK split phase, but at half the voltage. I presume the 50A breaker is actually two 50A breakers joined together (DP), and the minimum current rating for each wire will need to be 50A.

 

[-Hube-]

Dang. So my RV box with a 50, 30 and 20 amp receptacle should be wired with #2 wire according to the charts... Also, I had some #8 I was going to use for a 50 amp circuit, but looks like I need to beef it up. Thanks for the reply!

 

[brianmoooore]

#2 or#8 means nothing to us in the UK. We specify wires by the cross sectional area of the conductor, measured in square millimetres. For 50A it would be 10 or16mm2, depending on how it was installed.

 

[-Hube-]

Interesting... Looks like #2 would be 35mm2. We have a 15' lenth of 8/3 (10mm2) feeding a 240v 50 amp rv recepracle box. It seems like the wire may be too small, or is it ok?

 

[brianmoooore]

A 10mm2 twin and earth cable (which I think is known as 'Romex' in the US) is rated at 63A if fixed, unenclosed , on a wall. This drops to 52A if enclosed in conduit or trunking on a wall, and down to 43A if the conduit is enclosed in a thermally insulating wall.
These are the 'base' figures. They can be reduced further by things like bunching cables together.

 

[-Hube-]

Yes, Romex is the brand name of the wire here. Looks like the 8/3 is fine then for that 50a outlet. It's unenclosed in an air conditioned room with only about 2' of it outside. Thanks for the info!

 

[-Hube-]

What size would you use to go about 4' in conduit from the main to the 100 amp rv box?

 

[Avo Mk8]

What size would you use to go about 4' in conduit from the main to the 100 amp rv box?

What size is the (presumably existing) breaker that is going to feed it?

 

[-Hube-]

A 100amp breaker will be installed to feed it, just in case we end up using all of the outlets at the same time.

 

[Avo Mk8]

A 100amp breaker will be installed to feed it, just in case we end up using all of the outlets at the same time.

In that case, at least in the UK, and I imagine true for the NEC, you will need a cable rated at 100A, so if there's a fault, the breaker will protect the cable. So I think that means probably #2 or 3 AWG depending on the cable type.