Breaker Size?

[kneedeep]

I have a Miller Thunderbolt AC/DC machine in a shed that has been wired with a 100 amp sub-panel. The feed from the main is about 160' to the Equipment shed with 2/0 Aluminum wire with a ground rod. Most of my welding is repair and medium size fabrication.
My question is, what size breaker would the welder require to operate?

TIA

 

[John Fitzgerald]

Probably a 50 amp two pole breaker would be fine. Three wire #6 copper plus ground to the 50 amp outlet.

 

[gary49]

Receptacle that fits the plug on welders is generally 50 amps. Breaker should be 50 amps. Only 3 prongs on the plug, so 3 conductors, 2 rated at 50 amps, the 3rd conductor is the ground, could be as small as 10 gauge copper for that one. Least expensive cable to use would be #6 aluminum service entrance cable.

 

[John Fitzgerald]

Some locales specify four wires for all 240V circuits. I agree not needed for a welder.

 

[grsthegreat]

there will be a name plate on the welder. my thunderbolt lists 50 amps. dont need a neutral on welder. only 2 hots and aground

 

[medic0648]

Depending on how far from the panel, the duty cycle for the welder, and if you plan on upgrading to a welder with a higher duty cycle here are a couple charts to help. Below 100 amps use the 1st column and multiply using the derating factor for the duty cycle. Or don't de-rate and you are good for 50 amps non continuous use.

 

[Fallon]

Depending on how far from the panel, the duty cycle for the welder, and if you plan on upgrading to a welder with a higher duty cycle here are a couple charts to help. Below 100 amps use the 1st column and multiply using the derating factor for the duty cycle. Or don't de-rate and you are good for 50 amps non continuous use.View attachment 527482View attachment 527483

 

[dragoneggs]

Some locales specify four wires for all 240V circuits. I agree not needed for a welder.

Yes, I understand 4 wire is code in WA state.

 

[Eric102]

Yes, I understand 4 wire is code in WA state.

I wonder if that's a recent change? When I built my house in 2000 the electrician put in a 50 amp 3 wire in the garage for my welder.

 

[buickanddeere]

Personally I avoid derating. I just stick with the standard NEMA guidelines. Wire Current Ampacities NEC Table 310-16 A bit more expensive for the extra copper, but no chance for confusion or problems down the road. I do tend towards overkill though. Makes upgrading easier.

I also go with NEMA L14-50 plugs. 50@ of 120v or 240v power. You need an extra wire for it, but you gain flexibility. Most generators in the 50@ range will use this plug so it makes it easy to go mobile if needed. It also becomes easier to make a sucide cable & back feed your house if needed as well. Although if you couldn't figure out from the cable name, that's not always the smartest move.

How pray tell so you obtain a ground , neutral and two live lines from a three prong plug and receptacle ? Anyone advocating the use of a double male suicide cord and without a fail safe transfer switch. Their opinions should be ignored .

 

[Fallon]

How pray tell so you obtain a ground , neutral and two live lines from a three prong plug and receptacle ? Anyone advocating the use of a double male suicide cord and without a fail safe transfer switch. Their opinions should be ignored .

NEMA 14-50 is a 4 pin plug (hot, hot, neutral, ground).

And I did say a sucide cord wasn't a great idea.

 

[dragoneggs]

I wonder if that's a recent change? When I built my house in 2000 the electrician put in a 50 amp 3 wire in the garage for my welder.

Don't know when the code changed but when a hot tub service panel was added (50amp) in 1998, it was 3 wire. This was before our time in the house. Our hot tub died earlier this year and when I spoke with the shop about putting a new one in, the guy said how old was your tub... I told him and he said I'd better check if you have 3 or 4 wire.

 

[dougtrr2]

The breaker is to protect the wires to the outlet and should be sized accordingly.

Doug in SW IA

 

[buickanddeere]

The breaker is to protect the wires to the outlet and should be sized accordingly.

Doug in SW IA

Short circuit protection or thermal protection? It depends . Do you agree that a 90 amp breaker is acceptable on a 38 amp motor with #8 R75 copper .

 

[Tractor Seabee]

Short circuit protection or thermal protection? It depends . Do you agree that a 90 amp breaker is acceptable on a 38 amp motor with #8 R75 copper .

You will burn up that #8 wire, maybe cause a fire, long before the breaker will trip except for maybe a solid short circuit. There are motor rated breakers that will withstand the starting inrush w/o tripping unless the rotor locks up.

Ron

 

[Fallon]

Short circuit protection or thermal protection? It depends . Do you agree that a 90 amp breaker is acceptable on a 38 amp motor with #8 R75 copper .

Breakers & fuses protect wire from overheating & starting fires. They aren't there to protect devices plugged into ir connected to the wires. Sockets are considered part of the wiring in that aspect.

 

[buickanddeere]

You will burn up that #8 wire, maybe cause a fire, long before the breaker will trip except for maybe a solid short circuit. There are motor rated breakers that will withstand the starting inrush w/o tripping unless the rotor locks up.

Ron

You are not up to date on the electrical code . Perfectly legal and safe with 38GLA , #8 R75 wire and a 90 amp breaker . . Do you know the difference between thermal protection and short circuit protection ? Why would the wire burn up?

 

[buickanddeere]

For a random 50 amp wall receptacle use a 50 amp breaker and #8 R75.
From that 50 amp wall receptacle and 50 amp breaker it is legal to use #10 SOW Cab Tire cable rated for 30amps if the welders FLA is 24 amp.