3 ms·

In the US, you don’t need a neutral for a 240V 50A circuit on a residential single-phase service, there are two line conductors (120V to ground) both connected

In the US, you don’t need a neutral for a 240V 50A circuit on a residential single-phase service, there are two line conductors (120V to ground) both connected to a 2-pole single-phase breaker, line-to-line between the two is 240V. You would need a neutral if it was a 208/120V three-phase service. Neutrals and grounds are sized per the NEC, neutrals are the same size as the line conductors and equipment grounds are sized off of a table. #6 conductors and #10 ground is what the NEC calls for.

knollimar 10mo ago
I just haven't seen server rooms that don't demand a doubly sized neutral when one is required. I live the NYC 208V life doing mostly resi, though. Quick search of the spec for that is 6 power supplies, 2 of which are redundant. Looks to use a neutral to me. Says it uses C19/C20 connectors edit: wait most ranges use 14-50R outlets and need a neutral ran. I am calling your statement into question. Surely harmonics and 120V internal draws cause non-zero neutral current. And I'm sure GPUs have harmonics being semiconductor flavored.
- quickthrowman 10mo ago
  Turns out you are correct on both points! My bad, NEMA 14-50R is a 4-wire receptacle with a neutral. I learned something new today, 200% neutrals are not required by the NEC but can help with non-linear loads, and certain transformers that mitigate harmonics need 200% neutrals.
  - knollimar 10mo ago
    I'm thinking you'd have a hard time fitting it in a smaller residential unit purely because of the load calculations. You'd probably have to add 3000W worth of AC units or heat pumps. Considering it's 4+ space heaters worth of output, I think you could fit it on a 200A service. 150A if you're bold and use optional calcs (these assuming you have electric cooking). To your point, basically the same as if you have an EV but with some cooling in there.

knollimar 10mo ago

I just haven't seen server rooms that don't demand a doubly sized neutral when one is required. I live the NYC 208V life doing mostly resi, though. Quick search of the spec for that is 6 power supplies, 2 of which are redundant. Looks to use a neutral to me. Says it uses C19/C20 connectors edit: wait most ranges use 14-50R outlets and need a neutral ran. I am calling your statement into question. Surely harmonics and 120V internal draws cause non-zero neutral current. And I'm sure GPUs have harmonics being semiconductor flavored.

quickthrowman 10mo ago
Turns out you are correct on both points! My bad, NEMA 14-50R is a 4-wire receptacle with a neutral. I learned something new today, 200% neutrals are not required by the NEC but can help with non-linear loads, and certain transformers that mitigate harmonics need 200% neutrals.
- knollimar 10mo ago
  I'm thinking you'd have a hard time fitting it in a smaller residential unit purely because of the load calculations. You'd probably have to add 3000W worth of AC units or heat pumps. Considering it's 4+ space heaters worth of output, I think you could fit it on a 200A service. 150A if you're bold and use optional calcs (these assuming you have electric cooking). To your point, basically the same as if you have an EV but with some cooling in there.