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Load Balancing Between Circuits (infosec.pub)

submitted 6 months ago by [email protected] to c/[email protected]

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I am not an electrician, but an end user.

I am planning to build a very powerful server for running LLMs. It will have many GPUs and can realistically hit a 1500 watt sustained load. The PSU in my computer can handle 240v but I do not have access to a 240v circuit.

My question is whether it is a good idea to somehow balance the load between 2 or 3 120v circuits. If so, what are some methods to safely do this?

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[–] Omgpwnies 1 points 6 months ago* (last edited 6 months ago) (1 children)

Except that's exactly how it works. Your house has two live feeds coming in that are 180 degrees out pf phase with each other. When combined, they create a 240V total potential. Your stove, clothes dryer, and water heater all use 240V circuits. A 240V breaker is actually two breakers adjacent to each other (because each alternating 'blade' in your panel is separate phases) with their switches linked together, so when one trips it forces the other off as well.

To OP: you can get a 240 breaker from Home Depot or wherever, but you will also need to replace your receptacle with one that can handle the increased power as well as 240V. You will also need to upgrade to 12/2 wiring on that circuit most likely. Also also... unless you have a 1500W or greater PSU, it doesn't make a difference if you have 120 or 240. Also also also, you can run multiple PSUs with multiple 120V standard household circuits, just without a joined breaker they won't all trip together.

[–] eth0slash0 3 points 6 months ago (1 children)

Ok fair. Two 120V rails in series would supply 240V but I think the dangerous part comes from the 'also' and that's where an electrician would come in and turn this from 'just a breaker' to rewiring your house.

you will also need to replace your receptacle

True.

You will also need to upgrade to 12/2

True.

I just don't think it's safe to say 'yes just add a 240V breaker and plug it in' which appears the OP may be at their with level of understanding.

[–] Omgpwnies 1 points 6 months ago

Agreed, it would be not a great idea, but also pretty useless unless OP is actually building a rackmount server which has power supplies that use 240V, at which point they would need 10/2 and an L6 receptacle, probably an upgraded panel... and really good home insurance.

Consumer grade PC power supplies that are rated for use here top out at 1600W, which is juuust enough to run on a dedicated 120V 15A circuit (though I'd feel more comfortable with 20A). Just dumping 240V into it doesn't automatically double it's power output, it would just use half the current from each phase