old construction in the US sometimes did this intentionally (so old, the house didn’t have grounds. Or to “pass” an inspection and sell a place) but if a licensed electrician sees this they have to fix it.
I’m dealing with a 75 year old house that’s set up this way, the primary issue this is causing is that a 50amp circuit for their HVACs are taking a shorter path to ground inside the house instead of in the panel.
As a result the 50 amp circuit has blown through several of the common 20amp grounds and neutrals and left them with dead light fixtures and outlets because they’re bridged all over the place.
If an HVAC or two does this, I’d advise against this for your 3200 watt AI rig.
EU, you don’t want to try to energize your ground. They use step down transformers or power supplies capable of taking 115-250 (their systems are 240-250V across the load and neutral lines. Not 120 across the load and neutral like ours.)
in the US. you’re talking about energizing your ground plane with 120v and I don’t want to call that safe… but it’s REALLY NOT SAFE to make yourself the shortest path to ground on say. a wet bathroom floor. with 220V-250v.
> It definitely comes in at a higher voltage.
The voltage supplied to a US house is 120V RMS measured phase-to-ground. You will not find a higher voltage in your house. This does not mean that it’s appropriate to run any non-negligible current from phase to the ground (green / “equipment grounding conductor”) wires.
One can get vaguely close to an accurate understanding by imagining that there are four wires coming out of your main panel: +120V, -120V, 0V white (the “actually use me” wire) and 0V green (a safety wire where any current more than a few mA or maybe tens of mA depending on application is at least a mistake). There’s no 240V to be found.
This explanation falls apart pretty quickly — the US system is AC, not DC.
I can’t tell what practice you’re referring to. Are you perhaps referring to older wiring that connects large appliances to a neutral and two hots but no ground, e.g. NEMA 10-30R receptacles? Those indeed suck and are rather dangerous. Extra dangerous if the neutral wiring is failing or undersized anywhere.
But even NEMA 10-30R receptacles are still 120V RMS phase-to-ground. (And, bizarrely, there’s an entire generation of buildings where you might find proper 4-conductor wiring to the dryer outlet and a 10-30R installed — you can test the wiring and switch to 14-30R without any rewiring.)
The exception for residential wiring is when the neutral feed from the utility transformer fails, in which case you may have 240V phase-to-phase with the actual Earth floating somewhere in the middle (via the service’s ground connection), which can result in phase-to-neutral and phase-to-ground measured anywhere in the house varying from 0 to 240V RMS.
> wet bathroom floor
A GFCI receptacle adds a considerable degree of safety and can be installed with arbitrarily old wiring. It’s even permitted by code to install one with no ground connection as long as you label it appropriately — look it up in your local code.
I believe that’s kinda naughty.
It works, but it energizes your ground plane and people do get mildly shocked. that’s making me a little nervous.
So holes have been drilled in ceilings and walls and single wire neutrals or grounds have been fished down the walls, repeatedly, by yours truly , but there’s still at least one “gfci” outlet that’s wired this way And they’re balking at getting an electrician back out here for.
bridging neutral to ground because the neutral lines dead, uh, “works” to be technical but whoever did this moved on years ago and heaven only knows how many outlets or fixtures this was done in. I’m just finding out one by one as someone goes “hey this stopped working!”and you pull it and the neutral or ground blew like a fuse.
So that’s my whole point, this is an extremely bad idea for a 3200watt computer.
yes, they are all getting snipped and blank wall plated and marked as hazards that need to be remediated with a Dymo labeler as I discover them.
I don’t work here I just live here and have kind of a slummy owner who doesn’t want to do anything about any of it and doesn’t care if the plumbing or electrical works.
But they paid some guy like $4000 to install a totally unnecessary subpanel that’s bridging conflicting phases into the same circuits because he didn’t figure out this was what was going on. Dios Mio. I would have fixed the whole house for $1000. Miracle this hovel hasn’t burned to the ground yet.
I’m putting up with it for now but should probably bail before it does.
In Europe, you could plug the two power supplies into an appropriately sized 240V circuit.
In an apartment you can't rewire, you could set it up in your kitchen, which in the modern US code should have two separate 20A circuits. You will need to put it to sleep while you use appliances.
But this is re: European 240/250 which is 240 between its load and neutral
I’d say don’t energize either systems ground plane, but , really, don’t do this in EU
So basically you need a brand new circuit run if you don't have two 120V circuits next to each other. But if you're spending $65k on a single machine, an extra grand for an electrician to run conduit should be peanuts. While you're at it I would def add a whole-home GFCI, lightning/EMI arrestor, and a UPS at the outlet, so one big shock doesn't send $65k down the toilet.
He's not saying you would use it as two separate 120v circuits sharing a ground but rather as a single 240v circuit. His point is that it's easy to rewire for 240v since it's the same as all the other wiring in your house just with both poles exposed.
Of course you do have to run a new wire rather than repurpose what's already in the wall since you need the entire circuit to yourself. So I think it's not as trivial as he's making out.
But then at that wattage you'll also want to punch an exhaust fan in for waste heat so it's not like you won't already be making some modifications.
Can confirm.
The only place where there's isolation is stuff like USB ports to avoid dangerous ground loop currents.
That said I believe the PSU itself provides full isolation and won't backfeed so using two on separate circuits should (maybe?) be safe. Although if one circuit tripped the other PSU would immediately be way over capacity. Hopefully that doesn't cause an extended brownout before the second one disables itself.