220-250VAC outlet wiring (OT-ish)

I know a bit of electrical house wiring, but not enough to be *certain* that I can safely do what I am asking about here. So before I destroy equipment or fry myself, I'd appreciate feedback from those familiar with and experienced in such things.

My house has regular split-phase 220VAC service at the box, with most of the house wired as 110VAC on one phase or the other. Two accesible points in the house are wired to the 220VAC across the phases, with a NEMA 10-30 receptacle, as HHN (Hot-Hot-Neutral). One is for a clothes dryer, and the other is for the kitchen stove/oven, both on 40A/phase breakers. The air conditioner is also on there, on separate 50A/phase breakers, but there is no accessible receptacle; it's direct wired.

The Sorenson DCS 55-55 lab supply I've got on loan has a NEMA L-6 plug on it, wired as HHG (Hot-Hot-Ground). It only needs 14A input with three phase, but with single phase like I have it'll take 20A (at max DC output, limited to ~2500W).

Given that it is unlikely any conductor will break to cause a shock hazard, using the spare cord off a dryer I have here, is it safe for the equipment to wire from the NEMA 10-30 as Y-W-X to the NEMA L-6 as Y-G-X? Meaning, tie Equipment Ground to House Neutral, as there is no separate ground available in the receptacle configuration I have?

I do realize that any internal equipment short by design or failure that allows neutral to short to case would then leave the case at whatever voltage Neutral is at, relative to ground, presenting a possibly fatal shock hazard; I'd be setting up the unit so contact with the case while attached to AC power is not easily possible even in my stupider moments (and impossible for the dogs to do so).


If it's not safe to do the way I describe, I'll have to find an install a NEMA L-6 receptacle, and wire it up.

This question is also posted at DIYEC, so I can confuse myself with as many opinions as possible.

Just wire it up with a leg from each hot side out of the breaker box, tie ground to the outlet ground/neutral. No need for fancy plugs.

Yeah, I could (at the outlet, though, not the box, since the box is outside in the backyard, but the outlets are at small junction boxes inside), and considered this first.

But I will need to sometimes take this with me as a charger, for long-distance trips once I get any really high-capacity pack going. I'd like to be able to just plug it in wherever I end up at, so as long as I have both cords with me, I can use whichever one the place has available. (The unit has a connector block at the rear to swap cords at; I've only got the one block but can easily use Anderson Multipoles or similar to make an interconnect). Lots of older houses like mine only have NEMA 10-30 HHN outlets, so having this option expands my list of destinations.

Also, it's faster to unplug should I get smoke somewhere along the line, if it's not wired straight in.


Ideally, having a charger that will run on 110VAC and still get me 30A+ to the pack is even better, but I don't have that option right now.

Probably safe, but electrical code says wiring downstream of a breaker or fuse has to handle the full current without getting warm (i.e. no more than a specified voltage drop) and provide enough overcurrent on a direct short at the end of the run to blow the breaker. The proper transition cable would be a 40 amp plug to a 15 amp socket with a <15 amp fuse in between, with 40 amp wiring up the fuse and (optionally) 15 amp wiring after the fuse. Similar to the construction of 12 volt devices that plug into automobile cigarette lighters, a fuse in the lighter plug allows smaller wires and plugs to the device.

Sounds like a decent plan, then. I can install a fuse inline with the wiring; it would be at the device end, however, rather than in or prior to the receptacle. I also can install per-phase 15A breakers, as I have a number of these rated up to 230VAC out of a UPS (they used to protect the individual outlets on the back of it, one per pair of outlets).

I mostly just needed to be sure that using the Neutral as Ground wasn't a fatal idea (shouldn't be, since that's how the dryer itself and the stove are both wired).

If you don't see me posting at all in the next few days, send someone to collect the body.

amberwolf said:

If you don't see me posting at all in the next few days, send someone to collect the body.

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I usually have someone come over for pizza & to hang-out while I work on >200V. (You should already have someone to fill-in for the muttz if you become temporarily disabled. That person might be a good candidate.)

That's probably a good idea.

FWIW, I discovered that the outlet on the stove end is (of course) a higher-current version of the HHN type plug, so it's got three straight blades rather than two straight and one L. I don't have a plug for that one, so I have to use the one the dryer plugs into, which naturally is in a small utility room off the back family room (which was a back porch when the house was built, I think). This means I can't put any bikes right next to the power supply for charging/etc, so I'll have to run a longer charging lead than I would like, by a few feet.

I went ahead and did it alone, since all it involved was wiring the cord/plug to the Sorensen, and then plugging that into the wall receptacle. Just to be sure, I left the breaker for that receptacle off at the main box during plugin, and only turned it on after. Then I went back inside and turned on the front panel switch of the Sorenson, which is a rocker that toggles the three panel-style breakers inside (one for each 220 leg). Powered right up, and verified no voltage AC or DC to case from floor, walls, objects, etc.

Turned it off and pulled out the original powerchair motor I used on CrazyBike2, and wired that to the big bolt-on terminals on the back, braced the motor, and turned it on. Cranked voltage up to 24 (nominal for this motor) while turning up current limiting to let it have the full ~4A it takes unloaded. Pushed voltage up to 51V (which is where the OVP on the Sorensen happens to be set right now) and no problems, with the motor spinning very noisily away. I don't have a way to load the motor down since it's not attached to anything, so I'll later wire up a cable that can run from the small utility room to the family room just outside it's door.

Then I can connect that to CB2's mounted motor, and load it down to verify current limiting/etc at higher loads. Of course, that's after I fix CB2's drivetrain, which might be a while.

In the meantime, I'll use it to charge up various batteries I have around, mostly SLA. Still building the LiCo pack, and that one I'm tempted to run charging wires out the window in the family room to the backyard and charge it out there. :lol:

you used the term "three phase". if this supply requires three phase power then you cannot use it on your normal house wiring.

if it is single phase, then you can wire the hot legs to each side of the 240V. ground to equipment ground.

dnmun said:

you used the term "three phase". if this supply requires three phase power then you cannot use it on your normal house wiring.

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As the original post says, it can use either single or three phase (it just takes more current on single phase, and is limited to a 500W lower power output than with three phase).

I'd rather have three phase, but as you point out, normal house wiring won't have that. (Some do, when they've had it installed special).

if it is single phase, then you can wire the hot legs to each side of the 240V. ground to equipment ground.

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I don't have the option of ground (other than tying to a water pipe, perhaps) in the utility room it has to go in, unless I run the ground wire separately to a 110V outlet that's elsewhere in the house.

I've already successfully tested it using the HHN wiring, after verifying this should be ok with a few sources (between this thread, the DIYEC thread, book/web research, and local info). I tried asking Sorenson (Ametek), but they just put me on hold and hung up on me.

you should stop now if you say there is no ground. you really need to understand how the wiring works before going forward. you have a ground with your service entrance cable and if you don't know that, you need to stop before you do something really bad.

dnmun said:

you should stop now if you say there is no ground. you really need to understand how the wiring works before going forward. you have a ground with your service entrance cable and if you don't know that, you need to stop before you do something really bad.

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I do understand how the wiring works, or at least I am sure enough to work with it, carefully as always. It's possible that I don't understand, which is part of why I made this thread (and the one on DIYEC). The responses I got so far that refer to safety, except yours, have said that using the neutral for ground does not create a safety hazard, unless the neutral were to become disconnected. Since that's also true if ground were to become disconnected, it's a moot point.

What specifically is not safe about how it's setup now? I ask because it is now the same setup as the dryer and the stove are. If it's unsafe I want to fix it.

There is no separate ground at that outlet (or for several others around the house). Neutral is grounded because of the ground for all the neutral connections at the main breaker box (which is outside the house, about half the length of the house away).

When I say there is no ground, I am specifically meaning that I have no point in that room that is already wired as a ground pin at a receptacle, or a ground wire in the cables leading into the room. So in order to run HHG instead of HHN, I would have to run a ground wire from that room to another room that does actually have a ground.

Due to the age of the house there weren't grounds for most points in the house originally. The prior people fixing or adding/upgrading electrical stuff in the house added a few. Some they added grounds to the receptacle boxes but not to the actual receptacles. Some of them I have added grounds, where I could verify that the existing ground wire to the receptacle box is actually a real ground to the main breaker box, that was used.

If I could, I'd replace the entire house wiring setup, including main breaker box, but I don't have the money for that, and I am just a renter anyway (and currently only paying less than 1/2 rent at that, thanks to my understanding landlord who is just about as strapped as I am these days--but I'll owe the rest of it as soon as I can start earning enough to pay it back).

Is your neutral and gound bus bars bonded together in the panel?

Hmm...I had thought I had answered and replied to this, but I guess not. Yeah, they are actually the *same* buss bar as far as I can tell (it's an old house).

I attached the dryer type cord and tested the Sorenson on that outlet ok; no grounding, case voltage, or other issues that I can determine with a meter.

amberwolf said:

dnmun said:

you should stop now if you say there is no ground. you really need to understand how the wiring works before going forward. you have a ground with your service entrance cable and if you don't know that, you need to stop before you do something really bad.

Click to expand...

I do understand how the wiring works, or at least I am sure enough to work with it, carefully as always. It's possible that I don't understand, which is part of why I made this thread (and the one on DIYEC). The responses I got so far that refer to safety, except yours, have said that using the neutral for ground does not create a safety hazard, unless the neutral were to become disconnected.

Click to expand...

1) the neutral line could carry current so may have quite a high AC voltage on it with respect to ground (that you are standing on). This can give you a "surprise" even when there is no other fault!

2) If there is another fault (disconnected neutral, mis-wired outlet, etc) then you have no other protection. That's the whole point of having a protective ground circuit as well as neutral which is bonded to ground.

Provided you understand this, you can make your own decision about whether it's safe to use.

Personally I would not connect the equipment ground to Neutral, unless you are sure that the wire from that outlet goes directly to the breaker panel and isn't shared with any other outlets. And that there is a working GFI breaker in use (take your own if you are charging at other peoples properties).