I have a 5kW appliance that normally accepts 3-phase power, but can also run on 220V. The manufacturer indicates that when running on single-phase 220V, to connect 220V hot to all three input phases as shown in the picture below: 220V connection diagram

I am in the US, however, so I don't have a single 220/240V hot conductor with respect to neutral. How can I power this thing?

Technically I can see that a solution would be to use a 1:1 transformer to turn the two hots into a single 240V phase with respect to neutral, but I am not sure if that is how this kind of appliance is typically powered. What is the normal way to do this?

  • What kind of appliance is this? (It sounds like a range or cooktop to me, but it could be some other sort of heating appliance instead.) Furthermore, are you running a new circuit for it, or are you wanting to run it off an existing branch circuit? – ThreePhaseEel Dec 22 '18 at 16:14
  • I do plan to run a new circuit, of course. The appliance is—well it’s not really an appliance per se—it’s a Pcb reflow oven – Zane Kaminski Dec 22 '18 at 18:34
  • Can you post a photo of the appliance's labeling? – ThreePhaseEel Dec 22 '18 at 18:47
  • I don’t actually presently have the unit. I’ll contact the manufacturer, I think – Zane Kaminski Dec 22 '18 at 19:34

Its made to operate on 5-continent power, in which 400V "wye" 3-phase is delivered to the neighborhood, then each house gets 1 phase + neutral (230V), or more than one phase if load warrants. The device is designed to support using 3 phases separately, so they can be evenly loaded.

Whether this is well insulated enough to use in North American/Philippines split phase 240V, with no neutral and center-tap ground, is a question for the manufacturer.

And the manufacturer's reputation.

Note the sections of US NEC:

110.2 Equipment shall be approved. [by UL or other responsible testing lab, or some equivalent satisfactory to your local authority].

110.3 Equipment shall installed and used according to its labeling and instructions.

Your insurance company has a say too, if shabby, unlisted equipment caused your fire, they don't need to pay. That's why UL is called Underwriter's Laboratories.

  • 400v? Is that just what it's called or do you get that across 1p and the neutral? Why would there be no neutral on NA power? If you use a 3p transformer, you lose the neutral? – Mazura Dec 22 '18 at 16:42
  • 2
    @Mazura 400V is what you get pole-pole on a 400V "wye" system of the 5-continent style. "Wye" means you are using the neutral, it's wired like a Y, not a delta. Pole-neutral is 230v, which is not coincidentally 400V divided by sqrt(3). – Harper - Reinstate Monica Dec 22 '18 at 16:51
  • Note that your parenthetical isn't quite right -- "approved" in Code means the AHJ has the final say, although they often delegate to UL or some other test lab. The code says "listed" when it explicitly wants a NRTL listing for the appliance (i.e. the call's no longer in the AHJ's hands) – ThreePhaseEel Dec 22 '18 at 17:55
  • Well I certainly didn’t plan on connecting one of the split-phase hot conductors directly to the neutral of the machine… That’s why I mentioned using a 1:1 transformer. – Zane Kaminski Dec 22 '18 at 19:34
  • @ZaneKaminski nothing inherently wrong with the concept of hotting neutral. The question is whether the manufacturer will or has certified that the machine is sufficiently insulated to permit you to do so. Neutral is not ground, and neutral should be insulated from chassis. – Harper - Reinstate Monica Dec 23 '18 at 0:05

If this was a portable appliance under ~3KW we were talking about then I would say go ahead and connect one of your hots to the appliances "neutral" and the other to it's "live". Unpolarised mains plugs are common enough that only a crazy manufacturer would build a low power portable appliance that depended for it's safety on the neutral actually being neutral.

But this is a 3 phase appliance (albiet one that can be wired up single phase as well if desired) intended for fixed installation. In such cases the manufacturer may have been less concerned about the possibility of Neutral not actually being Neutral.

I suspect most likely it will be fine, but I'd want confirmation from the manufacturer to be sure.

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