At my place of work, which is in the US, I had an electrician install a 3-phase outlet. He used a NEMA L14-20 receptacle and left us a NEMA L14-20 plug to connect to the device which uses the power. This is a 208 V installation (measures at 212V phase-to-phase, and all three phases present, plus GND). We plan to use it to power a servo-motor drive. The drive model is SVA-2300 from automation direct.


This doesn't seem right. Seems like he should have used a NEMA L15-20 receptacle and plug. Is it common or correct to use NEMA L14-20 receptacles for 3-phase power? Should I ask him to redo it or just use the plug he left for us? Obviously it will work and be safe for us, but it seems like if someone came along and plugged in something else to that outlet, it could be a problem for them.

He is a professional electrician and the work is well done and neat otherwise.

Edit History: added 'L' prefix. This is a locking connector. It is a 208 V outlet (measures at 212 phase-to-phase). Noted that all three phases are present. Added information about load.

  • What voltage is this at? Jul 22 '16 at 1:15
  • I didn't measure it. I assume it is 208 or 240.
    – mkeith
    Jul 22 '16 at 1:29
  • That's a big difference -- 208 would mean you have wye, while 240 implies delta Jul 22 '16 at 1:42
  • I'll measure it. I think it is Delta, though.
    – mkeith
    Jul 22 '16 at 1:44
  • It is 208 V phase-to-phase.
    – mkeith
    Jul 22 '16 at 1:50

NEMA 14-20 are intended for two phase power. Of the four conductors, two are energized, one is neutral, and one is ground.

enter image description here (NEMA 14-20 diagram)

A NEMA L15 is specifically intended for 3 phase power including a ground (but no neutral). The number after the hyphen is the current rating. That is, NEMA L15-60 is for 60 ampere conductors.

enter image description here (NEMA L15-20 diagram)

As you can see, they look vitually identical. See the full chart here.

I can see why one would make the substitution. The NEMA 14 is like a $25 connector. The L15-20 is closer to $60, each side. They both accommodate four wires. I am sure it would not pass muster to substitute one for the other, but in a private, non-commercial, non-permanent installation where there is no possibility of intermixing the connectors with other devices and outlets, it might be okay safety-wise with durable signage present.


Since you are dealing with 208Y/120V three phase power, the L14-20 isn't quite right -- its presence signifies two phases/neutral/ground, and you don't have a neutral here. The L15-20 is 3phases/ground without a neutral, so it can be used in your application; a L21-20 + adapter can be used instead if something that needs the neutral might be plugged in here in the future.

  • There is no 120 anywhere. It is three phase 208 + GND. I mean, there is 120 elsewhere in the building, but not at this outlet. There is no reason I can see to connect neutral to the outlet.
    – mkeith
    Jul 22 '16 at 5:24
  • @mkeith -- Eh? What are you plugging into this thing that can run off of 208Y without a neutral? Jul 22 '16 at 11:40
  • It is a servo-motor drive. automationdirect.com/adc/Shopping/Catalog/Motion_Control/…
    – mkeith
    Jul 22 '16 at 16:38
  • @mkeith -- interesting...it indeed doesn't require a neutral Jul 22 '16 at 22:11
  • 2
    @mkeith -- I'm still not sure what the requirements for 3 phase wye receptacles are -- I went through section 406 in the code and it's silent as to whether the receptacle needs to provide the neutral or not Jul 23 '16 at 18:34

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