I am running both single phase 240 and three phase 240 in my shop. I discovered that each of the locking, industrial round plugs for these (L14-30R and L15-30R) can fit in one double gang box. Is there any code problem with doubling them up? The single phase 240 comes from the breaker, and the three phase 240 comes from a three phase converter fed from the same panel.


Yeah, the plugs may not physically clear when installed next to each other at 1-gang spacing. I would recommend using 2 separate boxes for that reason.

That said, you can put both voltages in the same junction box, but you must clearly mark them to distinguish them.

  • Having 3phase means you have single phase available...
    – Solar Mike
    Mar 26 '20 at 8:41
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    @SolarMike Not necessarily, OP might have 240V plain (non-wild-leg) delta and 120/240V split-phase. Mar 26 '20 at 8:55
  • Ok, 3phase I have seen in two different countries is 3 phases and a neutral plus earth...
    – Solar Mike
    Mar 26 '20 at 9:23
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    Wouldn't the delta voltage of a 3 phase system with 120V star voltage be ca. 208V, and not 240V?
    – xeeka
    Mar 26 '20 at 10:28
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    @SolarMike Yes, 240V3ph often has neutral stuck halfway down one leg, allowing 120/240V split-phase along that leg. This is called "wild leg" because it's asymmetrical. However, given that there's already a 120/240V service present, the 240V service doesn't need to be wild-leg, and may be plain delta in some fashion as TPE describes. Mar 26 '20 at 15:17

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