I understand that in 1996, NFPA outlawed the NEMA 10 series outlet for new work. This is an ungrounded outlet, which provides 120/240v split phase (hot-neutral-hot).

I wonder if the same is also true of its ungrounded brothers in multiphase: The NEMA 2 series, for 240v single phase. The NEMA 11 series, which were used in 208/240v delta 3-phase. And the NEMA 18 series, used typically in 208v wye 3-phase. Are these also outlawed?

Of course, NEMA 1-15 remains universally common despite being ungrounded.

I guess what I'm asking is, did NFPA outlaw all >120v ungrounded outlets? Or did they only single out NEMA 10 because of its frequent appearance in household circuits?

1 Answer 1


The outlets themselves are not "outlawed".

Article 250.20 lists AC systems that are required to be grounded. Article 250.21 lists AC systems that are not required to be grounded.

The receptacle or plug configuration you use depends on the system you are connecting it to. NEMA 1-15 receptacles are still allowed to be used on ungrounded systems.

As long as the plug or receptacle is rated for the system it is to be used on, it can be used. The NFPA does not dictate the style of devices we use. If I had a device with straight 240 power with no neutral load I could use a NEMA 10 if I so desired with the third prong used for the equipment ground. For instance a large compressor. Normally this would be hard wired but the Code does not require that.

To summarize the NEC does not dictate the style of plug or receptacle used it only requires the system to be either grounded or ungrounded. The devices follow that requirement. Trade practice is followed to install the receptacles and plugs most used here in the US.

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