Code question - 3 phase 208v nema plugs

[jkeyser14]

Is there anything that specifies the proper 3 phase connector to use in residential applications? I'm going to start setting up my metalworking shop in my garage and wanted to know what style plugs to use on the machines (NEMA 18-30's or NEMA 21-30's?). At a previous shop, we had used 18-30's, but this wasn't residential. Equipment being run will be mills, lathes, an air compressor, and a welder. Due to load requirements, I'm guessing that the welder will have to be directly wired to the phase converter with a disconnect switch in between.

[LoneGunman]

No idea, I don't see a reason for cord connected 3 phase machines besides a welder.

[Stuart in MN]

One's a twistlock and the other has straight blades, I think it's up to you which one you prefer. As long as the plugs and receptacles are NEMA and sized for the voltage and ampacity, it shouldn't matter which one you use.

[jkeyser14]

One's a twistlock and the other has straight blades, I think it's up to you which one you prefer. As long as the plugs and receptacles are NEMA and sized for the voltage and ampacity, it shouldn't matter which one you use.

There is a difference, one has both earth and ground, whereas the the other just has ground. I'm obviously not an electrician and I will be hiring one to do the work, but I was hoping to figure out what components I would need so I can start to keep an eye out for them at the local industrial surplus center.

[W-Cummins]

One's a twistlock and the other has straight blades, I think it's up to you which one you prefer. As long as the plugs and receptacles are NEMA and sized for the voltage and ampacity, it shouldn't matter which one you use.


The nema #18 is available in straight blade or twist lock, the nema #21 is locking only but, normally neither is used for what he want's to do.

You should probably be using a 15 series plug (3 phase, 3 pole, 4 wire grounding 250v )

So a 15L-30-p for a locking or a 15-30-p for a non-locking plug


FYI

the #18 plug is a 4 pole 4 wire w/o ground 3 phase "Y" 120/208V

and

the #21 plug is a 4pole 5 wire grounding plug 3 phase "Y" 120/208V

BTW there are lots of reasons to use plug attached 3 phase equipment, and I use multi-receptacle branch circuits all the time too...

William....

[jkeyser14]

You should probably be using a 15 series plug (3 phase, 3 pole, 4 wire grounding 250v )


Thanks. What's the reason the 18 and 21 aren't normally used?

[W-Cummins]

Thanks. What's the reason the 18 and 21 aren't normally used?


They are both dual voltage plugs, and most 3 phase machines don't require 120V single phase and/or if they do ( ie. control circuit voltage) they make it at the machine with a small transformer. The number 18 also doesn't have a equipment ground with it, so I don't see a lot of use for it anymore. I guess you could have a 120/208 Y double insulated device that didn't require an equipment ground but I have never seen one.

William....