Plug Explanation

T

TORQUIN

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I just bought a surface grinder and it had a 20A, 3 phase (4 conductor) plug. I use a 3 phase, 20A, 4 conductor plug for my old surface grinder. When I compared the two plugs I found they are different. The one I use has a smaller spade circle then the one that came with the new grinder and new grinder's plug has the lock lug on a different spade then the plugs I use. I purchased the plugs and sockets I use from Lowes/Home Depot. I have not been able to find info on the internet to tell me what's the reasoning behind this different size/configuration between these 20A, 3 phase, 4 conductor plugs.
Can someone explain to me what's going on here?

The two plugs, a new one I just bought on the left, identical to the ones I already use in the shop, and on the right, the plug that came with the new grinder.
2020-10-11 17.51.42-33.jpg

Thanks,
Chris
 
I'm no electrician, but here's an attempt to explain.

The L14-20 (orange) plug on the left is actually designed for "center tapped" 230V AC single phase. The center tap allows you to take 115 volts as needed. See http://www.generatorsforhomeuse.us/l14-20/

The grey-faced plug on the right is an "official" 3 phase connector. Note that is it's labeled "3øY" on the face. Both of these connectors are rated for 20 amps.

The fact that the L14-20 has 4 lugs makes it usable on 3 phase power, and I'm sure it's commonly used for such. But they're designed to be different for safety reasons - so that you don't try plugging a 3 phase machine into a single phase 230V outlet (or vice versa)

Notice that the next thread in this section, https://www.hobby-machinist.com/threads/wiring-my-3-phase-lathe-to-my-rpc.87560/ that the discussion is about L15-30 and L15-20 connectors. Both of these are are marked for 3 phase, 15 and 30 amps, respectively.

I'm sure that if Bi11Hudson joins the discussion, he can correct any mistakes I've made. Not only is he knowledgable, but also writes good, clear explanations.
 
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Since the are both 3 phase and both 20amps. You could switch the grinder to the L14-20 style.
 
Thanks, RJ! The Nomenclature chart does a good job distinguishing between 230V single phase and 3 phase.
...but...
Can't find the "stove/clothes dryer(?)" outlet that my shop was wired with ... NEMA 10-50
HPIM0268 copy.jpg
 
Papa Charlie said:
Since the are both 3 phase and both 20amps. You could switch the grinder to the L14-20 style.
Click to expand...
Already did. Changed the plug on the new grinder to use what I already use in the shop. I hate mismatched plugs and wiring.

Chris
 
Just figured out why my NEMA 10-50 isn't on the chart that RJ referenced - it's no longer "legal," just grandfathered. Wikipedia has a good discussion of current and old NEMA plugs/receptacles:
en.wikipedia.org

NEMA connector - Wikipedia

en.wikipedia.org en.wikipedia.org
... and here's another chart, which includes the 10-50, also does a good job of distinguishing between single and 3 phase connectors:

NEMA Straight Blade Reference Chart

StayOnline has created the NEMA Straight Blade Reference Chart so you can learn about NEMA configurations, such as NEMA 14 30 and NEMA 5 15. Contact us today!
www.stayonline.com www.stayonline.com

Enjoy!
 
Seems like the grey plug has no NEMA info on it. I don't know what the significance, if any, the "30Y" has.

Chris
 
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