3P 208/120 L21-30 SO workbench drop

[cyamaha2007]

Hello,

I’m setting up a new construction shop at work and have a question about multi wire branch circuits. I have 10 work benches that need 3 phase 208 and single phase 120.

I want to mount a multi gang box to a Lista cabinet and have a 4 or 5 pin 208 receptacle (my 208 equipment does not use the neutral). And a quad 120 receptacle.

I understand that doing this will load 1 phase unevenly but the 3 phase equipment only pulls 7 amps and the 120 load is to charge cell phones & power tool batteries. Secondly I would use a different leg on the next bench to help balance the phases.

I cannot find any reason this is not legal but 1 electrician says that you cannot use a leg of 208 to neutral to make 120 in the multi gang box.

I’m a machine tool electrician so I’m not the best with the NEC.

I want to use the 5 wire 12 or 14 gauge SO cord I have in stock if possible.

Thanks for your time.

 

[loganb]

First question....why SO drop cord with a plug at the top instead of conduit to the box? That cord/plug/receptacle has to be substantially more money then EMT and pulling the necessary THHN.

 

[cyamaha2007]

The benches are on wheels and I need to reconfigure the layout if we get a large project.

There are no walls to mount drops to. The work area is in the center of a 60000sqft building with 50ft column spacing. If I had partition walls I would prefer EMT.

The other benefit is that I can wire up the boxes on the benches and just plug them in on move day.

 

[cyamaha2007]

Duplicate post

 

[alfredeneuman]

A NEMA 21 is a 4 pole (5 wire), not 3 pole.
You cannot use a 30A breaker with a 15 or 20A receptacle.

 

[cyamaha2007]

A NEMA 21 is a 4 pole (5 wire), not 3 pole.
You cannot use a 30A breaker with a 15 or 20A receptacle.

Does it make a difference if I have 2 or 3 15a duplexes? Similar thinking that we are allowed to put a 15 amp duplex on a 20 amp circuit?

 

[cyamaha2007]

Does it make a difference if I have 2 or 3 15a duplexes? Similar thinking that we are allowed to put a 15 amp duplex on a 20 amp circuit?

Alfred,
I see now that this is not allowed.

For arguments sake let’s say that i change the ceiling plug to a L21-20 and I change the boxes on the bench to qty 2 L-18-20 and a Quad 120 duplex? All fed off a 3 pole 20amp breaker?


Last goofy idea is to keep everything 30 amp with no 120v receptacles. Then I cut the plugs off my HD power strips. Then I wire on a L21-30p. Now it’s a plug in device? I don’t really like that idea because it seems like I’m pushing my luck for a permanent setup. But I am curious if it’s legal.

Thanks
Chuck

 

[dave*99]

Does it make a difference if I have 2 or 3 15a duplexes? Similar thinking that we are allowed to put a 15 amp duplex on a 20 amp circuit?

No it does not. Still can’t do it.

 

[cyamaha2007]

No it does not. Still can’t do it.

Yes I see that now.

 

[walta]

No it does not. Still can’t do it.

You may well be correct that the answers is NO If you do not give us a clue as to what rules would be broken we do not learn much.

Please help us understand why not.

Are you allowed to have a 20A 208 3P multi branch circuit mixing 20A single phase outlets & 20A 3P outlets?

Walta

 

[wyliesdiesels]

You cannot use a 4-pin receptacle. You need 3 hots 1 neutral 1 ground

 

[cyamaha2007]

You cannot use a 4-pin receptacle. You need 3 hots 1 neutral 1 ground

For arguments sake let’s say that i change the ceiling plug to a L21-20 and I change the boxes on the bench to qty 2 L-18-20 and a Quad 120 duplex? All fed off a 3 pole 20amp breaker?

 

[American Locomotive]

I do not see why you could not do that. As long as the everything is 20A rated (including the breaker). There are plenty of 240v single-phase machines that have 120v convenience outlets on them.

 

[wyliesdiesels]

For arguments sake let’s say that i change the ceiling plug to a L21-20 and I change the boxes on the bench to qty 2 L-18-20 and a Quad 120 duplex? All fed off a 3 pole 20amp breaker?

18-20r is non-grounded 208Y/120 4 pole 4-wire

You need a 15-20r- 250v 3Ø 3 pole 4-wire

 

[cyamaha2007]

18-20r is non-grounded 208Y/120 4 pole 4-wire

You need a 15-20r- 250v 3Ø 3 pole 4-wire

Ok that makes sense to use a 15-20r.

Would I be allowed to use a L21-20R on the lower receptacle? I’m trying to understand if there is some magic problem that happens if the neutral is shared between the 110 and 208.

Thanks for your time.

 

[Chuckster in NJ]

Ok that makes sense to use a 15-20r.

Would I be allowed to use a L21-20R on the lower receptacle? I’m trying to understand if there is some magic problem that happens if the neutral is shared between the 110 and 208.

Thanks for your time.

No Magic!…….. Just basic electricity 101.

TIP! Call a pro!

 

[wyliesdiesels]

Ok that makes sense to use a 15-20r.

Would I be allowed to use a L21-20R on the lower receptacle? I’m trying to understand if there is some magic problem that happens if the neutral is shared between the 110 and 208.

Thanks for your time.

U want to use an L21-20 for a 3phase machine? Why does it need a neutral?

 

[cyamaha2007]

U want to use an L21-20 for a 3phase machine? Why does it need a neutral?

I don’t really want to use a L21-20 for a 3 phase machine. I just wanted to understand if it’s allowed.

Most people I’ve asked have told me it’s not possible but haven’t explained why. Even the electrical design engineer for the shell modification seems worried that it’s not allowed.

 

[wyliesdiesels]

I don’t really want to use a L21-20 for a 3 phase machine. I just wanted to understand if it’s allowed.

Most people I’ve asked have told me it’s not possible but haven’t explained why. Even the electrical design engineer for the shell modification seems worried that it’s not allowed.

I cant think of any reason why it isnt code permissible to do so. The neutral just wouldnt have a connection to the machine.

If someone tells you its not possible, ask them to explain themselves. if they cant then theyre full of BS

 

[jfleisher]

We use these in our data center racks for 208v 3 phase and 120v single phase. Just plug them into your 5 pin L21-30 receptacle.

AP8865 - APC NetShelter Metered Rack PDU, 0U, 8.6kW, 208V, 3 phase, 30A, 36 C13, 6 C19 and 2 NEMA 5-20R outlets | Schneider Electric USA

Schneider Electric USA. AP8865 - APC NetShelter Metered Rack PDU, 0U, 8.6kW, 208V, 3 phase, 30A, 36 C13, 6 C19 and 2 NEMA 5-20R outlets.

www.apc.com

 

[dave*99]

We use these in our data center racks for 208v 3 phase and 120v single phase. Just plug them into your 5 pin L21-30 receptacle.

AP8865 - APC NetShelter Metered Rack PDU, 0U, 8.6kW, 208V, 3 phase, 30A, 36 C13, 6 C19 and 2 NEMA 5-20R outlets | Schneider Electric USA

Schneider Electric USA. AP8865 - APC NetShelter Metered Rack PDU, 0U, 8.6kW, 208V, 3 phase, 30A, 36 C13, 6 C19 and 2 NEMA 5-20R outlets.

www.apc.com

Not sure how this fits the OP’s application…sure is pricey too.

 

[alfredeneuman]

Why not 2 separate cord drops (1 for the machine and 1 for the receptacles)?

 

[wyliesdiesels]

Why not 2 separate cord drops (1 for the machine and 1 for the receptacles)?

KISS