208 volt circuit and receptacle

[Greg1707]

I have a job installing a circuit for a 208 volt copy machine. The specifications call for a NEMA 6-15 2 pole, 3 wire, grounding rated at 250V/ 15AMP.

What is up with this? If I install this type of receptacle on a 208 volt circuit--what would prevent some unsuspecting person from plugging a 240V device into this receptacle?

 

[480sparky]

You have to install a 250v receptacle.... there is no such thing as a 208 volt receptacle.

 

[Greg1707]

You have to install a 250v receptacle.... there is no such thing as a 208 volt receptacle.

Great. So there is nothing to alert the consumer that the receptacle is actually supplied by 208 and not 240 volts?

 

[zbang]

Great. So there is nothing to alert the consumer that the receptacle is actually supplied by 208 and not 240 volts?

Only the label that you put on it. (And the knowledge that most larger commercial buildings are 120/208, so nothing will actually be 240v.)

 

[iwire]

You have to install a 250v receptacle.... there is no such thing as a 208 volt receptacle.

Take a look at a NEMA 18.

But for 2 pole, 3 wire, grounding plugs and receptacles I agree with you.

 

[LarryFine]

So there is nothing to alert the consumer that the receptacle is actually supplied by 208 and not 240 volts?

Only the knowledge that almost everything is rated for 208v or 240v these days.

 

[Greg1707]

minimun number of conductors

minimun number of conductors

Thanks for the information. I don't have much experience with this voltage so please excuse the following question. Am I correct in assuming that I can run two 208 volt circuits using a three wire MWB?

 

[iwire]

Thanks for the information. I don't have much experience with this voltage so please excuse the following question. Am I correct in assuming that I can run two 208 volt circuits using a three wire MWB?

No.

Two 208 volt single phase circuits requires four conductors plus a equipment grounding means.

 

[Greg1707]

No.

Two 208 volt single phase circuits requires four conductors plus a equipment grounding means.

Thanks for saving me on this one!!

 

[LarryFine]

Of course, Bob's answer didn't include: "But, you can run a single MWBC (Multi-Wire Branch Circuit) to supply two loads, depending on whether the loads require individual supplies."

For two copiers, or any two similar loads, I wouldn't even consider doing it.

 

[Greg1707]

Of course, Bob's answer didn't include: "But, you can run a single MWBC (Multi-Wire Branch Circuit) to supply two loads, depending on whether the loads require individual supplies."

For two copiers, or any two similar loads, I wouldn't even consider doing it.

Larry, could you please expand on your comment? It will educate a lot of us who work primarily with 120/240.

 

[LarryFine]

Larry, could you please expand on your comment? It will educate a lot of us who work primarily with 120/240.

Unless I'm mistaken, Bob was saying that two separate circuits cannot, by definition, share any CCC's. A MWBC is (or can be) considered to be a single circuit.

You can supply two 208v 1ph loads with three conductors, as long as you realize the shared conductor will carry more than the others, and it's okay with the loads.

 

[iwire]

You can supply two 208v 1ph loads with three conductors, as long as you realize the shared conductor will carry more than the others, and it's okay with the loads.

We could do a lot of things but normally we would like the circuits to work and comply with the NEC.:roll:

Unless he is running dedicated circuit for very two very small loads he would have a capacity issue with the shared conductor.

I am willing to bet a 208 volt printer uses more than 50% of the circuit that supplies it.

 

[LarryFine]

We could do a lot of things but normally we would like the circuits to work and comply with the NEC.:roll:

If the right-sized conductors and multi-pole breaker are used, why couldn't such an install be compliant?

Unless he is running dedicated circuit for very two very small loads he would have a capacity issue with the shared conductor.

Agreed. I was just generalizing; it is doable under the right conditions.

I am willing to bet a 208 volt printer uses more than 50% of the circuit that supplies it.

Agreed, as evidenced by the last line of post #10.

 

[Greg1707]

mwb 208v

mwb 208v

Now I am confused. I thought that in a 208/120 system:

there is 120v between any leg to ground?
there is 208 v between any two legs?
If I used a 3wire cable with a two pole breaker and share a grounded conductor would not I have 120 volts to ground on each leg?

 

[iwire]

Greg you are right, what Larry is describing would not use the neutral and would be at best a very unusual circuit arraignment.

 

[LarryFine]

Now I am confused. I thought that in a 208/120 system:

there is 120v between any leg to ground?
there is 208 v between any two legs?
If I used a 3wire cable with a two pole breaker and share a grounded conductor would not I have 120 volts to ground on each leg?

Greg you are right, what Larry is describing would not use the neutral and would be at best a very unusual circuit arraignment.

As Bob said, you're right.

I was talking about using a 3p breaker, and supplying one 208v 1ph load between, say, A and B phases, and the other between, say, B and C phases.

Basically a variation of a MWBC.

We have discussed using such a wiring scheme to provide simultaneous two-element operation of a water heater to provide faster heating/recovery time.

 

[iwire]

We have discussed using such a wiring scheme to provide simultaneous two-element operation of a water heater to provide faster heating/recovery time.

I would love to see what you come up with as a practical and code compliant use of the circuit to supply two receptacles as the OP was asking about.

 

[LarryFine]

I would love to see what you come up with as a practical and code compliant use of the circuit to supply two receptacles as the OP was asking about.

Me, too.

 

[Greg1707]

three phase

three phase

Okay, final questions.
Where can I find information on three phase to educate myself?

On a 208/120 system was is the minimum number of conductors I can use to install 2 15amp receptacles each on a dedicated circuit?

I assume there are only two choices? 3 or 4?