3 phase oven question

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horrorsix

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I have 2- 3 phase ovens to hook up in a local restaurant. The ovens are rated 10kw at 208v each. My service is 208v so the ovens each draw 48A. Would I need to use a 50A or 60A 3 pole breaker and would #6 copper wire be sufficient for the feed. Also what size ground is needed for a 50A circuit.

Last thing, I'm not sure if I'm running both oven feeds through the same conduit or not but if I do that would be 6 #6 wire and 2 grounds. Would 1 1/4" conduit be ok and should I use metal or schedule 40 conduit?
 
horrorsix said:
I have 2- 3 phase ovens to hook up in a local restaurant. The ovens are rated 10kw at 208v each. My service is 208v so the ovens each draw 48A.
Click to expand...

Are they three phase or not? If they are single phase the answer is 48A

10 KW * 1000 / 208 = 48

If they are three phase they are 28A

10 KW * 1000 / 208 / 1.73 = 28A

I will assume three phase and 28 amps. This can be done with 10 AWG on a 30 amp breaker. There is no reason that this circuit needs to be 125% of the KW as it is not a continuous load. If you run both circuits in a single raceway that will result in an 80% derate.

10 AWG THHN is rated 40 amps

40 x .8 = 32A

So if it was me doing the work.

Seven 10 AWGs in a single 3/4" EMT (six hots, one ground) or I might run Seven 8 AWGs in a single 1" EMT.

How would I choose?

It depends on how tight the price was for the work, in my opinion the 10 AWGs are legal but marginal, the 8 AWGs a bit better design.
 
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The ovens are 3 phase. Which I'm a little unfamiliar with. What does the 1.73 number stand for?
I understand how to figure out amps an a regular 120/240 circuit but the 3 phase has me a little confused.
 
The number 1.73 is a factor used when calculating power and amps of 3 phase loads. For a given KW load at a given voltage, current flow with a single phase supply will be 1.73 times current with a 3 phase supply. Probably not worded very well but might help.
 
horrorsix said:
The ovens are 3 phase. Which I'm a little unfamiliar with. What does the 1.73 number stand for?
I understand how to figure out amps an a regular 120/240 circuit but the 3 phase has me a little confused.
Click to expand...


1.73 is equal to the square root of three. For 3 phase calculations would always include this as a multiple of the voltage.

So for your oven current:

I=P/E

Since this is 3 phase you would multiply 1.73 by the voltage and end up with this:

I=P/E*1.73

I=10000/208*1.73

I=27.8 Amps


Bob had all of this info in his post.
 
iwire said:
Are they three phase or not? If they are single phase the answer is 48A

10 KW * 1000 / 208 = 48

If they are three phase they are 28A

10 KW * 1000 / 208 / 1.73 = 28A

I will assume three phase and 28 amps. This can be done with 10 AWG on a 30 amp breaker. There is no reason that this circuit needs to be 125% of the KW as it is not a continuous load. If you run both circuits in a single raceway that will result in an 80% derate.

10 AWG THHN is rated 40 amps

40 x .8 = 32A

So if it was me doing the work.

Seven 10 AWGs in a single 3/4" EMT (six hots, one ground) or I might run Seven 8 AWGs in a single 1" EMT.

How would I choose?

It depends on how tight the price was for the work, in my opinion the 10 AWGs are legal but marginal, the 8 AWGs a bit better design.
Click to expand...


You may notice that there is an asterisk on the 10 gauge wire, which takes you to the bottom of the table of 310.16 and tells you to look at 240.4D. Its my opinion that this disallows the #10 for this application ? (I believe that the load is continuous and above 30 amps). this means you would have to use a #8 (unless I'm completely wrong, which has been known to happen :grin: )
 
nakulak said:
You may notice that there is an asterisk on the 10 gauge wire, which takes you to the bottom of the table of 310.16 and tells you to look at 240.4D. Its my opinion that this disallows the #10 for this application ? (I believe that the load is continuous and above 30 amps). this means you would have to use a #8 (unless I'm completely wrong, which has been known to happen :grin: )
Click to expand...

I said 10s with a 30 or 8s with a 30.

There is no way that the oven fits the Article 100 definition of continuous load.
 
iwire said:
I said 10s with a 30 or 8s with a 30.

There is no way that the oven fits the Article 100 definition of continuous load.
Click to expand...

Didn't we recently have this discussion about a self cleaning oven operating for more than 3 hours?
 
infinity said:
Didn't we recently have this discussion about a self cleaning oven operating for more than 3 hours?
Click to expand...

Yes, but that still does may not meet the definition of continuous load.

The maximum load must last more then 3 hours and self cleaner I have seen had surface elements as well.


Do they make self cleaning commercial ovens?
 
So now that I understand 3 phase and how to calculate the correct amps how do I know if this oven is continues power or not. That will change my wire and conduit size. The ovens are beside each other so I'll be running all wires in the same raceway.
There's been a couple different opinions on this being continuous or not. From what I could find online I don't believe it draws continuous power which means with this rating ,10 KW * 1000 / 208 / 1.73 = 28A, I can use #10 wire and a 30amp breaker. Correct?
 
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