# Wire size, 3ph Delta, 120/240

Show 40 post(s) from this thread on one page
Page 1 of 4 1234 Last
• 07-10-2012, 09:53 PM
Homeownerinburb
Wire size, 3ph Delta, 120/240
Hey, anyone want to tell me the de-rating?

The engineer has decided for reasons that I am not privy to, to spec a 125a 3pole on the switch gear to feed the sub panel I hope to be installing next week.

He had originally drawn it with a 100a 3pole, and spec'd #1 cable.

I'm going to need to pull 1/0, yes?

I don't work a lot of three phase. Happily the switch gear is less than a year old, and there is a blank open for the new breaker.

Not like some Frankenstein equipment in some damp basement.
• 07-10-2012, 11:41 PM
ActionDave
If you have less than three current carrying conductors in a conduit then you may not need to derate. For 3phase delta you would only have three. If you are under '11 code then there is a whole new set of rules concerning temperatures.

310.15 is still the place to look.
• 07-11-2012, 08:01 AM
jwelectric
A #1 copper THW conductor is good for 130 amps so I see no problem.
• 07-11-2012, 08:16 AM
Homeownerinburb
Quote:

Originally Posted by jwelectric
A #1 copper THW conductor is good for 130 amps so I see no problem.

Three hots and a neutral (four conductors) does not demand a derating?

I'm not complaining, the pull will be by hand, down 50' of 2", probably 3 x 90 degrees. With a #6 ground.
• 07-11-2012, 10:43 AM
jwelectric
145*.80=116 (use the 90 degree column for derating)
240.4(B) next highest OCPD = 125 amp
I see no problem
But it was a good question, it shows you are thinking
• 07-11-2012, 01:36 PM
Homeownerinburb
Quote:

Originally Posted by jwelectric
145*.80=116 (use the 90 degree column for derating)
240.4(B) next highest OCPD = 125 amp
I see no problem
But it was a good question, it shows you are thinking

I'll tell you one thing for sure. I don't want to buy 200' of #1, get the businesses in the building to understand that they are going to lose power over night, call the alarm Co and tell them the same, get some burly guy (likely the plumber I will be working across from on this one) to show up at 7pm, help me tug that crap thru, only to have the inspector at rough inspection ask me why I was keeping my head in my ass, and tell me that I had to do all that again, plus buy 200' of 1/0 on my own dime. A mistake like that and I'd pretty much be doing the rest of the damned job for free.

I'd sooner put in some backstab outlets!
• 07-11-2012, 07:47 PM
ActionDave
Quote:

Originally Posted by Homeownerinburb
Three hots and a neutral (four conductors) does not demand a derating?
.

The neutral does not count as a CCC for derating if it only carries the imbalance of the load.
• 07-11-2012, 08:45 PM
Homeownerinburb
Quote:

Originally Posted by ActionDave
The neutral does not count as a CCC for derating if it only carries the imbalance of the load.

I keep forgetting. I do so little 3 phase.
• 07-13-2012, 12:58 PM
ballvalve
I have 3 phase, 3 hots and a neutral . One wire is 277 or so volts to N - the other 2 wires are 240 volts to each other. Those 2 to neutral are 120 volts. This I assume is the 4 wire [ ground] 120-240 delta configuration. The POCO warns me not to try and start more than a 20 HP motor without a soft starter.

Its a great system as one need not have the burden of transformers.

But my question is why would the feed wires not be down sized as in all of the feeds to the 3 phase motors? Certainly the "stinger" high voltage wire could be smaller.....
• 07-13-2012, 06:17 PM
Homeownerinburb
Quote:

Originally Posted by ballvalve
One wire is 277 or so volts to N

Are you sure that it is not 208 to neutral?
• 07-13-2012, 09:30 PM
ActionDave
Quote:

Originally Posted by Homeownerinburb
Are you sure that it is not 208 to neutral?

Couldn't be anything else.
• 07-13-2012, 09:37 PM
ActionDave
Quote:

Originally Posted by ballvalve
I have 3 phase, 3 hots and a neutral . One wire is 277 or so volts to N - the other 2 wires are 240 volts to each other. Those 2 to neutral are 120 volts. This I assume is the 4 wire [ ground] 120-240 delta configuration. The POCO warns me not to try and start more than a 20 HP motor without a soft starter.

Its a great system as one need not have the burden of transformers.

But my question is why would the feed wires not be down sized as in all of the feeds to the 3 phase motors? Certainly the "stinger" high voltage wire could be smaller.....

In a Delta service all three hots read 240V phase to phase.
• 07-13-2012, 11:05 PM
Homeownerinburb
Quote:

Originally Posted by ActionDave
Couldn't be anything else.

• 07-13-2012, 11:06 PM
Homeownerinburb
Quote:

Originally Posted by ActionDave
In a Delta service all three hots read 240V phase to phase.

What color code is most common in your experience with this arrangement?

Black, Red, and Orange for the wild leg?
• 07-13-2012, 11:18 PM
ActionDave
Black, orange, blue- three phase delta.

Black, red, blue- three phase wye.

I have heard that in California purple is used for the high leg.
Show 40 post(s) from this thread on one page
Page 1 of 4 1234 Last