3 phase different size wire

B

Brownetown

Member
Location
Va
Occupation
Electrican
I ordered 3/0 wire for 175 amps(over sized it)

Factory sent me 1-2/0 and 2- 3/0. I didn’t catch it until after we pulled it in. Will resistance affect it in anyway possible with installing like it is. 2/0-is good for 175 but am I just over thinking it?
 
As far as I know, it would not be a code violation. Perhaps a slightly increased amount of voltage drop on the smaller conductor but unless you're going thousands of feet that should not be a functional issue. As long as your overcurrent device is sized to the smallest conductor it shouldn't be a problem. BUT it is generally good engineering practice to have all your current carrying conductors be the same size (except perhaps your neutral in some cases where you are allowed to downsize it and if you have one in the first place). My question to you is: will you be ok knowing that you left a slightly wonky wiring job behind?

I know demoing that 2/0 to replace with a 3/0 is going to suck. Leaving it as is would technically be correct, but making all 3 conductors the same would be the more correct option IMO.
 
Is this a 120/240 volt system and one of the conductors is the neutral? If so it is very common for the neutral to be smaller than the ungrounded conductors.
 
Oh and if this is for a 3-phase feeder for continuous loads, then you have to take Article 215.2 into consideration. Depending on the loads you intend on supplying, that 2/0 may be insufficient depending where you are on the ampacity table for your conductors.
 
3 phase 480 no neutral. It’s for a chiller min amps 132. I do understand tha with a voltage drop the 2/0 wil run hotter. But considering the 2/0 is still good for the amps would anything else be affected or any violations. I saw that on a parallel feed it is a violation
 
Ah a branch circuit feeding a chiller. Then 440.32 applies. That 132 min amps is probably the highest of the two between that and motor-compressor rated load current. So 132A x 1.25 = 165A, your 2/0 is good for 175A like you said, you're not running parallel conductors, so everything should be good to go. You may want to wait for more input from other users before finalizing your work though.
 
How long is the run?

A possible secondary impact is you will have different voltage drop on the different phases, which means the motor in the chiller will see unbalanced voltage, and unbalanced voltage increases motor heating.

Generally this isn't a problem unless the imbalance is greater than 1%, so I don't think different voltage drop will be a problem unless total voltage drop is too much anyway. Rather this is a small additional factor that might add to existing voltage imbalance issues.
 
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