What do you make of this?

Saw a main breaker today on inspection. 200 amp breaker labeled for 1/0-4/0 copper SEC. Is 1/0 copper sufficient for a 200 amp breaker? I’ve seen it twice now and both times I’ve deferred it to an electrician to evaluate. Now, I see this breaker saying its ok to use 1/0 on this 200 amp but was always told (and taught) that 1/0 is for 100 amp and 2/0 is for 200 amp. What’s the story??

1/0 copper can be OK up to 175a using the residential main feeder rule 310.15(B)(6) but not 200, Good call.

I doubt you will ever see a 175a panel so 1/0 is effectively 150a

and both times, the panel had the “approved” sticker by the electrical inspector when the house was built. I was starting to doubt myself which is why I am trying to find this out.

Here is a pic of the breaker

irving 003.jpg

NO. 240.6 of the NEC list the size of overcurrent devices as outlined here

Here we can see that a 175 is a standard size for a breaker. Using Table 310.16(B)(6) a 1/0 conductor can be used on a 175 amp service for a dwelling unit only. Being that 175 is a standard rating for an overcurrent device the rule outlined in 240.4(B) clearly states that a 175 must be used.

It would be better to look at 310.16(B)(6) as you can see that a 100 amp service can be supplied with a #4 copper or #2 aluminum conductor.

How would the electrician go about fixing this problem? Do they replace the 1/0 SEC with 2/0 or replace part of it? Not sure how this would work. thanks

Replace the SE or replace the breaker. The tradeoff is labor vs cost. The breaker may be over $100 depending on what panel it is.

Scott, I read that breaker label as ONE 4/0 cable, I could be wrong I have been before.:smiley:


I can see how you can see it like that but that’s gotta be wrong cause there’s no way they’d say that you gotta use only a 4/0 for a measly 200 amp breaker.

so that would be a #1 up to a 4/0:D

The information is for the terminal lugs, showing you what size conductors you can use in those terminals, along with the specified torque. It is not there as an indication of what wire size is acceptable for a 200 amp load, it is there to indicate what size wire is acceptable for those terminals. The correct wire size for the load is determined by referring to the applicable code.
Any electrician who would size conductors to this label is not really an electrician.

nope…it means…CU it will accept Size # 1 THRU 4/0 in AWG sizes of CU…not that it needs (1) 4/0…:slight_smile:

I have a 30 horse power 240 volt three phase motor.

Looking at Table 430.250 this motor is rated at 80 Full Load Amps.

Looking at 430.22 a 125% factor must be applied to the Full Load Amps of this motor in order to size the branch circuit supplying this motor. 80 times 125% equals 100 amps for the conductor.

Looking at Table 310.16 for a TW copper conductor for this motor I find that it will require at least a #1 AWG conductor.

Table 430.52 gives 250% as the multiplier for an inverse time circuit breaker and this will look a little like this 80 X 250% = 200 amps.

Now I have a 200 amp breaker that will have a #1AWG conductor and all is legal.
Thus the listing for 1 through 4/0 on the terminals. :wink:

Hey Mike, how you been?

lol…very nice…but I hope these guys don’t actually see a 30HP 3-phase motor in a normal dwelling anytime soon…tehehehe…

The good Lord keeps blessing me more and more, thank you kindly for asking and giving me a chance to praise his name again

Just wanted to explain one way that a #1 AWG conductor could land under a 200 amp breaker as there seem to be some question raised in an earlier post about the #1 AWG conductor.

Looking to get me another one of them boxes like you got.

They might see one if Tool Time Tim sells his place.

lol…I hear ya Brian…Mike…I got ya brother and I will give ya one of them green boxes…:slight_smile: