Question on upsizing conductors
- Thread starter Mustwin351
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Mustwin351
Senior Member
- Location
- Texas
The system is a 4 wire 3 phase wye 120/208 and I am using
Two 30 amp breakers which are 2 pole............equals 6 ccc
Four 20 amp breakers which are single pole.....equals 8 ccc
for a total of 14. Is that correct?
if i were to use a double pole breaker for the 20 amps and share neutrals I could get down to ten ccc but that still puts me at 50% derating.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
For a 208Y/120 volt system a 3 wire MWBC would be considered 3 CCC's.
Mustwin351
Senior Member
- Location
- Texas
Yes but if i used a double pole 20 amp breaker instead of two 20 amp single pole breakers...I could share a neutral and have two less CCC's....so that would put me at 12?
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Yes that's correct, initially you said 10 but either way, 10 or 12 you're still at 50%.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
OK, say a 30 amp double pole breaker is handle tied to a 20 amp single pole breaker on the third phase. Then the 3 ungrounded conductors could be run with a single 30 amp neutral as an MWBC that counts as only 3 CCCs. Any problem with that?
If not, do that twice, and use a double pole 20 amp breaker with a 20 amp neutral for another MWBC. That makes only 9 CCCs, so 70% derating would apply.
Cheers, Wayne
If not, do that twice, and use a double pole 20 amp breaker with a 20 amp neutral for another MWBC. That makes only 9 CCCs, so 70% derating would apply.
Cheers, Wayne
No that's not correct. You got it right earlier. Must have a 4-wire mwbc before the neutral don't count.Yes that's correct, initially you said 10 but either way, 10 or 12 you're still at 50%.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Then make the splice in a neat and workmanlike manner.
What is the load on the 30 amp circuit? 15 and 20 amp circuits with general use receptacles might need to be counted as 15 or 20 amps when figuring ampacity adjustments. 30 amp circuits are not so much general use and you may be able to count the actual load instead of full 30 amps - 27.5 amps of load only needs 8 AWG instead of 6 AWG @ 50% adjustment of 90C values. If no receptacle outlet on the circuit - then you definitely only need to look at the connected load.
- Occupation
- Licensed Electrician
Just adding a handle tie won't do it. You would have to re-wire the circuits and abandon the extra neutrals; even though that would work electrically I'm not sure it satisfies 210.4(C) ex. 2 because the handle ties do not the breaker a common trip.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
Yeah, it looks like 210.4(C) exception 2 is stricter than necessary. It seems like it should be enough for all ungrounded conductors serving a single piece of equipment to open simultaneously, which the double pole/single pole handle tied together would achieve in the OP's load case.
If the OP can install (2) 20 amp single pole OCPDs at the load end, then my idea would still work using a 30 amp 3 pole breaker.
Cheers, Wayne
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Which part is not correct? If he goes from the original 4-20 amp 2 wire circuits (8 CCC's) to two 3-wire MWBC's he still has the 4 circuits but ends up with 6 CCC's then add the 6 CCC's for the two 30 amp circuits he ends up with 12 CCC's.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
You must count the neutral unless it is full house-- one neutral and 3 hots. If you have two hots and one neutral then you have to count the neutral. Of course, I am assuming linear loads.
You have to count the neutral of a 3-wire circuit on a 208/120 system. While it meets the definition of a multiwire branch circuit, the neutral "discount" only applies to a full boat [310.15(B)(5)(b)].
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