- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I don't believe you can go up to the next size breaker so you have to use a 50 amp
240.21(C)(6)(1)
- Thread starter chris kennedy
- Start date
- Status
I don't believe you can go up to the next size breaker so you have to use a 50 amp
- Location
- Connecticut
- Occupation
- Engineer
If the primary OCPD is greater than 400A, then the max secondary OCPD is 175A.
If the primary OCPD is 400A or smaller, then there is no max size on the secondary OCPD.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
- Location
- Connecticut
- Occupation
- Engineer
It's Table 450.3(B)
But we also have to comply with 240.21(C)?
- Location
- Connecticut
- Occupation
- Engineer
Yes.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
The op says the secondary overcurrent protection is 175 amps
Are we saying that a #6 is still good? Not how I see it
Are we saying that a #6 is still good? Not how I see it
- Location
- Connecticut
- Occupation
- Engineer
#6 is the minimum allowable conductor size under 240.21(C)(6)(1) for this installation.
#2/0 is the minimum allowable conductor size under 240.21(C)(6)(2) for the 175A secondary c/b.
#2/0 is larger than #6, so #2/0 complies.
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
I guess I'm I'm a little confused on the OP. I thought he wanted to know the minimum secondary ampacity he could use. We agreed that would be 58 amps. I didn't think we even knew what his load was. I'm just saying that with the minimum ampacity secondary in his case of 58 amps the minimum conductor size (75 degree C) would be a #6 and a max. OCPD of 60 per 240.21(C)(6)(2). Don't know where this 173 amp load came from.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
OKay now we are making sense. You all had me confused because I thought you were saying #6 was compliant.. Thank you for clarifying
chris kennedy
Senior Member
- Location
- Miami Fla.
- Occupation
- 60 yr old tool twisting electrician
Thats what I wanted to know. I have 2/0 feeding a 175A main breaker PNL.
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
OK, I get it. Missed the part that said you had 2/0 and a 175 breaker. I thought we were looking for the absolute minimum regardless of load. All good I get it.
kwired
Electron manager
- Location
- NE Nebraska
That wasn't mentioned until recently.
For no more information then was given in OP, all we could initially answer with was minimum allowed tap conductor has to be at least 58 amps. If actual load supplied is more then that then obviously it needs to increase.
- Status