- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
This is hypothetical. Not a hard question but very curious one, IMO
What size conductor?
- Thread starter Dennis Alwon
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- Location
- Massachusetts
This is hypothetical. Not a hard question but very curious one, IMO
Assuming a 120/240 service 400 copper or 600 AL.
- Location
- Massachusetts
Sorry, did not pay attention to the 'TW'
I will now say 600 cu or 900 al.
I will now say 600 cu or 900 al.
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Table 310.15(B)(6) {or (B)(7) in the 2011} does not list type TW. So I would have to go back to 310.16. Type TW only has a 60C rating. That gives me either a 600 copper or a 900 aluminum.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Now use the 2011?
The TW is the catch. T. 310.15(B)(6) allows 400KCM if it is THW but since it isn't that means 600 KCM according to the 2008 and 700 KCM by the 2011.
The TW is the catch. T. 310.15(B)(6) allows 400KCM if it is THW but since it isn't that means 600 KCM according to the 2008 and 700 KCM by the 2011.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Why do they even list TW anymore? I can't imagine using it.
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Did you intend for your statement of the problem to say that the load was 355 amps?
At 350 amps, you can use 600 MCM under both the 2008 and the 2011.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Did you intend for your statement of the problem to say that the load was 355 amps?
Not on a 400 amp breaker. 240.6(A)
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Nothing in the statement of the problem included information about the breaker. The phrase "400 amp service" does not give us that information. Indeed, all it tells me is that the utility equipment (transformer, meter) have sufficient capacity to allow me to install a 400 amp breaker on my main panel. But if the load is 350, and if I use 600 MCM copper, and if I use a 350 amp breaker, I have an acceptable installation that falls within the description of the problem.
However, I do see the intent of your question, and the tricky aspect that comes into play under the 2011 NEC.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I guess a 400 amp main breaker could be added to the question. It is just interesting the difference in size when TW occurs. Not only must you use the 60C column but you don't get the benefit of using T.310.15(B)(7) formerly (B)(6).
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