1/0 or 1 SER al.

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JDB3

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Feeder to a sub-panel that has less than 100 amp load, but feed with a 100 amp breaker & feeder will be 130 feet with contact with insulation on each end for approximately 8 feet at each end. Connected to Square D breaker on one end & Square D panel lugs on other end.

Permissible for #1 SER Al. or is 1/0 SER Al. required. Code references please.

Thanks
 
JDB3 said:
Feeder to a sub-panel that has less than 100 amp load, but feed with a 100 amp breaker & feeder will be 130 feet with contact with insulation on each end for approximately 8 feet at each end. Connected to Square D breaker on one end & Square D panel lugs on other end.

Permissible for #1 SER Al. or is 1/0 SER Al. required. Code references please.

Thanks
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Based on the info given and assuming no part is underground I say 1/0 min.
338.10(B)(4)(a)
....Where installed in thermal insulation the ampacity shall
be in accordance with the 60C (140F) conductor temperature
rating....
 
JDB3 said:
Feeder to a sub-panel that has less than 100 amp load, but feed with a 100 amp breaker & feeder will be 130 feet with contact with insulation on each end for approximately 8 feet at each end. Connected to Square D breaker on one end & Square D panel lugs on other end.

Permissible for #1 SER Al. or is 1/0 SER Al. required. Code references please.

Thanks
Click to expand...

1/0. 338.10(B)(4)(a)

#1 SER would only be good for 85A, so your load could not exceed that.
If your load was that or less, you would need a 90A breaker as that is a next standard size. 250.4(B), 250.6
 
The section in contact with insulation at each end is under 10 feet and also less than 10% of the other part of the circuit so derating for temperature just in those sections may not reduce the allowed ampacity of the wire.
 
GoldDigger said:
The section in contact with insulation at each end is under 10 feet and also less than 10% of the other part of the circuit so derating for temperature just in those sections may not reduce the allowed ampacity of the wire.
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You cannot double dip that 10%/10' exception, by using the two ends separately.

At least I think you cannot.:?
 
jumper said:
You cannot double dip that 10% exception, by using the two ends separately
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I do not see why not. The two ends are thermally independent.
You cannot, IMHO, take a 20 foot segment in the middle and try to call it two segments of 10 feet, each connected to 100 feet of high ampacity on the outer end.
My reasoning is that the exception is based on avoiding heating of the wire rather than avoiding voltage drop.

But that discussion deserves a separate thread. :)
 
GoldDigger said:
I do not see why not.
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I see your point and it would probably work but the code IMO does not state that and , in fact, states 10'. If you have 20' in the circuit run even if the run is over 200' and the 10' sections are separate by 100' I still see the limit at 10' of the circuit run.
 
Dennis Alwon said:
I see your point and it would probably work but the code IMO does not state that and , in fact, states 10'. If you have 20' in the circuit run even if the run is over 200' and the 10' sections are separate by 100' I still see the limit at 10' of the circuit run.
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And I see that as applying separately to each low calculated ampacity segment, so it really comes down to how each inspector sees it. :)
 
GoldDigger said:
And I see that as applying separately to each low calculated ampacity segment, so it really comes down to how each inspector sees it. :)
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But Goldy, you are using the same middle portion for the calculation. I do not see that as viable.

I do not not mind applying the exception twice or more in a total given conduit/cable run, but I believe each insulated section should be calculated against its own uninsulated section.
 
Dennis Alwon said:
I see your point and it would probably work but the code IMO does not state that and , in fact, states 10'. If you have 20' in the circuit run even if the run is over 200' and the 10' sections are separate by 100' I still see the limit at 10' of the circuit run.
Click to expand...

I agree. IMO 338.10 trumps 310.15(A)(2) in the same way that 110.14(C) does.
 
jumper said:
You cannot double dip that 10%/10' exception, by using the two ends separately.

At least I think you cannot.:?
Click to expand...

I would think that you can do this it as long as the two segments together add up to less than or equal 10%/10ft.

For instance, consider a 66 ft conductor, with a 3 ft stub on the rooftop at both ends. The two 3 ft stubs add up to 6 ft, which is within your 10%/10ft limit.
However, a 72 ft conductor with a 6 ft stub at both ends (and 60 ft in the region of greater ampacity), that would be a double dip on this exception.
 
iwire said:
I think you can and that makes it work better as they are counting on the sections on both side to work as hear sinks to pull the temp down on that 10'.
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I agree that it will probably work but I don't see it as meeting the code as written
 
GoldDigger said:
No it says ten feet for the segment....
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(2) Selection of Ampacity. Where more than one ampacity
applies for a given circuit length, the lowest value shall be used.

Exception: Where two different ampacities apply to adjacent
portions of a circuit, the higher ampacity shall be permitted
to be used beyond the point of transition, a distance equal to
3.0 m (10 ft) or 10 percent of the circuit length figured at the
higher ampacity, whichever is less.
 
Seems perfectly clear to me that there can be more than just two "portions", and that wherever a low ampacity portion adjoins a high ampacity portion you get to apply the higher ampacity a certain distance beyond that particular point of transition. Nothing about it being cumulative over multiple points of transition.
 
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