Critique my plan for 100 amp sub feeders.

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iwire

Moderator
Staff member
Location
Massachusetts
Sid any feeder to a separate building or structure triggers the need for a grounding electrode system at the building or structure served by the feeder.

The GEC will connect to the feeders EGC at the panel.

See 250.32.
 

electricmanscott

Senior Member
Location
Boston, MA
The SE cable installed inside of the dwelling falls under part two of the rules for NM. That being the case #2 AL SE will have to be fused at 75 amps max using the 60 degree column in table 310.16
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
You might find a 2 ft wireway (ie: 4 x 4 x 2ft) easier to work with than a 16 x 16 box.
 

mpd

Senior Member
electricmanscott

does the original OP state what code cycle they are in?

I am surprised nobody has said to use SER cable underground in conduit to the garage, (just kidding)
 
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electricmanscott

Senior Member
Location
Boston, MA
mpd said:
electricmanscott

does the original OP state what code cycle they are in?


I didn't see it anywhere so I answered to the current edition. I also added a note to my signature to keep things clear.

Whatever the case the OP's plan is not code compliant anyway and if he is on the '08 NEC it is even less compliant.
 
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Buck Parrish

Senior Member
Location
NC & IN
iwirehouses said:
Im about to run the feeders to a 100 amp sub panel in a detached garage. I already roughed in the garage and got it inspected. The next inspection will be for the finish and feeders. This is my plan...

The difference between 90 and 100 amp breaker on #2 AL is the outter insulation on your ser or seu they require a 90 amp breaker. It's the direct burial cable that is allowed to be on a 100 amp breaker. It has no outter insulation.
In the south we use direct burial cable to the garage. It comes with 4 wires colored. Then we sleeve it when it comes up to the panel or j-box with schedule 80 pvc. no expansion fitting. Connector with bushings on both ends. A lot less work then running conduit the whole way. Isolate the neutral from the ground and use a 8 ft'. rod. :cool:
 
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stickboy1375

Senior Member
Location
Litchfield, CT
buckofdurham said:
iwirehouses said:
.

The difference between 90 and 100 amp breaker on #2 AL is the outter insulation on your ser or seu they require a 90 amp breaker. It's the direct burial cable that is allowed to be on a 100 amp breaker. It has no outter insulation.


I disagree. Its based on 310.16 and 310.15(B)(6) and when you can actually use 310.15(B)(6)
 

frizbeedog

Senior Member
Location
Oregon
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iwire said:
I know it is not going to hurt anything but you should be aware that it is still a NEC violation and your name will always be attached to it. (It is also a very common violation.)

Thank you, Bob and Stickboy. Looked into this today. I asked an inpsector at my job site, and he confirmed my error in my understanding of the use of table 310.15(B)(6). And I ran it by a member of the State's code adoption commitee also. I've been misunderstanding the intent of that article for years. However, both agreed that it is not really enforced. I didn't ask why. Now I have a delima, but I think I already know what both of you would say.

That's why I come here.
 

stickboy1375

Senior Member
Location
Litchfield, CT
buckofdurham said:
No, but I thought it was well known through out the industry. However if you take the State test and it is not specified you have to use the 75 degree coloum.


If your equipment is not rated for 90 degree then how can you possible use the 90 degree column? I have NEVER seen a 90 degree lug.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
As I understand the reasoning behind 310.15(B)(6), the code making panel understood that the characteristics of a residential service are such that a 'service' with an OCPD of X could be safely supplied with conductors of ampacity Y, with Y < X. That determination has only been made for feeders that supply 'the main power feeder' of a residence.

IMHO an average residential garage will likely have similar use characteristics to a residence, so that if you use 310.15(B)(6) to size the garage feeder, there is very little likelihood of a problem. The fact is that this particular requirement is frequently not enforced, yet I've not heard of any failures or problems attributed to this failure to enforce this particular code. So while it _is_ a code violation to install a garage feeder using 310.15(B)(6), it is unlikely to cause a hazard. I would never advise you to violate this code requirement, but I wouldn't loose sleep about past installations.

-Jon
 
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