Too many opinions

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Esthy

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50% says YES, AWG 4 THHN can be use as a feeder for a 100 amps sub-panel and 50% says NO for a separated garage/shop. I am in doubt, but I would like to use it as I have a full spool and I am donating it.
 
Esthy said:
50% says YES, AWG 4 THHN can be use as a feeder for a 100 amps sub-panel and 50% says NO for a separated garage/shop. I am in doubt, but I would like to use it as I have a full spool and I am donating it.
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Facts as I see them.

A garage/shop is not a dwelling unit so the reduced wire sizes allowed for dwelling units cannot be applied. {See 2014 NEC 310.15(B)(7)}

4 AWG copper THHN is rated 85 amps at 75C

I will assume the equipment is rated 75 C.

The next standard size breaker is 90 amps (see 240.6)



Those being the facts the largest load that could be supplied to this garage shed with 4 AWG copper would be 85 amps and the largest breaker would be 90 amps after applying 240.4(B)



So, no you cannot code compliantly use 4 AWG with a 100 amp breaker for this installation.
 
A garage shop is not a dwelling and does not carry the full load of the dwelling so the answer is NO. If install at a 90C or 75C conductor then you could use a 90 amp breaker if the load is limited to 85 amps. 240,4(B)

Sorry Bob posted as I was typing
 
Esthy said:
50% says YES, AWG 4 THHN can be use as a feeder for a 100 amps sub-panel and 50% says NO for a separated garage/shop. I am in doubt, but I would like to use it as I have a full spool and I am donating it.
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Use it with a 90A breaker and you will be just fine. Unless there is a serious growing operation going on in the garage the main will never trip.
 
Thanks! I don't know why I still listening to all those "opinionated individuals" outside the forum. Maybe it is my fault as I was trying hard to use a 100 amps panel and a spool of #4 that I have in stock because a 90 amps breakers are too expensive. Mea Culpa!

Maybe do a load calculation and see if I can install in the same box and in the main panel a 60 amps breakers and run this existing #4. Uggg

Happy Easter! ... Too late?
 
Esthy said:
Thanks! I don't know why I still listening to all those "opinionated individuals" outside the forum. Maybe it is my fault as I was trying hard to use a 100 amps panel and a spool of #4 that I have in stock because a 90 amps breakers are too expensive. Mea Culpa!

Maybe do a load calculation and see if I can install in the same box and in the main panel a 60 amps breakers and run this existing #4. Uggg

Happy Easter! ... Too late?
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You can still use the 100A panel with the #4 and I'll bet a hundred dollars you will be fine with a 60A breaker.
 
I paid $40.00 for this load center including the 100 breaker and I have in stock an extra 100 for the main panel. If I have to buy two 90s it will be too expensive, but I have extra 60s, so I will do the load and see if 60 will be enough.
 
Esthy said:
I paid $40.00 for this load center including the 100 breaker and I have in stock an extra 100 for the main panel. If I have to buy two 90s it will be too expensive, but I have extra 60s, so I will do the load and see if 60 will be enough.
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You only need the 90 at the supply end of the feeder. The one at the garage panel can be any size.
 
Wait, I only need one 90 at the main panel and use the sub-panel with the 100 breaker in the garage? How a fault in the garage will bypass the 100 to the 90. Whoa, old, confused, worried and little sleep ... Should the 100 be in the main and the 90 in the garage
 
Sorry, it makes sense. If I can go with 60 (after load calculation) I can install a 60 breaker with the same #4 and the 100 sub-panel and it will be ready for future expansion. Thanks
 
thanks, I posted in another section about this feeder for MH, but can I use it for a separated structures (this garage) See photo. Any experience with this feeder?
 
Esthy said:
Sorry, it makes sense. If I can go with 60 (after load calculation) I can install a 60 breaker with the same #4 and the 100 sub-panel and it will be ready for future expansion. Thanks
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Yes, that will work.

Also, just for the record, I've never had an inspector ask for a load calculation on a 100A or less feed to a shed, garage, barn, etc.

Using the 90A breaker and #4 wire, they would have a right to but they never have.
Your inspectors may be different. Most wouldn't worry too much over a small shed and the load on it unless it was drastically undersized.
 
Is the cable you are running aluminum or copper? If it is aluminum then you are limited to 65 amps at 75C.. So a 70 amp breaker would work if the load is less than 65 amps
 
Esthy said:
50% says YES, AWG 4 THHN can be use as a feeder for a 100 amps sub-panel and 50% says NO for a separated garage/shop. I am in doubt, but I would like to use it as I have a full spool and I am donating it.
Click to expand...


There is a way to use #4 wire for this application and leave the 100A breaker in place, but it is complicated.
09e_PauleyFIG9.jpg



See above diagram. If it is #4 wire that is rated at 90C, then you can install it from connector to connector as shown above. The connectors both need to be rated 90C, and the wire to which it connects needs to have insulation rated at 90C.

The wire to which it connects, needs to be sized for the terminations/equipment, which is likely at 75C. That would be #3 wire, and you would only need to run it locally to the equipment at both sides. This allows you to construct a 100A feeder from #4 wire for the majority of its length.
 
I would like to add that it is not just the termination that needs to be rated 75C, I believe many panel lugs are 90C rated, but the equipment must be rated 75C. The 90C lugs in my example will not help if the equipment is not rated 90C and it won't be.
 
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