Load side of the service in the attic?

[prattz99]

I went to look at potentially doing this single phase 200A residential overhead service change today and it looks like a total nightmare. It's 100A and the main panel is in the middle of the house and with no basement I'm forced to run the new load side of the service feeders up and through the attic. I was originally thinking of using SER but I'm now thinking to run PVC on the outside and up into the attic for only about 15-20'. I like the idea better as SER is a pain to work with and sleeve in PVC.

My questions are:
1) Is there anything in the NEC prohibiting me from running the load side through the attic space? (I've thought about de-rating for the ambient temperature)
2) I'm thinking of using a expansion fitting on the outside as the total run is about 20-30' Is that necessary/good design?
3) What other potentials might I not be seeing at the moment?

 

[Little Bill]

If there isn't a disconnect on the outside, you will have to have one. You can run the load side through the attic as long as there is OCPD before it enters the house.

 

[kwired]

You usually can not bring service conductors that far into the house though NEC doesn't really give specific distance how far you can enter.
With service disconnect outside or immediately inside anything beyond that is a feeder and no longer has this restriction.

2020 NEC can get more complex as there must be an outside disconnect for emergency purposes, but said disconnect doesn't necessarily have to be the service disconnecting means, though a majority of them likely will end up also being the service disconnect I would guess.

 

[infinity]

You'll need the service disconnect on the outside adjacent to the meter. From there you can run either SER or a raceway. If you use PVC you'll need to consider expansion fittings as you mentioned. Also you'll need to adjust your feeder for the attic temperature so you may end up with larger conductors. All GEC's will need to be routed to the service disconnect on the outside.

 

[hillbilly1]

In the 60's, that seemed to be pretty common, boss's daughter bought an old house in the prestigous area of Atlanta, service hit the corner of the garage, ran through the attic, down to the basement where the meter and panel was. I put a new disconnect and mast at the corner of the garage, then ran across the attic to the new panel in the basement. Boss didn't like the service wires over the drive, so I had to move it to the other end of the house, install an underground service conduit to a pole that didn't exsist at the time. Georgia Power had to get a permit for them to sink a pole there and move the transformer!

 

[prattz99]

Great! Yes, I'm planning on using a meter main outside. The derating is interesting to me because it's currently a 100 amp service and the load demand will not be changing much for the house. The portion in the attic will only be 8-10' if I run the PVC the way I'm thinking. How does the derating calculate when you're already given a discount for the service wire size?

 

[augie47]

De-rating still applies the same. On a 200 amp service, with your allowable 83% factor you need a conductor with an adjusted ampacity of 166 amps. If you are using a 2/0 Cu 90° conductor it has an ampacity of 195. The ambient adjustment would allow for a environment of 113° which should cover the attic.

 

[infinity]

Great! Yes, I'm planning on using a meter main outside. The derating is interesting to me because it's currently a 100 amp service and the load demand will not be changing much for the house. The portion in the attic will only be 8-10' if I run the PVC the way I'm thinking. How does the derating calculate when you're already given a discount for the service wire size?

A meter main is a good choice. For sizing your conductors since this is an upgrade the load doesn't really matter. After you do your calculation you would still need a conductor ampacity that it at least 83% of the feeder OCPD size.

 

[kwired]

Great! Yes, I'm planning on using a meter main outside. The derating is interesting to me because it's currently a 100 amp service and the load demand will not be changing much for the house. The portion in the attic will only be 8-10' if I run the PVC the way I'm thinking. How does the derating calculate when you're already given a discount for the service wire size?

Your conductor will be plenty large to handle what load you have, but after derating the conductor for ambient temp your overcurrent protection can be too high if you are using 200 amp breaker.

Quick calculation of what might be typical around here tells me if you use 4/0 aluminum and the allowance for dwelling supply conductors to be 83% of what they must be elsewhere you would likely need at least 175 amp overcurrent protection or increase conductor size.

Other thing to do would be to keep the run below thermal insulation to reduce the ambient temp.

 

[ramsy]

De-rating still applies the same. On a 200 amp service, with your allowable 83% factor you need a conductor with an adjusted ampacity of 166 amps. If you are using a 2/0 Cu 90° conductor it has an ampacity of 195. The ambient adjustment would allow for a environment of 113° which should cover the attic.

Augie may suggest SER cable with 90c rated XHHW-2 insulated conductors, & ambient-adjustment Exception per NEC 310.15(B)(3)(c)

 

[ramsy]

..a environment of 113° which should cover the attic.

130 - 160F is also commonly reported for attics

 

[infinity]

Augie may suggest SER cable with 90c rated XHHW-2 insulated conductors, & ambient-adjustment Exception per NEC 310.15(B)(3)(c)

Isn't that exception for rooftops with direct sunlight?

 

[augie47]

130 - 160F is also commonly reported for attics

If that's the case, one should increase conductor size above 4/0 AL or reduce the size of he over-currenrt device although it's sledom done in this area.

 

[ramsy]

Isn't that exception for rooftops with direct sunlight?

Yes, the exception to "this ampacity adjustment" if OP skips attic to run raceway on roof, or <=90c XHHW-2 using the formula in [310.15(B)(2)]

 

[ramsy]

On a 200 amp service, with your allowable 83% factor you need a conductor with an adjusted ampacity of 166 amps. If you are using a 2/0 Cu 90° conductor it has an ampacity of 195. The ambient adjustment would allow for a environment of 113° which should cover the attic.

The formula in [310.15(B)(2)] shows 166A on your 2/0 Cu @ 30c ambient operating at 74c, within 110.14(C) limits for ampacity.

If that's the case, one should increase conductor size above 4/0 AL or reduce the size of he over-currenrt device although it's sledom done in this area.

Adjusted for worse case 160F attics (71c ambient ), 166A on your 2/0 Cu ampacity is still within 110.14(C), if the formula in 310.15(B)(2) shows an ambient adjustment to 85c, which works with XHHW-2 limit of 90c, and higher-ambient sections may not affect terminations, when the terminations still operate near 110.14(C) limits of 74c.

 

[prattz99]

So this all sounds confusing to me and has a lot of room for error. I'm thinking about avoiding the attic space all together and running it on the surface in the utility room.

 

[kwired]

So this all sounds confusing to me and has a lot of room for error. I'm thinking about avoiding the attic space all together and running it on the surface in the utility room.

IMO running it up in the corner of wall/overhang will look better. Also IMO raceway will look better than SE cable.

 

[prattz99]

Ideally I'd like to keep the PVC run on the bottom but that light I think is in the way. If I run it up top the whole way I'll need to have 3 90's to get up there from the bottom of the meter main. It'll be very ugly but it is what it is. Good thing it's subsidized housing.

 

[kwired]

LB into meter main, one less elbow and you will thank yourself for that when pulling conductors, especially with PVC conduit.

 

[infinity]

LB into meter main, one less elbow and you will thank yourself for that when pulling conductors, especially with PVC conduit.

I prefer LB's also but you have to be careful with PVC LB's, typically the permitted conductor size in the LB is smaller than the maximum fill of the raceway.