Runnign 100 amp service to garage

[SteadyEddie]

I work for a Utility Co. in NY, dealing with customers on this very issue. Try checking your Utilitiy's website for information on "service installations". Most have an online book for "General Specifications", which for my company, would answer almost all your questions listed here. If they don't, contact their New Business Dept., between that and the local electrical inspector, you'll have your answers. Be aware that every utility has their own set of rules, for instance, my Co. won't connect you if you used the 2.5" conduit, you would need 2" or 3" instead. But the next Company over insists on 2.5" conduit & won't allow 2" on their system. The Utility has the right, per NEC code, to demand things above & beyond the code books, so check with them before you buy anything.

 

[timswi]

I work for a Utility Co. in NY, dealing with customers on this very issue. Try checking your Utilitiy's website for information on "service installations". Most have an online book for "General Specifications", which for my company, would answer almost all your questions listed here. If they don't, contact their New Business Dept., between that and the local electrical inspector, you'll have your answers. Be aware that every utility has their own set of rules, for instance, my Co. won't connect you if you used the 2.5" conduit, you would need 2" or 3" instead. But the next Company over insists on 2.5" conduit & won't allow 2" on their system. The Utility has the right, per NEC code, to demand things above & beyond the code books, so check with them before you buy anything.

All true...I ran 3" sch 40 underground and sch 80 where it was exposed and the utility company was very happy with that.

 

[ThomasH]

Hi -

If you use direct burial cable (and that cable seems to be considering it's jacket construction) in a conduit, you will need to de-rate the cable ampacity 10-20%. Direct burial cable or cable rated for outdoor use (overhead feeds) cools by having free air or contact with soil to dissipate some of the heat when used at it's max power. You are better off buying the correct size THHN/THWN wire rated to be in a raceway (conduit) in the proper size.

According to the cable calculator I use, you are right on the cusp *if* you are heavily utilizing the service. If you were going to expect the service to be utilized in excess of 70 amps continuously, you need to step up to #1 for the current carrying legs.

 

[CurlyDave]

Hi -

If you use direct burial cable (and that cable seems to be considering it's jacket construction) in a conduit, you will need to de-rate the cable ampacity 10-20%. Direct burial cable or cable rated for outdoor use (overhead feeds) cools by having free air or contact with soil to dissipate some of the heat when used at it's max power. You are better off buying the correct size THHN/THWN wire rated to be in a raceway (conduit) in the proper size....

I completely agree with this.

Putting direct burial wire in conduit is usual not allowed by code, and will cause the wire to overheat.

I like conduit a lot better than direct burial, and I think the individual wires are less costly than the direct burial anyway. Last year when I ran underground power from my house to the garage, there were two grades of wire available 60 degrees C and 90 degrees C. The 90 degree wire has greater ampacity and may let you go down one wire size.

 

[EddieWalker]

An electrcal supply house ususaly has an engineer on hand to figure out what you need.

If money wasn't an option, I like copper. Since it's so expensive, I like Aluminum. Just be sure that you use a quality anti oxident with it and size it properly. You need thicker Aluminum to do what copper does.

Eddie

 

[StanR]

Good thread... I got that exact cable from Lowes and will use it to run power to my Ocean Container.

 

[tlbuser]

Did you ask your utility co. if you could take a homeowners exam? Some will allow that and once passed, you can pull your own permit.

 

[jonnysteals]

Did you ask your utility co. if you could take a homeowners exam? Some will allow that and once passed, you can pull your own permit.

No I did not. I have been battling this for over two years. This will be a second service to my rental property. my township considers all second service commercial service and you have to be certified to do this work. I originally wanted 200 amps but they thought I was operating a buisness out there and wanted to add all kinds of different restrictions and such. I tried explaining to them its for me to restore and play around with cars/trucks but it didn't matter. It seems that if I went with 100 amps they were much less hostile about running the electric.

I did some more reaserch on the ground rods and it seems from what I need are two 5/8 ground rods for my service and they need to be ten feet apart. It seems overkill to me but hey thats cheap to do anyway.


I appreciate all the input guys; I have also done some reasearch on aluminum wire vs copper. If copper wasn't so expensive the choice would be easy. Due to its price I feel that it is worth using aluminum wire. The electrician hunt still continues as only one out of 7 electricians has called back and he didn;t seem very interested to me.

 

[jonnysteals]

Hi -

If you use direct burial cable (and that cable seems to be considering it's jacket construction) in a conduit, you will need to de-rate the cable ampacity 10-20%. Direct burial cable or cable rated for outdoor use (overhead feeds) cools by having free air or contact with soil to dissipate some of the heat when used at it's max power. You are better off buying the correct size THHN/THWN wire rated to be in a raceway (conduit) in the proper size.

According to the cable calculator I use, you are right on the cusp *if* you are heavily utilizing the service. If you were going to expect the service to be utilized in excess of 70 amps continuously, you need to step up to #1 for the current carrying legs.

I completely agree with this.

Putting direct burial wire in conduit is usual not allowed by code, and will cause the wire to overheat.

I like conduit a lot better than direct burial, and I think the individual wires are less costly than the direct burial anyway. Last year when I ran underground power from my house to the garage, there were two grades of wire available 60 degrees C and 90 degrees C. The 90 degree wire has greater ampacity and may let you go down one wire size.

I truthfully doubt I will ever be contantly using all that power at once. I would have to be using my air compressor plams and welder all at the same time.

I want a 100 amp main breaker; what wire do you recomend; 1 AWG aluminum? I will have to find out the price of this. Will you still downsize the neutral or just the ground?

This link has a chart:
USE-2 / RHH / RHW-2 Direct Burial Aluminum Conductor 600 Volts - Aluminum Building Wire - Aluminum Building Wire

 

[ThomasH]

If it were my decision, I would not install cable with inadequate insulation to be utilized in conduit with the size main breaker that you are using. So since you have said a 100 amp breaker will be installed, and that you have motor loads that can be considerable at start up (air compressor), I would buy cable that could handle the 100 amp load plus a small cushion. Looking at my calculator, that means #1 or 1/0 in aluminum with at least 75 degree centigrade insulation, (XHHW, THWN-2 or similar spec) for the current carrying legs. I suspect that it can be bought at the same price or maybe less than the direct burial cable and is better suited to this application.

You can read about cable size, insulation, etc. at Product Catalog in the aluminum building wire section.

So this would mean about 300 feet of this cable and 100 feet of #4 for the ground, assuming that the meter is at the pole. For single phase residential service, the ground bus is normally established at the meter box and disconnect.