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Kapt 01-12-2007 03:39 PM

detached garage
 
I just finished my detached garage except for the wiring. I'm planning for a 100A panel in the garage. My house main panel is only 100A, although the feed to my house is suitable for 200A.

I read in the NEC about the unlimited tap rule of feeding my garage from the base of my meter socket using a double lug meter socket. Essentially, I'd be splitting the main power entering the meter, half going to my house and the other half going to my garage. The power feed to my garage would terminate at the 100A breaker in my garage panel, and the ground and nuetral bus bar would be bonded, just as in my house panel. I'd have to get the power company and/or electrician to change out my meter socket, but I wouldn't have to upgrade my house panel to 200A. Every large appliance in my house is run off natural gas, so my electrical needs in my house are small.

Has anyone done this type of setup? Before I get too far in my planning, I'd like to know if I'm barking up the wrong tree.

jwhite 01-13-2007 08:18 AM

I have a question on this type of intall not an answer. You may need to call a local electrician or your local building dept for the answer.

Would the feeder to the garage need to have a disconnect on the house?

I believe that by national code the answer would be no, but you should check to see what is required in your area.

If you do not need the disconnect at the main house then be sure to wire your main panel at the gargage as a main. Two ground rods, grounds and neutrals bonded etc.

jbob 01-13-2007 06:35 PM

I had the exact same situation recently.
I needed 100 amps to my garage, but the house main panel
is only 100 amps because all appliances are NG.

In my area, central indiana, I did not have to have a disconnect
at the house main as long as the garage panel was installed
as a second main. As jwhite said, Two ground rods, grounds and neutrals bonded etc....

Kapt 01-13-2007 11:56 PM

Jbob, did the feeder for the garage come from the house meter or did they run another meter to the garage?

I still have to call the local building dept to see if this is legal in my area.

TIA, Tom.

jbob 01-14-2007 08:30 AM

I used a double lug meter, so no 2nd meter was needed.

I would have rather had a 200 amp service to the garage
for my welder, compressor, and other tools, but the new
line would have necessitated the removal of a nice tree
that I wasn't willing to lose.

When I say "I used", I should be more clear.
My electrical ability extends to replacing a receptacle
or switch now and then. I hired a local electrical contractor
to install the new meter socket and panel. I saved a little
by digging the trench for the new line:)

Kapt 01-14-2007 10:21 AM

Quote:

Originally Posted by jbob (Post 29888)
I used a double lug meter, so no 2nd meter was needed.

I would have rather had a 200 amp service to the garage
for my welder, compressor, and other tools, but the new
line would have necessitated the removal of a nice tree
that I wasn't willing to lose.

When I say "I used", I should be more clear.
My electrical ability extends to replacing a receptacle
or switch now and then. I hired a local electrical contractor
to install the new meter socket and panel. I saved a little
by digging the trench for the new line:)


Your setup with the double lug meter is exactly the setup I envision for my garage. I'd like to do as much as the installation as my county will allow, but they are requiring me to come in and take a homeowners electrical test. I guess this sounds reasonable.

I just have a few more questions about the installation. Do you know what size wire the contractor ran out to the garage? I came up with #2 copper. Also, how deep were you required to dig the trench and did you use direct burial wire or some conduit like the grey sched 40 stuff? TIA.

jwhite 01-14-2007 10:33 AM

Unless the garage is a long way off, over 100 feet, you will not have a voltage drop problem. You can use #4 copper or #2 aluminum.

If you use a direct burial cable you need to dig the ditch 24 inches to the top of the wire.

If you use PVC conduit you need to dig the ditch 18 inches to the top of the conduit.

1 inch pvc would be legal, I would use 1 1/4.

The electrical inspector will most likely want to see the ditch with the wire or conduit in it, before you back fill. So he/she can check the depth.

Kapt 01-14-2007 06:29 PM

Quote:

Originally Posted by jwhite (Post 29902)
Unless the garage is a long way off, over 100 feet, you will not have a voltage drop problem. You can use #4 copper or #2 aluminum.

If you use a direct burial cable you need to dig the ditch 24 inches to the top of the wire.

If you use PVC conduit you need to dig the ditch 18 inches to the top of the conduit.

1 inch pvc would be legal, I would use 1 1/4.

The electrical inspector will most likely want to see the ditch with the wire or conduit in it, before you back fill. So he/she can check the depth.

Thanks for the info, but a question about the #4 copper.

I'm using chart 310.16 of NEC for allowable amps and that's where I came up with the #2 or #3 copper. Am I using the wrong chart, because I come up with 95A max for #4 cu? The chart 310.15 on the previous page allows 100A for #4, but I'm not sure if this applies to me.

jwhite 01-14-2007 07:07 PM

use table 310.15 (B) (6) for dwelling unit services and feeders.

use table 310.16 for comercial services and feeders and all branch circuits.

Kapt 01-15-2007 08:54 AM

Quote:

Originally Posted by jwhite (Post 29938)
use table 310.15 (B) (6) for dwelling unit services and feeders.

use table 310.16 for comercial services and feeders and all branch circuits.

OK, thanks. I think some lawyer wrote the NEC, it sure reads that way.

Thanks again,
Tom

jwhite 01-15-2007 05:53 PM

the NEC IS written to be easily enacted as a law. That is true.

RobertWilber 01-15-2007 06:14 PM

-
*
Robert Wilber
Licensed Philadelphia Electrician
Philadelphia License # 3516 - 16765
*
NEC does not require a disconnect at the house. The code reads that a disconnecting means is required nearest the point of entrance of the service conductors. No entrance, no disconnect.

jbob 01-17-2007 09:37 AM

Quote:

Originally Posted by Kapt (Post 29899)
Your setup with the double lug meter is exactly the setup I envision for my garage. I'd like to do as much as the installation as my county will allow, but they are requiring me to come in and take a homeowners electrical test. I guess this sounds reasonable.

I just have a few more questions about the installation. Do you know what size wire the contractor ran out to the garage? I came up with #2 copper. Also, how deep were you required to dig the trench and did you use direct burial wire or some conduit like the grey sched 40 stuff? TIA.

I can't tell you what type of wire was installed.
The electricians did the job while I was at work.
The inspector passed it...so I was happy:)

The one difference from what was stated above is that
the local inspector wanted the line below frost-line, which
is 36 inches in this area. The wire was in a gray conduit.


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