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Old 06-09-2019, 08:16 AM   #1
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Default Conductor Sizing

Customer with a 200 amp single gang meter socket and a main panel back to back with a 200 amp main breaker in it. The main panel contains a 100 amp breaker that feeds a sub panel in a carriage house. I assume there is currently 4/0 AL triplex from the weatherhead to the meter socket.

Customer is renting the carriage house out and wants a separate meter from the utility for that. Utility says that is OK.

I want to replace the single gang meter socket with a 2 gang meter / main disconnect. Will contain a 200 amp breaker for the main house and a 100 amp breaker for the carriage house.

There is no load increase. No changes whatsoever in their electrical loads.

How do I size the wires from the weatherhead to the meter socket? Do I have to size it for 300 amps? That feels correct to me because I typically determine the size of my feeder by the size of the main disconnect as that is the theoretical maximum load that could occur on the conductors. But it seems like overkill. I just want to make sure I am not missing anything.
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Old 06-09-2019, 08:36 AM   #2
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Why don't you leave the service at the house alone and just add another meter at the carriage house. Let the power company run the underground or overhead to it
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Old 06-09-2019, 09:06 AM   #3
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Originally Posted by shocksystems View Post
How do I size the wires from the weatherhead to the meter socket? Do I have to size it for 300 amps? That feels correct to me because I typically determine the size of my feeder by the size of the main disconnect as that is the theoretical maximum load that could occur on the conductors. But it seems like overkill. I just want to make sure I am not missing anything.
This is the same as a multi-family house.

I routinely install a 200A service with 4/0 AL conductors for 3-5 100A main panels.

As soon as you have more than 1 main disconnect you no longer use those disconnects to determine the "service size" of the house. The service is sized by the size of the service conductors, and those should be sized for the calculated load of the house (or multiple structures, in your situation).

So you would be perfectly fine with that 4/0 AL (200A service) for both the 200A and 100A discos.
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Old 06-09-2019, 09:08 AM   #4
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Why don't you leave the service at the house alone and just add another meter at the carriage house. Let the power company run the underground or overhead to it
The PoCo does that in your area? Here they would make the owner do it in most situations, unless they can string an overhead line from the street to the garage without any extra poles.
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Old 06-09-2019, 09:16 AM   #5
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The PoCo does that in your area? Here they would make the owner do it in most situations, unless they can string an overhead line from the street to the garage without any extra poles.
Here underground over 50' from the pole or transformer is on the customer aerial the utility will handle..
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Old 06-09-2019, 09:50 AM   #6
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The power company will do t but there may be a charge. It used to be that for a new service there was no charge but a lot has changed in recent years.

When I first started Duke Power would run the riser from the meter to the overhead drop for a dwelling. They also supplied the meter base. As I said alot has changed
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Old 06-09-2019, 11:47 AM   #7
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Why don't you leave the service at the house alone and just add another meter at the carriage house. Let the power company run the underground or overhead to it
I am considering placing another single gang meter socket next to the existing one and put a second riser up, in parallel with the first one and connecting them both to the same service drop. However this customer is very conscious of the look of his property and I suspect he will hate it. Running a separate overhead to the carriage house is not an option due to location.
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Old 06-09-2019, 11:48 AM   #8
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This is the same as a multi-family house.

I routinely install a 200A service with 4/0 AL conductors for 3-5 100A main panels.

As soon as you have more than 1 main disconnect you no longer use those disconnects to determine the "service size" of the house. The service is sized by the size of the service conductors, and those should be sized for the calculated load of the house (or multiple structures, in your situation).

So you would be perfectly fine with that 4/0 AL (200A service) for both the 200A and 100A discos.
Thanks Hack. I thought I must be missing something!
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Old 06-09-2019, 11:55 AM   #9
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Originally Posted by shocksystems View Post
I am considering placing another single gang meter socket next to the existing one and put a second riser up, in parallel with the first one and connecting them both to the same service drop. However this customer is very conscious of the look of his property and I suspect he will hate it. Running a separate overhead to the carriage house is not an option due to location.
Milbank makes these taps.

Conductor Sizing-tap-connectors.jpg

This would allow you to put a 100A meter right next to the existing 200A meter with a PVC offset nipple. It would be an easy way to add the 100A meter without having the re-work the existing service or run a new riser up to the overhead line.

Note that you would be tapping into the line side meter lugs at the top, unlike in the image I posted.
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Old 06-09-2019, 06:46 PM   #10
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Milbank makes these taps.

Attachment 134316

This would allow you to put a 100A meter right next to the existing 200A meter with a PVC offset nipple. It would be an easy way to add the 100A meter without having the re-work the existing service or run a new riser up to the overhead line.

Note that you would be tapping into the line side meter lugs at the top, unlike in the image I posted.
This looks like the winner, thanks!
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Old 06-22-2019, 12:44 AM   #11
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Originally Posted by brian john View Post
Here underground over 50' from the pole or transformer is on the customer aerial the utility will handle..
Greetings from a fellow Virginian,
MechanicalDVR suggested I contact you soon about apprentice work or related. I am a Junior member and lack the 20 posts required to contact you directly. I hope this finds you well and I have the opportunity to introduce myself in a proper way. My apologies to the original post, thank you for understanding @brian john

Last edited by Dennis Alwon; 06-22-2019 at 10:21 AM.
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