Feed house from new service in detached garage

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richwaskowitz

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Shelby Twp. MI, near Detroit
I have two fairly succinct questions I just can't seem to answer clearly myself and would really appreciate some assistance. I looked at quite a few related posts but am still not quite clear.

Customer builds a new detached garage. It will get a new 200 A service. He wants to then feed the house with a 100 A underground feeder, replacing the old overhead service. For the point of this discussion, this very small house has very little load currently, but it does have a 100 A main breaker panel with 8 circuits.


1. The customer wants a "100 Amp Feeder" to the house and turn the panel into a sub panel. If I want to protect the feeders with a 100A breaker at the main panel and use conduit and aluminum XHHW conductors, do I use 1-1-2-4 for the feeder conductors or am I wrong?


2. I will drive two ground rods at the new service and connect with #6 copper. How does the incoming water main get connected to the new service in the garage?
 
Well you can actual use #2 aluminum for a residence at 100 amps as the code allows you to use the 83% rule. Thus your conductors only need to be rated 83 amps.

You will need ground rods at both buildings and the water line at the garage must be bonded to the service. If it is copper in the ground more than 10' then you must use it as an electrode along with the ground rods
 
How does the incoming water main get connected to the new service in the garage?
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Not clear but I think that he's saying that the water line comes into the old house with what will now be the sub panel.

If so it would get connected to the ground buss in the sub panel along with the two ground rods.

-Hal
 
richwaskowitz said:
I have two fairly succinct questions I just can't seem to answer clearly myself and would really appreciate some assistance. I looked at quite a few related posts but am still not quite clear.

Customer builds a new detached garage. It will get a new 200 A service. He wants to then feed the house with a 100 A underground feeder, replacing the old overhead service. For the point of this discussion, this very small house has very little load currently, but it does have a 100 A main breaker panel with 8 circuits.


1. The customer wants a "100 Amp Feeder" to the house and turn the panel into a sub panel. If I want to protect the feeders with a 100A breaker at the main panel and use conduit and aluminum XHHW conductors, do I use 1-1-2-4 for the feeder conductors or am I wrong?


2. I will drive two ground rods at the new service and connect with #6 copper. How does the incoming water main get connected to the new service in the garage?
Click to expand...

It doesn't. It gets bonded to the EGG buss at the house and nothing else.
 
230.40 exception #3 would be a lot less work if you just double tap the load side of the meter and run service entrance conductors to the house and another set of service entrance conductor to the garage.
 
the 83% rule can only be used for dwelling units, due to diversity of loads (not all on at the same time)
The garage feeder has to be sized at 100% as the table saw, sawdust vac and grinder could all be operating at the same time.
 
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