Upgrading Service including detached garage

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unshaken

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Hello All,

I am replacing my detached garage and upgrading my electrical service. The electrical service enters near the detached garage at the rear of the property, and the house is another 70 feet away. The existing overhead service will be converted to underground. The house service will be upgraded from 100 to 200 amps, and I need less than 100 amps to the garage. The meter will be mounted on the side of the new garage nearest the PoCo lines.
It seems there are at least 4 options, and I was hoping for some feedback on a couple of them.

Option 1 seems the most logical. The plan would have 2 sets of service conductors by connecting to dual lugs on the load side of the meter. One set for the house, and one set for the garage. I believe this is allowable since the property is a single-family dwelling with 2 separate structures. This plan would include a new 200 amp MB Panel in the house near where the new underground service enters, and this plan would also include a new 100 amp MB panel (by the meter but inside the garage). Is this approach widely accepted, or am I likely to get some pushback from the Inspector or the PoCo? Can the service conductors to the house and garage be sized for the loads rather than based on the meter size?

Option 2 seems a little backward but was suggested by my garage designer. This plan calls for a 400 amp MB panel in the garage. The garage panel would be equipped with a 200 amp subfeed breaker feeding the house. This approach feels dirty to me for a couple reasons. First, having the 400 Amp panel in a garage that needs less than 100 Amps seems odd. Also, the house circuit will have passed through 2 breakers (unnecessarily) before it ever reaches the house. Does this approach strike you as odd, or does this seem perfectly reasonable? I’m thinking maybe there are some benefits to this approach that I just don’t understand.

For both options 1 and 2, I was hoping to avoid unnecessary rewiring in the house by repurposing the existing 100 amp MB panel in the house as a subpanel. Let me first mention that the new 200 amp MB panel will be located on the opposite side of the basement relative the existing panel. This is where the new underground feed enters the house. To reuse the existing panel, a 100 amp subfeed breaker would be installed in the new 200 MB house panel, and that subfeed would be routed to the existing panel. Since the old panel is now a subpanel, the neutral and ground will be separated. But otherwise, the existing house wiring could remain intact. Is it reasonable to repurpose the existing 100 amp main panel as a subpanel, or am I missing something here?

Thanks a million for any insight you can provide. I am trying to learn, and sometimes it feels like I’m drinking from a firehose.
 

charlie b

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Lockport, IL
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Retired Electrical Engineer
This thread was temporarily closed because it appeared to be a DIY situation. I received a PM from the originator who assured me that this is not the case. He has a garage design consultant who has brought on board an electrician that he frequently works with. The purpose of this thread is to determine whether that electrician is offering the best option for this work. I therefore am reopening the thread, and I offer my apologies to the OP for the delay and inconvenience.
 

drcampbell

Senior Member
Location
The Motor City, Michigan USA
Occupation
Registered Professional Engineer
The first question that needs to be answered: What are the actual loads going to be? Why does the house need more than 100 amps?

I suggest installing a combination meter-base/load-center on the outside of the garage, and main-lug subpanels inside the house and garage. The conductors can be sized for the loads, each independently protected by an appropriately-sized breaker. It also provides a convenient connection point for the portable standby generator and the solar panels.
 

unshaken

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Why not dual-lug meter base

Why not dual-lug meter base

Thanks for the reply.

To answer your first question, the house panel is completely full, and additional lighting and outlets are needed in 2 floors of the house. Additionally, a just-in-time water heater is under consideration. For the new garage, it will be a shop with some sort of HVAC that is yet to be chosen. The choice for 200 and 100 amps for the house and garage respectively leaves plenty or room for current needs and future growth.

Would you mind explaining Why you suggest a combination meter-base/load center at the service drop rather that using a dual-lug meter base?
 

Chamuit

Grumpy Old Man
Location
Texas
Occupation
Electrician
What are your load calculations? If the total load is <200A, you could do the following.

Meter ---> 200A well panel--->feed through lugs--->200A house panel.
 

unshaken

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Feed-through Lug Panel

Feed-through Lug Panel

Thanks Chamuit.

I also considered that approach. The feed-through lugs would avoid using a subfeed from the garage to the house as suggested by the original design (i.e. option 2 in the original post). That certainly seems like the simplest approach. I may have to reconsider just how much future growth I really need.

Thanks for the feedback.
 

david

Senior Member
Location
Pennsylvania
Option 1 seems the most logical. The plan would have 2 sets of service conductors by connecting to dual lugs on the load side of the meter. One set for the house, and one set for the garage. I believe this is allowable since the property is a single-family dwelling with 2 separate structures. This plan would include a new 200 amp MB Panel in the house near where the new underground service enters, and this plan would also include a new 100 amp MB panel (by the meter but inside the garage). Is this approach widely accepted, or am I likely to get some pushback from the Inspector or the PoCo? Can the service conductors to the house and garage be sized for the loads rather than based on the meter size?

.

this option is compliant and allows service entrance conductors to each of the service disconnects.

the supply to the house would be allowed three conductors since it is a service entrance rather than a feeder
 

unshaken

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Only 3 conductors needed from Meter to House

Only 3 conductors needed from Meter to House

Thanks much David.
I was thinking the same thing about needing only 3 conductors from the meter to the house, and that should save some money.
I appreciate the input.
 
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