Two Panels - Two Main Breakers?

I saw a detatched house with two main Service Panels side by side today - neither was a sub. Both fed off the meter. Is this common? Anything I need to be aware of when inspecting these or is it just two panels?

Sorry for the crappy pictures. I’ll have a decent camera soon.

Common for larger homes require more than a 200 amp service.

So do they usually just “double tap” off the meter as this case appeared to be? It was underground service and the meter was on the other side of the wall of where they were mounted. I know this is not a double tap that gets written up - just asking.

Typically you will have a double lugs at the meter listed for two conductors so it’s not really a “double tap”.

Okay, thanks Robert.

Like Robert said, it’s not double tapped-it’s double lugged at the meter base.

Be sure and check the meter to verify the service.

(2) 200 amp panels don’t always mean 400 amp service.

How would two 200A panels not equal 400A? Can the amperage coming in through the service entrance cables be less than 400A?

If there is no disconnect at meter or before the panels, what you have is two 200 amp service panels.

Wouldn’t that be a 400A service?

Yes its a 400amp service coming in to a 320 meter base or should be.

I agree.

SEC could be sized differently.

It depends on the meter rating. It’s probably 320 like Kenneth said.

This base states 320A continuous & 400A maximum (burst).

http://www.homedepot.com/p/Milbank-320-Amp-Ringless-Underground-Meter-Socket-R1129-O-5T9/202504264

This is what should be there as per your question, 400amp noncontinuous 320amp continuous.
So for a 200amp service the meter base is 200amp noncontinuous 160amp continuous
This is how meters are rated.
So per your question 2-200amp panels do not make 400 amps, it’s the service coming in that should be 400 amps as Larry mentioned and then split off with 4/0 aluminum or 2/0 copper to the panels from the meter base, then you have your 2/200amp panels with main breakers.

Two 200s gives you the capacity of 400, but does not make it a 400 amp service.

Deciphering this type of services is tricky because of many different variables when you have two service disconnects. According to 230.40 when you have only one drop or underground service lateral you have only one service. In this case you have one service with two service disconnecting means (2-200 amp CB’s) grouped in one location.

The tricky part is based on the size of the conductors feeding the meter enclosure and the size of the conductors feeding the two service disconnects. Since the 2-200 amp service disconnects do not individually carry the entire load of the structure their associated service entrance conductors must be sized according to 310.15(B)(16) which would be #3/0 copper or #4/0 aluminum. {180 amps up to next standard size 200}

Although #4/0 Al in T310.15(B)(7) is permitted for 200 amps technically the table cannot be used. Also for the “next size up rule” {240.4(B)} to be used the connected load cannot exceed the ampacity of the conductor in this case 180 amps.

Simple. :cool:

So Robert is the reason for 3/0 copper is because the load is split and diversity is lost off the service.

The NEC has allowed for decades (since 1956) a reduction in the size of the service entrance conductors or feeders for single family dwellings providing the reduced size conductors would need to supply the entire load of the dwelling. The feeling has always been as you suggested that dwellings have built in load diversity and therefore can safely get away with a lower conductor ampacity.

In the 2014 NEC there has been a change to the old table where now instead of looking up a service size and finding the minimum conductor size, under the 2014 you would do a calculation using an 83% factor.

So for a 2 flat it would have to be 3/0 but for a single family you can get away with 2/0 is what I am understanding.