400 Amp Service and GFCI Limitations

This weekend I did and inspection on a 5,500SF home. It appears that the service is 400amp’s. There are 2 200amp service disconnects, and the label on the panel indicated that the panel is rated for 400 amp the the service is determined by the totaling up the 2 service disconnects.

On another note one of the breakers was a 20 amp breaker that was connected to and exterior GFCI outlet that had 15 outlets connect down stream. Is there a limit to how many outlets can be downstream and protected by a GFCI outlet.

That’s a 320 amp service, which is sometimes called a 400 amp service for slang (don’t ask me why, because I don’t know). Really and truly, it’s max rating is 320 amps. An electrician would refer to that service as a “three-twenty”.

No, there is no limit as to how many downstream receptacles may be protected by a GFCI breaker or receptacle. In real life, one would try to keep this to a reasonable amount to assist in later troubleshooting when it trips. I, personally, favor point-of-use GFCI receptacles at each location where GFCI protection is required. This eliminates lots of headaches later on, but at additional initial cost. This exterior circuit you saw, with 15 downstream receptacles on the GFCI, while legal, is just nuts. It’s the outdoor equipment and outdoor receptacles that cause the biggest headaches trying to sort out what tripped the GFCI. As an electrician, I’d highly advise you to note that in your report as a very probable nuisance in later years, and consideration should be given to point-of-use GFCI protection at each exterior receptacle. Many manufacturers have a functional limit of 250 feet of wire on the load side of the GFCI also.

Thanks for the input on the CL320 because I was ready to call it out as a 400amp service.

A future note on the GFCI outlet; it was located on the exterior of the house but it also controlled the 9 garage outlets and 6 or more outlets on the front and back side of the house. I made many trips around that 5,500 sf house. I have no problem recommending future evaluation by an electrician because there were may other electrical issues with this house.

Word it however it pleases you most, but I’m not sure it needs evaluated by an electrician now. They just at least need to be on notice that it’s going to be a royal pain in the donkey for them one day.

Generally we see 320/400 meter enclosures as 320A Continuous and 400A Non-Continuous.

But do refer to them as 320A services as well, but I would venture to say 3 of 4 electricians would call it a 400A service.

I like to call them 400 amp services too, looks better on the invoice!

I think that 320A Continuous and 400A max if on the label of the panel posted.

or just call it 320 Amp since that’s the rating of the meter.


Right, because there certainly are “real” 400 amp services.

For myself when I writeup the service size typically I will marked down R400 or C400 The R is 320 resdential service while the C is a true 400 amp commercal and normally it will be either CT’ed or bolted on depending on which POCO I deal with it.


The listing on this equipment is just as Paul has mentioned, that is the reason some call them 400A services.

Just a small hijacking…
We see a ton of 400A services being installed around my area. We have tested a bunch of these services to see loads of less than 150A. Talk about keeping upe with the Jones.

Very True - I have a 4000+ sq. ft. house that the AHJ insisted had to have a 400 A service in spite of the fact that only the A/C is electric. The rest of the usually large loads are natural gas (water heaters, cooktop, furnaces, clothes dryer, etc.). They base the requirement strictly on square footage, reasoning that someone in the future may want to convert to all electric. I haven’t measured the total load under various conditions, but would bet that it would be hard to find 150 A at any time.