garygid wrote:I had to remove the 150-amp input breaker on my 150 amp service box, and replace it with a 110-amp breaker when I added a 40-amp breaker to connect my 7kW PV system into the service box. So, now at night, I can only draw 110 amps, not 150! The reason, a 150-amp "rated" metal "service" box is not allowed to have more "possible" input than the box's rating.
Warning - getting OT here!
Actually, with PV there is a 20% exception - you are allowed to exceed the busbar in your panel (which typically has the same rating as the panel) by 20% when backfeeding power for residential applications. This is explicitly allowed by the NEC. The only caveat is that the breaker should be located at the opposite end of the bar as the main breaker. This is to avoid overloading any one section of the busbar. The theory is that if you short out your busbar, no section of the bar will see more than the busbar rating.
So if you have a 150A panel/breaker, you can use a 30A breaker to feed in your solar power. Of course, since you need a 40A breaker for a 7kW PV system, that still means you have to downsize your main breaker, but you should only have to downsize it by 10A to 140A.
150A * 120% = 180A - 40A = 140A. 140A breakers aren't common, but 125A breakers are so you would be safely able to get another 15A from the electric company if you wanted.
garygid wrote:And, if I wanted to put in a higher-capacity service box (even if I stayed with the original 150-amp breaker), SDG&E said that they would require me to trench out to the street, approx 28" deep and lay in a conduit. They would inspect and pull in the new wires required for the (potentially) larger demand. The trench would have to cross all the other utilities except water (gas, phone, cable, and the existing electrical conduit).
I ran into that issue, too with my house. I currently have a 100A panel and the main feed wires are only rated to 125A. Upgrading to 200A service means running new wires (which are buried) up to the latest code in a trench to the street. At the street, the trench actually needed to be 3" deep thanks to the handhole it would be connecting to. There are all sorts of crazy requirements for the trench - only 2 90* bends allowed, 2" PVC conduit, feed entrance can't be within 3" of the gas meter (and right now my gas meter is right under the main service panel), has to be filled with proper material, etc.
Quote I got would end up being like $6,000 to do the work. Ouch! It's the only time I wish I had overhead lines - upgrading those are easy in comparison.
I suspect that these sorts of issues will be fairly common when people start getting pre-checks done to see what it will take to get a 240V 20-40A charger hooked up.
My breaker box is full after adding my 3.24 kW PV system. Hopefully I can get away with a 125A main service feed to get the charger. Actually, if I can get a 200A box with a 125A main breaker, then I'll have plenty of room to upgrade my PV system in the future.
200A * 120% = 240A - 125A = 115A of PV power - about a 22 kW system.
I'll run out of roof space long before I get anywhere close to that.