I have 300 amp meter box and do to some last minute changes – I have done the following:
I have two conduit connected to the meter box. One conduit has a 300 amp wire running from the meter to a 200 amp service panel and the other conduit has a 100 amp wire running from the meter to a second panel (100 amp) on the second level. I heard that having two different size cables is not a good idea due to the 300 amp would pull all the current because it has a lower resistance. Is this true? Would the 100 amp wire not get much current?
Replies
Electrically, there is no problem with it.
I haven't the slightest idea what the code requirements will be in this case.
I don't know about the wire size.
But you need to have all service disconnected located in one immediate area. You can have up to 6 disconnects.
So you will need to run the 2nd line to a location by the 200 amp panel and install a disconnect, then to the 2nd floor panel and that will be a sub-panel.
Electrically it's fine. I suspect you may have some code issues, if the wiring feeding the 100 amp panel is smaller than the service entrance cable.
There's also the issue of disconnects, as was mentioned. The requirement for disconnects varies by jurisdiction.
Are there 100 and 200 amp breakers in that box ahead of the 100 and 200 amp feeders to the panels? If so, what you describe sounds OK. If not, our DWP out here wouldn't sell you a single electron.
Power systems are extremely low impedance, so the amount of current you draw anywhere is pretty much determined only by the lights and stuff you're using. If any of the runs are extremely long, you have to figure out voltage drop, but that's rarely a problem inside an ordinary house.
-- J.S.