Main Service Panel Upgrade Question.

I have a 1950s stucco home with a 100A flush service panel with meter; the panel does not have a main breaker. I would like to upgrade to a 200A service with a main, but a new 14.4 wide panel will not fit in the bay where the original panel is located. The original panel is 12” wide and so is the bay (it is close to a corner and all other bays are 16” O.C.).
One idea is to install a surface mount panel over the smaller original flush 100A panel. But if I do this the mast head conduit would be left attached to the original panel and the service conductors feed into the new 200A panel from a knockout in the back. Would this be a NEC violation? The service conductors would be replaced and continuous from the new panel to the mast head.

Thanks in advance for any advice.

  • How deep is the existing panelboard cabinet? Dec 17, 2017 at 11:01
  • Also, is there an existing disconnect outside, and if so, is the neutral-ground bond made at that outside disconnect? (i.e. is the feed into your current panel a 3-wire cable, a 4-wire cable, or 3 wires in conduit?) Dec 17, 2017 at 11:35
  • Thank you for your feedback. The existing panel is 4 " deep. There is no disconnect at all and the house does not contain a ground in any circuits except in the kitchen where a separate bare ground wire was daisy-chained to counter outlets and then connected to the cold water pipe. The feed into the original panel are three individual wires.
    – user79192
    Dec 18, 2017 at 15:45

1 Answer 1


I would consider the old panel a gutter or wireway at since it is no longer used (no connections in it) at that point it would be legal be sure to install an insulated bushing in the knockout hole and it should be good to go.

  • If his existing panelboard is shallower than 3", then he's likely to break the 312.6 wire bend rules by trying to bring the service cabling out the front. Dec 17, 2017 at 18:05
  • As long as you don't make joints or termination in it, I believe you can cover it up. I agree with Ed about using an insulating bushing.
    – ArchonOSX
    Dec 17, 2017 at 19:49
  • In our area we are required to include a 2" inspection hole as well between the two containers for the inspector.
    – Paul Logan
    Dec 17, 2017 at 20:53
  • Thank you Paul. I will use the insulating bushing. I may end up having to move the new panel away form the existing if I am required to upgrade my service entrance conduit from 1.5" to 2" .
    – user79192
    Dec 18, 2017 at 15:49

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