The old panel in my shop is giving up , the old aluminum buss bars are just getting too bad to continue using it . So Thursday while we were down in Memphis I picked up a new box - 20 slots/20 ckts/100 amp in-feed breaker (also gets a 100A feed breaker in the main panel) . It has 2 neutral/ground connection strips , connected by a link at the bottom and not bonded to the enclosure . I plan to move the ground strip from the old box and use both of the ones in the new for neutrals .
Here's where I'm not sure what I want to do - the supply from the main panel in the house is 3 wire 2/0 aluminum . I'm not sure at this point how I want to handle the neutral/ground issue . I'm inclined to let the neutral float and drive a separate ground rod for the shop . Ground will be bonded to the enclosure . I don't think that will give me any ground loop issues , but there may be a problem with a difference in potential between the ground and neutral . I guess I could just let the neutral act as ground too , they are bonded in the main panel - oops , no they're not bonded in the main panel , the only place the neutral is grounded is up on the pole at the transformer . Main panel ground is a standard 8' ground rod and it's bonded to the enclosures (meter base too) . The other issue I have is what to use to connect a copper pigtail to the end of that 2/0 al wire . The al wire may be too large in diameter for the in-feed breaker in the new panel .
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Snag
electrical question
Dec 09, 2017
1 Replies
The answer is simple. If you only have an existing 3 wire feeder leave the panel as it is, put the bonding jumper in (green screw or a strap) and exploit the exception. Drive a rod. That is still required in any configuration. You can't just use a rod as your ground, it needs to be bonded to the neutral somewhere. If you only have a 3 wire feeder that will be in the sub panel.
250.32(B)(1) Exception No.1: For installations made in compliance with previous editions of this Code that permitted such connection, the grounded conductor run with the supply to the building or structure shall be permitted to serve as the ground-fault return path if all of the following requirements continue to be met: ( 1) An equipment grounding conductor is not run with the supply to the building or structure. (2) There are no continuous metallic paths bonded to the grounding system in each building or structure involved. (3) Ground-fault protection of equipment has not been installed on the supply side ofthefeeder(s). NATIONAL ELECTRICAL CODE 2014 EditionJoin the Discussion
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