.common grounding??

Is there any reason that a generator and commercial power cannot share a common ground?
I am thinking of installing a select duplex outlet as follows: 1. Isolate the 2 outlets by removing the hot and neutral jumpers. 2. Connect commercial power to one of the outlets and a generator circuit to the other outlet. 3. However the ground is common to both outlets and cannot be separated. So is there any reason other than purely theoritical that the ground wire of both romex runs cannot be connected at the outlet?
If done at an ng furnace, during an outage power could be applied to the thermostat, igniter, and blower simply by moving a plug from one outlet to another. Am I missing anything? Bob S.
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Yes they can if done correctly. Your generator is PROBABLY grounded internally to establish the neutral, grounded conductor. This meets OSHA. If you do not break this connection then you have a dual/multiple ground which is prohibited by the NEC. 2 places that have a ground potential. Let us not get into "supplemental grounding"' Find someone locally that can help with the installation. If this is a convince thing then your better off with an extension cord. Personally I would not like the idea of half an outlet being dead at any one time. Lots of folks make mini transfer switches that are a whole lot easier for everyone to understand. What is the guy that buys your home going to think of your proposed idea?
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There was a discussion last week about damaging equipment connected to cheap generators, so make sure you buy a good one and have an electrician check everything. It's against code to have a furnace plugged into an outlet.

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It's going to cause less grief to install two completely separate boxes with their own receptacles for this.
Our electrical code would have a serious conniption fit over two independent power feeds to the same receptacle box.

Another poster suggested that it was code-illegal to connect a furnace by an outlet. I don't think ours prohibits it. Even if yours does, I _believe_ that provided you didn't try to share the receptacle box between the two feeds and otherwise did it right, an inspector would likely grant you an exception since this is for a specific purpose: emergency backup.
[I'm not entirely up to date on generator connects w.r.t. grounding interconnects to the rest of your system, so that's something you're going to have to research. Generally speaking, by powering the furnace this way, the ductwork will be grounded thru the generator. I believe that implies you have to bond the generator's ground to the house ground.]
--
Chris Lewis, Una confibula non set est
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