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ground loops

Posted By: Steve T

ground loops - 06/20/06 09:12 PM

I had an engineer tell me today that a tankless hot water heater with sensitive electronic controls was not operating properly because a 'second ground' run thru a correctly installed emt was connected directly to the neutral bus in the service panel and not to a separate ground bus. He understands the two busses connect directly to one another in the panel, but he says it makes a difference and can create a ground loop which affects the point of reference of the electronic controls at the unit.

Could a foot and a half of #4 really make a difference? Maybe this should be in the technical area, but I was having trouble getting that one up.
Posted By: gfretwell

Re: ground loops - 06/20/06 09:19 PM

Sounds pretty shaky to me
Posted By: LarryC

Re: ground loops - 06/20/06 09:35 PM

Is there a significant amount of current running thru this 'second ground' wire? If so, is the temperature sensor wiring wrapped around this current carrying wire?

LarryC
Posted By: Larry Fine

Re: ground loops - 06/20/06 10:30 PM

Sounds like a shipment of male bovine excrement to me.
Posted By: Larry Fine

Re: ground loops - 06/20/06 11:10 PM

To add: I'd be willing to move the redundant ground to the other bus just to shut him up (meaning call his bluff).
Posted By: gfretwell

Re: ground loops - 06/21/06 12:58 AM

If there is a ground loop it is in his equipment not your wiring. There should be no way a "ground loop" in the line side of any equipment should affect the "data" side. He may have something grounded that shouldn't be but it is not in an article 300 wiring method. It is in his LAN or internal wiring.
Posted By: Steve T

Re: ground loops - 06/21/06 01:27 AM

Thanks. I tend to agree with you guys, but this guy says their company does a lot of engineering for sensitive equipment--Honeywell and some others-- and says somethings dealing with inductance, capacitance (unspecific) he may not have known exactly, can cause this situation. When they removed the second ground all together, the unit works fine.

Like I said, I don't see how a short piece of wire can change all of this (especially when it is a #4 in a 200amp panel or a direct connection thru the panel enclosure itself) I guess I'd need to see the technical specs.

He said they were measuring a 1/2 amp on the ground wire. I don't know how they know there isn't current on the conduit.

Where's Scott? He usually has a complex answer.
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