Maybe a stupid question

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Gar,.. you never fail to impress me ..

Joey ,.. don't let it eat you up ,.. and be diplomatic in your discussions ,.. perhaps the boss would like this site??

My guess would be that he wouldn't ,.. but you never know??

You are well on your way....
 
That was a very scientific answer Gar, hopefully that just didnt go right over my head....Im just a country fella here...lol...Basically because of resistance, there is a potential difference from one end to the other in the EMT, or any conductor for that matter, so if there is imposed current from paralleling neutral current by bonding at both the service disconnect and a subpanel you could read voltage between two points on the conduit at the subpanel and back to the MDP when you had a length long enough to create enough a potential difference because of resistance?
 
090225-0836 EST

joeyww12000:

You got it.

5 A flowing thru a 10 ft piece of 1/2 EMT as I used in the experiment is going to produce a readable voltage drop. EMT seems to have a coating that made it hard for me to get good contact. If you do not have good contact, then capacitive coupling to the meter leads may produce a greater signal than that from the voltage drop along the conduit. Once you make good contact the circuit impedance is very low and capacitive coupling has no contribution.

On my Fluke 27 on AC MV I can resolve 0.1 MV (100 microvolts). Shorting the leads on this meter produces a reading of 0.0 MV. On my Fluke 87 (true RMS) there is a higher internal noise level in the meter and it does not read quite this low with shorted leads.

In any of these experiments the measuring loop did not have significant magnetic induced voltages. However, in my yard below the power lines I have placed a rectangular loop about 8' by 40' and this does get enough magnetic coupling from the lines to get a noticable reading. I do not remember the magnitude. I believe between 10 and 100 MV.

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joeyww12000 said:
Basically because of resistance, there is a potential difference from one end to the other in the EMT, or any conductor for that matter, so if there is imposed current from paralleling neutral current by bonding at both the service disconnect and a subpanel you could read voltage between two points on the conduit at the subpanel and back to the MDP when you had a length long enough to create enough a potential difference because of resistance?
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Keep in mind that the same thing happens one the neutral. We just don't want what should be grounded surfaces to be likewise enrgized.

A voltage between neutral and ground at subpanels is normal. Not desired, but understood to exist; our goal is to minimize it.
 
090225-1401 EST

joeyww12000:

I am home at the moment and I made a measurement of the voltage drop on my EGC between my main panel and a work bench. Probably 50 ft or more of EGC. With most things off I read 12 MV. It is not unlikely that some of this is inductive coupling. This is not at all a controlled experiment. As I turn on fluorescent lights and computers this rises to about 45 MV. All of these loads have RFI filters to the EGC as the source of high frequency current in the EGC.

With any tests like these you have to be able make judgements and other tests to determine the significance of the data.

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