Continuous current on an equipment ground conductor.

[brian john]

Re: Continuous current on an equipment ground conductor.

Steve: I really wanted acess to this site to see this condition.

 

[brian john]

Re: Continuous current on an equipment ground conductor.

Karl:

This bothers me also, I am so use to finding hard connections causing this type of ground current.
One issue is did removing the conductor transfer the current to other conducting paths that have yet to be discovered. So many times I have seen problems moved, covered or hidden, while the problem still exist the it is out of site.

That's why I was hoping to see this site doing a zero sequence reading on the feeders , measuring ground current possible, all the typical stuff.

But if the problem was truly resolved, I still would liked to have seen the problem.

 

[charlie b]

Re: Continuous current on an equipment ground conductor.

Originally posted by karl riley:The phase fields cancel each other, with the neutral taking up the vector imbalance, giving the EGC very little to pick up as induced current. A twist in the cable, such as in service drops, also prevents induction. Right?

Right!

I don't know that 100A would induce 100A with even 1/8 inch separation, since you don't have the iron core to carry the field across.

Right again! That is why I said that the maximum would be 100 amps (intending that to mean a theoretical maximum), and that the actual current would be less.

Also, it would depend on the impedance of the ground loop, since current will not flow unless the ground circuit is a circuit.

And that makes three for three! Please keep in mind that the magnetic field created by the primary current will call into existence a voltage in the secondary, not a current. You can prove that by measuring the voltage with the secondary open. It is that secondary voltage that calls into existence a secondary current, the value of which will certainly depend on the impedance of the ground loop.

 

[charlie b]

Re: Continuous current on an equipment ground conductor.

Originally posted by don_resqcapt19:Then how are we getting 140 to 200 amps on the EGC in this installation?

I was speaking in general terms, not in mathematical terms. It all depends on the way the ?transformer? (i.e., parallel lines) is constructed. Put the wires too far apart, and the mutual induction drops dramatically. Use small wires (i.e., high resistance), and the amount of current that will be induced in the secondary drops dramatically.

None of us (not even the original poster, I infer) really knows how the facility under consideration was really built. But as I said earlier, 10 Phase A cables lying on 1 EGC can induce a ?theoretical maximum? current of 1000 amps.

 

[karl riley]

Re: Continuous current on an equipment ground conductor.

Charlie, everything you say makes sense. It is on questions like this that I wish I had a grant to pay for the rent in a warehouse where we could lay out conductors and actually measure some of these values, changing the conditions as we went along.

Brian, I am interested in this partly because I once measured an average of about 16A on each of 6 large EGCs which ran with 6 3-phase feeds to roof-top HVAC stuff. I was puzzled, and so I put my flexible ammeter probe (AMEX) around pairs and recorded results. This showed that they were at different phase angles which were not necessarily 120 deg apart. All I could conclude was that the current was induced from the 6 conduits they came from. (There was in addition current on building steel, plus some leakage N/G, so it was complicated).
I was not able to snake a probe around all of them, but wondered if it would read something close to zero.

Karl

 

[brian john]

Re: Continuous current on an equipment ground conductor.

Karl I have load banks and conductors just need the warehouse and time to set it up.

 

[brian john]

Re: Continuous current on an equipment ground conductor.

Assuming there is a site with induced on the EGC in. If zero sequence readings were taken on all phase conductors and neutral/grounded conductors would the current measured be the net current measured on the EGC?

If this EGC was bonded in multiple locations in the trough would this minimize the induced current?

If one knew there would no downstream neutral grounds or phase to ground high resistance shorts (such as through a heater element). Could one assume that as the load was reduced the net current measured on the EGC would lower?

Lastly if one was measuring induced current on the EGC, could one expect to see a change in measured current as one moved the conducotr around in the trough?

 

[earlydean]

Re: Continuous current on an equipment ground conductor.

Charlie,
Mutual induction does not work that way. Each of your parallel wires will have it's voltage in phase with the others, they cannot combine to make any voltage increase. that is why transformers are wound, to put each wire head to tail with the other, so the voltages can combine. Putting parallel wires together for 10 miles will only produce like voltages in perfect phase.