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Commercial Inspections; open for discussion


Joe Tedesco
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How would this reading affect your decisions related to 250.6 in the NEC that covers Objectionable Current?
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Can you show any similar readings; or have you encountered any similar readings on any system conductors other than phases and on grounded conductors or neutrals, bonding and equipment grounding conductors?
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Thanks for your professional opinions!
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What exactly is that reading?

Is it Amperage which I assume it is? AC or DC? The photo is out of focus.

Is there cathodic protection in this system?

Is there a lot of electronic equipment in this building?

Jeff:

Yes it shows amperage, and there is no cathodic protection on this system which is supplied by a 50 hz generator.

There are lots on Nonlinear Loads (See definition in the NEC) on the distribution here.

Reading between the connections when disconnected shows less than 2 volts. The photo is out of focus but it does show the reading.

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More than likely harmonic current is loading the neutral so I would try to oversize the neutral conductor to carry the load with less resistance so that it takes away from the grounding system. This is a system that is grounded correct? It is not a European system where all current goes back to the POCO transformer and there are no ground rods/UFERs, etc., is it? 50Hz is not American.

The system needs a good power analyzer that can look at harmonics in detail. I am assuming that this is a 3 phase 4 wire wye of course.

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Jeff:

You ask lots of good questions, and this is not in the USA.

I am schedulted to go out into the field tommorrow and look into this situation in more detail. It gets really tricky and sometimes has flavors of the NEC, and in others the British Standards. I will keep you posted.

What I was looking for is to have someone who will use their amprobe and check the GEC and MBJ to see what their readings show.

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. . . What I was looking for is to have someone who will use their amprobe and check the GEC and MBJ to see what their readings show.

Over the years, we've had a few people here who regularly find current flowing on the GEC. (Jerry Simon?) It seems to be related to their geographic location. I made a habit of checking for it for about 6 months straight and never found more than a few fractions of an amp. Finally, I gave up.

It would be different, I'm sure, if I were looking at buildings with lots of non-linear loads and harmonic issues.

I wouldn't know where to begin with a non-North-American system.

- Jim Katen, Oregon

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Sirs:

OK, we inspected a few distribution systems yesterday and when the amprobe was used found readings that varied around 20-40 amps; and when disconnected and measured the voltage readings were never greater than 4 volts.

The Main Bonding Jumper was a busbar and showed zero amps!

We had to stop because the temperature was over 115 degrees yesterday!

http://www.timeanddate.com/worldclock/city.html?n=27

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Sirs:

OK, we inspected a few distribution systems yesterday and when the amprobe was used found readings that varied around 20-40 amps; and when disconnected and measured the voltage readings were never greater than 4 volts.

The Main Bonding Jumper was a busbar and showed zero amps!

We had to stop because the temperature was over 115 degrees yesterday!

http://www.timeanddate.com/worldclock/city.html?n=27

Sounds like it would be easier to troubleshoot the electrical systems in hell.

My hat is off to you, Joe. I hope you can help those folks before anyone else gets zapped in the shower.

- Jim Katen, Oregon

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