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#1636 05/19/01 10:04 AM
Joined: Apr 2001
Posts: 109
Hello from Colorado!!!!
Ok Guys, I need some help.

I went on a service call Friday to PETsMART Vet Clinic. All of there computer monitors keep blowing up, and have lost two CPU,'s.

The two CPU,'s, and monitors are all they have lost. None of the Vet equipment has been effected at all.

I went to each individual outlet and checked for loose wires, went to the main panel and did the same. Went to the outside of the building to find the transformer and to my surprise it is a straight feed from the city to the meter to the panel. So I checked the wires in the meter.

After that I checked all of my voltage, Phase1 - 121.2v, Phase2 - 122.4v, Phase 3 - 123.1, And 209v - 210v between.

I left my meter hooked up for over an hour to see if there were any fluctuations, but there were not.

ALL of the circuits that are having problems are IG, and have surge arrestors on them.

Someone please give me an Idea of where to go from here. I have come to a mental block.

HHHEEELLLPPP!!!! From Colorado!

Jon Niemeyer
#1637 05/19/01 12:51 PM
Joined: Apr 2001
Posts: 21
check to see if all the effected circuits are all on teh same phase.. what sounds to me is like there is a phase thats leakin to the iso grund bus bar.. im not sure.. this is a good one.. maybe it has something to do with harmonics and the surge sup's


Remember when you read my posts, im only 17, still learning... "Hey, its takes what it takes!"
#1638 05/19/01 05:31 PM
Joined: Apr 2001
Posts: 109
I thought the same thing about something going back on the ground, or even stray current.
I put a large load on the service including all of the normal equipment, and the only thing that changed was the load on the neutral.
I also had the thought that all the effected circuits were on the same phase, so I checked and they are all equal, three on each phase.
I would not know how, but could the Isolated ground cause some weird problem?

Jon Niemeyer
#1639 05/19/01 05:49 PM
Joined: Jan 2001
Posts: 18
check to see if the circuit is on a shared neutral, sounds like it could be an intermittent neutral connection, causing the monitors to be in series on 208 volts. (intermittently)

#1640 05/19/01 06:00 PM
Joined: Apr 2001
Posts: 507
You can chase this indefinitely IMO. What you have already done has eliminated the obvious problems that we all would look for.

Unless you have logging type instrumentation so you can actually see what happens you are spinning your wheels.

Sell them a UPS to cover all effected equipment and call it good.


#1641 05/19/01 08:11 PM
Joined: Jan 2001
Posts: 1,044
Tom Offline
This is not meant as an insult, but what do you do when the UPS you just sold them not only doesn't cure the problem, but goes up in smoke too? This falls in the realm of a mechanic who changes parts until he finally gets to the right one. A UPS system is not a cure all for every power quality problem.

A detailed survey and analysis of the power system & grounding system is usually called for. I cannot over-stress the importance of investigating this area as most power quality surveys show that there are multiple deficiencies in the groounding system.

I find it strange that the surge arrestors have not smoked out as would be the case if a loose neutral was involved in either the service conductors or multi wire branch circuit.

You might wnt to take a look at all equipment in this building. Even some of the most innocent looking stuff can throw some serious transients on the line. Any X-ray equipment, copy machines or refrigeration equipment (including air conditioners) should be closely examined.

Whatever the outcome is, please let us know.

For more info on power quality, visit


Few things are harder to put up with than the annoyance of a good example.
#1642 05/19/01 08:45 PM
Joined: Dec 2000
Posts: 4,293
Be sure to take your voltage readings at the equipment being served, when the circuit is at its peak load. Long distances,bad connections, and/or small wire can cause problems that a voltage test at the panel or meter won't show.

#1643 05/19/01 09:06 PM
Joined: Nov 2000
Posts: 2,148
Where is the isolated gorund terminated?

#1644 05/19/01 09:38 PM
Joined: Feb 2001
Posts: 60
We have an old saying from my days in the Coast Guard. 95% of all equipment failure is due to operator error. Make sure the staff is not doing something stupid before you waste your time.

Computer monitors are very sensitive to the voltage supplied. A loose or missing neutral will have disastrous effects on the flyback transformer and should be eliminated before you continue your search.

I also agree with the bonding and grounding statement posted earlier. Bonding and grounding are the most common violations electrically speaking. It a subject that is sometimes misunderstood even by experienced electricians. Thee are often discrepancies between utility company specs, city specs and the NEC.

#1645 05/19/01 10:28 PM
Joined: Apr 2001
Posts: 507
Thanks for the link....some good info. there.


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