I'll bet his neutrals are cooked and you can measure several volts from his neutral to ground at the computers.
It's funny the Code allows a reduced neutral but with the advent of computers (non-linear loads) 200% neutrals are becoming the "in" thing.
We had a medical clinic that fried a computer or server everytime a black cloud came over but they didn't have any money for correcting the "cause" of the problem.
I told the owner that there could be a problem with the neutrals.
I also explained that due to high harmonics, the transformer may need to be replaced (with a K type).
Another thing to check is if it supplied by an isolated ground, that it is properly grounded. I have seen many Isolated ground bars that are so isolated that they didn't ground it at all!
Since the Isolated ground bar is insulated like a neutral bar, if no ground is taken back to the service the equipment is effectivly ungrounded. I have seen "electricians" take the ground to a sole ground rod, thinking thats what "Isolated Ground" means!
IGs are over rated (no pun intended)... I believe if we (electricians) do our job correctly, there should never ever be a need for IGs.
Just a personal belief.
I'm assuming that this was thought of before, but it is worth checking...
Is it always the same power supply or is it a different power supply every time? Has the same power supply failed 2 or more times since they have been at that location?
What about the area/room that the equipment is in? Is it sufficiently ventilated and/or cooled? Are the power supplies/servers in electrical enclosures or are they simply on a free standing metal rack? If they are in electrical enclosures, are the enclosures ventilated, and if they are, do the vent openings have filters on them (you would be surprised at how infrequently people change filters).
These are a few questions that should be answered or given thought to before it is automatically assumed that it is a PQ problem. I have seen MANY power supplies and VFD's fail simply because of insufficient cooling/ventilation. Sometimes the same power supply or drive has failed at least 2 times before anyone thought about ventilation.
As I said, I am assuming that was thought of already, given the fact that they have this much expensive equipment, but it doesn't hurt to check!
There are multiple PS that have failed, on multiple circuits. Again, each circuit being a HR back to the panel.
The servers have blown PS and the server room a 4' x 4' closet has serious venting... it will close the door on you... I already asked that.
The desktop / workstations have had power supplies fail as well. However, not as often.
Check voltage at the panel.
Check the voltage at the loads.
Check neutral and all phase currents you can determine if harmonics are high based on this.
Measure zero sequence currents on all phases and neutral
Check the current at the neutral to ground bond.
Check for neutral issues in the panel and upstream of the panel.
Look for the always noted loose connection.
Last 3 times we had this happen the manufactures finally admitted defective power supplies.
Time before that it was whiskers.
One time it was excessive dust dirt blocking cooling.
If they have one item in particular causing problems get a double conversion (true UPS) to isolate the issue.
Isolated ground or not should make no difference.
I'd bet on the manufactures.
1. I have those items noted. I was going to use a PQ monitor and log the data at the panel. Then download the data and look for spikes / sags and excessive neutral current.
2. Good idea on the loose connection.
3. At this rate, I think the guy will let a few more PS go before he hires us.
Considering each unit has it's own UPS and the power supplies are failing while other tenents have no problems--they have a batch of bad power supplies. Of course the manufacturer and/or supplier is pointing fingers at the building. The UPS is designed to prevent any possible damaging voltage to reach the device it is protecting. But we always installed our data loggers and provided documentation to make them happy and it's easy work
I agree that it would be easy work. We could make a good profit on the job. What's a good price to perform data logging for 24 hours... and then interpret the data for them?
