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How much power fluctionation is too much?

Posted on 2016-11-03
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Last Modified: 2016-11-04
I have a customer in a downtown area that has potential power issues.  We have run an analysis internally (input power on UPS's in the server room) and externally (power company).  The graphs on what is reach us match the graphs from the outside of the meters, so we do not have an issue within the building.  Our power fluctuates between 125V to 130V, sometimes hovering around 129V for 2-3 hours.

All the equipment in the server room is protected by Line filtering UPS's, so I am not overly concerned about that room.  My concern is everything else.... computers, printers, copiers, scanners, etc.  

The power company and the electrical contractor stated that the constant fluctuation and power levels are "normal".  The power company stated that they consider plus or minus 10% acceptable.  So on a 120V, they are happy with 108V-132V.  I honestly do not know enough about the tolerances of computer equipment to know if this will cause an issue.

I am asking this because the electricians have told us that they can install an isolated transformer on our side of the power meters that will level out the voltage being delivered to our office space.  I am assuming this is basically a line filter to get rid of the spikes and provide us a solid 120V.  Such a device does not come cheap.

So my question is "How much is too much"?  How much fluctuation.  How much voltage.  At what point do we concern ourselves with the damage (if any) being done to our equipment.

Thanks
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Question by:tcampbell_nc
4 Comments
 
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Assisted Solution

by:Dave Baldwin
Dave Baldwin earned 200 total points
ID: 41872454
10% sounds fine to me.  PC power supplies are designed to handle the variations in line voltage.  Installing an isolated transformer won't help anything unless you have much larger changes in the incoming line voltage.  I don't see any potential power issues in what you have said.
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garycase earned 300 total points
ID: 41873090
10% fluctuation is not an issue.   If you're confident that's all you are experiencing, then I don't see any reason to get an isolation transformer.    An isolation transformer is essentially a 1:1 transformer with line filtering and usually an AVR circuit that adjusts for any out-of-range voltages.   It still won't eliminate voltage fluctuations -- it will just ensure they're within the range specified for the particular unit (e.g. 5% or 10% tolerance from nominal).

Your sensitive equipment is already being protected by UPS's with AVR.   If you have some equipment you'd like to give the same level of AVR protection to, but don't need UPS capabilities, you could buy a few APC Line-R units, which provide the same AVR protection a UPS unit would, but without the battery backup feature.
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Expert Comment

by:nobus
ID: 41873528
normally, as said, the 10% (slow) fluctuation is not a problem
but when that is added with spikes - the problems can arise.
the only thing that protects you better is a good ups - so maybe the ups has to be checked ?
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Author Closing Comment

by:tcampbell_nc
ID: 41873908
Thanks for the comments folks.  I feel better educated now regarding the tolerances of computer equipment.  I am somewhat familiar with fluid dynamics, do I understand the causes of fluctuations, and that they will always be present.  I was just uncertain if spikes, and actually extended periods, above 130VAC were damaging my customer's equipment.  I will be looking into the AVR's.  They seem like an affordable option where the power is questionable.
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