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Normal range of variations of line voltage?

Posted by rogerv (My Page) on
Tue, Nov 19, 13 at 19:34

We're seeing some interesting line voltage variations that are causing my UPS's to make clicking noises...One of them has a line voltage meter on the front, and I'm seeing variations between about 113VAC and 120VAC on it. As I look at that meter it is almost continuously varying from time to time, a volt change at a time, but when it gets below 114VAC, the UPS clicks.

Is this normal, to get this much variation? Could be just a bad day for the power lines, but not windy or anything.

Is there anything that I should be doing to check this out? I could have an electrician come out, but if we're experiencing something normal here, I don't want to do that.


Follow-Up Postings:

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RE: Normal range of variations of line voltage?

On the UPS, not sure what it's doing. When it clicks, the voltage reading goes up to 120, then the next reading seems to be the actual voltage. Maybe the 120V reading is the reading on the battery, then, I'm not sure. But the power isn't going off, it's just lower voltage than the UPS would like as far as I can tell.


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RE: Normal range of variations of line voltage?

My house is way out in the sticks on POCO primary lines installed in between 1940 and 1942. At my previous residence next door, years ago, the lights would dim and brighten a bit from time to time. With some upgrades to the system by the POCO that problem essentially disappeared. But the old line conductors remain. I now have a voltage monitor plugged in here and readings vary from about 126 (which is a bit too high) down to about 119 over several hours. No sudden voltage changes. Your readings are a greater change but the range you are experiencing should not damage any electrical equipment.
I would prefer that mine never exceed 123-124 volts.


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RE: Normal range of variations of line voltage?

I'm getting a feeling it's not the POCO, but that particular circuit. The hint is the clicking sound. It's a relay in the UPS that disconnects it from the plug power and puts the equipment on battery backup. That removes load from the circuit which reduces Voltage Drop(brings the V back up to 120).

VD is a function of amperage(total load) and resistance(ohms). You want to draw the amps, so the solution is to improve the ohms. One way is to check all connections upstream of the UPS. There may be many outlets or receptacles on that circuit. Connections need to be clean and tight. Backstabs are bad. Wire nuts are best.

The other way to improve ohms is to increase wire size in the circuit. #14 wire is not made for long distances. It's also not made for long term maximum draw. I.E. 15 minutes of blow drying is fine. 4 hours of it would be bad. With distance from panel to receptacle and total load we can calculate needed wire size.

Lastly, 114V is too high for the UPS to cycle. Most don't cycle until 110V or lower. Check with the manufacturer and/or repair or replace.

This post was edited by glennsparky on Wed, Nov 20, 13 at 3:44


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RE: Normal range of variations of line voltage?

Thanks, I am looking for new UPS's now, you're verifying what I've been reading on the internet about this situation. I have two on the same circuit that are older and may not be behaving well at this point. They used to be much better, so I'm going to replace one and see if it behaves better than the one that it replaced. If so I'll replace the other one, too.


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RE: Normal range of variations of line voltage?

I have a CyberPower UPS for my computer equipment. Their software allows me to configure the low/high voltage and sensitivity when the UPS would "click" into action.

As for the voltage display, those instantaneous readings are just quick samples. You would need a different meter/recording device to more accurately follow the voltage.

You could have a bad connection on a neutral (or the POCO could as well). Have you tried moving the UPS to a different circuit?


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RE: Normal range of variations of line voltage?

I too was thinking 114 was too high for a UPS to take action. Is the UPS adjustable in any way?


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RE: Normal range of variations of line voltage?

I have an APC UPS and the software allows me to control the threshold voltage before it kicks in. It also reports the voltage. Mine varies about 10-12 volts through the course of the day, with late afternoon being the lowest.


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