Exceptable voltage levels for 120V?

[Jriker1]

I recently had an electrician install some new lines in my basement for a server rack and am doing constant monitoring of all systems including my UPS's. Here is the deal:

Recently installed:
- 1 30A 120V circuit
- 2 20A 120V circuits.

My APC battery backup is attached to the 30A circuit.
My PowerWare battery backup is attached to one of the 20A circuits.

Using SNMP I am monitoring the input/output voltage of these battery backups. I'm having the following problems:

1. Frequently the battery backup on the 30A circuit is reporting an input voltage of 126V
2. Frequently the battery backup on the 20A circuit is reporting an input voltage of 114V

Is this normal? Obviously the output voltage is controlled by the battery backup however is there a certain voltage level that I should be monitoring as a warning and critical if it gets X number to high or low?

Thanks.

JR

 

[Reach4]

At the same time? Worth checking. Get a voltmeter and read the voltages with the same voltmeter.

If the meter confirms the difference, check the voltages at the breaker panel to see what the legs coming in measure. If the difference exists there, I would contact the power provider asking them to check their neutral path.

 

[Sponsor]

 

[Jriker1]

No not at the same time. Don't think they ever happened at the same time but I do see these things happen frequently. Now my next comment will spawn call the electrician, however is there documentation on how to use a multimeter to do this? I do have one, though may be of the analog variety, but don't want to cause the wiring to burst or get blown across the room if I connect things and short something out. I can be very handy with the right documentation to educate me. Guessing the 20A circuit will be easier to test than the 30A as the 30A has the circular turn on connector and there is only one of them so can't access the plug when this is going on.

Thanks.

JR

 

[Reach4]

Not at the same time? Don't worry. Especially if the low is during prime air conditioning time.

The electricity should come to your house at 120 volts plus or minus 10%. You are well within that range at the extremes. That difference at the same time would be worth checking out.

is there documentation on how to use a multimeter to do this?

Put the meter into AC volts (VAC or maybe a "~" character) at the right voltage range (a 200 or 250 volt range might be available on your meter).

Put one probe into each of the flat blade slots and look at the meter. Done. If your probes are too wide to fit the slots, You can sometimes stick a plug in part way, and probe the two flat blades at the same time. I am not going into what I might do with alligator clip leads and paper clips and extra care. One nice thing about AC-- you don't have to distinguish which line to probe with red and which with the black test lead.

Be very careful not to put your meter into the current / amps/ mA /milliamps setting. That will damage your meter if you probe the power that way. You want volts.

While you are checking, note that one flat blade is wider. That is your neutral (white wire). Probing from that conductor to your protective ground (roundish hole) should show max -- I don't know-- 3 volts??? Lets put it this way; if it is over 4, I would check that out. What is acceptable would depend on the length of the run and the load being drawn.

 

[Jriker1]

Thanks I will try this when I am home tonight. So from a software monitoring perspective, is there a particular voltage that I should be setting my software for that it should warn about and go critical about if it's below something or above something? In some of the videos I watched people were testing the voltage at the breakers and getting 124V and were like this shows it's good so wondering if my settings to warn at 114V on the low side and 126V on the high side is not really what I should be setting my alerts to.

By the way, wiring is a direct shot in the basement. Probably about a 20 foot run.

Thanks.

JR

 

[Reach4]

Thanks I will try this when I am home tonight. So from a software monitoring perspective, is there a particular voltage that I should be setting my software for that it should warn about and go critical about if it's below something or above something? In some of the videos I watched people were testing the voltage at the breakers and getting 124V and were like this shows it's good so wondering if my settings to warn at 114V on the low side and 126V on the high side is not really what I should be setting my alerts to.

108 and 132 if you want real alerts to a condition that needs looking into. Out of curiosity, you could tighten those to maybe 112 and 128. An alert would not be an action item at those levels, but you might want to know anyway.

Expect the numbers to be higher at 4 am and lower at 4 PM on a hot day.

Your connectors are NEMA 5-20 and NEMA L5-30.

 

[WorthFlorida]

APC has a very large white paper listings. Go to http://www.apc.com/us/en/prod_docs/results.cfm?DocType=White+Paper and search on "power factor" and click on Understanding Power Factor, Crest Factor, and Surge Factor. This may explain to you why there might be a different voltage reading but you are within operating limits and I see no problem. The voltage difference is most likely different loads on each leg as Reach4 explains.