Power Quality

[cadpoint]

I was just pondering if one was to take a voltage reading at service point or to say branch service, or any service and note that there seems to be
a higher or lower than expected, Voltage.
I've watched my house for years and always note conditions on jobs and the reading obtained locally, they frankly all are riding a little higher!Thoughts ?

 

[mdshunk]

Depends on the time of day, the particular transformer you're hooked to, and how much it is or isn't loaded.

 

[cadpoint]

gezz I just realized I created a 2 volt gap ....

 

[cadpoint]

well, OK, I never monitored my house for 24 hours : )

 

[chris kennedy]

I see
277= 281
120= 124
208=211
more often than not around here. This is at main disco's under load. Often I find 1 phase to be dead nuts and the other 2 slightly high.

 

[wirenut1980]

Most utilities have a range of voltages plus or minus nominal according to their state's public utility commission. The utility I work for goes by ANSI C84.1 which says for Range A, which is steady state range, the voltage should be +/- 5% of nominal.

So my answer is 114 to 126 V for a 120 V base.

There is also range B for short duration variances outside Range A.

 

[76nemo]

What about +4V's?

 

[zog]

You should expect 5-10% below nominal at around 4AM, then steady increase until peak at around 3PM where it reaches 5-10% above nominal, starts to taper off, big drop around 5PM, another drop around 10PM, and low values from 1AM to 4AM

 

[quogueelectric]

No load xformer voltage high if the little red light is on in the hood that means overload and the volts will be low unless they bumped up the taps.

 

[brian john]

than expected, Voltage

I never expect to see anything, I test the service/conductors, phase to neutral, phase to ground and phase to phase. I make any Power Quality determinations base on this and amperage readings.

 

[zog]

You should expect 5-10% below nominal at around 4AM, then steady increase until peak at around 3PM where it reaches 5-10% above nominal, starts to taper off, big drop around 5PM, another drop around 10PM, and low values from 1AM to 4AM

 

[Jraef]

Some utilities allow +- 10%, so most devices are built to that as a standard voltage tolerance. +- 10 volts on a 240V (<5%) system is not a problem. If you measure that at a 120V connection, its possibly a little high, but still not likely a problem for your equipment.

 

[don_resqcapt19]

Zog,
Why lower voltage at the times of low load?

 

[brian john]

Typically when monitoring the main I see highest usage at 11:30-1:30 When elevators, HVAC and office loads are on same source/service.

30 Day voltage graph.

11 day (same project) current graph average.

One day Monday, red is from 7:55 AM through 6:40 PM, purple line is 5:00 PM-6:00 PM

 

[zog]

Zog,
Why lower voltage at the times of low load?

Oh, reverse everything I said in my last post, I was thinking about load and typing about voltage.

 

[Sharpie]

At the facility I work at, we were seeing 500v on a 480v nominal service. That's not that far out there, but we reported it to our POCO and they took a few caps off line at the local sub-station. That brought the voltage back to just over 480V.