On rural electric line. I have a voltage that fluctuates

Thread Starter

txplanebuilder

Joined Jan 14, 2020
2
I'm the last customer on a rural electric line. I have a voltage that fluctuates (no surpirse) but is typically in the 245 range and has spiked to 252 (per the ONCOR electric folks). He claims meter data shows highest voltage every 15 minutes... But I caught him in a few fudging lies. He claims that they have a target voltage of 240V and can deviate as much as 10%. In other words, 216 to 264. To which I call BS. On individual legs I've seen 127V in one instance. Obviously, I see LED bulb lifespans of 3 months or so, incandesants 6 months, and CFLs maybe 6 months. I'm getting pretty annoyed... My normal average load is 4-8 kW. So, any ideas that are affordable and will help? I'm obviously not going to get any from ONCOR. Anyone have a link to power standards that I can read up on? Thanks in advance....
 
They are allowed 10% deviation. I had a problem myself at one time and I was quoted the same. Normally things will work within that range and beyond to some extent.

I do have to ask are the individual legs to neutral the same voltages? A loose neutral connection between your neutral bus bar and transformer will cause an imbalanced load and make one of the 120 volt legs way high and the other low. It finally took me calling a the right time and talking to a supervisor one night after it finally got bad enough to spin ceiling fans out of control, dim lights, and blow a computer power supply to finally track down the problem. I had meter in hand checking things out while taking to the guy and as soon as I started with numbers it made sense to him. The guy they just sent out before it all went bonkers checked the input side of the transformer, but not the output side. It's been right ever since.

Another place to check is evergreen trees especially are known to eat away at incoming lines. If your service lines pass through a tree it would be a good place to look.
 
Last edited:

ebeowulf17

Joined Aug 12, 2014
3,160
Wikipedia says 120V +/-5% for each leg of split phase in the USA:

https://en.m.wikipedia.org/wiki/Mains_electricity#Standardization

That works out to 114-126 per leg, or 228-252 across the legs. Sounds about right to me.

They cite two references for the USA tolerance, but one costs a bunch of money and the other is from PGE, the utility in the Seattle area. Not sure how much proof you want when arguing with your local provider, but it's a starting point.

However, if it is +/-5%, the 252V you mentioned wouldn't be out of spec (just very, very close!)
 

debe

Joined Sep 21, 2010
1,156
What country are you in ,& are you on a Single Wire Earth Return system & is there a lot of customers on your line with Solar systems?
 

MisterBill2

Joined Jan 23, 2018
5,211
Constant voltage transformers do a good job, but they are expensive to use because all of that heat they produce comes from the input power. So they have a serious no-load current draw.
My suggestion for your sensitive circuits, is a step-down autotransformer to reduce the voltage a bit. Providing 110 volts to the lights will allow a much longer life, likewise for a number of other types of loads. For the computer and electronics loads, one possibility is a rectifier/ regulated inverter setup. Not cheap but very effective, with the added benefit of serving as a UPS if you add batteries. The obvious real power company solution is moving the tap-changing transformer closer to you, but that is far from cheap. The other option is running the much higher voltage line closer to you and adding another distribution transformer, also not cheap.
But just to prove to them that the problem is real, there are quite a few recording power monitor devices available.
If you want to fix it your self, an automated tap changing transformer just for your system is another option.
 

Reloadron

Joined Jan 15, 2015
5,128
Here in the US there is no Federal Standard for residential voltage. Some power distributors work from +/- 10% and others +/- 5% and I have also seen +5% / -10% so actually a pretty wide margin to work from. I can tell you my own power delivery is 246 VAC at the entry with a nice split of 123 - 0 - 123. Most appliances and lighting I have worked with doesn't seem to care all that much. Then too, I never paid much attention to the longevity of the lighting.

At work for equipment deemed sensitive we had AC Line Regulators in place, also called Line Stabilizers and a few other names. I recall a few large transformers labeled Topaz. While the stuff works fine and does what it is supposed to do however there is always a down side:
Constant voltage transformers do a good job, but they are expensive to use because all of that heat they produce comes from the input power. So they have a serious no-load current draw.
That was it. We never cared as power was abundant and inexpensive which is not the general residential case. :(

Ron
 

MaxHeadRoom

Joined Jul 18, 2013
20,023
That was it. We never cared as power was abundant and inexpensive which is not the general residential case. :(
One of my customers also tried them, but they had to be shielded on the shop floor due to the heat from the saturation current they ran at.
Sola was the big name in them back then.
Max.
 

MisterBill2

Joined Jan 23, 2018
5,211
I have specified SOLA brand constant voltage transformers in dozens of production machines for a big auto company. The 1 KVA and 5KVA varieties. They protected our systems and the PLCs and the instrumentation all very well. the one time that there was a problem was with a test stand that used a PDP11/04 computer. They moved the Sola transformer to a different area because of the heat. It was a 480 to 120 volt step down model. But they accidentally connected it in reverse. So instead of 490 in and 120 out, it was 480 in and 1920 volts out for a short time. That did quite a bit of damage. From this we learn to ALWAYS check the output voltage of a transformer before connecting it to the load.
 

MaxHeadRoom

Joined Jul 18, 2013
20,023
I have specified SOLA brand constant voltage transformers in dozens of production machines for a big auto company. The 1 KVA and 5KVA varieties. a test stand that used a PDP11/04 computer.
The customer I quoted also had PDP11 based CNC machines. (one of the first).
The biggest problem was maintenance welders erasing the magnetic core memory when working close by!!
Fortunately that was the only time I saw them (Sola) used. :rolleyes:
Luckily I have not come across them for some decades now.
Max.
 

Reloadron

Joined Jan 15, 2015
5,128
One of my customers also tried them, but they had to be shielded on the shop floor due to the heat from the saturation current they ran at.
Sola was the big name in them back then.
Max.
Oh yeah, another name from the past. We had quite a bit of the SOLA stuff. Funny as come May I will have been away from the plant for 7 years and it's amazing how much I have forgotten, not so much how things worked but manufacturers names we used. While I don't know who mage it we had a large 10 KVA unit which was part of another unit we were dumping. I had wanted that thing but never managed to drag it away. :(

Ron
 
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