Transformer voltage drop question

[VTguy]

Hi all first time post here and yes I have searched the forum before posting. I am doing a side job for friend and was hoping for some validation of what I was told by the PoCo. The customer had me install a new 200a service the original was a 20 space box with every space filled with the double breakers instead of fitting a new panel (what a mess!) along with a sub panel on a 50a breaker for the hot tub. The guy is a rabid audiophile with tons of tube amps and other gear and had complained he could "hear" a voltage drop in the equipment. Sure enough when I tested it with the dryer or elec water heater on it was around 228v with both on around it was about 224v. So the PoCo engineer came out and said they would have to replace the almost 200' of #4 wire and upgrade the 10kva can. Well yesterday they came out and did the line but the lineman would not change the can saying I was miscalculating the loads as they never use close to the nameplate capacity. I tried to no avail to explain these are resistive loads and that they use pretty much what their rating is (am I correct on this?) and that they are on often. The dryer and water heater alone pull 9500w its a 4200sq. ft. house with 2 adults and 3 daughters hence almost constant laundry running. After the new line with the 9500w running we gained about 2v only and he is not very pleased thus far.

I guess my question would be does this sound like an average voltage drop? And would a larger can do a better job at raising the voltage? And yes I understand they like to undersize the cans but i'm not sure about the voltage or operating characteristics when they are running at full or over capacity. There is also a noticeable flicker in many of the lights most notably the led's when it's running like this. Thanks!

 

[Dennis Alwon]

Did the line replacement help? Voltage sounds pretty low also-- around here we are looking at better than 240v

 

[VTguy]

Did the line replacement help? Voltage sounds pretty low also-- around here we are looking at better than 240v

It did to a small degree about a 2v increase with those 9500w running. As for the light flicker I am sure I will hear about it tomorrow.

 

[don_resqcapt19]

You need to check with the state utility commission to see what the minimum permitted voltage is. I would expect that it would 228 volts. Typically the state utility commission has a lot of power to force a utility to comply with the requirements.

If the utility is in compliance with the commission rules, there is not a lot that you can do to get the power company to change anything. You may be able to use a constant voltage transformer or a dual conversion UPS to supply the audio equipment.

 

[Ingenieur]

Measure the current and voltage with the dryer, water heater and ac on
gotta be 100 A or > 20 kva

Al or Cu service?

 

[VTguy]

You need to check with the state utility commission to see what the minimum permitted voltage is. I would expect that it would 228 volts. Typically the state utility commission has a lot of power to force a utility to comply with the requirements.

If the utility is in compliance with the commission rules, there is not a lot that you can do to get the power company to change anything. You may be able to use a constant voltage transformer or a dual conversion UPS to supply the audio equipment.

Thanks the UPS is way out of the price range for how much power he would need. And yes it is 228 here and I am sure if I turn on everything it will get below that I just need to make the trip out there again odd thing though that the engineer said they would replace the can but the lineman fought about it. I guess I am starting to feel that it is indeed the can.

 

[VTguy]

Measure the current and voltage with the dryer, water heater and ac on
gotta be 100 A or > 20 kva

No ac but there is an empty hot tub I can try to have him fill a bit that for sure should do it with the other big items running. I plan to bring my meter out there tomorrow.

 

[Ingenieur]

Al or Cu service?
OH or UG?

did he measure no load voltage at the xfmr taps?

 

[VTguy]

Al or Cu service?
OH or UG?

did he measure no load voltage at the xfmr taps?

4/0Al panel to drop and no clue if they tested as I was not on site for the PoCo install.

 

[gar]

160823-2400 EDT

VTguy:

The tests to run are voltage at the main panel at ( directly on ) the input service wires coming into the panrel under no load, and with specific known loads. With a 10 kVA transformer and the loads you mention the change in voltage from no load to full load I believe will be much greater than 4 V. 4/240 = 1.7 %. The transformer alone is likely to have an internal impedance of 3 to 5 %.

If you measure line A to neutral and apply a 100 A load from line B to neutral I would expect a slight increase in the voltage reading. This is mostly from the voltage drop on the service neutral.

Measure the same line A to neutral voltage and apply a 100 A load between line A and line B, then I expect a voltage drop resulting from transformer internal impedance and the impedance of the single line A current. With this test there is no neutral current. This means the neutral voltage at the main panel is essentially the same voltage as at the transformer center tap.

If you did a measurement from the ground rod at the transformer to the main panel Line A and load the B line to neutral, then the line A to transformer center tap should only show a small voltage drop resulting from the transformer internal impedance common to both line A and B.

.

 

[Bugman1400]

The 10kva can sounds too small. A bigger can (20kva) will help out significantly with the voltage drop. In addition, a 4200 sqft house is around where you would start to use a 320A service. I would have asked the lineman to measure the voltage at the secondary terminals with and without all the load you mentioned.