voltage drop

[melanconelectric]

Got a call to move a service on a scrap metal shredding business. Looked at the job, come to find out they're experiencing a very sporatic voltage drop on one particular leg, 120 to 80.6 for approx. 6-10 seconds ( at times). Its not consistent with spikes in current, though. Its not consistent with anything, A/C start windings, heat strips, nothing. Could it be loose connections somewhere? Analysis engineer from utility is monitoring right now. All is inconclusive. Doesn't matter if its an a/c day or a heat day. Is causing battery backup for computers to kick in but not before the servers are crashing. Never before!!!!

 

[Rewire]

Loose connection sounds like a place to start if it is not a utility problem,had a motel call the hot tub pump not working ,checked the timer it showed 120v turned it on and opened the contactor for the pump and it was not closing just humming checked voltage and had 80v removed timer(power off) and replaced it with a toggle switch and the contactor closed and pump worked put a new timer on.

 

[hardworkingstiff]

I agree with Rewire, a loose connection or a high resistance connection (corrosion?).

 

[melanconelectric]

Loose connection sounds like a place to start if it is not a utility problem,had a motel call the hot tub pump not working ,checked the timer it showed 120v turned it on and opened the contactor for the pump and it was not closing just humming checked voltage and had 80v removed timer(power off) and replaced it with a toggle switch and the contactor closed and pump worked put a new timer on.

Would the 80 v be readable anywhere in the service? Its not always 80v either, it shows up as 106v, 99v, 96v, 87v, etc... the lowest the past thirty days was 80.6v

 

[ptonsparky]

I would think that the POCO would know within minutes if the problem was on their end. Loose connection is the first thought. How long have they been suffering with this problem?

You need to know how much current is flowing on the affected leg when the voltage drops. If your service drop is long, conductors small, etc an intermittent fault may show up as sporadic low voltage.

Is the service underground? Conductors deteriorate at varying rates causing the wire to become smaller and voltage drop to increase as time goes by.

I have seen overhead ACSR service drop fail mid span as well.

 

[melanconelectric]

I would think that the POCO would know within minutes if the problem was on their end. Loose connection is the first thought. How long have they been suffering with this problem?

You need to know how much current is flowing on the affected leg when the voltage drops. If your service drop is long, conductors small, etc an intermittent fault may show up as sporadic low voltage.

Is the service underground? Conductors deteriorate at varying rates causing the wire to become smaller and voltage drop to increase as time goes by.

I have seen overhead ACSR service drop fail mid span as well.

service is 4/0 triplex overhead, not that long, you know unusually. Is there a recorder that will time stamp so i will know what the current is when the voltage drops? POCO tells me that his hunch is a loose connection, its isolated to just one particular leg and that his equip. says its in a 240v load, like A/C. Problem has been going on for 6 mos.+ Not more or less in hot or cool mos., just very sporatic, june 6 times; august 3 times; december 8 times and a few inbetween all different hours of the night and day.

 

[rdelauter]

There are several recorders out there. Fluke and Dranetz/BMI are the two we use and are popular. I know you can rent them from different places. Do some research on what you need it to trigger and record on. The 4400 by Dranetz would work for you but I know others would as well, that is just one I am familiar with, others should work for you as well. Good luck.

 

[weressl]

Got a call to move a service on a scrap metal shredding business. Looked at the job, come to find out they're experiencing a very sporatic voltage drop on one particular leg, 120 to 80.6 for approx. 6-10 seconds ( at times). Its not consistent with spikes in current, though. Its not consistent with anything, A/C start windings, heat strips, nothing. Could it be loose connections somewhere? Analysis engineer from utility is monitoring right now. All is inconclusive. Doesn't matter if its an a/c day or a heat day. Is causing battery backup for computers to kick in but not before the servers are crashing. Never before!!!!

124/240 or 208/120 service?
- high resistance ground fault
- faulty capacitor centrifugal switch on a motor
- misbehaving switching power supply on a computer
- measure the current and voltage on all phases AND netural/ground
- methodically unplug equipment one-by-one to see if you can isolate the faulty one or the faulty circuit with a potentially high resistance connection.
-

 

[LarryFine]

Would the 80 v be readable anywhere in the service?

That depends on where the intermittent connection is, but the service is a good place to start. Everything will be normal ahead of the problem, and that phase will show the problem everywhere downstream of it.

 

[danickstr]

What amperage are you talking about? Oh I see it is the main service, but is this happening without any load?

 

[cadpoint]

Best Guest !

Best Guest !

What the terrain of the Plant Site, sounds like a fence post , something in contact with the main service, or metal shards down service ...

The electrical is a magnet for metals of a scrap yard!!! ...

What did the main service look like ?