Electrician Talk banner
1 - 20 of 38 Posts

·
Swimmer
Joined
·
692 Posts
Discussion Starter · #1 ·
I have 13V between GND and Neutral in a Grocery Store.
I can see it at the output of the 150KVA 480V Delta to 208V Wye transformer.
I'm pretty sure the service meter inputs to this transformer.

Anyway, I don't think there is anyway this can be anything but a separately derived system (as shown in he top picture) and the system bonding jumper is missing. Is this right or can it be other stuff?

The only other thing I can think of is that the neutral to ground connection is made upstream of the this transformer and one of these wires or connections has degraded as shown in the lower picture. I've never heard of a setup like this but I don't do a lot of commercial work either.

Thanks
 

Attachments

·
Swimmer
Joined
·
692 Posts
Discussion Starter · #6 ·
Where are you measuring the 13 VAC?

What is the phase to neutral voltage
What is the phase to ground voltage

13 VAC is between neutral and ground in the switch equipment about 1 foot down stream from the transformer.

Phase to neutral is approx 121V on all 3 phases
Phase to ground is:
BLK: 124V
RED: 110V
BLU 130V
 

·
Swimmer
Joined
·
692 Posts
Discussion Starter · #7 ·
Harmonics can do that. What are loads?
I'm not sure about the loads. Computerized cash registers, a DVD dispenser and fluorescent lights are a few of them.

I'm working on the DVD dispenser. It gets a high phase to ground voltage at night. Sometimes as high as 140V. I've got it connected phase to neutral tonight.
 

·
Registered
Joined
·
4,154 Posts
13 VAC is between neutral and ground in the switch equipment about 1 foot down stream from the transformer.

Phase to neutral is approx 121V on all 3 phases
Phase to ground is:
BLK: 124V
RED: 110V
BLU 130V
MY GUESS - Screw the harmonics (why chase ghost), the system appears to have a neutral to ground bond issue.
 

·
Fond of three phase
Joined
·
1,649 Posts
MY GUESS - Screw the harmonics (why chase ghost), the system appears to have a neutral to ground bond issue.
Once in a while, you have to go back to the old Simpson 260, when tracing a problem like this.
Any installation like this, that has discharge lighting, switching power supplies and all the rest of the high tech equipment, all the circuits will be rich in harmonics.
Some places, where they switched to electronic ballasts, it's even almost impossible to get FM reception, where before it was almost immune to electrical interference. :eek:
 

·
Registered
Joined
·
4,154 Posts
The connection should be in the transformer housing as shown in my top picture right?

I don't think a modern grocery store would be wired as shown in the bottom picture.
Could be either way.

What I would do, I'd shut off the loads, install a temporary jumper, turn on the loads and measure the Neutral to ground voltage.

How far from the panel to the transformer?

The other issue would be voltage drop but that would require a long distance, under sized conductors and possibly a bad connection in the transformer?
 

·
Registered
Joined
·
4,154 Posts
Once in a while, you have to go back to the old Simpson 260, when tracing a problem like this.
Any installation like this, that has discharge lighting, switching power supplies and all the rest of the high tech equipment, all the circuits will be rich in harmonics.
Some places, where they switched to electronic ballasts, it's even almost impossible to get FM reception, where before it was almost immune to electrical interference. :eek:
I'd be highly surprised and eating my hat if this were the case. But I have been wrong many times. Never rule anything out.
 

·
Donuts > Fried Eggs
Joined
·
17,042 Posts
...Phase to neutral is approx 121V on all 3 phases
Phase to ground is:
BLK: 124V
RED: 110V
BLU 130V
That's a lot more phase imbalance than I would want to see.

What's the current on each phase?

I almost wonder if you're completely ungrounded.
 

·
Swimmer
Joined
·
692 Posts
Discussion Starter · #15 ·
How far from the panel to the transformer?
I'm pretty sure the service panel meter is outside and below the transformer. Maybe 15 feet max. The transformer is on a 2nd story atrium in the back of the store. The switch gear where I measure the 13V between gnd and neutral is 1 foot down stream from the transformer. The circuit beaker panels that feed the loads are 150 feet away from the transformer at the other end of the store. I see the same 13V there.
 

·
Registered
Joined
·
4,154 Posts
I'm pretty sure the service panel meter is outside and below the transformer. Maybe 15 feet max. The transformer is on a 2nd story atrium in the back of the store. The switch gear where I measure the 13V between gnd and neutral is 1 foot down stream from the transformer. The circuit beaker panels that feed the loads are 150 feet away from the transformer at the other end of the store. I see the same 13V there.
See Big John's post above and do what I posted.

No way in heck is this harmonics.
 

·
Swimmer
Joined
·
692 Posts
Discussion Starter · #17 · (Edited)
That's a lot more phase imbalance than I would want to see.

What's the current on each phase?

I almost wonder if you're completely ungrounded.
I mixed up BLK and BLU voltages previously


Voltage to GND: BLK 130V, RED 111V, BLU 125V, WHT 13V

Voltage to Neutral: BLK 123V, RED 122V, BLU 121V, WHT 0V

Current: BLK 3.0A, RED 4.8A, BLU 4.8A, WHT 4.0A
 

·
Swimmer
Joined
·
692 Posts
Discussion Starter · #19 ·
Silly question, what happens when you try for continuity ground to neutral? I agree with your first post, I think the bonding jumper is missing.
I did it with power on at breaker panels that serve the loads. These panels are 150 feet from the 150kVA 480 - 208 transformer. Sometimes I got a few ohms and sometimes I got open circuit. I think its an invalid measurement with power on.

This 13V does not seem to be affecting the grocery store. I don't even know if it is affecting the DVD dispenser I'm working on. It does create confusion and I have safety concerns. I'm concerned about disrupting store operation so I haven't cut power to the store, or a big chunk of it, to properly ohm the GND to Neutral connection.
 

·
Registered
Joined
·
4,154 Posts
I did it with power on at breaker panels that serve the loads. These panels are 150 feet from the 150kVA 480 - 208 transformer. Sometimes I got a few ohms and sometimes I got open circuit. I think its an invalid measurement with power on.

This 13V does not seem to be affecting the grocery store. I don't even know if it is affecting the DVD dispenser I'm working on. It does create confusion and I have safety concerns. I'm concerned about disrupting store operation so I haven't cut power to the store, or a big chunk of it, to properly ohm the GND to Neutral connection.
As noted several times neutral to ground bond.

The store equipment could care less if there is a ground.
 
1 - 20 of 38 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top