Electrician Talk banner
1 - 17 of 17 Posts

·
Electrical Simpleton
Joined
·
3,350 Posts
Discussion Starter · #1 ·
I need help understanding how this would work:

We have baseball fields here at our City. The field lighting is controlled via 3-way switches in two separate buildings which are approximately 1300 feet apart. The switches control the power to coils on lighting contactors.

The contactors have 120 volt coils. In each of these buildings is a 480 to 208Y/120 transformer. The 3-ways are fed from building A.

Last year a contractor hit the direct bury wires (USE) going between the two buildings while doing some trenching. During their repair the contractor re-wired the travelers but then did something I didn't think would work.

The feed for the 3-ways comes from building A and then they tied to a neutral from building B for the coils in the contactors. I found this when I was informed that one of the diamonds lighting quit working.

How would this even have worked given that the feed for the 3-ways was from one transformer and the neutral from a different transformer 1300 feet away?

Pete
 

·
RIP 1959-2015
Joined
·
10,750 Posts
I need help understanding how this would work:

We have baseball fields here at our City. The field lighting is controlled via 3-way switches in two separate buildings which are approximately 1300 feet apart. The switches control the power to coils on lighting contactors.

The contactors have 120 volt coils. In each of these buildings is a 480 to 208Y/120 transformer. The 3-ways are fed from building A.

Last year a contractor hit the direct bury wires (USE) going between the two buildings while doing some trenching. During their repair the contractor re-wired the travelers but then did something I didn't think would work.

The feed for the 3-ways comes from building A and then they tied to a neutral from building B for the coils in the contactors. I found this when I was informed that one of the diamonds lighting quit working.

How would this even have worked given that the feed for the 3-ways was from one transformer and the neutral from a different transformer 1300 feet away?

Pete
Keep in mind the neutral is doing the same job, so it will work,but the breaker will never Tripp because the current is taking the return path to the other service, that would be bad news if someone shut down that panel and lifted that neutral because the current from the other building would be running through it.
 

·
Registered
Electrician & Electronics Technologist
Joined
·
1,245 Posts
Through grounds at the neutral on secondaries of the xfmrs would be my guess if I am anderstanding correctly. Or neutrals A and B have been mistakenly conencted together somewhere else in the system.

Measure the current through the grounds maybe with contactor on vs off. Won't be much, some mA's, but still should register if that is how it is happening.
 

·
Registered
Joined
·
12,167 Posts
My answer is that PoCo references all of their neutrals to ground, so all of the neutrals are at the same potential (not considering VD), so any hot from any transformer would make a circuit to any ungrounded conductor from any transformer.
 

·
Registered
Joined
·
12,167 Posts
... that would be bad news if someone shut down that panel and lifted that neutral because the current from the other building would be running through it.
Yea, that would suck.

I have to question whether you are even allowed to bring the travelers into a building that does not house the service disconnect for the branch breaker feeding the travelers.
 

·
Registered
Electrician & Electronics Technologist
Joined
·
1,245 Posts
Keep in mind the neutral is doing the same job, so it will work,but the breaker will never Tripp because the current is taking the return path to the other service...
Breaker should still trip. It is on the hot side, and if it sees the trip current, it will trip and break the circuit. Somehow current is returning to the transformer whence it originally came from; it has to be!
 

·
Banned
I make all the electrons line up for their Flu shots
Joined
·
33,456 Posts
Don't let the kids slide into home on rainy days at that park....
 

·
Registered
Electrician & Electronics Technologist
Joined
·
1,245 Posts
My answer is that PoCo references all of their neutrals to ground, so all of the neutrals are at the same potential (not considering VD), so any hot from any transformer would make a circuit to any ungrounded conductor from any transformer.

Agreed, and the VD would be pretty low since the contactor current is likely pretty low. Add good grounding continuity and wet ground conditions, you have yourself a complete, functioning circuit.
 

·
Retired Account
Joined
·
39,697 Posts
Poco xformer noodles are bonded from the substation to the secondaries, to the guy wires, and pole grounds

so anything will serve as a return , not that it makes it right.....

~CS~
 

·
Donuts > Fried Eggs
Joined
·
17,042 Posts
Dollars to donuts it's just feeding back through the bonds and equipment grounds back to the original circuit transformer.

Do you have an ammeter sensitive enough to pick up the load of the contactor coil? Get a reading on the bonding-jumper for the transformer feeding this circuit, I'll bet you'll see the same current flow there.
 

·
Electrical Simpleton
Joined
·
3,350 Posts
Discussion Starter · #11 ·
FWIW, these are not POCO x-fmrs. I don't think that makes a huge difference as far as grounding and bonding is concerned.

It just seemed strange to me that this configuration would work at all.

Pete
 

·
RIP 1959-2015
Joined
·
10,750 Posts
FWIW, these are not POCO x-fmrs. I don't think that makes a huge difference as far as grounding and bonding is concerned.

It just seemed strange to me that this configuration would work at all.

Pete
Yup I like John's answer too.

And that also creates this question. Is the USE 4 wire where the EGC is still connected?
 

·
Registered
Joined
·
4,154 Posts
Through grounds at the neutral on secondaries of the xfmrs would be my guess if I am anderstanding correctly. Or neutrals A and B have been mistakenly conencted together somewhere else in the system.

Measure the current through the grounds maybe with contactor on vs off. Won't be much, some mA's, but still should register if that is how it is happening.
Winner Winner, chicken dinner.
 

·
Electrical Simpleton
Joined
·
3,350 Posts
Discussion Starter · #14 ·
Yup I like John's answer too.

And that also creates this question. Is the USE 4 wire where the EGC is still connected?
This was all built prior to me working for this city... there is no EGC, that I know of, between the buildings.

Pete
 

·
Electrical Simpleton
Joined
·
3,350 Posts
Discussion Starter · #16 ·
No utility?

30 seconds and an amp clamp resolve this.
There is a utility transformer feeding the whole complex. 12470 to 480/277.

Then there are customer owned transformers scattered about in the different buildings on site to get the 208Y/120.

Pete
 
1 - 17 of 17 Posts
Top