Odd L-N readings on a unknown 3ph service

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I called First Energy back today, they finally got the lineman department to call me back. According to that department (and after some battering as he "is not authorized to give out that information"), they say we have an open delta. Since there are 3 pigs on the pole and they all connect to the conductors feeding us, I knew this wasn't correct, so I asked to be put in contact with engineering. He was however keen to tell me that we and the two other tenants are only using 30% of capacity, good to know I suppose, as I thought it was just us and the tenant attached to our building that it was feeding, but there is another building as well. Anyhow..

The engineer called me back, super helpful guy to talk to. We do in fact have a ungrounded delta. I brought up the safety concern of feeding multiple tenants with the same ungrounded configuration, he said "that's just how it is". He was glad to put me in touch with their sales department to drop a transformer inside for us to give us whatever configuration we wanted, of course.

A quick Google search shows that we're looking ~$1500 for a 240v 3ph delta primary > 208/120 3ph wye transformer, which for safety sake, we may consider (though it's a REALLY bad time for us financially).

In the event that we forgo a transformer and want to install a ground fault detector, is this something along the lines what I'm after?;

http://www.rammeter.com/atc-diversi...-Cw4rzBan8J_xse834lw_vqinvmEZEnmL4aAucD8P8HAQ


Any other recommendations on hardware for monitoring? The above product seems very basic. At the very least, I would want something with a relay output that I can hook an audible alarm up to. I understand that most facilities that use ground fault detection usually have it in some sort of control room where production would be monitoring such things. We don't have such an area.
 
Brandon_K said:
I called First Energy back today, they finally got the lineman department to call me back. According to that department (and after some battering as he "is not authorized to give out that information"), they say we have an open delta. Since there are 3 pigs on the pole and they all connect to the conductors feeding us, I knew this wasn't correct, so I asked to be put in contact with engineering. He was however keen to tell me that we and the two other tenants are only using 30% of capacity, good to know I suppose, as I thought it was just us and the tenant attached to our building that it was feeding, but there is another building as well. Anyhow..

The engineer called me back, super helpful guy to talk to. We do in fact have a ungrounded delta. I brought up the safety concern of feeding multiple tenants with the same ungrounded configuration, he said "that's just how it is". He was glad to put me in touch with their sales department to drop a transformer inside for us to give us whatever configuration we wanted, of course.

A quick Google search shows that we're looking ~$1500 for a 240v 3ph delta primary > 208/120 3ph wye transformer, which for safety sake, we may consider (though it's a REALLY bad time for us financially).

In the event that we forgo a transformer and want to install a ground fault detector, is this something along the lines what I'm after?;

http://www.rammeter.com/atc-diversi...-Cw4rzBan8J_xse834lw_vqinvmEZEnmL4aAucD8P8HAQ


Any other recommendations on hardware for monitoring? The above product seems very basic. At the very least, I would want something with a relay output that I can hook an audible alarm up to. I understand that most facilities that use ground fault detection usually have it in some sort of control room where production would be monitoring such things. We don't have such an area.
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You said in the OP that there was also 120/240 single phase service to your building. Any chance the three phase is from two of those transformers as open delta, and the single phase is from the third transformer? If so probably would be pretty easy to convert what is there to high leg delta system, but you would need to pull a neutral conductor to your previously ungrounded service. Would also have to address the fact that another customer is supplied from it.

POCO's around here generally won't put two separate systems on same pole, just so there is no confusion down the road and someone interconnects something that shouldn't be.
 
kwired said:
You said in the OP that there was also 120/240 single phase service to your building. Any chance the three phase is from two of those transformers as open delta, and the single phase is from the third transformer? If so probably would be pretty easy to convert what is there to high leg delta system, but you would need to pull a neutral conductor to your previously ungrounded service. Would also have to address the fact that another customer is supplied from it.

POCO's around here generally won't put two separate systems on same pole, just so there is no confusion down the road and someone interconnects something that shouldn't be.
Click to expand...

Our single phase comes off of a single 100kva can directly outside of the shop.

The 3ph comes off of a bank of three 100kva cans that are two poles down from the service entrance.

The engineer said it is definitely an ungrounded delta and that the guy in the lineman department was wrong about it being an open delta (which I don't doubt, speaking to the lineman a few times yesterday did not instill confidence). The engineer also said that it isn't terribly uncommon for the buildings in that area to have ungrounded deltas.

I would love for them to convert it to a center tapped delta, but since two other customers are fed from it, I don't see this happening. That said, the tenant behind us is a small auction house, I would be absolutely shocked if they actually have anything connected to their 3ph service at all. The lineman says the total service is at 30% utilization, so the 3rd customer is obviously using it and I'm sure they don't want to deal with the costs associated with reconfiguring their service to a high leg, just to help us out. That said, it may be cheaper for us to pay to have the neutral pulled to their disconnect (as well as ours). If they are currently running everything as an ungrounded delta, as far as I can tell in my head, they would just need the neutral pulled to their disconnect, bonded, and that would be all. Nothing further down the line would need to change for them.
 
Brandon_K said:
Our single phase comes off of a single 100kva can directly outside of the shop.

The 3ph comes off of a bank of three 100kva cans that are two poles down from the service entrance.

The engineer said it is definitely an ungrounded delta and that the guy in the lineman department was wrong about it being an open delta (which I don't doubt, speaking to the lineman a few times yesterday did not instill confidence). The engineer also said that it isn't terribly uncommon for the buildings in that area to have ungrounded deltas.

I would love for them to convert it to a center tapped delta, but since two other customers are fed from it, I don't see this happening. That said, the tenant behind us is a small auction house, I would be absolutely shocked if they actually have anything connected to their 3ph service at all. The lineman says the total service is at 30% utilization, so the 3rd customer is obviously using it and I'm sure they don't want to deal with the costs associated with reconfiguring their service to a high leg, just to help us out. That said, it may be cheaper for us to pay to have the neutral pulled to their disconnect (as well as ours). If they are currently running everything as an ungrounded delta, as far as I can tell in my head, they would just need the neutral pulled to their disconnect, bonded, and that would be all. Nothing further down the line would need to change for them.
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It is maybe a little amazing that after who knows how old the set up is that there isn't a ground reference on it already - whether it is faulted equipment, unintentional, ignorant or untrained worker additions, etc.
 
kwired said:
It is maybe a little amazing that after who knows how old the set up is that there isn't a ground reference on it already - whether it is faulted equipment, unintentional, ignorant or untrained worker additions, etc.
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I had an opportunity to talk to our landlord. His father had had the building built sometime in the late 50's (as well as quite a few others in the area, come to find out). He believes the electric service to be original to the building. I'm not sure if I completely buy into that, but on the other hand, both the 1ph and 3ph disconnects are quite vintage. Just for curiosity, next time I go up I'll have to take a look and see if there are any identifying marks to see if I can find a year of manufacture. The 400A is absolutely massive compared to a modern disconnect, with a giant rotary type lever on the front panel. But I agree, even if it's only 35 years old, shocking to find there are no faults between any of us.

So how about those ground fault detector recommendations? :)
 
The only good reason to have a non grounded system is if you have a process that needs to be shut down in an orderly fashion. If sudden shut down of one part of the process because of a ground fault opened the circuit to that part of the process can cause unavoidable damages then the idea is you get an indication of the ground fault, but no immediate shut down. You should shut down ASAP though, because a second fault on a different line will cause immediate shut down anyway.

Without that need for orderly shutdown, ungrounded systems are not all that practical or desired.
 
kwired said:
The only good reason to have a non grounded system is if you have a process that needs to be shut down in an orderly fashion. If sudden shut down of one part of the process because of a ground fault opened the circuit to that part of the process can cause unavoidable damages then the idea is you get an indication of the ground fault, but no immediate shut down. You should shut down ASAP though, because a second fault on a different line will cause immediate shut down anyway.

Without that need for orderly shutdown, ungrounded systems are not all that practical or desired.
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Notice "REALLY bad time" is not included in the reasoning.
 
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