Replacing ABB commercial inverters

pv_n00b said:
I've run into a few of these, always kind of freaks me out. I think it happens when a utility replaces an old transformer with a delta on the customer side with one that has a WYE on the customer side on an 3W service. They don't run a neutral to the customer since there is no place to land it in the existing 3W service equipment. From the customer's point of view it's still a 3W ungrounded service, so they are happy they don't have to change anything. Since there is no neutral at the service entrance equipment I still treat it as an ungrounded service for the PV system interconnection.
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Does the utility ground the wye point or leave it floating?
 
ggunn said:
How would you do that? If it were truly an ungrounded delta service, most three phase inverters cannot connect to it.
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In the systems sizes I work with there are many inverters that can work on a 3W service, some even require a 3W system. But I understand that in smaller systems the inverter options are more limited.
 
electrofelon said:
Perhaps y'all could be more specific about the scenario, but I was assuming a ln earth connection at say the utility pole but no conductor bonding that to the building GES and equipment grounds.
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Specifically, it's a utility transformer whose secondary is wye but the only connection from the center, or neutral, of the wye is to the the GES. Isn't that connection the MBJ?
 
electrofelon said:
No, the MBJ is the connection of the EGC's to the grounded conductor (wye point)
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But that's what it is doing; the wye point (neutral) is connected to the GES and the EGC; it's just not connected to anything else, i.e., loads.
 
ggunn said:
But that's what it is doing; the wye point (neutral) is connected to the GES and the EGC; it's just not connected to anything else, i.e., loads.
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If the utility does not being the neutral to the service then per the NEC it has to be treated as an ungrounded service and there is nothing to connect an MBJ to. On the customer side such a service needs ground detectors and to meet the other requirements in 250.21.

Seems very sketchy to me for the utility to ground a wye point on transformer supplying a service with no grounded conductor, but what do I know. I think pv_noob thought it was sketchy too. Not sure if anything in the NESC addresses this, but I'm not aware of anything in the NEC, so it may be a case of no regulation that overlaps.
 
ggunn said:
But that's what it is doing; the wye point (neutral) is connected to the GES and the EGC; it's just not connected to anything else, i.e., loads.
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The grounded conductor must be brought to the service equipment. Sounds like there is some sort of "bonding conductor" brought to the service disconnect yes? If so then sure that's just a regular grounded service just the color or terminology of that conductor might be wrong.
 
jaggedben said:
If the utility does not being the neutral to the service then per the NEC it has to be treated as an ungrounded service.
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I'm not so sure. 250.24(C) says "where an AC system operating at 1000 volts or less is grounded at any point, the ground conductor shall be routed with the ungrounded conductors to each service disconnecting means.....".

I guess if the utility has grounded the system on their end, but does not provide a grounded conductor at the service point, you are in a pickle
 
electrofelon said:
The grounded conductor must be brought to the service equipment. Sounds like there is some sort of "bonding conductor" brought to the service disconnect yes? If so then sure that's just a regular grounded service just the color or terminology of that conductor might be wrong.
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You understand that I am speaking only of the secondary side of the utility transformer, don't you? In one system I had to deal with a group of buildings that were a couple hundred feet from the utility transformer had a 480V three phase set of conductors run to them with no neutral, but the neutral point of the wye secondary was grounded at the transformer.
 
ggunn said:
You understand that I am speaking only of the secondary side of the utility transformer, don't you? In one system I had to deal with a group of buildings that were a couple hundred feet from the utility transformer had a 480V three phase set of conductors run to them with no neutral, but the neutral point of the wye secondary was grounded at the transformer.
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We understand. We are discussing that it seems quite wrong for a utility to actually ground a system on their side of the service point but at the same time not bring a grounded conductor to the service point in order for the customer to comply with 250.24(C). (Or, as it may be in many of these cases, to replace an ungrounded transformer secondary with a grounded one on an existing service, without telling the customer. Which amounts to the same thing.)
 
jaggedben said:
We understand. We are discussing that it seems quite wrong for a utility to actually ground a system on their side of the service point but at the same time not bring a grounded conductor to the service point in order for the customer to comply with 250.24(C). (Or, as it may be in many of these cases, to replace an ungrounded transformer secondary with a grounded one on an existing service, without telling the customer. Which amounts to the same thing.)
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Be that as it may, I have seen it in the real world as I referenced above. It may indeed have been a replacement transformer but I have no idea what the customer was told about it if it had been changed out. It was a very old system.

Assuming that the service secondary had originally been an ungrounded delta and replaced by a wye with a grounded neutral, it wouldn't have required any other changes to the feeders and loads, would it?
 
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