grounded conductor is green???

Status
Not open for further replies.
M

mjmike

Senior Member
We are working on a project design where we will be removing a control panel that incorporates the service disconnect and placing a regular knife switch service disconnect to allow additional changes to take place. The building is served by a 480V utility transformer with an underground utility secondary feed to the control panel. The original design plans called for 4-#3/0; which makes sense for a 200A service disconnect. However, when at the site we opened the control panel. The phase conductors are terminated at the service disconnect breaker but the expected grounded conductor is not there. Instead, there is a smaller sized conductor with green tape (ran with the phase conductors) landed under a lug labeled "equipment ground only". There does not appear to be a place to land the grounded conductor. There is a grounding electrode system present. We will be contacting the utility to open the transformer and see where smaller conductor is attached. It kind of looks to me like the grounded conductor is improperly identified and it has been downsized from the original drawings which looks like it may be allowed per 250.24.C.1. Anybody suspecting something otherwise or see this before?

Based on 250.24.C, I believe the grounded conductor must be ran and must be terminated at both ends. We will need to check the size and see if it is of adequate size even though it is not the same size as the phase conductors. We would like to see it changed out to the same size as the phases, but we are thinking the size may be allowed as it is.
 
mjmike said:
We are working on a project design where we will be removing a control panel that incorporates the service disconnect and placing a regular knife switch service disconnect to allow additional changes to take place. The building is served by a 480V utility transformer with an underground utility secondary feed to the control panel. The original design plans called for 4-#3/0; which makes sense for a 200A service disconnect. However, when at the site we opened the control panel. The phase conductors are terminated at the service disconnect breaker but the expected grounded conductor is not there. Instead, there is a smaller sized conductor with green tape (ran with the phase conductors) landed under a lug labeled "equipment ground only". There does not appear to be a place to land the grounded conductor. There is a grounding electrode system present. We will be contacting the utility to open the transformer and see where smaller conductor is attached. It kind of looks to me like the grounded conductor is improperly identified and it has been downsized from the original drawings which looks like it may be allowed per 250.24.C.1. Anybody suspecting something otherwise or see this before?

Based on 250.24.C, I believe the grounded conductor must be ran and must be terminated at both ends. We will need to check the size and see if it is of adequate size even though it is not the same size as the phase conductors. We would like to see it changed out to the same size as the phases, but we are thinking the size may be allowed as it is.
Click to expand...
Is it a 480 delta, maybe, with no neutral? The green is the Equipment Grounding Conductor (not the grounded conductor), which is supposed to be green and is usually smaller than the phase conductors.
 
Last edited:
ggunn said:
Is it a 480 delta, maybe, with no neutral? The green is the Equipment Grounding Conductor (not the grounded conductor), which is supposed to be green and is usually smaller than the phase conductors.
Click to expand...

Lets answer this in 2 parts:

part 1: The original design plans call for 480/277V 3-phase 4-wire. This to me says it it "Y".

Part 2: However, the transformer has no info or data plate on it so lets assume is is delta. If it is delta, then the voltage would be 480 and there would not be a grounded conductor. However, I think the feed from the transformer would just be 3-wire (no grounded conductor). I do not think the equipment ground would go back to the transformer since there are ground rods installed at the service.
 
Kudos to ggunn for thinking of that possibility.
With the "equipment ground" marking, a ungrounded system seems a distinct possibility.

I would agree to checking to how where the conductor terminates. I fairly often run across installs where the required service groundED conductor is marked green.
If you do have a grounded system and the conductor is properly sized it seems to me to be simply a case for proper identification.

In both grounded and ungrounded systems, I find engineers often include a "grounding conductor" back to a utility transformer for reasons only they understand.
 
Last edited:
If it is an ungrounded system, where would the conductor in question land at the transformer? Would it be bonded to the case as opposed to the neutral bar?

Does the NEC say anyplace about installing an equipment ground back to the transformer for an ungrounded system?

The utility should be able to tell me if it is a Y or delta transformer. If it is Y, then it must be grounded. If it is delta, I would then assume it is ungrounded or do they have both corner grounded and non-corner grounded 480V delta systems? I would bet it is a Y transfromer, but this is all good info.

If it is indeed Y, what is the benifit to the grounded conductor being the same size as the phase conductors? I am trying to determine what was lost by the small conductor from what the plans called for.
 
augie47 said:
Kudos to ggunn for thinking of that possibility.
With the "equipment ground" marking, a ungrounded system seems a distinct possibility.

I would agree to checking to how where the conductor terminates. I fairly often run across installs where the required service groundED conductor is marked green.
If you do have a grounded system and the conductor is properly sized it seems to me to be simply a case for proper identification.

In both grounded and ungrounded systems, I find engineers often include a "grounding conductor" back to a utility transformer for reasons only they understand.
Click to expand...

Wow, really?? In my 29 years as an electrician and an electrical designer, I have never seen or designed a set of plans with a groundING conductor to a utility transformer. What are those guys thinking up there where you are? :jawdrop:
 
mjmike said:
If it is indeed Y, what is the benifit to the grounded conductor being the same size as the phase conductors? I am trying to determine what was lost by the small conductor from what the plans called for.
Click to expand...

If there are single phase loads, the possibility is there for all the loads on one phase to be turned on at once and all the rest to be off.
 
ggunn said:
If there are single phase loads, the possibility is there for all the loads on one phase to be turned on at once and all the rest to be off.
Click to expand...

Can you please clarify, didn't quite understand.

Also, have confirmed with the power company the transformer is grounded so the ungrounded delta is out.
 
Last edited:
Knightryder12 said:
Wow, really?? In my 29 years as an electrician and an electrical designer, I have never seen or designed a set of plans with a groundING conductor to a utility transformer. What are those guys thinking up there where you are? :jawdrop:
Click to expand...

Same here, we also don't incorporate a grounding conductor back to the utility, just the phase conductors and full size grounded conductor.
 
250.24(C)(1) simply gives you a minimum size conductor. You would have to go back to 220.61 to justify reducing the size smaller than your phase conductors.
Are any of your loads 240 v or are they all 120v ?
 
mjmike said:
Can you please clarify, didn't quite understand.
Click to expand...
If the loads are single phase (phase to neutral) and all the loads which are powered up are on the same phase, the current in the neutral is the same as in that phase conductor.
 
templdl said:
Yes, I agree. Scary. Oh well.
Click to expand...

I've not noticed...it may all come from the same local engineering firm. The design is almost always ignore by the contractors but on occasion they will call and ask.
 
augie47 said:
250.24(C)(1) simply gives you a minimum size conductor. You would have to go back to 220.61 to justify reducing the size smaller than your phase conductors.
Are any of your loads 240 v or are they all 120v ?
Click to expand...

That is interesting. good info. The voltage is 480/277. Higher voltage is for a couple motors then a step-down transformer for 120V loads.

From what I gather from 220.61.C, summarizing, is if you have any non-linear loads, don't reduce the size of the grounded conductor.
 
Last edited:
mjmike said:
That is interesting. good info. The voltage is 480/277. Higher voltage is for a couple motors then a step-down transformer for 120V loads.

From what I gather from 220.61.C, summarizing, is if you have any non-linear loads, don't reduce the size of the grounded conductor.
Click to expand...

I had some comments based on it possibly being a delta with a grounded conductor, but they are somewhat irrelevant now that you say it is 480/277. It has to be a wye system at that voltage, and the neutral has to be the conductor that is grounded.

My guess is the original installer ran smallest allowed grounded conductor to this service because there was no neutral load to require any more than minimum allowed size. That size would need to be based on table 250.66 according to 250.24(C)(1). They then mistakenly marked it green because it was essentially used as an equipment grounding conductor only since there were no loads utilizing a neutral. Had this been a feeder that would be acceptable,though the size could have been according to 250.122 instead, but a service must have a "grounded" conductor brought to it if it is a grounded supply, and the proper identification of a "grounded" conductor is white or gray.
 
Status
Not open for further replies.
Top