Ok, it's a grounded service and the green wire should have been marked white, whether it is sized correctly is another story but that's not real important considering the other issues.
Roger
Does a 480/277 volt main disconnect need a neutral conductor?
- Thread starter LadyDi
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Roger
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Di, keep in mind that there is only the grounded conductor in an incoming service. The grounding system doesn't begin until you reach the service disconnect/OCP.
LadyDi
Member
- Location
- Lubbock, Texas
- Occupation
- Electrical Contractor, Master Electrician, BA Texas Tech University, College Instructor: Electrician Education
Then the incoming wire cannot serve as an equipment grounding conductor. Is this how Roger knew right away that the installer’s incorrectly labeled the 4th wire?
- Occupation
- Licensed Electrician
From the service disconnect back upstream to the power company transformer the grounded conductor and the equipment grounding conductor are the same.
I went back and read the earlier posts. My first time on this thread...
i see these all the time.
We set the transformer, CT meter it, and the customer brings the wires to us.
we connect the green to the X0, which is connected to our XF ground rods and circle ground system in the pad mount.
now once the inspector approves it, I don’t care what they call it.
But... it’s usually for heavy motor loads with a dry pack for the small office loads and 120 stuff.
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Don't the NEC and the NESC which governs utility wiring both require that all WYE connected 480/277 volt systems be grounded?
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Tom Horne
I used to, before my retirement, see these types of disconnects on every single fire pump that was installed locally. The required separate service for the fire pump nearly always came from the same 277/480 WYE connected transformer which supplied the regular service to the building. The utility would not install a separate transformer of any configuration unless they are paid to do so. Just like my employers they are in business to make a profit and that did not involve giving work or materials away. The most common installation defect on fire pumps in this area was the failure to wire it as required for a 277/480 volt WYE configured service by running the required neutral conductor to the Service Disconnecting Means. Given that the neutral for such a service which is only serving a fully balanced load can be sized several sizes smaller than if that service were a general purpose one it was often a matter of ignorance rather than cost shaving. I often saw the same error in pulling the Derived Service Conductors from a generator on several installations done under different foreman by different contractors. The thinking seemed to be that the nature of the load was what mattered and the practice continues because there is usually no immediate consequence for the installers. The installation works! "Just put it on the wall. It only has to last 365 days."
For comparison I was on the crew which wired the branch circuit for a pathogens refrigerator at a medical research laboratory and that customer had payed for a 480 volt delta connected transformer. The refrigerator was the only load for that Delta configured service. I asked permission to propose an extra for a field assembled ground fault detection alarm but my employing electrical contractor refused permission so it remained a floating 480 volt delta configured service with no fault detection. I guessed that the reason for the unique service configuration was to minimize the risk of failure of refrigeration containment for some fairly nasty pathogens. But that didn't explain the absence of any way to know about a ground fault until a second one occurred on 1 of the other 2 phases.
For comparison I was on the crew which wired the branch circuit for a pathogens refrigerator at a medical research laboratory and that customer had payed for a 480 volt delta connected transformer. The refrigerator was the only load for that Delta configured service. I asked permission to propose an extra for a field assembled ground fault detection alarm but my employing electrical contractor refused permission so it remained a floating 480 volt delta configured service with no fault detection. I guessed that the reason for the unique service configuration was to minimize the risk of failure of refrigeration containment for some fairly nasty pathogens. But that didn't explain the absence of any way to know about a ground fault until a second one occurred on 1 of the other 2 phases.
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