Does a 480/277 volt main disconnect need a neutral conductor?

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LadyDi

LadyDi

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Lubbock, Texas
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Electrical Contractor, Master Electrician, BA Texas Tech University, College Instructor: Electrician Education
Hello~

Does a 480/277 volt main disconnect need a neutral run with the ungrounded conductors for ground fault protection?

Note: The disconnect in question contains a black wire run with the ungrounded wires that is marked with green tape. The conductor is attached to the service bonding locknut, and then it is attached to the metal case. I believe the conductor serves as the equipment grounding conductor.

After considering the bonding and grounding DVD's, I believe that the service needs a neutral. Am I thinking correctly? If answered, then I'll share the results with my electrical students.
 
LadyDi said:
Hello~

Does a 480/277 volt main disconnect need a neutral run with the ungrounded conductors for ground fault protection?
Click to expand...

Yes, the neutral must land in the main disconnect, which is where the premises EGC and GES conductors join it.
 
IMHO, you are asking two different things.

Ground fault protection doesn't require a neutral or a ground to work correctly.

A POCO service disconnect needs a neutral, and a ground, and they need to be bonded together at this location and only this location.
 
Russs57 said:
IMHO, you are asking two different things.

Ground fault protection doesn't require a neutral or a ground to work correctly.

A POCO service disconnect needs a neutral, and a ground, and they need to be bonded together at this location and only this location.
Click to expand...

Where does the "ground" come from?
 
Russs57 said:
IMHO, you are asking two different things.

Ground fault protection doesn't require a neutral or a ground to work correctly.

A POCO service disconnect needs a neutral, and a ground, and they need to be bonded together at this location and only this location.
Click to expand...

It doesnt necessarily need a neutral. We need to know if this is a grounded system.
 
Yes, the 3 phase disconnect is the main service.
 
If this is a 480Y/277 volt service then a neutral must be brought to the service disconnect. It should be identified according to Article 200 and should not be green.
 
Since it is the Main Service Disconnect see 250.24(C)

Roger
 
roger said:
Since it is the Main Service Disconnect see 250.24(C)

Roger
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Hello:

That's the way I read 250.24 (c), but some say that the type of load matters.

On the contrary, I think that the neutral needs to run to the service disconnecting means to provide a low impedance path back to the transformer for clearing ground faults. Therefore, the type of load is not a factor.

Indeed, in this situation, one questions if a fault occurred, then would the fuse ever blow?

Best,

Diana
 
Here is a pic of the disconnect. Of course, the make-shift fuses are bizarre as is the absent GEC and electrode.
 

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LadyDi said:
Hello:

That's the way I read 250.24 (c), but some say that the type of load matters.
Click to expand...
They are wrong, it only depends on whether it's a grounded or ungrounded supply.

LadyDi said:
On the contrary, I think that the neutral needs to run to the service disconnecting means to provide a low impedance path back to the transformer for clearing ground faults. Therefore, the type of load is not a factor.
Click to expand...
You've got it except "ground" should be removed before faults.

LadyDi said:
Indeed, in this situation, one questions if a fault occurred, then would the fuse ever blow?
Click to expand...
Not with out the neutral which serves dual purposes at the service equipment.

LadyDi said:
Best,

Diana
Click to expand...

Roger
 
roger said:
They are wrong, it only depends on whether it's a grounded or ungrounded supply.

You've got it except "ground" should be removed before faults.

Not with out the neutral which serves dual purposes at the service equipment.



Roger
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Ok, I feel better about asking my administers to ban the use of the equipment until the disconnect is redesigned and appropriately installed. Thank you.
Best regards,
Diana
 
LadyDi said:
Ok, I feel better about asking my administers to ban the use of the equipment until the disconnect is redesigned and appropriately installed. Thank you.
Best regards,
Diana
Click to expand...

As already pointed out by others, if this is a grounded service then the neutral must be brought to the service disconnect in a compliant manner. The fact that the load does not require a neutral is irrelevant as you know for fault return path.
That conductor you mention that is marked as an EGC is of interest. Do you know where it connects at the other end? If it is connected to the POCO transformer X0 terminal you may have a fault return path, just not a technically compliant one. To be compliant the conductor should be marked white and terminate in a proper neutral bar in the service disconnect and have a proper main bonding jumper. Also, I don't see any evidence of a GES.
 
Is it possible it’s a privately owned transformer and not a utility owned?

Or maybe even another disconnect grouped at another location?
 
The transformer is utility owned, and the disconnect is the main service. Good question though.

In the end, Roger made clear the issue and Article 250.24 (c). Thank you for taking the time to respond.

Best,

Diana
 
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