Service Entrance 6 Disconnect Rule Ground Fault Protection

[mull982]

I had a question related to ground fault requirements when there is no main breaker with service entrance equipment used in conjunction with the Six Disconnect Rule. The current design uses a 13.8kV main breaker which feeds a 13.8-480V transformer which in turn feeds a switchboard with (4) feeder breakers rated for 1000A trip. For Arc Flash mitigation purposes there will be a set of CT's on the Switchboard main bus that will be wired back to a trip unit located at the MV breaker in order to quickly trip the MV breaker in the event of a fault.

I know for typical services 1000A or greater ground fault protection is required. I'm assuming with no main then the ground fault protection would be required on the 1000A feeders since they are rated 1000A. Is this correct?

These feeders do not have ground fault protection so I was curious if the CT's located on the Switchboard main breaker used to sense fault current at the main bus and trip the high side breaker, could be considered the required ground fault protective device in this case?

 

[Smart $]

I had a question related to ground fault requirements when there is no main breaker with service entrance equipment used in conjunction with the Six Disconnect Rule. The current design uses a 13.8kV main breaker which feeds a 13.8-480V transformer which in turn feeds a switchboard with (4) feeder breakers rated for 1000A trip. For Arc Flash mitigation purposes there will be a set of CT's on the Switchboard main bus that will be wired back to a trip unit located at the MV breaker in order to quickly trip the MV breaker in the event of a fault.

I know for typical services 1000A or greater ground fault protection is required. I'm assuming with no main then the ground fault protection would be required on the 1000A feeders since they are rated 1000A. Is this correct?

These feeders do not have ground fault protection so I was curious if the CT's located on the Switchboard main breaker used to sense fault current at the main bus and trip the high side breaker, could be considered the required ground fault protective device in this case?

I don't see how in one paragraph you say it has a main, and in another say the service does not have a main. Where is the service point?

Beyond that, the question would be whether GFPE is req'd for both service and SDS... (or just service if the service point is after that 13.8kV breaker).

 

[don_resqcapt19]

The code requirement for GFP protection only applies to solidly grounded wye electric systems of more than 150 volts to ground but
not exceeding 1000 volts phase-to-phase. There are rules that require the GFP protection for services, feeders and branch circuits. You need to provide GFP for the feeder breakers.

I think that the protection scheme used for the switch gear bus would be permitted to provide the required feeder ground fault protection. The only issue is that you would lose power on all 4 feeders if there is a ground fault. If the feeder breakers had their own GFP, you would only lose the feeder that had the ground fault.

 

[mull982]

I don't see how in one paragraph you say it has a main, and in another say the service does not have a main. Where is the service point?

Beyond that, the question would be whether GFPE is req'd for both service and SDS... (or just service if the service point is after that 13.8kV breaker).

I guess this would not really constitute as a service. Its a new 13.8kV feeder being tapped off of existing overhead distribution lines on the customers property. The 13.8kV breaker then feeds transformer and 480V Switchboard.

When I stated there was no main breaker I was referring to the fact that there was no secondary main breaker. I guess the HV breaker on the 13.8kV side of the transformer can still be considered a "main breaker"?

Not sure if this is considered a "service" or just a new feeder circuit? Either way I wanted to make sure CT's on transformer secondary tripping breaker on transformer primary would satisfy any ground fault protection requirements.

 

[augie47]

I see an possible problem.
Where is our service point ?
If the 480v board is the actual service disconnect I see no problem but if the service point is on the high voltage side of the transformer then the transformer secondary conductors would fall under Art 240 and the "service equipment" exemption in 480.36 would not apply and a main would be required at the panel, IMO

 

[mull982]

I see an possible problem.
Where is our service point ?
If the 480v board is the actual service disconnect I see no problem but if the service point is on the high voltage side of the transformer then the transformer secondary conductors would fall under Art 240 and the "service equipment" exemption in 480.36 would not apply and a main would be required at the panel, IMO

I guess I've always been a little confused about what defines a "service"

For this particular system the utility provide a 13.8kV service via overhead lines to the facility property. There is a utility metering point where the lines first enter the property and then the overhead lines continue to run the perimeter of the property. The overhead line is tapped at various locations in order to provide power to various unit substations which step voltage down to 480V for use in facility. Each of these unit substations consists of a 13.8kv breaker or fuse along with a transformer and then secondry 480V distribution equipment.

This new project in reference consists of a new 13.8kV underground feeder which will be tapped from the existing OH line on the property. This UG feeder will then terminate into a new 13.8kV breaker which will in turn feed a 3000kVA 13.8kv-480V step down transformer which will then feed the 480V Switchboard in question (4 feeders no main).

So based on the description of this system what would be defined as the "service disconnect"?

Thanks

 

[iwire]

I guess I've always been a little confused about what defines a "service"

It would be worthwhile to check article 100 definitions of service, service point, service conductors and feeder.

I agree with Gus, dependent on the location of the service point you may have an issue.

 

[Smart $]

I guess this would not really constitute as a service. Its a new 13.8kV feeder being tapped off of existing overhead distribution lines on the customers property. The 13.8kV breaker then feeds transformer and 480V Switchboard.

When I stated there was no main breaker I was referring to the fact that there was no secondary main breaker. I guess the HV breaker on the 13.8kV side of the transformer can still be considered a "main breaker"?

Not sure if this is considered a "service" or just a new feeder circuit? Either way I wanted to make sure CT's on transformer secondary tripping breaker on transformer primary would satisfy any ground fault protection requirements.

From your description, I'm still not certain whether it's a service or not... or where the service point is if it is a service.

Is there any POCO meter in this schema? That'd be a dead giveaway that it's a service... and perhaps a clue as to the service point, so location if present.

Do you have a one-line diagram? Can you post a scan of it (or picture as long as annotations are readable)?

 

[Smart $]

FWIW, all sections requiring GFPE essentially except any system, feeder, or branch circuit which supplies power to a continuous industrial process where a nonorderly shutdown will introduce additional or increased hazards.

 

[iwire]

FWIW, all sections requiring GFPE essentially except any system, feeder, or branch circuit which supplies power to a continuous industrial process where a nonorderly shutdown will introduce additional or increased hazards.

For sure but IMO the AHJ can make that call.

Having the facility make the call is self serving.

 

[mull982]

From your description, I'm still not certain whether it's a service or not... or where the service point is if it is a service.

Is there any POCO meter in this schema? That'd be a dead giveaway that it's a service... and perhaps a clue as to the service point, so location if present.

Do you have a one-line diagram? Can you post a scan of it (or picture as long as annotations are readable)?

Yes there is a POCO meter and its located on the 13.8kV overhead lines where they enter the property. The overhead lines continue past the POCO meter and run along the property at which point they are tapped at several locations to feed power do different parts of facility. The lines behind the POCO meter are on facility property and owned by facility.

I will try to post One-Line tomorrow if its still not clear.

Thanks

 

[Smart $]

For sure but IMO the AHJ can make that call.

Having the facility make the call is self serving.

Agree... but the self-serving route right now keeps open the possibility of no additional GFPE being required.

 

[Smart $]

Yes there is a POCO meter and its located on the 13.8kV overhead lines where they enter the property. The overhead lines continue past the POCO meter and run along the property at which point they are tapped at several locations to feed power do different parts of facility. The lines behind the POCO meter are on facility property and owned by facility.

I will try to post One-Line tomorrow if its still not clear.

Thanks

That establishes that the 13.8kV distribution line are likely service conductors, but it does not establish a service point. You will have to verify the service point to determine Code compliance with what Gus (augie47) brought up. As a guess, and assuming the facility owns the 13.8kV breaker, the breaker is the service disconnect.

BTW, is this a single piece of equipment, i.e. a manufactured unit, likely assembled on site but a single unit all the same?

 

[mull982]

I see an possible problem.
Where is our service point ?
If the 480v board is the actual service disconnect I see no problem but if the service point is on the high voltage side of the transformer then the transformer secondary conductors would fall under Art 240 and the "service equipment" exemption in 480.36 would not apply and a main would be required at the panel, IMO

Not sure what reference you listed here with 480.36? I'm assuming you maybe mean 450.3? Note 2 in table 450.3 allows for up to (6) circuit breakers to provide protection of the transformer as long as the combined breaker ratings didn't exceed the 125% rating listed in 450.3. So even if the 480V Switchboard is not a service then as long at the feeder breakers add up to less than 3758A (125% of 2500kVA transformer secondary rating @ 480V) then we are o.k.

Even if feeder breakers added to greater than this value wouldn't the CT's on the transformer secondary still act as a main since they will trip the high side breaker with the trip rating set to 125% of transformer secondary?

 

[Smart $]

I see an possible problem.
Where is our service point ?
If the 480v board is the actual service disconnect I see no problem but if the service point is on the high voltage side of the transformer then the transformer secondary conductors would fall under Art 240 and the "service equipment" exemption in 480.36 would not apply and a main would be required at the panel, IMO

I was reviewing what had been stated in this thread and came across this. I didn't give it a second thought yesterday, but today is a new day.


Anyway, 408.36 applies to panelboards. At 1000A x 4, I'm thinking the 480V equipment is likely switchgear and not subject to 408.36. Need OP'er to confirm the equipment is switchgear...

 

[augie47]

Agree there are some unknowns that can make a difference here.
It is looking a lot like the transformer secondary might well be feeders and not service conductors.
If so, in addition to Art 408, it is very possible that Art 240.21(C) might well requires a single OC device {ie: 240.21(C)(4)}
Just trying to cover all possibilities.

 

[mull982]

Anyway, 408.36 applies to panelboards. At 1000A x 4, I'm thinking the 480V equipment is likely switchgear and not subject to 408.36. Need OP'er to confirm the equipment is switchgear...

480V Equipment is a Switchboard. I've attached a One-Line that will hopefully clear up some of the confusion.

All HV and LV is new equipment and are separate pieces of equipment as shown on One-Line. All equipment will be owned by customer.

 

[Smart $]

Agree there are some unknowns that can make a difference here.
It is looking a lot like the transformer secondary might well be feeders and not service conductors.
If so, in addition to Art 408, it is very possible that Art 240.21(C) might well requires a single OC device {ie: 240.21(C)(4)}
Just trying to cover all possibilities.

I'm of the impression that is not an issue if there are 4 separate secondary conductor sets, one set to each 1000A breaker.

 

[Smart $]

480V Equipment is a Switchboard. I've attached a One-Line that will hopefully clear up some of the confusion.

All HV and LV is new equipment and are separate pieces of equipment as shown on One-Line. All equipment will be owned by customer.

From what I can tell by the one line furnished, the 13.8kV breaker is the service disconnecting means (still unverified), and the secondary is a single feeder to busing in the 480V switchboard. You have a violation of 240.21(C) as Gus mentioned (sorta kinda ).

AFAICT, GFPE on the supply would negate the need for GFPE on 1000A and greater feeders [ 215.10 Exception No. 2].

 

[don_resqcapt19]

.... You have a violation of 240.21(C) as Gus mentioned (sorta kinda ).
...

I am not sure about that. You have CTs on the secondary that are connected to a protective relay that trips the primary. That can be set up to provide the protection that is required by 240.21(C) as well as the GFP required by 215.10.