ATS with GF protection

[augie47]

I can't get my head around a system that I am currently inspecting to the point that I can say "no problem". Assistance will be appreciated.
(a) A new installation has a pad transformer feeding a 3000 amp MDP.
The system is 480/277 so my 3000 amp main is GF protected.
(b) A 400 amp feeder from MDP feeds a ATS. The ATS does not switch the neutral, therefore the generator is not an SDS and there is no N-G bond at the generator, but we do have a EGC to the generator.
(c) Now we add a fire pump with combination controller ATS. The transformer supply has a grounded conductor bonded to the service rated ATS.
The generator supply has no grounded conductor brought to the fire pump but an EGC bonded to the generator frame and ATS.



Two questions
(1) Is the above Code compliant ?
(2) Will the system as wired pose any conflict with the MDP being GF protected ?
(the few systems I have seen with a GF main have had ATS systems with a switched neutral)

 

[ATSman]

I can't get my head around a system that I am currently inspecting to the point that I can say "no problem". Assistance will be appreciated.
(a) A new installation has a pad transformer feeding a 3000 amp MDP.
The system is 480/277 so my 3000 amp main is GF protected.
(b) A 400 amp feeder from MDP feeds a ATS. The ATS does not switch the neutral, therefore the generator is not an SDS and there is no N-G bond at the generator, but we do have a EGC to the generator.
(c) Now we add a fire pump with combination controller ATS. The transformer supply has a grounded conductor bonded to the service rated ATS.
The generator supply has no grounded conductor brought to the fire pump but an EGC bonded to the generator frame and ATS.



Two questions
(1) Is the above Code compliant ?
(2) Will the system as wired pose any conflict with the MDP being GF protected ?
(the few systems I have seen with a GF main have had ATS systems with a switched neutral)

1 Depends on the AHJ
2 Attachment was too large to send. Will try to send link.

 

[ActionDave]

......
Two questions
(1) Is the above Code compliant ?
(2) Will the system as wired pose any conflict with the MDP being GF protected ?
(the few systems I have seen with a GF main have had ATS systems with a switched neutral)

1.I have very little experience with fire pumps so I can't comment on the code legalities.

2. I can't see the set up not causing problems with GF protection at the main.

 

[Canton]

I can't get my head around a system that I am currently inspecting to the point that I can say "no problem". Assistance will be appreciated.
(a) A new installation has a pad transformer feeding a 3000 amp MDP.
The system is 480/277 so my 3000 amp main is GF protected.
(b) A 400 amp feeder from MDP feeds a ATS. The ATS does not switch the neutral, therefore the generator is not an SDS and there is no N-G bond at the generator, but we do have a EGC to the generator.
(c) Now we add a fire pump with combination controller ATS. The transformer supply has a grounded conductor bonded to the service rated ATS.
The generator supply has no grounded conductor brought to the fire pump but an EGC bonded to the generator frame and ATS.



Two questions
(1) Is the above Code compliant ?
(2) Will the system as wired pose any conflict with the MDP being GF protected ?
(the few systems I have seen with a GF main have had ATS systems with a switched neutral)

Augie,

If I'm reading and drawing your one-line correctly your generator feeds the Emergency Side of your Fire Pump ATS and a "Separate" ATS?

The only Neutral/Ground bond for fault current from your generator is in your 3000 amp MDP.

If we trace the current path during a generator fault, the fault current would have to go through your MDP's main bonding jumper, and could trigger the GFP on the Normal Source.


Edit: To add, I think this set-up should have had the Generator as a SDS with the Fire Pump ATS as is and used a 4-pole ATS for the other load. It would also depend on what type of GFP was being used, Zero sequence, Modified differential....etc. as some depending on the CT's and logic being used would not even see the additional current on the MBJ and pay no attention.

 

[augie47]

Augie,

If I'm reading and drawing your one-line correctly your generator feeds the Emergency Side of your Fire Pump ATS and a "Separate" ATS?

The only Neutral/Ground bond for fault current from your generator is in your 3000 amp MDP.

If we trace the current path during a generator fault, the fault current would have to go through your MDP's main bonding jumper, and could trigger the GFP on the Normal Source.


Edit: To add, I think this set-up should have had the Generator as a SDS with the Fire Pump ATS as is and used a 4-pole ATS for the other load. It would also depend on what type of GFP was being used, Zero sequence, Modified differential....etc. as some depending on the CT's and logic being used would not even see the additional current on the MBJ and pay no attention.

For clarification:
The generator has no neutral/ground bond.
Neither ATS switches the neutral.

#1 ATS is fed by a 400 amp feeder from the 3000 amp service
#1 ATS also has a 4 wire + equipment ground run to a 400 amp generator breaker.

#2 ATS, the fire pump, has a 4 wire (3 phases plus grounded neutral) from the same utility transformer and a 4 wire (3 phase plus equipment ground) from the generator.

GF protection on the 3000 amp service if achieved by a Siemens Main with "WL" trip units.

That change anything with your answer ?

 

[ceb58]

Not sure about the fire pump but I am in agreement that it not being installed as a SDS will cause problems with the GFP.

 

[JoeStillman]

I'm imagining that the point of common coupling between your 3000A MDP and the Fire Pump service is upstream of the GF protected MCB, since this is what 695.3(A)(1) requires. If this is so, the extra bonding jumper in the fire pump ATS won't interfere with your 3000A GF scheme, although it can result in "objectionable neutral currents" in your 400A ATS (250.6) if that has GF protection too. It creates a parallel path to the generator neutral point. via the fire pump ATS. If there is no GF on the 400A breaker, then you should be fine.

If the fire pump was fed from a different transformer than the 3000A MDP, you would need to bond the generator neutral and use 4P ATS's.

 

[Canton]

For clarification:
The generator has no neutral/ground bond.
Neither ATS switches the neutral.

#1 ATS is fed by a 400 amp feeder from the 3000 amp service
#1 ATS also has a 4 wire + equipment ground run to a 400 amp generator breaker.

#2 ATS, the fire pump, has a 4 wire (3 phases plus grounded neutral) from the same utility transformer and a 4 wire (3 phase plus equipment ground) from the generator.

GF protection on the 3000 amp service if achieved by a Siemens Main with "WL" trip units.

That change anything with your answer ?

Hey Augie,

I have to admit this set-up is a little strange. I have seen similar. The job i am currently on is almost the same as yours with one exception. I have two (2) ATS and (1) Fire Pump ATS. The difference with mine is my Generator is a SDS and my (2) ATS's (Life Safety/Elevator) are 4-pole ATS's. My normal power for my Fire Pump comes off the same utility Transformer as my normal 3000 amp service in the gear. My feeder from the Generator to the Fire Pump ATS is also 3-phases and a EGC.

Other than a strange design I cannot point out any definitive code violations. I assume your doing your initial inspection for them to get their TPF. That being said has a GFP test been done for the MDP? Usually the independent testing contractor picks-up on things like this during testing which is required in a lot of areas around here before the TPF is given.

The only thing that stands out to me that could interfere with the GFP in your MDP's Main is a fault at the Fire Pump ATS or any where on the Generator Feeders.

For Instance, a Ground Fault in the feeder going from the Generator to the Fire Pump ATS could follow a couple of paths. It will go to ground back to the Generator (no Neutral/Ground bond) keep going, continue back on the ground from the Generator to ATS 1 on the ground from ATS 1 to your MDP, MBJ to the Generator feeder Neutral, and then back agian to the generator.

The fault can also go from the Fire Pump ATS (Neutral/Ground bond) on to the Utility Neutral, then utility neutral/SE neutral to your MDP, ATS 1 and back to your Generator. Everything would depend on the physical layout of your job and the total impedance and path any fault current would take. Then I start to see some code violations, Parallel Neutral Paths, Objectionable Current (especially if it interferes with the GFP).

The biggest thing that stands out in my eyes is the Set-up as is without utilizing 4-pole ATS's and a Generator that is not a SDS. But if in testing the GFP and it functions properly it may be alright. There are a lot of options available for GFP, especially in double ended gear where there are multiple paths for current to flow.

 

[Pharon]

Not sure about the fire pump but I am in agreement that it not being installed as a SDS will cause problems with the GFP.

What makes you say this?

I could be wrong, but this installation sounds Code-compliant to me. The fire pump is connected ahead of the 3000A main, and I can't wrap my head around how GF on the 3000A main would have anything to do with the fire pump operating correctly.

A non-SDS should be fine as long as there's only one neutral to ground bond.