Transfer switches & bonding jumper

[ohmhead]

Well question we have three transfer switches each ATS is fed from a different POC transformer each comes from its own source of normal power .


Each SEPERATE switchboard feeds one ATS normal power .

We have one generator with a gfi main breaker feeding a emergency switchboard that has a main 1200 amp and three smaller breakers for each ATS are inside this switchboard.

Each ATS has a 3 pole solid neutral connection .


I see NEC code as not grounding the generator bonding jumper . YES/ NO

I see grounding just the three seperate services that feed the three ATS ,s with normal power at there main bonding jumper YES /NO


The gfi is in the generator main breaker feeding the emergency sw board which then feeds each ATS with smaller breakers .


I see this as a waste of money on the main generator breaker and feel the gfi protection should be in each of the ATS emergency breakers in that emergency switchboard what do you think ?

A solid neutral 3 pole ATS for each 480/277 volts 3 phase

1200 amp main in generator with gfi protection .

Each normal switchboard is 4000 amp mains with gfi protection.


The emergency switch board has three seperate breakers feeding each of the three ATS . plus a 1200 amp main no gfi !

 

[don_resqcapt19]

If the generator has the ground fault protection, then you cannot have any down stream neutral to ground bonds and you will need transfer switches that switch the neutral.

 

[ohmhead]

If the generator has the ground fault protection, then you cannot have any down stream neutral to ground bonds and you will need transfer switches that switch the neutral.

Don let me give you a better picture of what we have this is a project which is designed by engineer not us or my company .

We have a generator with only one breaker and its GFI which feeds a switchboard this switchboard has a main breaker and a second section with three breakers for each ATS .

Now each of the ATS ,S has normal power fed from other switchboards total of three .

The one line drawns show neutral bonded in the emergency switchboard the one that feeds the emergency to the ATS.S only .

The one line shows the neutral bonded in each of the normal switchboards that feed the normal power to the ATS.S .


The oneline shows a GFI in the generator but no bonding jumper for neutral to ground.

Code says not to bond the generator if its a solid connection in ATS ?

The normal sw gear will have a jumper.

Now what are you saying about the GFI in the generator help me out here ?

I dont like it due to the fact if it trips you dont have emergency power any place .

Would GFI protection be better on each of the three ATS breakers in sw gear emergency what do you think ?

 

[Joe Villani]

Transfer switches and bonding jumper

Transfer switches and bonding jumper

Ohmhead,

Based on your description with all ATS'S being 3 pole there would be no neutral to ground bonding jumpers outside of the service disconnect switchgear. None in the generator, ats's or emergency switchboard, all grounds and neutrals will have to keep seperate.

Personally, I would eliminate the GFI protection for the emergency generator as per 700.26 and just have indication as per 700.7(D). A choice of mine, no violation in keeping it.

The problem the gfi protection and the unswitched neutrals is that tripping may occur due to the connection between the normal neutral and the equipment grounds via the main bonding jumper at the service disconnect. (Don can correct me if i'm wrong on that one )

All the best,

Joe

 

[ohmhead]

Rfi

Rfi

Thanks for all the help we will write the engineer a RFI and see if he can change the oneline for the electrical inspector .


We did read the code and since ive been in this trade its the first time ive seen a 3 pole ATS on the drawns so its a new thing for me . Thanks Don & Joe

 

[hurk27]

Well question we have three transfer switches each ATS is fed from a different POC transformer each comes from its own source of normal power .


Each SEPERATE switchboard feeds one ATS normal power .

We have one generator with a gfi main breaker feeding a emergency switchboard that has a main 1200 amp and three smaller breakers for each ATS are inside this switchboard.


A solid neutral 3 pole ATS for each 480/277 volts 3 phase

1200 amp main in generator with gfi protection .

Each normal switchboard is 4000 amp mains with gfi protection.


The emergency switch board has three seperate breakers feeding each of the three ATS . plus a 1200 amp main no gfi !

I think you need to look at 517.17(A)(1) and (2) think your engineer messed up.