ATS question

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oldschool

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Location
so.fla.
i have a 3 pole ats ,in an exsisiting bldg., we added another building,specs called for a rcvd., a 4 pole ats,, how do we bond ? nec does not address 2 different ats issue. thx...ps. gen has multiple brkrs,to feed the 2 bldgs., we bonded neut. at gen set, putting the 3-pole into ?
violation..??
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
If the neutral is being switched you treat the generator like a separately derived system with grounding electrodes and bonding jumper.
 
ceb58

ceb58

Senior Member
Location
Raeford, NC
Your best bet would be to submit a RFI. Explain that using the new 4 pole ATS would create a code violation. If the 4 pole ATS has been bought then just do not use the 4th pole for the neutral or explain that if the neutral is to be switched the original 3 pole will need to be replaced with a 4 pole.
 
H

hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
ceb58 said:
Your best bet would be to submit a RFI. Explain that using the new 4 pole ATS would create a code violation. If the 4 pole ATS has been bought then just do not use the 4th pole for the neutral or explain that if the neutral is to be switched the original 3 pole will need to be replaced with a 4 pole.
Click to expand...

Actually the three pole would be causing the violation, with two services, a four pole would be required to isolate the two services, It must be changed to a four pole, as well as the bonding at the generator will need to be installed.
 
O

oldschool

Member
Location
so.fla.
my bad! .. yes its a school, with a double vault tap,1 for each bldg....hence 2 services.all served by 1 genset...thx for the input....and the nuet. in the 3 pole is isolated,all 3 on a triple bar assy.......bond only to can........and the service for utility power to it is bonded at the disconnect switch....
 
ceb58

ceb58

Senior Member
Location
Raeford, NC
hillbilly1 said:
Actually the three pole would be causing the violation, with two services, a four pole would be required to isolate the two services, It must be changed to a four pole, as well as the bonding at the generator will need to be installed.
Click to expand...

OK, and please correct me if I am wrong. Now that we have a little more info on the install.
my bad! .. yes its a school, with a double vault tap,1 for each bldg....hence 2 services.all served by 1 genset...thx for the input....and the nuet. in the 3 pole is isolated,all 3 on a triple bar assy.......bond only to can........and the service for utility power to it is bonded at the disconnect switch....
Click to expand...

The way the 1st ATS was installed is compliant. Now adding the 2nd ATS would it not need to be treated as the 1st with the neutral not being switched. Dose the taps in the vault constitute 2 services or would it be only one service with the ability to tap for separate buildings?
 
O

oldschool

Member
Location
so.fla.
the vault tap feeds a new service disconnect, isolated from the exsisting gear , that feeds the rest of the campus. i think that this would make it another service ( 2nd).at least thats the opinion the AHJ has. We ( AHJ rep),my bosses, myself,and a few others,have never ran across this type of situation before. The electrical engineer for the architect says we should not use the 4th pole of the ATS..polaris tap them together,eliminating the violation... sounds feasible, it solves the issue,hopefully it wont bite any of us in the rear!..
 
O

oldschool

Member
Location
so.fla.
well, thats what we wound up doing.. polaris tapped the nuet. in the 4pole ats,took bond off of nuet. at genset,that was it...all ahj"s,engineers,bosses happy..

thanks to all for the input!..
 
O

oldschool

Member
Location
so.fla.
the genset frame is grounded,thats it.. each service feeding the utility side is bonded at the first means of disconnect...noone has ever had this problem around here before,AHJ"S,all three,masters themselves....my bosses,20 + and 30 years in the trade,. myself with over 32,,or any of our coworkers...the nuet. on the genset is not bonded at all, from us..
 
R

RUWired

Senior Member
Location
Pa.
Old school, when you have two services supplied from one generator you need to switch at least one of the neutral conductors from one or the other building. If you don't, the main bonding jumper at each buildings service disconnect will put the neutral and ground in parallel with each other. so by having the 4-pole transfer switch and using it, will break the parallel path. The grounded conductor in the gen set will be isolated because of the 3-pole switch in the first building. You can still use the ground rod to the frame at the gen set connected to the equipment ground conductor.

Rick
 
Pierre C Belarge

Pierre C Belarge

Senior Member
Location
Westchester County, New York
RUWired said:
Old school, when you have two services supplied from one generator you need to switch at least one of the neutral conductors from one or the other building. If you don't, the main bonding jumper at each buildings service disconnect will put the neutral and ground in parallel with each other. so by having the 4-pole transfer switch and using it, will break the parallel path. The grounded conductor in the gen set will be isolated because of the 3-pole switch in the first building. You can still use the ground rod to the frame at the gen set connected to the equipment ground conductor.

Rick
Click to expand...


I am curious.
What grounding scheme does one use at a single generator that has a 3-pole and a 4-pole transfer switch being supplied?

My understanding:

1. A 3-pole transfer switch, one treats the generator like a subpanel. Separate the EGCs and the Grounded conductors.

2. A 4-pole transfer switch, one treats the generator like a service. Bond the EGCs and the Grounded conductors.

So, if both types of transfer switches are supplied by the same generator, how is one to treat the grounding scheme?
 
R

RUWired

Senior Member
Location
Pa.
The first objective is to eliminate the parallel path between the 3 pieces of equipment, (service disconnect 1, service disconnect 2, and the generator). The main bonding jumpers in building 1 and 2 are required. Since the grounded conductor in the ats in building 1 is not switched, the grounded conductor at the generator needs to be isolated to prevent the parallel path in building 1. To keep the grounded conductor and grounding conductor seperate in building 2, a switched neutral transfer switch is required. The ground fault path, if a fault in building 1 or 2 should occur while the generator is running will travel through the main bonding jumper in building 1. There are better mouse traps to use such as two 4-pole switches or by making a 3-wire feeder in the building 2, but the are no articles preventing the use of a 3-pole and 4-pole,

Rick
 
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