Parallel generators- switching neutral

E

electro7

Senior Member
Location
Northern CA, US
Occupation
Electrician, Solar and Electrical Contractor
I'm working on a job where we have 3-150kw 3-phase generators in parallel going to a 2000A ATS. The plans from the EE show a 4 pole switch at the ATS. We are interrupting the bus at the gear on the load side of the main breaker. I don't think I want to switch the neutral, but I wanted to confirm. Do I run the neutral through the switch? The plans don't specifically show.

Also, the plans show a ground rod at each generator. From what I remember from a Mike Holt video, there shouldn't be ground rods at generators I thought. Is that correct?

Thanks ahead of time for your input and help.

Sent from my SM-S918U using Tapatalk
 
There can be ground rods at generators, but where they connect is the issue, it appears you have a separately derived system using the four pole switch. The ground rod, and any other grounding electrode conductor would terminate to the generator neutral. If it was a non sds generator, they would terminate to the frame, not the neutral.
 
What is a "non sds" generator- a non separately derived system?

I guess I need to ask the engineer what he wants. I'm getting confused on what to do with the neutrals and grounds and where to bond them if I should with this setup.

Sent from my SM-S918U using Tapatalk
 
Check the definition of an SDS in "Definitions"
Basically of the transfer switch switches the neutral the installation is an SDS.
Most often the neutral is not switched but I would agree, check with the engineer. There are situations where you need to switch the neutral

You are likely familiar with transformer installations. You would treat a SDS generator setup as you would a transformer secondary
 
augie47 said:
Check the definition of an SDS in "Definitions"
Basically of the transfer switch switches the neutral the installation is an SDS.
Most often the neutral is not switched but I would agree, check with the engineer. There are situations where you need to switch the nutral
Click to expand...
Not really, the majority of larger generators are SDS because of GF mains. So it’s about a fifty/fifty mix. Most Lowes stores are SDS, while most Home Depot’s are non-SDS. Though most residential generators are non-SDS.
 
electro7 said:
I'm working on a job where we have 3-150kw 3-phase generators in parallel going to a 2000A ATS. The plans from the EE show a 4 pole switch at the ATS. We are interrupting the bus at the gear on the load side of the main breaker. I don't think I want to switch the neutral, but I wanted to confirm. Do I run the neutral through the switch? The plans don't specifically show.

Also, the plans show a ground rod at each generator. From what I remember from a Mike Holt video, there shouldn't be ground rods at generators I thought. Is that correct?

Thanks ahead of time for your input and help.

Sent from my SM-S918U using Tapatalk
Click to expand...
What is voltage? If 480/277 GFP likely required and you about need to set up as separately derived to avoid nuisance tripping of the GFP from any stray neutral current that could occur with non SDS system.
 
electro7 said:
I'm working on a job where we have 3-150kw 3-phase generators in parallel going to a 2000A ATS. The plans from the EE show a 4 pole switch at the ATS. We are interrupting the bus at the gear on the load side of the main breaker. I don't think I want to switch the neutral, but I wanted to confirm. Do I run the neutral through the switch? The plans don't specifically show.

Also, the plans show a ground rod at each generator. From what I remember from a Mike Holt video, there shouldn't be ground rods at generators I thought. Is that correct?

Thanks ahead of time for your input and help.

Sent from my SM-S918U using Tapatalk
Click to expand...
Let me guess, Generac's? They are the only ones I’ve seen that parallel’s that small of generators in commercial or industrial.
 
Yes, Generacs. Each gen has a breaker, and I don't believe they are GF. Taking parallel conductors for each generator back to the ATS.

The EE has it to where we are interrupting the switchgear bus on the load side of the main breaker.

If it's an SDS setup, wouldn't the grounds and neutrals bond at each generator since that is the first disconnecting means?
220ddc78815e590e65af9bbee590cfab.jpg


Sent from my SM-S918U using Tapatalk
 
electro7 said:
Yes, Generacs. Each gen has a breaker, and I don't believe they are GF. Taking parallel conductors for each generator back to the ATS.

The EE has it to where we are interrupting the switchgear bus on the load side of the main breaker.

If it's an SDS setup, wouldn't the grounds and neutrals bond at each generator since that is the first disconnecting means?
220ddc78815e590e65af9bbee590cfab.jpg


Sent from my SM-S918U using Tapatalk
Click to expand...
The one and only parallel Generac I done was a long time ago, but if I remember correctly, they had a box with parallel controls and wiring between the generators before it went to the t’switch? If it is a four pole switch, switching the neutral, yes the neutrals and ground would be bonded at the generator.
 
The EE is not showing the paralleling equipment, I would strongly suggest getting with your generator vendor on what they need, as I don’t think the EE understands what is needed, or just did a boiler plate diagram.
 
hillbilly1 said:
The EE is not showing the paralleling equipment, I would strongly suggest getting with your generator vendor on what they need, as I don’t think the EE understands what is needed, or just did a boiler plate diagram.
Click to expand...
Generator paralleling in the last decade or so has not required any special paralleling SWGR. They just terminate on a bus (ATS in this application) and there is some sensing on the line side and load side of the set mounted breakers for deadbus and paralleling controls and interface with the ATS control.
Each gen has a paralleling controller now, not centralized as days of old.
 
So I checked with the EE and we will switch the neutral with the 4 pole ATS switch. I'll bond the neutral and grounds at each generator since there is an OCPD at each. Anything else I need to take into consideration? This will be the first time I have switched the neutral.

Sent from my SM-S918U using Tapatalk
 
You must log in or register to reply here.
Top