# clarification on transfer switch grounding



## Chris Kennedy (Nov 19, 2007)

newsparkster said:


> So, does this mean if the neutral is not switched in a transfer switch it s not considered a seperately derived system?


Correct, take a look at ART.100 def of Separately Derived System.

"Such systems have no direct electrical connection, including a solidly connected GROUNDED circuit conductor, to supply conductors originating in another system."

See 250.30 for grounding a SDS.


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## jrclen (Oct 23, 2007)

newsparkster said:


> the neutral from the meter and going to the mb panel are tied together with the grounding electrode conductors in the 200a dpdt switch, also we seperated all the grounds and neutrals in the mb panel because it was not the first point of disconnect anymore. One of the first things my boss told me when i started was remember to tie all grounds and neutral plus electrodes together at first point of disconnect, but Im thinking that may not apply here. Any info will be greatly appreciated.


So the main bonding jumper and grounding electrode conductor is in the transfer switch enclosure? It does sound like that is now the first disconnect. The generator feeder is a 4 wire circuit with no bonding at the generator correct?


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## newsparkster (Dec 1, 2007)

jrclen said:


> So the main bonding jumper and grounding electrode conductor is in the transfer switch enclosure? It does sound like that is now the first disconnect. The generator feeder is a 4 wire circuit with no bonding at the generator correct?


Thanks for the reply,
Yes, In the transfer switch the neutrals are connected to bolted on lugs then another ground bar is mounted which has the ufer, ground rod wire, and the neutral and the ground from the portable generator hooked to it.
the paint was scraped off the dpdt switch where the lugs and ground bar mounted then nol-lox was applied to the scraped off area to prevent corrosion.


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## brian john (Mar 11, 2007)

The main bonding jumper is in the main service for the utility service and in the generator termination housing or generator disconnect for the alternate source.


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## RIVETER (Sep 26, 2009)

*transfer switch grounding*



brian john said:


> The main bonding jumper is in the main service for the utility service and in the generator termination housing or generator disconnect for the alternate source.


/The code defines a separately derived electrical system...but why would we care if a system is separately derived?


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## brian john (Mar 11, 2007)

RIVETER said:


> /The code defines a separately derived electrical system...but why would we care if a system is separately derived?


If you have a 3 pole ATS (solid neutral) in a 4-wire system the generator is NOT AN SDS, if you ground the neutral at the generator and main service n you will have circulating current on the system ground.

If you have a 4 pole ATS where the neutral is switched you have an SDS and if you do not ground the neutral at the generator the system will operate ungrounded when on generator, assuming you do not have any unintentionally grounded neutrals downstream.


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## micromind (Aug 11, 2007)

Brians post above is exactly correct.

Very few people (including inspectors) understand this concept. 

I cannot even begin to think of how many times I've seen a transfer switch that doesn't involve the neutral being fed from a generator with the neutral bonded to the ground. Absolutely wrong!

Rob


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## brian john (Mar 11, 2007)

micromind said:


> Brians post above is exactly correct.
> 
> Very few people (including inspectors) understand this concept.
> 
> ...


About 95% of the time.


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## RIVETER (Sep 26, 2009)

*Transfer switches*



brian john said:


> If you have a 3 pole ATS (solid neutral) in a 4-wire system the generator is NOT AN SDS, if you ground the neutral at the generator and main service n you will have circulating current on the system ground.
> 
> If you have a 4 pole ATS where the neutral is switched you have an SDS and if you do not ground the neutral at the generator the system will operate ungrounded when on generator, assuming you do not have any unintentionally grounded neutrals downstream.


Okay, I guess my question is,about a portable generator that you bought at Lowes, or Home Depot, of which I have purchased three...and all of them are Neutral to Chassis Bonded.If I am a homeowner and I'm powering my home with the generator and all I have done is to turn off my main breaker, and not interrupted the neutral back to the pole, am I endangering anyone?


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## RIVETER (Sep 26, 2009)

*generators*



RIVETER said:


> Okay, I guess my question is,about a portable generator that you bought at Lowes, or Home Depot, of which I have purchased three...and all of them are Neutral to Chassis Bonded.If I am a homeowner and I'm powering my home with the generator and all I have done is to turn off my main breaker, and not interrupted the neutral back to the pole, am I endangering anyone?


 Well....anyone?


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## brian john (Mar 11, 2007)

NO but your equipment grounding conductor is in parallel with the neutral. and in the situation you note not of major concern IMO. Though there could be some current on the frame of the generator. 

You could lift the bond at the generator.

Sorry it took so long to answer I HAD TO WORK.


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## RIVETER (Sep 26, 2009)

*transfer switch*



brian john said:


> NO but your equipment grounding conductor is in parallel with the neutral. and in the situation you note not of major concern IMO. Though there could be some current on the frame of the generator.
> 
> You could lift the bond at the generator.
> 
> Sorry it took so long to answer I HAD TO WORK.


Okay, I assume you are at work, again. That's good, but when you get back to the forum, there are more questions. The code says that in order to have a separately derived electrical system, the permanent system in the house must be totally disconnected from the temporary system...at least in so many words. If the Neutral supplied by the utility is not switched with the phase conductors at the transfer switch the generator is not supplying a separately derived system, I believe. I am open for correction, if wrong. Also, why would I want a SDS in the first place. Just asking.And, if I lift the bond at the generator would I not be required to drive a ground rod or seek some grounding electrode?


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## micromind (Aug 11, 2007)

If the neutral is solidly connected throughout the system, then the generator is not a SDS. 

If the neutral is switched in the transfer switch, then the generator is a SDS. 

It's pretty rare to switch the neutral, I've seen it in hospitals and data centers, and not much else.

Rob


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## brian john (Mar 11, 2007)

The current seeks the source, it is being supplied from.

Speaking of 3 phase 4 wire or single phase 3 wire, there are two types of ATS a 3/2* pole only the phase conductors transfer and a 4/3* pole the phase and neutral conductors transfer. With a 3 pole ATS the neutral conductor in the generator MUST NOT BE BONDED TO GROUND. In a 4 pole ATS the neutral is bonded to ground as a 4 pole ATS is a SDS separately derived system.

* 3/2 3 pole 3 phase 4 wire, 2 pole single phase 3 wire
* 4/3 4 pole 3 phase 4 wire, 3 pole single phase 3 wire[/



> So, does this mean if the neutral is not switched in a transfer switch it is not considered a seperately derived system?


Correct

We live on the north coast and had lots of damage to homes due to the recent storm,and are installing lots of transfer switches,and repairing lots of meters taken down by trees. Today we installed a dpdt 200a switch. we ran from the meter to the dpdt with 3 wire se cable, ran from the dpdt to main breaker panel with 4 wire ser, then from portable generator to dpdt switch. The journeyman seemed to have problems with how the super was telling him to ground the dpdt switch. First, the neutral is not switched only the phase conductors, the neutral from the meter and going to the mb panel are tied together with the grounding electrode conductors in the 200a dpdt switch, also we seperated all the grounds and neutrals in the mb panel because it was not the first point of disconnect anymore. One of the first things my boss told me when i started was remember to tie all grounds and neutral plus electrodes together at first point of disconnect, but Im thinking that may not apply here. Any info will be greatly appreciated.[/quote]

Assuming your DPDT is a service rated switch with over current protection and the neutral is not switched

You do all grounding, bonding in the DPDT. 

At the house distribution panel the neutral and grounds are separate and the neutral ground bond is removed. 

At the generator you isolate the neutral from the generator frame/ground. That is you lift/remove/disconnect the neutral from the frame/ground.


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## brian john (Mar 11, 2007)

micromind said:


> It's pretty rare to switch the neutral, I've seen it in hospitals and data centers, and not much else.
> 
> Rob


We are seeing it more and more (switched neutrals) and with the added cost of the ATS, we had one project the engineer that was adamant about using only 4 pole ATS and spec'd all ATS's as such. The only issue most of the feeders were 3 phase 3 wire.

Oh well spend the tax payers dollars.


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## micromind (Aug 11, 2007)

Having an engineer specify a 4 pole transfer switch when the system is 3 phase 3 wire doesn't surprise me in the least. 

I really have to wonder how some of these idiots manage to get by.

Rob


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## manchestersparky (Mar 25, 2007)

newsparkster , make sure that transfer switch is service rated. 
Should be tagged suitable for use as service equipment or something along those lines


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## goodelectric (Nov 8, 2012)

If you are installing an ATS your main panel will become a sub panel. Your grounding ie water main, supplement ground and / or ground to building steel goes into your ATS not your main panel. In the main panel you must isolate and separate the ground wires and the neutral wires on two separate bars and remove any bonding to the neutral bar. For one of those manual transfer switches you dont need to do this.







newsparkster said:


> Originally Posted by *brian john*
> _The current seeks the source, it is being supplied from.
> 
> Speaking of 3 phase 4 wire or single phase 3 wire, there are two types of ATS a 3/2* pole only the phase conductors transfer and a 4/3* pole the phase and neutral conductors transfer. With a 3 pole ATS the neutral conductor in the generator MUST NOT BE BONDED TO GROUND. In a 4 pole ATS the neutral is bonded to ground as a 4 pole ATS is a SDS separately derived system.
> ...


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## brian john (Mar 11, 2007)

goodelectric said:


> If you are installing an ATS your main panel will become a sub panel. Your grounding ie water main, supplement ground and / or ground to building steel goes into your ATS not your main panel. In the main panel you must isolate and separate the ground wires and the neutral wires on two separate bars and remove any bonding to the neutral bar. For one of those manual transfer switches you dont need to do this.


Depends on how you setup your service, most commercial jobs the main service remains the main. Or you have to set a OCP ahead of the existing service panel and that is now where you would bond.

I believe there are too many situations to make a blanket statement about what is what. The only issue that remains true is you bond in the main OCP, be it a service rated ATS, or a stand alone fusible switch or CB. 

The other issue is covered in the above post is the neutral switched or is it a solid neutral in the ATS.


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## Nonstop2002 (Dec 23, 2012)

I have a similar question. 

Ok I'm installing a ats between a main panel and a sub panel. Ats only transfers the phase its a 240 system. Do I tie the main panel only neutral to ground or do I tie the ats Only? Its late and I'm pondering this since the main will be isolated in a power outage but the neutral and ground will still be connected. I can't quite wrap my brain around it.


Thanks


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## McClary’s Electrical (Feb 21, 2009)

Nonstop2002 said:


> I have a similar question.
> 
> Ok I'm installing a ats between a main panel and a sub panel. Ats only transfers the phase its a 240 system. Do I tie the main panel only neutral to ground or do I tie the ats Only? Its late and I'm pondering this since the main will be isolated in a power outage but the neutral and ground will still be connected. I can't quite wrap my brain around it.
> 
> ...


 
In this scenario, you would run 4 wires to the ATS and 4 wires out of the ATS. Remove the MBJ in the ATS.


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## ceb58 (Feb 14, 2009)

micromind said:


> If the neutral is solidly connected throughout the system, then the generator is not a SDS.
> 
> If the neutral is switched in the transfer switch, then the generator is a SDS.
> 
> ...


I would not say rare. If the system is large enough it will have GFP you must then switch the neutral to prevent tripping. You must switch the neutral if you are feeding 2 separate structures with 2 separate services from 1 generator.
I will say though that on systems where it makes no sense to switch the neutral, but someone specks it, they need to be reminded that even though you switch the neutral you will not break the bond between the utility and generator neutral due to the EGC.


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## Belg (Oct 23, 2011)

brian john said:


> NO but your equipment grounding conductor is in parallel with the neutral. and in the situation you note not of major concern IMO. Though there could be some current on the frame of the generator.
> 
> You could lift the bond at the generator.
> 
> Sorry it took so long to answer I HAD TO WORK.


 So if you don't lift the nuetral on the protable generator you could get stray voltage on the nuetral? Could this cause a tv or electronics to fry?
Are the better qaulity generators like Hondas and Yamahas not open to the same problems? I know you can't run the GFI protection on the Hondas to a generator subpanel in which the nuetral is bonded.


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