dolphins
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- California
I want to clarify the neutral switching of the 4 poles ats to the generator; is it to separate the main system from the generator once ground fault occur. Can any body help?
generators 4 poles switching
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Ed MacLaren
Senior Member
Re: generators 4 poles switching
No, switching the grounded (neutral) conductor is only required, when the generator neutral is bonded to the generator frame, to prevent the neutral from being in parallel with the equipment grounding conductor.
Ed
[ April 14, 2003, 12:51 PM: Message edited by: Ed MacLaren ]
No, switching the grounded (neutral) conductor is only required, when the generator neutral is bonded to the generator frame, to prevent the neutral from being in parallel with the equipment grounding conductor.
Ed
[ April 14, 2003, 12:51 PM: Message edited by: Ed MacLaren ]
dolphins
Member
- Location
- California
Re: generators 4 poles switching
if I have a GFP at main of service to detect ground fault to occur in the system don't I need a 4 pole ATS in this case to provide a SDS at the emergency stage.
if I have a GFP at main of service to detect ground fault to occur in the system don't I need a 4 pole ATS in this case to provide a SDS at the emergency stage.
Ed MacLaren
Senior Member
Re: generators 4 poles switching
Yes, you are correct, I forgot to mention that you need to configure the generator system as a SDS, when Ground Fault Protection is installed at the service.
Ed
Yes, you are correct, I forgot to mention that you need to configure the generator system as a SDS, when Ground Fault Protection is installed at the service.
Ed
chuck@apsinc.biz
Member
- Location
- Colorado
Re: generators 4 poles switching
In the event of a ground fault, doesn't current try to travel back to its source of origin, then that source of origion sends out a current strong enough to trip the associated overcurrent protection device? If so, what does configuring your generator as a SDS in lieu of a NSDS net, when your main on the normal power side of the ATS is GFP?
In the event of a ground fault, doesn't current try to travel back to its source of origin, then that source of origion sends out a current strong enough to trip the associated overcurrent protection device? If so, what does configuring your generator as a SDS in lieu of a NSDS net, when your main on the normal power side of the ATS is GFP?
Re: generators 4 poles switching
Chuck, when the ATS is in the emergency position a ground fault may cause a false trip of the GFP in the normal service even though no load current is flowing. The fault path back to the generator would be through the MBJ of the service back to the EGC of the generator. Hence a false trip of the service.
Chuck, when the ATS is in the emergency position a ground fault may cause a false trip of the GFP in the normal service even though no load current is flowing. The fault path back to the generator would be through the MBJ of the service back to the EGC of the generator. Hence a false trip of the service.
- Location
- Massachusetts
Re: generators 4 poles switching
The ones I work on are usually inside steel buildings. Take away the ground conductor and it will still be "grounded" by exhaust pipes, fuel lines, sheet metal plenums etc., along with block heaters and chargers that are required to be grounded.
So wouldn't it be better to plan on it being grounded?
[ April 14, 2003, 06:33 PM: Message edited by: iwire ]
The ones I work on are usually inside steel buildings. Take away the ground conductor and it will still be "grounded" by exhaust pipes, fuel lines, sheet metal plenums etc., along with block heaters and chargers that are required to be grounded.
So wouldn't it be better to plan on it being grounded?
[ April 14, 2003, 06:33 PM: Message edited by: iwire ]
chuck@apsinc.biz
Member
- Location
- Colorado
Re: generators 4 poles switching
Dereck, If a ground fault occured in emergency posistion on a NSDS configuration the path would be as follows.
1.Equipment grounding conductor(EGC) to Service entrance grounding Bar.
2.Service entrance grounding bar over Main bonding jumper (MBJ) to Grounded(neutral) bar.
3.Grounded(neutral)bar to Generator source.
If a ground fault occurs in emergency posistion and is strong enough to trip the main GFP before the local over current protection device, isn't it doing its job? Would it trip if the ATS was in normal posistion? If so way are you calling this a false trip?
Bennie, In a NSDS the equipment grounding conductors protects the metal parts of the generator and generator housing.
Dereck, If a ground fault occured in emergency posistion on a NSDS configuration the path would be as follows.
1.Equipment grounding conductor(EGC) to Service entrance grounding Bar.
2.Service entrance grounding bar over Main bonding jumper (MBJ) to Grounded(neutral) bar.
3.Grounded(neutral)bar to Generator source.
If a ground fault occurs in emergency posistion and is strong enough to trip the main GFP before the local over current protection device, isn't it doing its job? Would it trip if the ATS was in normal posistion? If so way are you calling this a false trip?
Bennie, In a NSDS the equipment grounding conductors protects the metal parts of the generator and generator housing.
chuck@apsinc.biz
Member
- Location
- Colorado
Re: generators 4 poles switching
Bennie, In a NSDS It protects the generator from a line to case fault with in the generator housing by carrying the current over the following path:
1.Generator housing over the equipment grounding conductor(EGC) to the service equipment grounding bar.
2.From the equipment grounding bar over the main bonding jumper(MBJ) to the Grounded(Neutral) Bar.
3.From the Grounded(neutral) bar over the grounded(neutral) Conductor to the generator power source.
4. From the generator power source over the ungrounded(HOT)conductor, through an overcurrent protection device back to the line to case fault.
When the ground fault current passes through the overcurrent protection device it trips the breaker and a thus protects the generator and generator housing from human electrical touch shock and equipment dammage from an overvoltage caused by an arcing fault.
Bennie, In a NSDS It protects the generator from a line to case fault with in the generator housing by carrying the current over the following path:
1.Generator housing over the equipment grounding conductor(EGC) to the service equipment grounding bar.
2.From the equipment grounding bar over the main bonding jumper(MBJ) to the Grounded(Neutral) Bar.
3.From the Grounded(neutral) bar over the grounded(neutral) Conductor to the generator power source.
4. From the generator power source over the ungrounded(HOT)conductor, through an overcurrent protection device back to the line to case fault.
When the ground fault current passes through the overcurrent protection device it trips the breaker and a thus protects the generator and generator housing from human electrical touch shock and equipment dammage from an overvoltage caused by an arcing fault.
Re: generators 4 poles switching
A generator winding is the same as a transformer secondary. A service from a transformer does not have an equipment ground wire due to there being nothing to trip. A generator is the same.
GFP sensors will see a fault at the service panel if supplied by a generator, or a transformer.
The core, and metal of the generator, will be connected to the star point. A winding to core fault will be seen by the exciter controls and will act faster than any overcurrent device.
Generators are often connected to the earth through an impedance.
[ April 14, 2003, 07:35 PM: Message edited by: bennie ]
A generator winding is the same as a transformer secondary. A service from a transformer does not have an equipment ground wire due to there being nothing to trip. A generator is the same.
GFP sensors will see a fault at the service panel if supplied by a generator, or a transformer.
The core, and metal of the generator, will be connected to the star point. A winding to core fault will be seen by the exciter controls and will act faster than any overcurrent device.
Generators are often connected to the earth through an impedance.
[ April 14, 2003, 07:35 PM: Message edited by: bennie ]
Re: generators 4 poles switching
Chuck, you have the sequence right on a fault in the emergency position on non-SDS, but consider this. Suppose you are testing the generator with load, and a fault were to occur in the generator. You would trip both the generator and service GFP?s at the same time.. That would be false trip of the service even though it didn't occur in the service.
The only way to prevent it is to configure the generator as SDS and switch the neutral if used. This will prevent any false or nuisance tripping of GFP in either source.
Here is my design philosophy: If a generator is permanently installed on site and/or the service has GFP, install the generator as SDS. If the generator is going to be portable and the service has no GFP, then the generator can be configured non-SDS. If a generator is configured SDS, then the ATS has to switch the neutral if it is used.
Chuck, you have the sequence right on a fault in the emergency position on non-SDS, but consider this. Suppose you are testing the generator with load, and a fault were to occur in the generator. You would trip both the generator and service GFP?s at the same time.. That would be false trip of the service even though it didn't occur in the service.
The only way to prevent it is to configure the generator as SDS and switch the neutral if used. This will prevent any false or nuisance tripping of GFP in either source.
Here is my design philosophy: If a generator is permanently installed on site and/or the service has GFP, install the generator as SDS. If the generator is going to be portable and the service has no GFP, then the generator can be configured non-SDS. If a generator is configured SDS, then the ATS has to switch the neutral if it is used.
chuck@apsinc.biz
Member
- Location
- Colorado
Re: generators 4 poles switching
Bennie, When a generator is connected as a Non-Separately Derived System(NSDS)it is not the same as a supply transformer which is a Separetely Derived System (SDS), the grounded (neutral)connection is floted and thus the core and metal of the generator are not connected to the star point(XO Terminal). Am I missing something?
Dereck, Your philosophy appears sound. However, if there is no GFP at the service does it really matter if the generator is connected SDS or NSDS?
Bennie, When a generator is connected as a Non-Separately Derived System(NSDS)it is not the same as a supply transformer which is a Separetely Derived System (SDS), the grounded (neutral)connection is floted and thus the core and metal of the generator are not connected to the star point(XO Terminal). Am I missing something?
Dereck, Your philosophy appears sound. However, if there is no GFP at the service does it really matter if the generator is connected SDS or NSDS?
Re: generators 4 poles switching
A generator is a generator, it may supply a separately derived system, it is not a separately derived system.
A separately derived system is a premises wiring system with no electrical connection to the utility supply.
The definition in Article 100, substantiates the above.
[ April 15, 2003, 12:35 PM: Message edited by: bennie ]
A generator is a generator, it may supply a separately derived system, it is not a separately derived system.
A separately derived system is a premises wiring system with no electrical connection to the utility supply.
The definition in Article 100, substantiates the above.
[ April 15, 2003, 12:35 PM: Message edited by: bennie ]
chuck@apsinc.biz
Member
- Location
- Colorado
Re: generators 4 poles switching
Bennie, When it comes to grounding generators there is a difference between connecting it as a NSDS and a SDS. The 2002 NEC hand book explains this in detail. See the commentary following 250.20(D)on page 180 of the handbook. This clarification helps to eliminate objectional current flow. I am not following your logic on this matter, and I am haveing trouble trying to figure out what you are saying.
Bennie, When it comes to grounding generators there is a difference between connecting it as a NSDS and a SDS. The 2002 NEC hand book explains this in detail. See the commentary following 250.20(D)on page 180 of the handbook. This clarification helps to eliminate objectional current flow. I am not following your logic on this matter, and I am haveing trouble trying to figure out what you are saying.
- Location
- Massachusetts
Re: generators 4 poles switching
Chuck, search this site for "SDS" or "derived" and you will get a ton of info.
I would bet money Bennie knows what the handbook says.
Chuck, search this site for "SDS" or "derived" and you will get a ton of info.
I would bet money Bennie knows what the handbook says.
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