Grounding a transfer switch
- Thread starter sonar1
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Re: Grounding a transfer switch
Simple answer, no. The answer lies in the transfer switch. If the grounded circuit conductor is switched, then the generator is considered a SDS and requires a GEC to grounded circuit conductor bond.
If the grounded circuit conductor is NOT switched then the generator is not SDS and is not permitted to have a GEC to grounded circuit bond.
Al your generator requires is conductors for L1, L2, N, and EGC. The bond in the panel will reference the generator and provide the fault path via neutral (oops, grounded circuit conductor).
Simple answer, no. The answer lies in the transfer switch. If the grounded circuit conductor is switched, then the generator is considered a SDS and requires a GEC to grounded circuit conductor bond.
If the grounded circuit conductor is NOT switched then the generator is not SDS and is not permitted to have a GEC to grounded circuit bond.
Al your generator requires is conductors for L1, L2, N, and EGC. The bond in the panel will reference the generator and provide the fault path via neutral (oops, grounded circuit conductor).
Re: Grounding a transfer switch
All portable generators come with a bonded neutral. Where lies the danger from hooking up this generator to a panel without breaking the neutral path at the service? Most home transfer switches don't break the neutral and most generators have the neutral bonded at the generator...
All portable generators come with a bonded neutral. Where lies the danger from hooking up this generator to a panel without breaking the neutral path at the service? Most home transfer switches don't break the neutral and most generators have the neutral bonded at the generator...
Ed MacLaren
Senior Member
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: Grounding a transfer switch
Won't that still happen via the EGC's being connected to both sources?
Won't that still happen via the EGC's being connected to both sources?
Ed MacLaren
Senior Member
Re: Grounding a transfer switch
With the load on utility power, the neutral path is from X to Z (Diagram 4)
When the load is on generator power, the neutral path is from X to Y (Diagram 5)
Note that when the neutral is switched in the transfer switch, the generator neutral will need to be connected to an acceptable grounding electrode.
Ed
No. The three-pole transfer switch, by breaking the neutral, actually creates two completely separate systems. The EGC is never in parallel with the neutral.
With the load on utility power, the neutral path is from X to Z (Diagram 4)
When the load is on generator power, the neutral path is from X to Y (Diagram 5)
Note that when the neutral is switched in the transfer switch, the generator neutral will need to be connected to an acceptable grounding electrode.
Ed
russ
Senior Member
- Location
- Burbank IL
Re: Grounding a transfer switch
ED: Both of your drawings are on the load side of the main disconnect.
ED: Both of your drawings are on the load side of the main disconnect.
If the transfer switch is on the line side of the main, do you think it makes any difference?
Ed MacLaren
Senior Member
Re: Grounding a transfer switch
The basic rules are still the same.
The only difference is that the transfer switch is now the main disconnect, and that is where the main bonding jumper, and the connection to the grounding electrode conductor would be located.
Ed
The basic rules are still the same.
The only difference is that the transfer switch is now the main disconnect, and that is where the main bonding jumper, and the connection to the grounding electrode conductor would be located.
Ed
russ
Senior Member
- Location
- Burbank IL
Re: Grounding a transfer switch
I don't think the transfer switch would be considered the main. I don't think they all have external arms to shut them off.
My point is being on the line side of the main, should the grounded conductor be bonded to the EGC like in the meter.
If the service feeders were non metallic it would be required,(bonding) because an equipment ground is not required for the service entrance feeder.
If it were a metallic conduit service entrance feeder, you would be bonded in the meter and at the main disconnect, with the transfer switch in the middle with current already on the conduit going in and out of it. Doesn't seem to hurt to bond it in that case. May be even a good Idea if not required by the power company.
I was of the opinion that it should not be bonded, but after a discussion with another inspector on another form, I might have been wrong about that.
I don't think the transfer switch would be considered the main. I don't think they all have external arms to shut them off.
My point is being on the line side of the main, should the grounded conductor be bonded to the EGC like in the meter.
If the service feeders were non metallic it would be required,(bonding) because an equipment ground is not required for the service entrance feeder.
If it were a metallic conduit service entrance feeder, you would be bonded in the meter and at the main disconnect, with the transfer switch in the middle with current already on the conduit going in and out of it. Doesn't seem to hurt to bond it in that case. May be even a good Idea if not required by the power company.
I was of the opinion that it should not be bonded, but after a discussion with another inspector on another form, I might have been wrong about that.
- Location
- Massachusetts
Re: Grounding a transfer switch
Take a look at 230.82 transfer switches are not allowed on the supply side of service disconnect.
In order to install a transfer switch between a meter and the existing main panel it must be a service rated transfer switch. Part of the service rating requires external manual operation.
From the 2004 UL White book
Part of TRANSFER SWITCHES (WPTZ)
This means all bonding must be done at the transfer switch and any original bonding must be removed at the old service panel.
The old service panel is now a 'sub' panel and requires the grounding isolated from the grounded conductors.
Bob
A transfer switch "installed between the electric meter and the main panel in an existing home" must become the 'main'.
Take a look at 230.82 transfer switches are not allowed on the supply side of service disconnect.
In order to install a transfer switch between a meter and the existing main panel it must be a service rated transfer switch. Part of the service rating requires external manual operation.
From the 2004 UL White book
Part of TRANSFER SWITCHES (WPTZ)
IMO a transfer switch installed between an existing electric meter and existing service disconnect becomes the new service disconnect.
This means all bonding must be done at the transfer switch and any original bonding must be removed at the old service panel.
The old service panel is now a 'sub'
panel and requires the grounding isolated from the grounded conductors. Bob
russ
Senior Member
- Location
- Burbank IL
Re: Grounding a transfer switch
Bob:
That works for me.
Glad I didn't bump into anything stumbling around in the dark
Bob:
That works for me.
Glad I didn't bump into anything stumbling around in the dark
Re: Grounding a transfer switch
My question is were is the transfer switch mounted in relationship to the panel cabinet that contains the Over Current Protective Devices. Since the code requires that the service Over Current protective Devices (OCPD) be in the same enclosure or immediately adjacent to the Service Disconnecting Means we cannot have the switch outside and the OCPD inside. If that is what is happening here then you will need to buy the manufacturers 3R enclosure for the main breaker and relocate it outside. You would then replace the main breaker with a Main Lug Only kit in the panel's enclosing cabinet.
Once you moved that main breaker outside then you might as well install it on the line side of the transfer switch as that will make working on the transfer switch far easier as you would no longer need to pull the meter in order to service the transfer switch.
The other remedy is to use a transfer switch that contains the service OCPD in the same enclosure.
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Tom H
230.91 Location.
The service overcurrent device shall be an integral part of the service disconnecting means or shall be located immediately adjacent thereto.
My question is were is the transfer switch mounted in relationship to the panel cabinet that contains the Over Current Protective Devices. Since the code requires that the service Over Current protective Devices (OCPD) be in the same enclosure or immediately adjacent to the Service Disconnecting Means we cannot have the switch outside and the OCPD inside. If that is what is happening here then you will need to buy the manufacturers 3R enclosure for the main breaker and relocate it outside. You would then replace the main breaker with a Main Lug Only kit in the panel's enclosing cabinet.
Once you moved that main breaker outside then you might as well install it on the line side of the transfer switch as that will make working on the transfer switch far easier as you would no longer need to pull the meter in order to service the transfer switch.
The other remedy is to use a transfer switch that contains the service OCPD in the same enclosure.
--
Tom H
230.91 Location.
The service overcurrent device shall be an integral part of the service disconnecting means or shall be located immediately adjacent thereto.
- Location
- Massachusetts
Re: Grounding a transfer switch
Tom your recommending a lot of labor when simply buying a service rated transfer switch with integral OCP would solve any issues.
[ February 17, 2005, 01:30 PM: Message edited by: iwire ]
Tom your recommending a lot of labor when simply buying a service rated transfer switch with integral OCP would solve any issues.
[ February 17, 2005, 01:30 PM: Message edited by: iwire ]
Re: Grounding a transfer switch
--
Tom H
Isn't that what I suggested in the last sentence of the previous posting? The only problem is that the price of such a switch can be a lot more than the cost of the MLO kit and the 3R enclosure for the main breaker. If you have a source for a cost effective service rated transfer switch that contains the Over Current Protective Devices (OCPD) in the same enclosure I would be most grateful if you would share it.
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Tom H
- Location
- Massachusetts
Re: Grounding a transfer switch
Many manufactures make service rated transfer panels (interlocked main and generator breakers)
You can also get Meterbase manual transfer switch's with OCPDs.
As far as removing a main breaker, finding, buying & installing a main lug kit in in it's place. Then finding and buying the right 3R enclosure for the removed breaker, to me that sounds like more labor than just leaving the breaker in the panel and buying any suitable 3R enclosure with breaker. It also sounds like more time spent tracking down parts.
I feel that my job is to provide a quality installation for a fair price, not go out of my way to do it as inexpensively as possible.
JMO, Bob
Tom if this thread was talking about an Auto Transfer switch I would agree. I believe this thread is talking about a manual transfer switch.
Many manufactures make service rated transfer panels (interlocked main and generator breakers)
You can also get Meterbase manual transfer switch's with OCPDs.
As far as removing a main breaker, finding, buying & installing a main lug kit in in it's place. Then finding and buying the right 3R enclosure for the removed breaker, to me that sounds like more labor than just leaving the breaker in the panel and buying any suitable 3R enclosure with breaker. It also sounds like more time spent tracking down parts.
I feel that my job is to provide a quality installation for a fair price, not go out of my way to do it as inexpensively as possible.
JMO, Bob
If a home has the neutral and EGC bonded together at the transfer switch, in the same situation as above, and only has a 3 wire SE cable coming out of transfer switch to the main breaker panel in the house, where the grounds and neutrals are not separated, would this burn up the generator and cause it to stop working?
- Location
- Illinois
- Occupation
- retired electrician
That is not a true statement...many currently available portable generators do not have any of the conductors bonded to anything.
Don
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Glancing at the posts above (this thread has had quite a bump list, looking at the dates!leggo said:
), I don't understand what you mean by "same situation as above". A few different setups were described.But I do not believe that a neutral touching an EGC in two spots would cause generator meltdown.
That is interesting, thank you, Don. I didn't know that.Don said:
Can you elaborate? Are there particular models, or do most of the brands do it up to a certain KW, is there any pattern?
I think another question would be, does a GFCI receptacle really enhance safety in that type of scenario?
Apparently, the generator manufacturers took a page from Bennie's book, I had no idea that any packaged equipment of that flavor would be unbonded/ungrounded.
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