grounding a sub panel at a separate building
- Thread starter dia480
- Start date
- Status
- Location
- Illinois
- Occupation
- retired electrician
Re: grounding a sub panel at a separate building
A second building fed by a feeder always requires a grounding electrode system. If there are no conducting paths, other than the feeder circuit conductors, between the two buildings, you are permitted to install the feeder without an equipment grounding conductor and rebond the neutral at the second building. If there is any type of conducing path between the building, you must have an EGC and the neutral is not rebonded.
Don
A second building fed by a feeder always requires a grounding electrode system. If there are no conducting paths, other than the feeder circuit conductors, between the two buildings, you are permitted to install the feeder without an equipment grounding conductor and rebond the neutral at the second building. If there is any type of conducing path between the building, you must have an EGC and the neutral is not rebonded.
Don
rasmithircgov.com
Member
- Location
- Florida
Re: grounding a sub panel at a separate building
What would be an example of the conducting paths. Would metal water piping be one of them if the water is fed from the other building and not a seperate supplied water service?
What would be an example of the conducting paths. Would metal water piping be one of them if the water is fed from the other building and not a seperate supplied water service?
Re: grounding a sub panel at a separate building
If its a sub panel that is fed out of a main panel your grounding would be either your conduit or other recognized method Art.250.118, you don't treat it as a seperate service, all your main grounding should be at the first point of disconnect, at the sub-panel you would not bond the grounded conductor.
If its a sub panel that is fed out of a main panel your grounding would be either your conduit or other recognized method Art.250.118, you don't treat it as a seperate service, all your main grounding should be at the first point of disconnect, at the sub-panel you would not bond the grounded conductor.
- Location
- Massachusetts
Re: grounding a sub panel at a separate building
Normally that would be true, but for a feed to a separate building you will have to bond the neutral to the ground if you chose not to run an equipment grounding conductor which is allowed if as Don pointed out there are no other metallic paths between buildings.
- Location
- Massachusetts
Re: grounding a sub panel at a separate building
dia480
You have two ways to handle a feeder between two buildings.
With both methods you need a grounding electrode as required by 250.32
Method one
Run separate ungrounded, grounded and grounding conductors from one building to the other, do not bond the grounded conductor to the grounding conductor. Put in a grounding electrode at the second building and connect it to the grounding conductor.
Method two
If there are no other metallic paths between buildings (water pipes, coax cables, gas lines, whatever) you are allowed to run just the ungrounded and grounded conductors out the to second building.
In this case you must bond the grounded conductor to the panel enclosure and again install a grounding electrode connected to the grounded conductor.
Hope this helps, Bob
[ June 07, 2003, 12:51 PM: Message edited by: iwire ]
dia480
You have two ways to handle a feeder between two buildings.
With both methods you need a grounding electrode as required by 250.32
Method one
Run separate ungrounded, grounded and grounding conductors from one building to the other, do not bond the grounded conductor to the grounding conductor. Put in a grounding electrode at the second building and connect it to the grounding conductor.
Method two
If there are no other metallic paths between buildings (water pipes, coax cables, gas lines, whatever) you are allowed to run just the ungrounded and grounded conductors out the to second building.
In this case you must bond the grounded conductor to the panel enclosure and again install a grounding electrode connected to the grounded conductor.
Hope this helps, Bob
[ June 07, 2003, 12:51 PM: Message edited by: iwire ]
pierre
Senior Member
- Location
- Westchester County, New York
Re: grounding a sub panel at a separate building
Hello dia480,
If this is a new installation that will or is being installed, I would 'advise' the installer to run the equipment grounding conductor (EGC) with the feeders (even though it is not required), and wire the same way as any 'subpanel'. Regardless of how you run the feeders, you are REQUIRED TO INSTALL A GROUNDING ELECTRODE SYSTEM as per 250.32(A). The purpose of the grounding electrode system at the 2nd building is for lightning protection. The grounding electrode conductor is connected to the grounding bus.
Good Luck,
Pierre
Hello dia480,
If this is a new installation that will or is being installed, I would 'advise' the installer to run the equipment grounding conductor (EGC) with the feeders (even though it is not required), and wire the same way as any 'subpanel'. Regardless of how you run the feeders, you are REQUIRED TO INSTALL A GROUNDING ELECTRODE SYSTEM as per 250.32(A). The purpose of the grounding electrode system at the 2nd building is for lightning protection. The grounding electrode conductor is connected to the grounding bus.
Good Luck,
Pierre
- Location
- Illinois
- Occupation
- retired electrician
Re: grounding a sub panel at a separate building
Ras,
Water piping, gas piping, and communications circuits are all examples of metallic paths other than the feeder circuit conductors that would be conductive paths between the buildings.
Don
Ras,
Water piping, gas piping, and communications circuits are all examples of metallic paths other than the feeder circuit conductors that would be conductive paths between the buildings.
Don
- Location
- Bremerton, Washington
Re: grounding a sub panel at a separate building
Pierre, "I would 'advise' the installer to run the equipment grounding conductor (EGC) with the feeders (even though it is not required)," excellent advice. In Washington State, it is not allowed to reground the neutral at a separate building or structure (state code), effective May 23, 2003.
And a sepatate building does not always require a grounding electrode system. A building with a single branch circuit does not require a GES, and Art 210 states a multiwire branch circuit can be considered a single branch circuit, IE a 12-3 w/G to a garage does not require a GES.
Pierre, "I would 'advise' the installer to run the equipment grounding conductor (EGC) with the feeders (even though it is not required)," excellent advice. In Washington State, it is not allowed to reground the neutral at a separate building or structure (state code), effective May 23, 2003.
And a sepatate building does not always require a grounding electrode system. A building with a single branch circuit does not require a GES, and Art 210 states a multiwire branch circuit can be considered a single branch circuit, IE a 12-3 w/G to a garage does not require a GES.
- Location
- Massachusetts
Re: grounding a sub panel at a separate building
If I was asked to do this I would not even think of not running a EGC, just out of habit from doing subpanels inside.
I do have a question for the theory guys though.
Wouldn't leaving the EGC behind and bonding at the second building be a good idea as that will create the shortest path for branch circuit fault clearing?
Say the buildings are 300' feet apart, by bonding at the second building you take 600' of conductor out of the circuit.
What is the down side of this method, other than the likelihood of a conductive path being established later?
Bob
If I was asked to do this I would not even think of not running a EGC, just out of habit from doing subpanels inside.
I do have a question for the theory guys though.
Wouldn't leaving the EGC behind and bonding at the second building be a good idea as that will create the shortest path for branch circuit fault clearing?
Say the buildings are 300' feet apart, by bonding at the second building you take 600' of conductor out of the circuit.
What is the down side of this method, other than the likelihood of a conductive path being established later?
Bob
- Location
- Illinois
- Occupation
- retired electrician
Re: grounding a sub panel at a separate building
Bob,
Don
Bob,
The current still has to travel back to XO at the transformer to clear the fault. The only difference is that when you have an EGC the fault clearing path is via this conductor and when you rebond the fault clearing path is via the grounded conductor. The lenght of the fault clearing path doesn't really change, but by bonding at the second building you do have a lower impedence fault clearing path because the path will be via the the feeder grounded conductor and not the smaller EGC.
Don
- Location
- Massachusetts
Re: grounding a sub panel at a separate building
Thanks Don, I should have realized that myself when I posted it.
Thanks Don, I should have realized that myself when I posted it.
- Location
- Bremerton, Washington
Re: grounding a sub panel at a separate building
Bennie, the impedance should be the same if all circuit conductors are in the same raceway. the change was made to prevent neutral current on metal raceways and other conductive paths which would be in parallel.Mike Holts Illustrated Grounding and Bonding 2002 text has details and graphics of this dangerous practice. I'd like to send you a copy of his text.
Bennie, the impedance should be the same if all circuit conductors are in the same raceway. the change was made to prevent neutral current on metal raceways and other conductive paths which would be in parallel.Mike Holts Illustrated Grounding and Bonding 2002 text has details and graphics of this dangerous practice. I'd like to send you a copy of his text.
Re: grounding a sub panel at a separate building
Tom: I should have been more clear with my thoughts. I am referring to SE cable, in residential applications, and outbuildings with no equipment ground.
Most outbuildings are either in PVC, direct burial USE,URD, or overhead spans. Very few will have metal conduit for the feeder.
The neutral conductor will be larger than an equipment ground conductor and will clear a fault quicker. Two ground conductors are not needed. One ground conductor is not dangerous. There is thousands of them in use.
Tom: I should have been more clear with my thoughts. I am referring to SE cable, in residential applications, and outbuildings with no equipment ground.
Most outbuildings are either in PVC, direct burial USE,URD, or overhead spans. Very few will have metal conduit for the feeder.
The neutral conductor will be larger than an equipment ground conductor and will clear a fault quicker. Two ground conductors are not needed. One ground conductor is not dangerous. There is thousands of them in use.
rasmithircgov.com
Member
- Location
- Florida
Re: grounding a sub panel at a separate building
Tom, If the multi wire branch circuit is attached to 2 20a breakers for lets say lights and recp's is that not 2 circuits just sharing a neutral?
Tom, If the multi wire branch circuit is attached to 2 20a breakers for lets say lights and recp's is that not 2 circuits just sharing a neutral?
jxofaltrds
Inspector Mike®
- Location
- Mike P. Columbus Ohio
- Occupation
- ESI, PI, RBO
Re: grounding a sub panel at a separate building
Ras YES
This is called a multiwire branch circuit.
Mike P.
Ras YES
This is called a multiwire branch circuit.
Mike P.
Re: grounding a sub panel at a separate building
Remember, multiwire circuits are ungrounded conductors with a voltage between the ungrounded conductors and also voltage between each ungrounded conductor and the grounded conductor ( neutral ).
Just to clarify that two or more ungrounded conductors of the same phase ( or leg of a 1? source) and an grounded conductor is NOT a multiwire circuit.
Remember, multiwire circuits are ungrounded conductors with a voltage between the ungrounded conductors and also voltage between each ungrounded conductor and the grounded conductor ( neutral ).
Just to clarify that two or more ungrounded conductors of the same phase ( or leg of a 1? source) and an grounded conductor is NOT a multiwire circuit.
Re: grounding a sub panel at a separate building
Iwire I belive there is a misunderstanding as to what an EGC is, and forgive me if I misunderstand your qoute, Art 250.118 Types of Equipment Grounding Conductors, an EGC is not always going to be a wire, although it is good practice to run an EGC wire within a raceway, but as Bennie states the cost of adding a fourth wire, Example:1phase 120/240v, 2 hots 1 nuetral 1 EGC, can add to the total cost of the job that could mean the differance between winning or losing a bid, and I am clear on the part of Art. 250.32 (B) (2) when no grounding electrode is present, then you would bond the nuetral at the outbuilding Sub-Panel to the can, Art 250.32 gives a clear answer to the grounding requirments for two or more buildings or structures, but say at the outbuilding I drive a ground rod and take an EGC to say cold water, would I still need to bond the nuetral to the EGC or would the added EGC violate any codes.
[ June 08, 2003, 10:20 AM: Message edited by: jro ]
Iwire I belive there is a misunderstanding as to what an EGC is, and forgive me if I misunderstand your qoute, Art 250.118 Types of Equipment Grounding Conductors, an EGC is not always going to be a wire, although it is good practice to run an EGC wire within a raceway, but as Bennie states the cost of adding a fourth wire, Example:1phase 120/240v, 2 hots 1 nuetral 1 EGC, can add to the total cost of the job that could mean the differance between winning or losing a bid, and I am clear on the part of Art. 250.32 (B) (2) when no grounding electrode is present, then you would bond the nuetral at the outbuilding Sub-Panel to the can, Art 250.32 gives a clear answer to the grounding requirments for two or more buildings or structures, but say at the outbuilding I drive a ground rod and take an EGC to say cold water, would I still need to bond the nuetral to the EGC or would the added EGC violate any codes.
[ June 08, 2003, 10:20 AM: Message edited by: jro ]
- Location
- Massachusetts
Re: grounding a sub panel at a separate building
Hi jro, I am not sure what you are getting at.
EGC = equipment grounding conductor
GEC = grounding electrode conductor
If the buildings have a feeder between them the second building will always need a grounding electrode.
But you are not required to bring out the EGC from the first building to the second, if there are no conductive paths between buildings.
You could run PVC raceway 2 hots and the neutral
between the two buildings and be code compliant, but you would have to rebond the neutral to the can.
Bob
[ June 08, 2003, 03:37 PM: Message edited by: iwire ]
Hi jro, I am not sure what you are getting at.
EGC = equipment grounding conductor
GEC = grounding electrode conductor
If the buildings have a feeder between them the second building will always need a grounding electrode.
But you are not required to bring out the EGC from the first building to the second, if there are no conductive paths between buildings.
You could run PVC raceway 2 hots and the neutral
between the two buildings and be code compliant, but you would have to rebond the neutral to the can.
Bob
[ June 08, 2003, 03:37 PM: Message edited by: iwire ]
- Status