separate outbuildings

Status
Not open for further replies.
T

TWsystems

Member
Location
California
If the Main Electrical Service and grounding electrode is located on an outbuilding at a farm - and all the other 5 buildings, including the home, are fed with existing 3 wire feeders to "sub panels" that have separate ground rods individually at those buildings - would you still separate the neutrals and grounds at the house "sub panel" - even though the grounding electrode system for the house is different from the main service?

Thanks
:?
 
TWsystems said:
If the Main Electrical Service and grounding electrode is located on an outbuilding at a farm - and all the other 5 buildings, including the home, are fed with existing 3 wire feeders to "sub panels" that have separate ground rods individually at those buildings - would you still separate the neutrals and grounds at the house "sub panel" - even though the grounding electrode system for the house is different from the main service?

Thanks
:?
Click to expand...

It is imperative to bond the neutral at each remote building sub panel in your case. Otherwise you have no fault return path to open OCPDs. Also, you must have a GES at each building.
You probable know that this type of installation would require a separate EGC for each feeder and an unbounded neutral since the 2008 edition and later of the NEC.
 
texie said:
It is imperative to bond the neutral at each remote building sub panel in your case. Otherwise you have no fault return path to open OCPDs. Also, you must have a GES at each building.
You probable know that this type of installation would require a separate EGC for each feeder and an unbounded neutral since the 2008 edition and later of the NEC.
Click to expand...

Yes, thanks for reply, It seemed to me that the neutral and grounds at each sub panel should be bonded together to the local GES at each building as if it was a "main" service even though they are technically sub panels ... because there are no EGC with each feeder going back to main (and can't be run) and each building has its own GES. Even though it bonds the neutral to different GES at each building - it seems the only safe way in this old existing application.
 
As Texie mentioned this was permitted by the NEC prior to the 2008. The one big requirement was that there no other metallic paths between the structures.
 
infinity said:
As Texie mentioned this was permitted by the NEC prior to the 2008. The one big requirement was that there no other metallic paths between the structures.
Click to expand...

Thanks Rob - that was my understanding as well - but this post below confused me a little - I read it as the grounds and neutrals still should be separated - there are no other metallic paths between structures, although the water well is bonded from the Main Service GES and the Water Heater is bonded from the House GES - it is in plastic pipe but what about the water itself? I feel like I should feed the sub panels with GFI breakers just to be double safe but not sure that would even help.

Separate Buildings and Structures (4-26-2K)
By Mike Holt, for Power Quality Magazine​
Metal parts of the electrical system in separate buildings or structures supplied by a feeder from another building must be grounded to the earth to limit imposed voltage. Also, the metal parts of the electrical system at separate building and structures must be properly bonded to a low impedance path that will remove dangerous voltage on the metal parts [250-2 and 250-32(a)].
Grounding Limits Imposed Voltage

Metal parts of the electrical system are grounded to the earth to limit voltage on the metal parts from lightning [250-2(a)]. Grounding of metal parts of the electrical system at a separate buildings or structures supplied by a feeder is accomplished by grounding the building disconnecting means [225-31] with a grounding conductor [250-62] to the separate building or structure grounding electrode system [250-32(a) and (f)], Figure 1 Note: Graphics not provided on the internet.
DANGER - Failure to properly ground the metal parts of the electrical system to the earth can result in electric shock, fires and the destruction of expensive electronic equipment from lightning or high voltage line surges.
Author?s Comment:A grounding electrode at separate buildings or structures is not required where only one branch circuit (with an equipment bonding conductor) supplies the building or structure [250-32(a) Exception] Figure 2.
Bonding Removes Dangerous Voltage
To protect against electric shock from a phase-to-ground fault, dangerous voltage on metal parts of the electrical system must be removed in less than 1/60th of a second by opening the circuit overcurrent protection device. To accomplish this, the impedance of the fault current path must allow the phase-to-ground fault current to rise to a value of at least 5 times and preferably 10 times the rating of the overcurrent protection device, Figure 3
In order for the circuit overcurrent device to open and prevent dangerous voltage from remaining on metal parts of electrical equipment, the equipment at the separate building or structure must be properly bonded. National Electrical Code allows two methods of accomplishing this [250-32(b)]:
250-32(b)(1) Feeder Equipment Grounding Conductor. An equipment grounding conductor (bonding wire) [250-118] installed with the feeder conductors to the separate building or structure can be use to provide the low impedance path to clear a phase-to-ground fault. To prevent dangerous neutral current from flowing on the metal parts of the electrical system, the grounded (neutral) conductor at the separate building or structure must not be bonded to either the equipment grounding conductor or to the grounding electrode system, Figure 4
Author?s Comment: The feeder equipment grounding conductor (bond wire) to the remote building or structure must ultimately terminate to the grounded (neutral) conductor at the service equipment or source of separately derived system, Figure 4
250-32(b)(2) Feeder Grounded (neutral) Conductor. Where a feeder equipment grounding conductor is not run to the separate building or structure, the feeder grounded (neutral) conductor can be use to provide the low impedance path to clear phase-to-ground faults.
DANGER ? The use of the grounded (neutral) conductor for equipment bonding is a dangerous practice and should not be done.
Author?s Comment:Interior metal piping system must also be bonded to a low impedance path in accordance with Section 250-2(c) and 250-104(a)(3), Figure 5.
In Summary:

  1. A grounding electrode must be available at all separate buildings or structures supplied with a feeder. A grounding electrode is not required at separate buildings or structures supplied with one branch circuit that has an equipment grounding conductor.
  2. The grounding electrode system at the remote building or structure must be bonded to the separate building or structure disconnect.
  3. An equipment grounding conductor (bond wire) run with the feeder supply conductors to the separate building or structure must terminate to the separate building or structure disconnect. No neutral-to-ground connection is permitted.
 
TWsystems said:
Thanks Rob - that was my understanding as well - but this post below confused me a little - I read it as the grounds and neutrals still should be separated - there are no other metallic paths between structures, although the water well is bonded from the Main Service GES and the Water Heater is bonded from the House GES - it is in plastic pipe but what about the water itself? I feel like I should feed the sub panels with GFI breakers just to be double safe but not sure that would even help.

1. An equipment grounding conductor (bond wire)IF IT IS run with the feeder supply conductors to the separate building or structure must terminate to the separate building or structure disconnect. No neutral-to-ground connection is permitted.
Click to expand...
Words and emphasis added by me. You don't have a separate EGC run with your feeders; if it is true that you don't have any metal paths between buildings or structures you don't need one.

You already meet conditions 1 and 2 in the summary by having a bonded neutral and ground rods at each structure.

The set up you have sounds perfectly legit. Until '08 I would have done it the same way. You don't need any GFCI's.
 
Metal pipe between buildings.

Metal pipe between buildings.

How would it change things if there were a copper water pipe between buildings and said pipe was used as a secondary GES at the service entrance and bonded to the neutral there?

I would think that you would have to pull a grounding conductor along with the 2 phase and 1 netural conductor to the sub panel and not bond the nuetral and the ground together at the sub panel because if not, the pipe could carry objectionable current back to the service entrance. Am I close on this?

Could you use the pipe as a secondary GES at the sub panel building as well or would there even be a need to have a GES at the sub panel building if you pull the grounding conductor with your other wires?

Thanks, Pbbb
 
pbbbfischer said:
How would it change things if there were a copper water pipe between buildings and said pipe was used as a secondary GES at the service entrance and bonded to the neutral there?

I would think that you would have to pull a grounding conductor along with the 2 phase and 1 netural conductor to the sub panel and not bond the nuetral and the ground together at the sub panel because if not, the pipe could carry objectionable current back to the service entrance. Am I close on this?

Could you use the pipe as a secondary GES at the sub panel building as well or would there even be a need to have a GES at the sub panel building if you pull the grounding conductor with your other wires?

Thanks, Pbbb
Click to expand...

In the nec 2005 and previous version you could run a feeder with no equipment grounding conductor however if there were metal pathways back to the original building then you had to use an equipment grounding conductor.

The 2008 and on requires a n equipment grounding conductor be run with the feeder no matter what the situation is between between buildings..

Look at 250.32(B)
 
Yes I did this previous to 2008

Yes I did this previous to 2008

This was work I had done previous to 2008. After understanding more, years later I wondered if I should update things.

Is the copper water pipe that is bonded to the neutral at the SE going to be a problem if at the other end is bonded to the neutral at the sub pnl in the wellhouse building. That sub pnl system also has an 8' ground rod.

My thoughts are that it is ok at the SE but at the sub pnl it should not because it could be a path for objectional current.

Pbbb
 
pbbbfischer said:
This was work I had done previous to 2008. After understanding more, years later I wondered if I should update things.

Is the copper water pipe that is bonded to the neutral at the SE going to be a problem if at the other end is bonded to the neutral at the sub pnl in the wellhouse building. That sub pnl system also has an 8' ground rod.

My thoughts are that it is ok at the SE but at the sub pnl it should not because it could be a path for objectional current.

Pbbb
Click to expand...
:thumbsup:
 
pbbbfischer said:
This was work I had done previous to 2008. After understanding more, years later I wondered if I should update things.

Is the copper water pipe that is bonded to the neutral at the SE going to be a problem if at the other end is bonded to the neutral at the sub pnl in the wellhouse building. That sub pnl system also has an 8' ground rod.

My thoughts are that it is ok at the SE but at the sub pnl it should not because it could be a path for objectional current.

Pbbb
Click to expand...

pbbbfischer said:
Would I then remove the bonding screw from the sub pnl because the pipe is a grounded conductor back the SE and treat it like a 4th wire to the sub?
Click to expand...

I would rather see "objectionable" current on the water pipe then see the bonding screw removed from a subpanel that is not supplied with a EGC. True it is not code compliant, but it is in many ways no different then two homes supplied by two separate services with a metal water pipe between them.

If that metal piping ever gets an non metallic section installed in it for any reason - you lose the EGC to the second structure, if you are depending on it for equipment grounding purposes.
 
kwired said:
I would rather see "objectionable" current on the water pipe then see the bonding screw removed from a subpanel that is not supplied with a EGC. True it is not code compliant, but it is in many ways no different then two homes supplied by two separate services with a metal water pipe between them.

If that metal piping ever gets an non metallic section installed in it for any reason - you lose the EGC to the second structure, if you are depending on it for equipment grounding purposes.
Click to expand...

So what you are saying is that if I ever lose the neutral between the 2 buildings you would rather see the return path be the copper pipe than the sub pnl circuit to just be interrupted?

Trying to think it all through in my head.

Pbbb
 
pbbbfischer said:
So what you are saying is that if I ever lose the neutral between the 2 buildings you would rather see the return path be the copper pipe than the sub pnl circuit to just be interrupted?

Trying to think it all through in my head.

Pbbb
Click to expand...
Yes. It is same thing that happens all the time with services and buildings next to one another, so it will not be anything we never see.

Sure it is somewhat undesirable to have that happen, but IMO it is less desirable to not have an EGC to the second building. You suggested earlier to not put in the bonding jumper at the second building and use the water pipe as an EGC. That would mean no EGC at all if that water pipe ever gets a change made and it is no longer electrically continuous. Bonding the neutral in that situation though may no longer code compliant, IMO is still the lesser of two evils if the separate EGC is not going to be ran. You can't count on a plumber to assure electrical continuity of that pipe should they ever work on it, but an electrician that has to do work on the feeder will have a much better chance of assuring a good EGC.
 
Status
Not open for further replies.
Top