grounding a sub panel at a separate building

[dia480]

do I carry the grounding/bonding electrode wire to the new subpanel in a seperate outbuilding or do I have to drive a new ground rod and then re-bond the whole thing like a new service?

[ June 06, 2003, 11:31 PM: Message edited by: dia480 ]

[don_resqcapt19]

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]

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?

[jro]

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.

[iwire]

Originally posted by jro:
at the sub-panel you would not bond the grounded conductor. 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.

[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]

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

[don_resqcapt19]

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

[tom baker]

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.

[iwire]

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

[don_resqcapt19]

Bob,
Say the buildings are 300' feet apart, by bonding at the second building you take 600' of conductor out of the circuitThe 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

[iwire]

Thanks Don, I should have realized that myself when I posted it. :o

[bennie]

The down side is the cost of the fourth wire when three will do the same thing better with less impedance.

Do you think some code panel members worked for the wire industry?

[tom baker]

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]

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]

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? :confused:

[jxofaltrds]

Ras YES

This is called a multiwire branch circuit.

Mike P.

[gwz2]

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 1Ø source) and an grounded conductor is NOT a multiwire circuit.

[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 ]

[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 ]

[jro]

Well Bob what I'm getting at is this, Example: Office building and shop area, I feed the shop area out of the main service that is located in the office building using buried ridgid conduit, 1 phase, 2 hots 1 nuetral, are you saying the shop would need a separate grounding electrode, or is the conduit now part of the grounding electrode conductor system since all metal parts pertainig to the electrical system are bonded at the main service, grounded conductor isolated at the shop panel. :)

[don_resqcapt19]

jro,
If the shop is a second building, it requires a grounding electrode system. In your case, with the metallic conduit, you cannot rebond the grounded conductor at the shop. If you would use nonmetallic conduit and there are no other metallic paths, then you would install a grouding electrode system and rebond the grounded conductor at the shop. All second buildings that are served by a feeder require a grounding electrode system. The installation of an EGC from the first building to the second building doesn't change this requirement.
Don
Don

[iwire]

jro, here are the code articles that deal with this.

2002 NEC
250.32(A)
250.32(B)(1)
250.32(B)(2)

Bob

[michael nye]

Stallcups code changes 99 clearly shows that if it is ran in pvc then no ground need be ran with the other conductors and a ground rod installed for the path at the seperate bldg. How ever if ran in grc or other approved metalic raceway a ground must go in the same conduit and have a ground rod and remain sep from the neutral in seperate bldg. I have to apologize as my copy of Stallcups book is in storage as our office is in mid move, so I could not quote the chapter or other info to back my statement.

[don_resqcapt19]

Michael,
There is no code requirement to install an equipment grounding conductor within the metallic conduit to a second building. The conduit is permitted to be the equipment grounding conductor.
Don

[michael nye]

Don then I have a question, I am dealing with a contractor who wired out of a standup service 800amp and dist 3 subs two 150 and a 200 and did not pull a ground, the systems are in 2 in emt this is not a ground it gets grounded correct but the path is not the raceway,due to the multiple mechanical connections that would be required to maintain the ground.

[iwire]

2002 NEC

250.118 Types of Equipment Grounding Conductors.
The equipment grounding conductor run with or enclosing the circuit conductors shall be one or more or a combination of the following:

250.118(4) Electrical metallic tubing.

[michael nye]

iwire, OK so the conduit is grounded but its not a pathway correct? It would still require a grounding conductor. In this system there is a neutral and the 3 hot conductors 208/110, 110 to ground or 208 between any two hots. Anyhow it still would need a ground per the NEC.

PS these are questions not statements this is what I've always understood to be the way.


Thanks

[don_resqcapt19]

michael,
The conduit itself along with its couplings and connectors is the equipment grounding conductor. There is no code requirement to installan EGC within the metallic conduit. See 250.118. All of the items listed in that section can be used as equipment grounding conductors. The conduit is the fault return path.
Don

[jro]

Don and Iwire are correct and that is due to the fact that all main grounding is made at the first point of disconnect in this case the 800amp service, Mike as long the main service is grounded properly then the installation meets code, the emt becomes part of the grounding system by the bonding of the metal parts at your main service.

[michael nye]

OK, I've just been slapped down like a res headed stepchild, I have been taught and have always ran the ground, I did not realize the conduit was a egc. Thanks for the schooling.

[iwire]

Originally posted by michael nye:
been slapped down like a red headed stepchild, It happens to all of us, do not worry about it. :)

99% of the time the job specs ask for a copper ground conductor pulled in with the feeds.

The code is just the minimums, I have installed some die cast couplings and connectors that I truly doubted would provide an adequate ground path, but they are UL listed for it. :roll:

[tom baker]

It may not be best to rely on the raceway as an equipment ground. I always pull an insulated equpment ground. Most of my installations are in wet, or damp concrete buildings. I have seen RMC rot away in concrete walls in parking garages.

[pierre]

I again agree with Tom, and note he said 'insulated' ground. I believe the ground should be insulated, to protect the other conductors in the raceway when a fault occurs. When the fault occurs, a tremendous amount of heat can build up very quickly and if uninsulated, can more easily damage the other conductors in the raceway. Also he mentioned the raceway corroding and becoming ineffective as an EGC, by pulling a EGC, we are protecting the next electrician as well as everything else. HEY, LETS ALL THINK ABOUT PROTECTING 'US GUYS IN THE TRADE'.
Good train of thought Tom!!!

Pierre

[pierre]

P.S.

I read over the post I just wrote, and I did not mean to sound like only Tom is thinking about the 'guys in the trade', I know the people in these forums are here because they do care ... just reiterating a good thought!!

Pierre

[iwire]

Originally posted by tom baker:
It may not be best to rely on the raceway as an equipment ground. ------- I have seen RMC rot away in concrete walls in parking garages. Tom I agree with you, I was just trying to show it was code compliant.