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Four ground rods

Merry Christmas
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david

Senior Member
Location
Pennsylvania
An electrician that I usually do inspections for did a service out side of the area that I travel in.

They ran service conductors from the service drop to a two gang meter can. From the two- gang, they ran service entrance into two separate premises separated by fire rated construction.

They then drove two ground rods ran the grounding electrode conductor from the service equipment in the first premise to the two ground rods, from the two ground rods they went to the second premise service equipment. The GEC was continuous from one premise to the other.

They failed the inspection. The inspector ask for four ground rods stating because the fire rated construction making the premises separate he wanted four ground rods.

They drove two more ground rods all six ft. apart. They called back the inspector, before he would pass the service with four rods; he wanted the GEC that was continuous, cut separating the ground rods into two for each of the premises.

They ask me what I thought.
1. I thought the two rods would be okay because of the two- gang meter socket.
2. I thought it was a code violation to separate the four rods because they were all six ft. apart.

What do you guys think?

[ July 29, 2003, 10:21 AM: Message edited by: david ]
 

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
Re: Four ground rods

The problem is, there is one drop which translates into one service, which means one GEC system. If we fed a multi gang sevice in a condo would he require individual sets for say a 50 unit building?

Roger
 

bbeste

Member
Location
Texas
Re: Four ground rods

David,
Here is my take on the subject, There is one service to the building going by the definition below that is straight out of the NEC. Also article 250.24 below very clearly states how many electrodes per service. Did the AHJ test the ohm's on the ground rod or give any reasoning for the need of 4.

Service. The conductors and equipment for delivering electric energy from the serving utility to the wiring system of the premises served.

250.24 Grounding Service-Supplied Alternating-Current Systems.
(A) System Grounding Connections. A premises wiring system supplied by a grounded ac service shall have a grounding electrode conductor connected to the grounded service conductor, at each service, in accordance with 250.24(A)(1) through (A)(5).
Barry
 

hornetd

Senior Member
Location
Maryland
Occupation
Journeyman Electrician, Retired
Re: Four ground rods

Just one more petty tin pot god AHJ that is making up rules as they go along. The installation he is requiring is a violation of 250.28.

250.58 Common Grounding Electrode.
Where an ac system is connected to a grounding electrode in or at a building as specified in 250.24 and 250.32, the same electrode shall be used to ground conductor enclosures and equipment in or on that building. Where separate services supply a building and are required to be connected to a grounding electrode, the same grounding electrode shall be used.
Two or more grounding electrodes that are effectively bonded together shall be considered as a single grounding electrode system in this sense.

Trying very hard not to get into rant mode.
--
Tom
 

rickg

Member
Location
Rhode Island
Re: Four ground rods

IMO the best way to ground this system would be to connect the 2 ground electrodes to the 2 gang meter base, end of story. The way the electrician origianally had the grounding was with the GEC in parallel with the neutrals, ie: the GEC ran from panel #1 to the electrode & continued to panel #2. In this case the GEC was carrying neutral current. You only need 1 ground electrode system per structure, not 1 per dwelling unit. The inspector was on the right path to make the electrician cut the GEC between the electrode systems, so not tom have a parallel neutral path.
RickG
 

pierre

Senior Member
Re: Four ground rods

The original post mentions 1 premise separated by a fire wall, which is 2 separate buildings. Article 100 states: Building- A structure that stands alone or that is cut off from adjoining structures by fire walls with all openings therein protected by approved fire doors.

This installation is 1 service drop with 2 separate buildings. Each separate building has to have it's own grounding system (250.50). They should be bonded according to 250.104(3).

Pierre
 

wocolt

Member
Location
Ohio
Re: Four ground rods

"This installation is 1 service drop with 2 separate buildings. Each separate building has to have it's own grounding system (250.50). They should be bonded according to 250.104(3).

Pierre "

How can you do that you only have one service. Would this not fall into the category of a multi-family dwelling.
If we use a double meter base, and the second apartment is away from the MB we will install a disconnect at the meter base run a feeder to the second apartment.
All grounding is done at the first panel which is behind the wall of the meter base and the disconnect for the second apartment.
In other words all service panels are bonded together at one point. In this case the disco, and the one service panel are bonded together to the one service panels grounding/neutral bus
from there we go to the water line and from there to the ground rods.
ONce the feeder is run to the second apartment it is of no concern as far as the gounding is concerned, just because it is a feeder and it tied to its own disconnect.
Now the inspector may have a problem with the SE cable running inside the building to the second panel panel, in order to keep it as a service panel, that is understandable, but the extra ground rods do NOT make sense.

WmColt

[ August 07, 2003, 11:10 AM: Message edited by: wocolt ]
 

hornetd

Senior Member
Location
Maryland
Occupation
Journeyman Electrician, Retired
Re: Four ground rods

Originally posted by rickg:
IMO the best way to ground this system would be to connect the 2 ground electrodes to the 2 gang meter base, end of story. The way the electrician originally had the grounding was with the GEC in parallel with the neutrals, i.e.: the GEC ran from panel #1 to the electrode & continued to panel #2. In this case the GEC was carrying neutral current. You only need 1 ground electrode system per structure, not 1 per dwelling unit. The inspector was on the right path to make the electrician cut the GEC between the electrode systems, so not to have a parallel neutral path.
RickG
Rick
I don't see how we can avoid having some parallel paths for neutral current. Even if we use a single grounding electrode system for this structure and run only one GEC that GEC will serve as a possible parallel neutral path. Since it is not in fact in parallel with the circuit conductors it is not likely to carry much current but if the neutral conductor serving either disconnect fails then it will carry that services neutral current. The only way to prevent that particular failure mode is to install ground fault protection of equipment.
--
Tom
 

brian john

Senior Member
Location
Leesburg, VA
Re: Four ground rods

HTD:

You say much current, what is MUCH?

How would Ground Fault Protection help in this case?
carry much current but if the neutral conductor serving either disconnect fails then it will carry that services neutral current. The only way to prevent that particular failure mode is to install ground fault protection of equipment.
 

david

Senior Member
Location
Pennsylvania
Re: Four ground rods

I thought this post had gone cold. Thank you all for your responses. There are at least three major power companies in this tri county area. One does not allow any GEC connections in the meter enclosure; I?m not sure which power co.?s area this installation was done in. The point is the GEC connection to the neutral may not have been allowed in the meter can.

I see this as one service drop. There is one neutral from the service drop to the double gang meter. The service entrance conductor?s bare neutral is a duel purpose conductor. It serves as the neutral and the bond between the meter enclosure and the service/ distribution panel for the apartment in the two family dwelling. Since the Code calls for all non-current caring metal parts of service equipment to be bonded together and there is a two gang meter can both service/ distribution panels in the two separate dwellings must be bonded together through the meter can enclosure.

The bond through the meter enclosure ties both separate metal water pipe grounding electrodes together in the two separate dwellings Since it is impossible to separate the grounding electrode systems between the two dwellings I would think that if you drove four ground rods in close proximity to each other you would be required to bond them together to form a single grounding electrode at that point.

This is just my thinking and since this brought up so many different points of view I may be missing something

Thank you all, David

[ August 08, 2003, 11:41 AM: Message edited by: david ]
 

hornetd

Senior Member
Location
Maryland
Occupation
Journeyman Electrician, Retired
Re: Four ground rods

Originally posted by brian john:
HTD:

You say much current, what is MUCH?

How would Ground Fault Protection help in this case?
carry much current but if the neutral conductor serving either disconnect fails then it will carry that services neutral current. The only way to prevent that particular failure mode is to install ground fault protection of equipment.
Ground Fault Protection of Equipment will open the service disconnecting means if the neutral fails as long as the neutral current exceeds the trip setting of the system.
--
Tom
 

pierre

Senior Member
Re: Four ground rods

Most 2 family dwellings do not have a firewall separating them, so they would be treated differently. It was mentioned in the opening post that there is a fire wall. This makes it 2 separate buildings and you have 2 separate services being fed from the 2 gang meter. Each disconnect is a separate service, therefore the neutral, GEC, EGC and the MBJ are all connected (bonded) at the 'first point of disconnect' of each disconnect in this case. Most utilities will not allow this connection in the meter equipment.
For informational purposes, 230.66 the last sentence says - "Individual meter socket enclosures shall not be considered service equipment.

Pierre
 

david

Senior Member
Location
Pennsylvania
Re: Four ground rods

?For informational purposes, 230.66 the last sentence says - "Individual meter socket enclosures shall not be considered service equipment.?

If you don?t fill this is one service, ask yourself if one dwelling decided to up grade the service how would the owner do it without changing the service conductors to the meter enclosure.

Another way to make this point would be ask your self if a tree comes down and rips the service wires off the dwelling that feeds the meter enclosure, who is going to pay the repair? Most likely the owners of both the dwellings would split the cost.


250.92 Services.
(A) Bonding of Services. The non?current-carrying metal parts of equipment indicated in 250.92(A)(1), (2), and (3) shall be effectively bonded together.
(2) All service enclosures containing service conductors, including meter fittings, boxes, or the like, interposed in the service raceway or armor.


Even if meter enclosures are not considered ?service equipment? they still are required to be bonded.

There is only one service on this premises, from the meter enclosure there are only service entrance conductors involved in this installation. There are no feeders just service entrances.

There are several ways this installation could have been done,
The installer could have installed separate services feeding each of the buildings if the power company would have agreed to provide a service drop to each of two separate service entrances.

Under the exceptions to the general rule the installer could have ran two service conductors to two separate meter enclosures at two separate locations. In this case the two separate service conductors could have been feed from one service drop.

This is one service drop feeding one set of service conductors to a two- gang meter enclosure. This makes this installation one service. There are two service disconnects in separate buildings(only because of the fire rated construction). The fire rated construction does not change this building definition. Two family dwelling according to the International building code, and a multiple family dwelling according to the definition in the NEC. The service disconnect is disconnecting the buildings from the service serving the premise.

[ August 09, 2003, 06:37 AM: Message edited by: david ]
 

brian john

Senior Member
Location
Leesburg, VA
Re: Four ground rods

HTD:

If the neutral fails (opens) downstream from the main switch the GFP will see balanced current between the phases (zero sequence) or no ground current, ground return method. The loads will burn up/ fault/short assuming the impedances across the loads are not identical. Then the GFP protected switch will open.

If you lose the neutral at the service upstream of the GFP the GEC will carry the current. Depending where the open is.

If the neutral shorts to ground the GFP may open depending on the system current and setting of the ground fault relay.

GFP’s are not designed to protect against open neutrals.
 

hornetd

Senior Member
Location
Maryland
Occupation
Journeyman Electrician, Retired
Re: Four ground rods

Originally posted by brian john:
HTD:

If the neutral fails (opens) downstream from the main switch the GFP will see balanced current between the phases (zero sequence) or no ground current, ground return method. The loads will burn up/ fault/short assuming the impedances across the loads are not identical. Then the GFP protected switch will open.

If you lose the neutral at the service upstream of the GFP the GEC will carry the current. Depending where the open is.

If the neutral shorts to ground the GFP may open depending on the system current and setting of the ground fault relay.

GFP’s are not designed to protect against open neutrals.
Brian
I never meant to imply that GFP was designed to protect against open neutrals. But I can't see any likelihood of a GFP relay not sensing an imbalance resulting from the neutral going open. As you pointed out the GEC would carry the imbalance current and one of two things would be true. That current would reach the GEC through the current sensing coil on the main bonding jumper and if that imbalance current exceeds the set point of the detector circuit the GFP opens, or alternatively the absence of the imbalance current induces a current flow in the sensing coil around the service conductors and if that imbalance current exceeds the set point of the detecting circuit the service opens. The ground fault protection circuit is not installed to protect against open service neutral conductors but that is a side effect of their installation if the imbalance current of the circuit exceeds the set point of the GFP equipment and the neutral is open.

I installed a GFP detection circuit at a dairy farm that energizes a local alarm instead of powering a shunt trip or protective relay. The reason for the installation was to warn the rancher of any substantial current that was returning to the utilities Multi Grounded Neutral via the farms grounding electrode system. The detector circuit is set very low at around five amperes. Any significant imbalance in the service conductors current will sound the alarm whether it is from on farm leakage or from current originating elsewhere. Obviously if that detector were operating a shunt trip or protective relay then an open neutral would cause the protective device to open.
--
Tom
 

brian john

Senior Member
Location
Leesburg, VA
Re: Four ground rods

htd:

With an open neutral there will be no imbalance. All current will flow on the phase conductors, nothing to ground. Flow is from the transformer to the loads on the phase conductors, through the loads and back to the transformer. Till such time as the loads fail (and maybe fault to ground) there is no connection to ground for the current to flow. The GEC will not see this current, unless the open is upstream of the Ground Return CT.
 

brian john

Senior Member
Location
Leesburg, VA
Re: Four ground rods

htd:

One more point; in your installation you're using the ground return metod for sensing neutral ground current to trigger an alarm, and protect cow's.

The Ground return strap sensing will not work as effectivly for GFP in an installation where you ground at the service per NEC and the utility grounds at their transformer. You have a parallel
path for neutral/ground current. While this current may be low during normal operation, the multiple paths can effect the operation of the GFP relay during ground faults.

The ground return method works better where customer owned transformers have the sensing CT located at the neutral ground bond.
 

hornetd

Senior Member
Location
Maryland
Occupation
Journeyman Electrician, Retired
Re: Four ground rods

Originally posted by brian john:
htd:

With an open neutral there will be no imbalance. All current will flow on the phase conductors, nothing to ground. Flow is from the transformer to the loads on the phase conductors, through the loads and back to the transformer. Till such time as the loads fail (and maybe fault to ground) there is no connection to ground for the current to flow. The GEC will not see this current, unless the open is upstream of the Ground Return CT.
I must be being really unclear, dense, or obtuse. The open neutral I'm talking about in the context of common grounding of two different services is an open in the grounded conductor of the service entrance, service drop, or service lateral all of which are upstream of the GFP sensing. With either method of ground fault protection the neutral current would flow via the common grounding electrode conductor. If that current were greater than the set point of the GFP it would trip and deenergize the service with the open neutral.
--
Tom
 

brian john

Senior Member
Location
Leesburg, VA
Re: Four ground rods

Tom:

Please I'm only trying to understand how this would work. The Ground return sensing would not be recommended for two services from a common service lateral (In my expierence). The multiple sources of ground could cause operational errors during normal operation, and de-sensitize the system under fault condition.

In the Zero Sequence system an open neutral would not be sensed, at least this is the way I see it.
 
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