ground rods at a townhouse

[earlydean]

A four family townhouse, with 3-hour rated partitions between units has a single location with all the electric metering grouped at one spot. The meter bank is fed from a single service lateral from the transformer. There are no disconnects or overcurrent devices at this location. There are four service laterals leaving the meter bank, which continue outside the building and enter each dwelling along one back wall. Each dwelling has a main disconnect panel in each cellar containing a two-pole 100-amp circuit breaker. Each main panel is bonded to each dwelling unit?s water main within five feet of where the copper water pipe enters each dwelling.
Where are ground rods required? Should there be 8 ground rods outside, 2 at each panel location, bonded at the same location as the water pipe? Or, may we install only 2 ground rods at the meters?
Are we allowed to have 4 services in this building? Or, should there be one service, with four meters and disconnects grouped together?

 

[tom baker]

Re: ground rods at a townhouse

We need to look at two items. Where the grounding electrode conductor (GEC)can terminate, and the rules for when a service requires a connection to the GEC and neutral.
250.24(A) tells us each service shall have a GEC connected to the neutral, from the load end of the service drop to and including the main bonding jumper
You have 4 services. You could make the connection in the metering equipment if the AHJ and POCO would allow (we can't in washington state, as its not considered accessible in the meter enclosure.
250.64(D) discusses grounding electrode conductor taps which may apply.

You could run a GEC from each service and connect them all to a common GE or rods, which is required by art 250.

If the building is not started the simplest solution would be to use the reiforcing steel in the footings as GE system common to all services, per 250.52(A)(3), and forget the ground rods, unless it is a time and materials job.

You should check with your AHJ....

 

[earlydean]

Re: ground rods at a townhouse

I'm in the middle of an argument between the contractor and the inspector. Townhouses are considered separate buildings by the building code, and therefore separate services are allowed by Section 230.2. Section 250.53(D)(2) requires supplemental electrodes to the water-pipe ground. The contractor chose to use ground rods. He located them at the metering location. 250.53(D)(2) allows the supplemental electrode to be bonded to the grounded service-entrance conductor, which the contractor says is satisfied by bonding at the meters. I advised that ground rods need to be installed at each of the four service locations, because each service needs to be bonded at one location. I feel it is wrong to allow the grounded conductors (neutrals) to perform double duty by carrying the unbalanced load and to serve to bond the supplemental grounds to the grounding electrode. Else, the utility ground rods installed at the transformer would be sufficient to perform the supplemental electrode function.
Am I wrong in this rational?

 

[don_resqcapt19]

Re: ground rods at a townhouse

Earl,
In my opinion the ground rods at the meter meet the requirement of 250.53(D)(2).
Don

 

[donnie]

Re: ground rods at a townhouse

Just a thought , but if one transformer feeds 4 meters or even 6 meters , with one service lateral, it is still only ONE service, not 4 or 6 services , (the number of services you have is not based on metering).
Hope this helps.

 

[earlydean]

Re: ground rods at a townhouse

But it serves 4 main disconnect panels in four separate basements. Does that make it four services?

 

[tom baker]

Re: ground rods at a townhouse

Don yes you are correct, but in my state we can not make a connection to the ground rods in the metering equipment, there is an exception if the utility requires ground rods connected for a meter loop.

 

[donnie]

Re: ground rods at a townhouse

earlydean,to answer your question,in your case having 4 meters serving four main disconnect panels, would still only be considered one service, if not you would be in violation of Art. 230.2.

 

[earlydean]

Re: ground rods at a townhouse

donnie,
doesn't 230.71(A) require that all service disconnects to be grouped together?
earl

 

[donnie]

Re: ground rods at a townhouse

earl, 230.72 ,Yes ,Service Disconnects must be grouped together, however the # of meters you have doesn't make them separate services, but the two to six disconnects does make it two to six disconnecting means for that one Service or the service lateral.
As an inspector, my interpretation of your case is that if you have 4 meters supplying 4 units, then the 4 meters must have the disconnects either located in the meter bank (as some are made), or the disconnects must be grouped together nearby.

 

[earlydean]

Re: ground rods at a townhouse

Donnie,
You would say, then, that the case I outlined at the start of this thread should be red-tagged because the disconnects are not grouped together?

Earl

 

[eprice]

Re: ground rods at a townhouse

Assuming that the 3-hour partitions meet the definition of a fire wall or area separation as required by the applicable building code, then by the definition of a "Building" in article 100, the situation described here would be four buildings. Wouldn't 230.2 allow four services, one for each building?

230.72 requires the two to six disconnects comprising a single service to be grouped, but I am not aware of a code requirement that several services on several buildings must be grouped, just because the buildings happen to have zero space between them. Maybe I am looking at this wrong?

However, if a single service lateral to the meter location then supplies four sets of service entrance conductors, I think it would be a violation of 230.40

[ September 23, 2003, 12:55 PM: Message edited by: eprice ]

 

[don_resqcapt19]

Re: ground rods at a townhouse

eprice,
Exception #1 to 230.40 permits each occupancy to have its own set of service entrance conductors. Exception #2 permits each set of service entrance conductors to supply 1 to 6 service disconnects.
Don

 

[eprice]

Re: ground rods at a townhouse

Don,

You're probably right. I glossed over exception 1 as requiring services to be of diferent characteristics, but I can see how it could be read to allow one service to each occupancy even though each such service has the same characteristics.

 

[earlydean]

Re: ground rods at a townhouse

I guess I'll never get it straight how identical services to identical townhouses are different:

230.2(D) Different Characteristics. Additional services shall be permitted for different voltages, frequencies, or phases, or for different uses, such as for different rate schedules.

I always thought "different uses" were referring to the duplicate metering allowed for buildings with both residential and commercial tenants.

Earl

[ September 23, 2003, 03:40 PM: Message edited by: earlydean ]

 

[pierre]

Re: ground rods at a townhouse

I have been following this and was going to stay out of the discussion, but...
Dean
I can see how this is confusing, so I am going to put my two cents in.
Some terms to be defined are in order, so we are all on the same page. I am going strictly by NEC, no local amendments.

Building - A structure that stands alone or that is cut off from adjoining structures by FIRE WALLS with all openings thererin protected by approved fire doors. (NEC)

230.66 Individual meter socket enclosures shall not be considered service equipment. (NEC)

230.2 permits 1 service per building - by definition, there are 4 buildings in this example. It seems the water company thought the same.
Therefore the four buildings are permitted to each have it's own service, and grouping of service disconnects is not required.
In commercial applications, you will see this time and time again. In dwelling units it is not as prevalent, therefore not understood as easily.

250.50 At each dwelling , you will be required to bond all of the available electrodes as specified in (A)(1) - (A)(6).
If and in this case, the water pipe is the GE, it is to be supplemented with another electrode which is most often a ground rod(s).

Here is where we have a situation that I do not see covered in the NEC. Multiple services at a structure that is separated by firewalls, making it 4 buildings.

MY INTERPRETATION, again my interpretation is that the ground rod(s) will have to be located by each service, therefore 4-8 rods will be required. 4 -8 because if you can prove 25 ohms or less to ground at any one of those locations, only one rod will be necessary at that location.

Pierre

 

[don_resqcapt19]

Re: ground rods at a townhouse

Earl,
I read the exception to 230.40 as saying each occupancy is permitted to have one service for each type of service that the occupancy requires. In this case each occupancy only requires one type of service, so each occupancy is permitted to have one set of service entrance conductors fed by a common service drop or lateral.
Don

 

[earlydean]

Re: ground rods at a townhouse

Pierre,
I interpreted it the same as you. that is where the fur started flying. Thank you for agreeing with me, right or wrong, it helps my self esteem.

Don, From what I read on exception 1 of 230.40, a building with more than one occupancy is allowed to have one set of service conductors for each service of DIFFERENT CHARACTERISTICS, not for each type of service. Different characteristics are as defined in 230.2(D), namely different voltages, frequencies, etc.
I agree that each occupancy may have its own service, but that each service requires a supplemental ground of its very own.
Am I right? or going astray?

Earl

 

[don_resqcapt19]

Re: ground rods at a townhouse

Earl,
How can different voltages or frequencies be supplied from a common service drop or lateral???
Don

 

[eprice]

Re: ground rods at a townhouse

The more I read exception 1 to 230.40, the more I have to agree with Don's interpretation. It says (and I'm paraphrasing so that some of the words don't get into the way), ...one set of conductors of each characteristic to each occupancy...

If there were two types of services, you could run two sets of conductors to each occupancy. If there were three types of services, you could run three sets of conductors to each occupancy. In the case being discussed, there is only one type of service, so you can only run one set of conductors to each occupancy, but that still equals four sets.