The scenario is a building with a 1000 Amp stand up U.G.utility pull section, main and distribution. The utility terminates the service lateral in the bottom of the pull section. A new 200 amp. meter is installed next to and fed from the utility pull section via rigid conduit. If the existing neutral is already connected to an existing grounding electrode system. Where does the NEC say you have to drive another rod at the new meter? We always do but after carefully reading 250.24(A)and 250.24(1)2002 NEC it seems like it is not really required. Any opinions besides more is better?
250.24 ...shall have a grounding electrode conductor connected,...at each service,... If the 200 amp service is the only service then no additional grounding electrode connection would be needed. However, you are starting with a 1,000 service and then there is the 200 amp service. You could stay with a single rod at the 1,000 but the GEC would have to be extended from there to the 200 amp. Does that help ?
Read 250-24 (A)& (1) and then read definition of "service". "The conductors and equipment for delivering electric energy from the serving utility to the wiring system of the premises served". That seems to read that all of the busing and conductors beyond the landing terminals of the utility are the "service". I can't find where it says a new meter and disconnect is a new separate/independent service. There is a photo in the 2002 handbook on page 185 that shows one electrode conductor in a common gutter and the service disconnects are just bonded. Now what do you think? Thanks for the input!
It could be one service or two. It would be one service if the two service disconnects were grouped. Then the single grounding would comply. (Mental picture of a multi pack with meters and disconnects.) It would be two services if the two service disconnects were seperated by a distance, (judged by the AHJ) and then would need two groundng electrodes or bonding to a common grounding electrode system. (Mental picture of a fire pump service tapped from a common point with the building service.) Are my mental pictures in focus ?
Driving a rod in an existing developed property can sometimes be a crap shoot. If you hit a undetected sub-structure, the cost to repair it can ruin a guys day/week/month. That is the reason for looking into this code section. To me it reads as one service and bonding the new meter/disconnect would be legal. If that is the case, does the inspecter have the right to demand a new rod? Also I don't see anything in 250.24 about grouping or distance. I only see that in 250.28 bonding. If it is a factor, what is the definition of grouping? Same building, same room, 2 ft, 20ft?? Thanks for the input!
I am a little corn-fused by the description, but let me take a shot at this anyway...
Isn't the Grounded Conductor bonded to the Service Equipment + Grounding Electrode System, in either the UGPS or the Service Section already?
Seems like it should be, and the Grounding Electrode Conductor would be sized per 250.66, according to the Service Feeders' size.
You would need to effectively Bond the new Service to the UGPS, via a Bonding Jumper or suitable Bonding Fitings), but I do not think you need to create an additional GES, or add supplimentary Electrodes (Ground Rods) to an existing GES: - *** unless there is nothing to suppliment an existing Cold Water Electrode ***, then I could see a need to add an additional supplimental electrode.
What's funny (wierd funny, not "haa-haa" funny) is there will be unbalanced current flowing on the GRC between the new Meter Socket / Service Section, and the existing Service Equipment; due to the solid bonding of the Grounded Conductor to the enclosure of the new Service.
Let me know if this is / isn't applicable to your question.
Scott " 35 " Thompson Just Say NO To Green Eggs And Ham!
It looks like the general consensus is that the neutral is already grounded in the 1000 amp existing panel. This should eliminate the need to reground the neutral in each new disconnect added. Which leads to bonding issues. As for the unbalanced current you mentioned Scott35(thanks), one thing I noticed, if you look at the drawing (Exhibit 250.12 on page 185 of the 2002 handbook),notice the conduit/nipple is back grounded by the bonding jumper? if everything is bonded I can't figure out what unbalanced current you are talking about?
I agree with Mr. Badger -A Service only needs a single Grounding Electrode (assume it meets 250.50) no matter how many Service disconnects are on it. This should not be confused with the the need to install a Grounding Electrode at a second building on a property when it is fed by a feeder from the first building.