I would like to hear your opinions on what the minimum size of grounding electrode conductor would be for this installation, if using the water pipe as an electrode.

This panel is rated for 400 amps. The two breakers towards the bottom are 150 amps and each feed a subpanel, the two breakers at the top are 40 amps and each feed an A/C unit.




Please try to justify your answer with a code reference.

Thanks to Joe Tedesco and Dave Nix. Please visit their sites at www.joetedesco.com and also www.grafixbynix.com

Ryan

This is a 400 amp combination service entrance device, Square D CU12L400B to be exact. The size of the grounding electrode is determined by the size of the service entrance conductors. In this case you don't actually have any service entrance conductors but do have service lateral conductors. If the service lateral conductors are going to be installed by the EC the grounding electrode conductor should be based on the size of these conductors. If the service lateral conductors are going to be installed by the POCO I feel the grounding electrode conductor should sized as if they used 400 amp conductors. If this is a residential service it would require 400MCM CU or 600MCM Al service conductors so the grounding electrode conductor should be 1/0 CU.

Curt

Depending on the Load Calcs, they may use 4/0 AL XHHW (seems to be the commonly used size so far...), or even smaller!

I guess one could just install 3/0 cu for the GEC and be covered in almost any situation!

As mentioned, need to have the Service Entrance feeder size first, then can figure minimum GEC size.

Not really adding anything helpful again huh?

Scott35

Thanks for your replies. The reason I poseted this is to pose a question...Is this the installation that added footnote 2 to table 250.66? Bear in mind the definition of service entrance conductors. In this application there are either no service entrance conductors or they are the bus bars that come off of the load side of the meter.

I am of the opinion that that the bus bars are the service entrance conductors and therefore a 1/0 GEC is required. I don't think you are ever permitted to use the service lateral conductors to size with.

Given that this is a service with four disconnects. . .I don't think the size is tied to the maximum possible service size (limited by the equipment), but rather by the calculated service size, determined by the occupancy's load where this is installed, plus a margin for growth that is the calculator's option. . .not requirement.

That is: What does the installers service calculation say the service is? The service conductor size used to determine the GEC size would be based on that "equivalent" conductor.

If we're taking a poll I would tend to agree with this (assuming it's an UG Service) because of the definition of Service Entrance Conductors in Art. 100.

In other situations the GEC is sized according to the Service Entrance Conductors and not the load. It wouldn't seem consistant to start looking at the load now.

Say this house has all Gas appliances and therefore a low calculated load. It's 200A OH service requires a #4 GEC. I change it to a UG service and with no change in loads it wouldn't make sense to me that I can now use a much smaller GEC.

JMO
Bill

I tend to agree with ElectricAl.


Lets say we had to provide the service entrance conductors to this service in Ryan's picture.

Would the NEC require 400 amp conductors, the panel rating or 380 amps, the sum of the breakers or will the NEC allow the service entrance conductors sized to the calculated load?

FWIW I think it would be easer to size the conductors to the panel size but I do not think that is what the NEC requires.

JMO Bob

Table 250.66 Note 2.

I would feel comfortable if the size of the GEC was based upon the size of the MBJ since the service size doesn't take us beyond the Table 250.66 sizes.

If the MBJ is factory installed, and it looks like it is, the only item would be to determine its size so that a properly sized GEC could be installed.

The images are posted on my site also and I asked Ryan to send them in so that we could see what the service looked like.

And I will throw this one out there as well.

2002 NEC


It seems clear to me that for services it is all about the load and in the absence of service conductors the GEC is based on the calculated load not the potential load.

JMO
Bob

[This message has been edited by iwire (edited 09-27-2003).]

I defer to Curt's hands on experience with these units. . .but it appears to me that determining the Main Bonding Jumper guage is complicated by the Neutral Bus being rivited or bolted to the enclosure by the manufacturer. . .

All of this sizing issue goes right out the window if there is no metal water pipe.

The GEC to a ground rod only needs to be 6 AWG and to a Concrete-Encased Electrode 4 AWG.

Thanks to Roger for pointing this out else where.

Bob

Deleted duplicate reply

[This message has been edited by Joe Tedesco (edited 10-01-2003).]

Ryan:

Are those grounded conductors I see in the picture, those with three continuous white stripes running along their entire length?

If so, I could use a close up so as to avoid misinterpretations where some changes images show three bands at the terminations of the neutral.

Bob brings up a good point and I am sure that if the water pipe you described as being the electrode in this case was not available that you knew that the 6 AWG and 4 AWG when they are the sole connections to the rod or CEE (Ufer Ground) would be adequate.

The water pipe is also required to be suplemented with another electrode, which one will be used on this job?

How do you handle the inspection process in SLC?

Do you leave a notice, send a notice, or tags when you are completed with an electrical inspection?

Are you the only electrical inspector, or are their others or combination types in your area.

Hi Joe. The white striped conductors are the grounded conductors of (2) SER cables feeding panelboards in the basement. The two wires next to them are their associated EGC's. We try to get a Ufer ground out on all structures, but on this one it got cut off or stepped on or whatever. It wouldn't matter in this case if there was a Ufer, because the pipe was available and therefore must be used, Ufer or not. The supplement electrode in this case is a ground rod and the installer chose to run a #2 to it, which was more than he has to. When I spoke to the installer this was a good example for me to use to try to push the Ufer onto him.

I actually inspect in Draper city, which is in the Salt Lake Valley, slightly south of SLC. We have 4 inspectors, 2 plans examiners and 1 building official. I do 50% of all commercial inspections and 100% of all commercial electrical inspections. I also inspect some residential in my area. The typical houses I inspect cost about $500,000-$1,000,000. I have inspected some houses here with 600 amp, full-blown commercial services...CT can, teh whole ball of wax.

When we perform an inspection we simply leave a carbon of the report on site, put one in the file and leave one in our book. We do about 15 inspections per day, per inspector, which is just about perfect.

In this state it is pretty common to use combination inspectors, but each typically has his/her strong point, mine being electrical. SLC and South SLC do not use combination inspectors, but they also do a lot less inspections since there is really not a lot of growth there, IMO. You'll get the chance to meet with some of my friends from SLC that are on the IAEI board of directors with me when you make it out this way.

Never mind.

[This message has been edited by Redsy (edited 10-01-2003).]