gec sizing and connection

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I have a 600 amp service that will have 4 individual service panels connected to it with each service having a 200 amp main disconnect. These will all be mounted below the C.T. adjacent to each other. This system will have service entrance condutors of 2 ea 500 mcm al. Table 250.66 tells me I need a 2/0 cu gec. Is it pemissible to run this from the ct can thru lay lugs in each panel in a continous fasion and then continue out to the gec electrode or do I have to bond it to each can and bring out a separate conductor from each to the g.e.?. I also assume that #4 cu is sufficient as an egc say from a bonding bushing at each raceway and then to the ground buss correct?
 
Re: gec sizing and connection

I agree with everything you have said, with the exception of the #4, which must be sized off of T250.66, as per 250.102(C). This would require a #2/0.
 
Re: gec sizing and connection

I was looking at the service entrance conductor size for the main gec size but using the 250.122 table for the egc of each panel.I planned on starting at a lug in the CT can coming thru the first conduit and looping the gec under a lay lug as a continous run thru the panels and then out to the ground rods all with 2/0. Then I was going to use #4 cu at bonding bushings from each the raceway in each panel to its corresponding ground buss. But you say I must use 2/0 for this? Each panel will be fed off the main lugs with 3/0 cu to a 200 amp main disconnect. I will also use a full size neutral as all the loads are 120 volt Grounding the neutral in each service panel. If this is wrong let me know and thanks for your help. Joe
 
Re: gec sizing and connection

If the bonding jumper is bonding a raceway containing service conductors, the 2/0 would apply. From your first post this is what I thought you were doing. Reading your second post it sounds as though you are using the EGC in the raceway containg the feeder circuit to bond the feeder raceways. If that is the case, table 250.122 applies, but the bonding would not be required unless it is concentric and over 250 volts.

Again, if the bonding jumper touches a service conduit, it must be 2/0 if bonding each service raceway, or 1/0 if it is only bonding one of the two service raceways. Make sense?
 
Re: gec sizing and connection

ryan let me try this once more.I size the grounding electrode condutor at 2/0 based on table250.66 and start it from a lug in the CT can to the first panel and thru a lay lug in each panel continuously out the last panel andown to the ground rods. I also bond each of the branch circuit raceways within each of the four panels from a grounding bushing to the ground bus in each panel using table 250.122 which specifies a #6 cu but I always just use #4 cu anyway. The egc does not go back to the CT can or touch the service entrance raceway. It is only within each service panel as that panels egc. Am I now making more sense?
 
Re: gec sizing and connection

I know i dont need a grounding bushing the poco only requires a grounding locknut in the service panel can .I just use them to satisfy both requirements for convenience.
 
Re: gec sizing and connection

I think I'm seeing this. This sounds fine to me.

The #4 is probably irrelevant, because the branch circuit (or feeder) conduits probably didn't need to bonded, again unless over 250V AND a concentric knock-out. Green-tag from me :)
 
Re: gec sizing and connection

pierre that where I thoght it should originate I did not think it actually made any difference however I get your drift it probably should originate at the first service panel as thats where the neutral wll be bonded.Makes sense I guess.
 
Re: gec sizing and connection

Now im being told within another thread in the grounding and bonding area that I cannot just use a lay lug to originate my GEC but that it must originate from the neutral buss. I guess I could start from the first bus thru a lay lug to the next panels and use a double barrel lug to tie back to the neutral bus in the second and so on to the last panel and then take a # 6 or larger(I like to use #4) out to the ground raods. Does this make sense or is there anothe way to do it?
 
Re: gec sizing and connection

Stew there are many ways to get it done, and the way you just described sounds OK. :)

I think that there is an easer way.

250.64(D) Grounding Electrode Conductor Taps. Where a service consists of more than a single enclosure as permitted in 230.40, Exception No. 2, it shall be permitted to connect taps to the grounding electrode conductor. Each such tap conductor shall extend to the inside of each such enclosure. The grounding electrode conductor shall be sized in accordance with 250.66, but the tap conductors shall be permitted to be sized in accordance with the grounding electrode conductors specified in 250.66 for the largest conductor serving the respective enclosures. The tap conductors shall be connected to the grounding electrode conductor in such a manner that the grounding electrode conductor remains without a splice.
Click to expand...

[ March 08, 2004, 07:23 PM: Message edited by: iwire ]
 
Re: gec sizing and connection

If the Main gec is to remain without a splice that would indicate that the main gec is to be taken out to the ground rds and not just tack on a #6 at the last enclosure or are they say ing that when the gec leaves the enclosure it shall then remain without a splice? This section seems to indicate that 3/0 would not be required but rather a conductor sized per table 250.66 for the largest entry conductor into each panel. In this case it would be 4/0 aluminum resulting in a #4 copper gec.does that sound right?

[ March 08, 2004, 10:37 PM: Message edited by: stew ]
 
Re: gec sizing and connection

Stew
If you mean 'common grounding electrode conductor', yes you can use a 4 AWG copper conductor GEC tap to the individual disconnect supplied by 4/0. Do not forget the connection to the common grounding electrode conductor with your 4 AWG 'tap' has to be made with an 'irreversible connection.

Pierre
 
Re: gec sizing and connection

As long as the GEC remains unspliced from the enclosures out to the first electrode you are all set.

The GEC taps do not have to be made with irreversible means, split bolt connectors or any connector that allows the GEC to remain uncut is OK.

It is possible you would have a trough feeding 6 service disconnects, the GEC will be based on the size of the conductors feeding this trough I will say 1/0 Copper.

The Taps from the GEC to each disconnect can be sized on the conductors supplying each disconnect I will say 3 AWG.

This connection from the 1 AWG taps to the GEC can be made with spiltbolts.

Now send the 1/0 GEC to the water pipe, once at the water pipe you can splice with any means you choose to continue on to a concrete encased electrode with 4 AWG and then you could splice again and continue to a ground rod with 6 AWG.

In the NEC Handbook they show two great examples of the taps and splicing on further electrodes.

Exhibit 250.21 and Exhibit 250.26

[ March 09, 2004, 04:44 AM: Message edited by: iwire ]
 
Re: gec sizing and connection

Ok let me sum this up again just for drill. In my case the largest "service conductor" is 2x500 mcm al or 1000 mcm equivalent. Results in 2/0 cu main gec.I will start from the first nuetral buss to the first can thru a lay lug to bnond at first service. Now comes the quandary. As there is no lay lug on the neutral bus in the second and remaining cans the only way to continue this run would be to leave it unspliced at that point under a lay in lug and stack another lug with it to bond it back to the neutral buss and continue int that manner to the last can. Then to connect to the ground rods you could pick up at the last can from a stacked lug or at the last neutral bus. The other way would be to bring a 2/o from each neutrl bus thru a lay lug for bonding at aech panel an then take them all to the last can and tap at taht point out to the gec rod with my #4 cu.Do both work or is the first one not correct due to being spliced so to speak at each can? They way I understand your reply it is ok to splice within the panels just not after it leaves the panels to the gec.
 
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