# How to bond a 320 amp service



## Paul S. (Sep 8, 2012)

I'm changing out two electrical panels for a 320 amp service. (They are both connected to a 320 amp meter base.) from the transformer to the meter there are two runs of 4/0 4/0 2/0, then from the meter base to each 200 amp panel one set of 4/0 4/0 2/0. There are differing opinions here where I am. Some say you can use one #4 and just bond the panels together. Another said I can either run one #2 and bond the panels together or I have to run one #4 from each panel to the main water bond/grounding electrode (within 5 feet of course) .... Any thoughts? I hope I have explained it good enough. Thanks in advance.


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## McClary’s Electrical (Feb 21, 2009)

Bonding the panels together with one electrode is not an option. You need seperate gecs sized per 250.66 running to your electrodes. When using ground rods, the second panels gec only needs to go to the first ground rod.


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## Paul S. (Sep 8, 2012)

Thank you!


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## Bootss (Dec 30, 2011)

Paul S. said:


> I'm changing out two electrical panels for a 320 amp service. (They are both connected to a 320 amp meter base.) from the transformer to the meter there are two runs of 4/0 4/0 2/0, then from the meter base to each 200 amp panel one set of 4/0 4/0 2/0. There are differing opinions here where I am. Some say you can use one #4 and just bond the panels together. Another said I can either run one #2 and bond the panels together or I have to run one #4 from each panel to the main water bond/grounding electrode (within 5 feet of course) .... Any thoughts? I hope I have explained it good enough. Thanks in advance.



Post a couple pics if you're up to it


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## Paul S. (Sep 8, 2012)

I already closed the meter base. There are just two panels connected to the meter base. I could probably take some pics tomorrow.... The meter can I believe is bonded through the grounded conductors. Just wasn't sure how I should size my wire or connect my panels to my grounding electrodes. Mainly the incomming water pipe.


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## J F Go (Mar 1, 2014)

I believe that all you need to do is run #6 cu from your 2 ground rods to the meter trim,ground rods are only rated for up to #6 cu,but that does not mean you can't put a larger conductor on them. If you have a water pipe, that you need to bond to this service,you will need to run #4cu, continuous , from panel to panel to water pipe. If you need to bond the structures steel to the service, you will need to run another #4 cu,continuous, from panel to panel to steel. Here this service would be considered a 400amp drop with 2 200's in parallel.


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## 3DDesign (Oct 25, 2014)

We install this same configuration several times a year.

Run #6 minimum to the ground rods, that conductor goes into one of the 200A panels, let's call it panel A. From panel A, run #2 to the copper water line. From panel A to the panel B you can run #4 but we always run #2.

If you have no copper water lines, drive three ground rod and use #2.

We installed one Monday with a dual 200A automatic transfer switch for a generator. The transfer switch had two 200A main breakers rated as service entrance and one 200A breaker for the generator. The generator feeds both panels automatically. 

We ran two 4/0 SEU from the meter to the transfer switch, then two 200A sub feed cables to the panels. We ran #2 to the water line and #4 to the ground rods. Both ground wires went into the transfer switch.


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## McClary’s Electrical (Feb 21, 2009)

3DDesign said:


> We install this same configuration several times a year.
> 
> Run #6 minimum to the ground rods, that conductor goes into one of the 200A panels, let's call it panel A. From panel A, run #2 to the copper water line. From panel A to the panel B you can run #4 but we always run #2.
> 
> ...


I don't care if you've been getting away with it, your installation would not pass here. In your case, panel b electrode conductor is not continuous to the first electrode. 

Also, to the op, you have to know what your power company requires on bonding the meter. 2 of the 3 power companies here require a #6 solid. The third of those three does not require a seperate bond.


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## 3DDesign (Oct 25, 2014)

mcclary's electrical said:


> I don't care if you've been getting away with it, your installation would not pass here. In your case, panel b electrode conductor is not continuous to the first electrode.
> 
> Also, to the op, you have to know what your power company requires on bonding the meter. 2 of the 3 power companies here require a #6 solid. The third of those three does not require a seperate bond.


How would Euphoria do it?


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## Dennis Alwon (May 9, 2009)

3DDesign said:


> How would Euphoria do it?


Your comment of 3 grouNd rods has no basis in the nec

No copper or metallic water line, then 2rods is all you need. I also don,t see how you can run a number 4 between panels when the install may req. larger.

a #2 copper is fine for two panels at 400 amps however for those using a meter main pain you would be required to use a 1/0 copper as an GEc to the water lines. This is based on the notes to t.250.66


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## 3DDesign (Oct 25, 2014)

Dennis Alwon said:


> Your comment of 3 grouNd rods has no basis in the nec
> 
> No copper or metallic water line, then 2rods is all you need. I also don,t see how you can run a number 4 between panels when the install may req. larger.
> 
> a #2 copper is fine for two panels at 400 amps however for those using a meter main pain you would be required to use a 1/0 copper as an GEc to the water lines. This is based on the notes to t.250.66


I just do whatever my AHJ says is required or suggests as a better way. He has a degree in Electrical Engineering from Penn State, I respect his opinion and ask for his advice.


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## Dennis Alwon (May 9, 2009)

3DDesign said:


> I just do whatever my AHJ says is required or suggests as a better way. He has a degree in Electrical Engineering from Penn State, I respect his opinion and ask for his advice.


I think that is not a good thing to do simply because he is making ec,s do thinks that are not required. What he thinks is a good idea has no merit and he should not do it


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## 3DDesign (Oct 25, 2014)

Dennis Alwon said:


> I think that is not a good thing to do simply because he is making ec,s do thinks that are not required. What he thinks is a good idea has no merit and he should not do it


I recognize the difference between code minimum and better ways of doing things.


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## Sparky J (May 17, 2011)

In this area we are required to #6 to the rods and #4 cu or #2 al, we used to have them be totally continuos because the AHJ's were ******ed. Now we hit the common bars and are good.


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## sbrn33 (Mar 15, 2007)

I either run separate #4's to the gec or I will* loop* one #2. Then 6's to the ground rods.


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## dogleg (Dec 22, 2008)

The situatuin is from a 320 at the pole and two 200 amp panels in the house then:


Here weve been looping a #4 cu continuous thru the two panels and to the ufer.
If there is insulation under the footing the loop a #6 cu between the two panels and then to 2 ground rods.
Many times there is black plastic water lines coming from the well in this instance just the ground rods or ufer if available
If there is a metal or copper water line coming into the house then # 4 cu looped between the panels and another to either the ufer or ground rods as mentioned above.


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## Pete m. (Nov 19, 2011)

It may not be permitted in some areas but I would take all my GEC's to the meter socket.

Pete


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## Dennis Alwon (May 9, 2009)

Basically you have this


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## McClary’s Electrical (Feb 21, 2009)

Dennis Alwon said:


> Basically you have this


I don't think that is what he described. He has a gec coming out of one panel, and a jumper between the two panels.


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## oldblue (Mar 2, 2013)

I just did a 200 amp 2 family service. I searched on here for a good way to run my grounds. Used elephates way. 

#4 to water continuous to one panel 4 to ground rods continuous to other panel criss-cross above the panels bond in the middle with a split bolt. Passed my toughest inspector here. He asked whats this I told him he just grumbled something, thought about it for a minute and passed it. You'd have to do #2 which probably doesn't make as much sense. 

Poco won't let us bond in the pan here.


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## oldblue (Mar 2, 2013)

Dennis Alwon said:


> Basically you have this



What do you use to tap when doing it this way? Crimp, weld or ? Does it not have to be irreversible when you do it this way, if ones continuous ? 

Anyone ever brazed a GEC? Seems about as irreversible as you can get. Never heard about anyone doing it. I don't have a crimper or cad welds. So the thoughts crossed my mind to get the oxy acetylene torch and a copper braze stick out.


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## Dennis Alwon (May 9, 2009)

mcclary's electrical said:


> I don't think that is what he described. He has a gec coming out of one panel, and a jumper between the two panels.


I know. I was showing an alternative. Interesting that you could bug onto the grounding electrode conductor but you cannot use the bus bar


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## Dennis Alwon (May 9, 2009)

oldblue said:


> What do you use to tap when doing it this way? Crimp, weld or ? Does it not have to be irreversible when you do it this way, if ones continuous ?
> 
> Anyone ever brazed a GEC? Seems about as irreversible as you can get. Never heard about anyone doing it. I don't have a crimper or cad welds. So the thoughts crossed my mind to get the oxy acetylene torch and a copper braze stick out.



I believe a split bolt is allowed. I am not sure why this is compliant but it apparently is a compliant install.


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## Dennis Alwon (May 9, 2009)

I think 250.64 (D)(1) allows this install-- #2

The tap conductors
shall be connected to the common grounding electrode conductor
by one of the following methods in such a manner
that the common grounding electrode conductor remains
without a splice or joint:
(1) Exothermic welding.
(2) Connectors listed as grounding and bonding equipment.
(3) Connections to an aluminum or copper busbar not less
than 6 mm × 50 mm (1⁄4 in. × 2 in.). The busbar shall be
securely fastened and shall be installed in an accessible
location. Connections shall be made by a listed connector
or by the exothermic welding process. If aluminum
busbars are used, the installation shall comply with
250.64(A).


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## oldblue (Mar 2, 2013)

Dennis Alwon said:


> I think 250.64 (D)(1) allows this install-- #2
> 
> The tap conductors
> shall be connected to the common grounding electrode conductor
> ...


That makes it sound like its ok to use the ground bar to jump from panel to panel. Depending on the definition of accessible. 

I read that when I was planning my 2 family service and thought about an external grounding bar. If you do that does the water bond have to go thru the bar to one panel? If I understand right with the bar I could run my rods in 6 end it at the bar then water thru for one panel and a jumper for the other.


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## Dennis Alwon (May 9, 2009)

oldblue said:


> That makes it sound like its ok to use the ground bar to jump from panel to panel. Depending on the definition of accessible.


Yeah except a busbar is not a ground bar. I think many people make that mistake.


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## JBlakemore (Aug 20, 2012)

Dennis- What is the difference between a ground bar and a bus bar? Is it just what the equipment is listed for?


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## Dennis Alwon (May 9, 2009)

A bussbar IMO would be what you see on a panel as a buss. Usually this is a flat metallic plate that you see in bus ducts etc.

A ground bar is exactly what you see as a ground bar. Now why one and not the other-- I don't know- perhaps they did not intend to exclude the ground bar but they did.


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## McClary’s Electrical (Feb 21, 2009)

As Denis mentioned, I have never seen a ground bar two inches wide. ....


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## JBlakemore (Aug 20, 2012)

I just did a service that is very similar to what the OP had to do. My circumstances were:

320 amp service
4/0 SEU from meter pan to one panel (main breaker) and 4/0 SEU to an ATS (service rated w/200a main breaker)
4/0 SEU from ATS to second panel (sub with main breaker)

The water line is poly. Foundation walls are Superior Walls so there is no Ufer available. I installed two ground rods and ran one solid conductor to service equipment.

In the first instance I ran the #4 GEC from the ground rods to the second panel (sub), then through an intersystem bond, then through the ATS, then to the first panel. I was inches shy so was not able to land the continuous #4 on the provided lug at the neutral lug. I installed the #4 to the ground bus bar and used a #4 jumper to the neutral lug in the first panel.

Inspector failed the first install due to not having continuous GEC to the grounded conductor lug on the first panel.

Take 2- I got a longer length of #6 CU (250.66a says #6 is as big as you need with ground rods) and ran the same route as noted above with the exception of the #6 running through the first panel ground bus bar and then to the grounded conductor lug. So all 3 panels and 2 rods have continuous #6 GEC. That passed.

I have a couple of questions for the experts. The first install, I believe, should have passed under 250.64 D1 (as Dennis posted above). Is that right?

Secondly (somewhat unrelated), for the sub panel, I installed three wire SEU and used the #6 GEC as the EGC for the feeder. Is this a violation of 250.121? It seems that what I did is backwards from the prohibition in that section, but I wonder if it should have failed? I cannot understand why it would be a bad idea to use the continuous GEC as opposed to relying on connections at a bus bar and installing a separate EGC, but perhaps I'm missing something.



*edit- I just saw Dennis's response about the bus bar- I guess what I did was worthy of failing.


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## Dennis Alwon (May 9, 2009)

JBlakemore said:


> *edit- I just saw Dennis's response about the bus bar- I guess what I did was worthy of failing.


I would not loose sleep over it.


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## McClary’s Electrical (Feb 21, 2009)

- I guess what I did was worthy of failing.[/QUOTE]







I agree


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## JBlakemore (Aug 20, 2012)

Any thoughts on using the GEC as the feeder ground?


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## RIVETER (Sep 26, 2009)

JBlakemore said:


> Any thoughts on using the GEC as the feeder ground?


My thought is that that's not it's purpose.


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## Dennis Alwon (May 9, 2009)

RIVETER said:


> My thought is that that's not it's purpose.


Actually the 2014 allows the equipment grounding conductor to be used as a grounding electrode conductor in some situations. 250.121 It does not say the grounding electrode conductor can be used as an equipment grounding conductor. Fine line there


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