310.15(B)(6) & Meterbase?

[jclint07]

Residential Service has a 400 Amp, 120/240 Single Phase meterbase, with no disconnects or overcurrent protection, feeding (2) 200 Amp service panels on wall directly behind it.

#1- Load side of meterbase has "double barrel" lugs to accomodate all 6 conductors going into (2) seperate 200A service panels, not for paralleling purposes. Shouldn't those conductors on load side of meter base be sized for 400 Amps (310.15B6)?

#2- This exact project was permitted under NEC 2002, what was the '02 requirement for landing the grounding electrode conductor at the service, when you had multiple service disconnects/enclosures? I only have NEC 2008 in my office currently.

 

[iwire]

Residential Service has a 400 Amp, 120/240 Single Phase meterbase, with no disconnects or overcurrent protection, feeding (2) 200 Amp service panels on wall directly behind it.

#1- Load side of meterbase has "double barrel" lugs to accomodate all 6 conductors going into (2) seperate 200A service panels, not for paralleling purposes. Shouldn't those conductors on load side of meter base be sized for 400 Amps (310.15B6)?

That is a common installation and assuming it was done correctly is fine.

#2- This exact project was permitted under NEC 2002, what was the '02 requirement for landing the grounding electrode conductor at the service, when you had multiple service disconnects/enclosures? I only have NEC 2008 in my office currently.

I don't have 2002 with me.

 

[Ponchik]

You may use 310.15(b)(6) but you dont have to.

You have two service disconnects for a single family or two disconnects one for each duplex?

you have one or two service riser/lateral?

 

[jclint07]

Edward, it is a Single family dwelling, with one service lateral. What do you mean by I don't have to use 310.15B6?

 

[Dennis Alwon]

If this is a 400 amp service(2-200 amp panels) then you may not use 310.15(B)(6) in this install. You must use 310.16

I am not sure what you are asking about the gec. I believe that has not change but what is the install.

 

[suemarkp]

You have multiple sets of service entrance conductors. Each set needs to be rated per the size disconnect it terminates into. Since each disconnect is 200A, each set of wires must be 3/0 Cu or possibly 4/0 Al. Whether you can use 310.15(B)(6) to size this service entrance conductor sets always causes a lot of debates. The consensus seems to be that you can't use it to size each set. If you just had a single set of 400A rated conductors terminating in a single 400A disconnect, then you could use 310.15(B)(6).

I don't think the grounding rules have changed much since 2002. There are multiple ways you can do it. You can have a 1/0 GEC from the meter base or a common gutter, you can run #4 cu GEC taps to each service enclosure, and probably some other ways. How was this one done?

 

[jclint07]

GEC is ran into just one of the 200A service disconnects. I was thinking the new NEC 2008 250.64D now required GEC taps to each seperate service enclosure. Being I do not have NEC 2002 book, I was just trying to verify the procedure that was required under that code cycle.

 

[Dennis Alwon]

There are multiple ways you can do it. You can have a 1/0 GEC from the meter base or a common gutter, you can run #4 cu GEC taps to each service enclosure, and probably some other ways. How was this one done?

Actually you only need #2 in this install or 2- #4's --- copper.

 

[iwire]

If this is a 400 amp service(2-200 amp panels) then you may not use 310.15(B)(6) in this install. You must use 310.16

Good point, I agree with you.

I think his concern is that it they did not use 400 amp conductors up to the breakers but I may be wrong.

 

[Dennis Alwon]

Good point, I agree with you.

I think his concern is that it they did not use 400 amp conductors up to the breakers but I may be wrong.

I don't know either. It does sounds like he thinks the wires to each 200 amp panel must be 400 amps when a 200 amp conductor is fine but based on 310.16 not 310.15(B)(6)

Load side of meterbase has "double barrel" lugs to accomodate all 6 conductors going into (2) seperate 200A service panels, not for paralleling purposes

 

[jclint07]

Dennis, yes my first concern was that the conductors on the load side of 400 amp meter base were supposed to be sized for the 400 amp service and not for (2) seperate 200 amp service enclosures. The conductors from the meter base to each 200 amp service panel are 3/0 THHN copper.

My second concern was if the second service panel had to have a GEC installed or if just one service panel having one, was all that was required. Which now I understand BOTH service enclosures need to be connected to the grounding electrode system, which for 400 amp service should be #2 copper to water main, and a #4 GEC jumper to the second service enclosure.

I have never come across install such as such so my head is still spinning a little bit. Please forgive me.

 

[suemarkp]

Actually you only need #2 in this install or 2- #4's --- copper.

He didn't say what size service entrance conductors he has. On my overhead service, it had 400 KCMil in the mast, and that is the single conductor size you use for 400A when using 310.15(B)(6). This size needs a 1/0 GEC. If you use parallel 2/0's, or parallel 3/0's, then a #2 GEC would be OK.

I don't believe you always have to run a GEC to each panel. Certainly if you tap off upstream of the disconnect panels for the GEC (in a gutter, in the meter base, or even at the top of a mast), the grounded conductor can do all bonding/grounding of the two panels as long as each is sized to 250.66 or larger. It seems more confusing if you choose to ground from just one panel whether you have to run a GEC tap to the other panel. Doesn't make sense to me to do that if the grounded conductor is large enough (and most people will run a 1/0 or larger neutral to a residential 200A panel).

 

[jclint07]

Suemarkp, POCO supplies the service lateral wires (which are 500 aluminum) into the 400 amp meterbase, which do not get installed until AFTER the entire service is installed. #2 copper is what he needs to install from at least one of the service enclosures to the metal underground water line serving this dwelling, correct? Or because the service panel conductors, from 400 amp meterbase are 3/0 copper, water line electrode conductor needs to only be #4?

#4 copper GEC, from the concrete-encased electrode, is terminated in the 400 amp meterbase, which according to 250.66(B) & 250.24(A)(1), is allowed. The second service panel not having a GEC of any type installed is what was confusing me, and of what size.

 

[Dennis Alwon]

Suemarkp, POCO supplies the service lateral wires (which are 500 aluminum) into the 400 amp meterbase, which do not get installed until AFTER the entire service is installed. #2 copper is what he needs to install from at least one of the service enclosures to the metal underground water line serving this dwelling, correct? Or because the service panel conductors, from 400 amp meterbase are 3/0 copper, water line electrode conductor needs to only be #4?

#4 copper GEC, from the concrete-encased electrode, is terminated in the 400 amp meterbase, which according to 250.66(B) & 250.24(A)(1), is allowed. The second service panel not having a GEC of any type installed is what was confusing me, and of what size.

Okay question #1 is settled in my eyes-- it is fine. 3/0 to each service panel works since the 3/0 is protected by a 200 amp breaker.

Question #2 involves the GEC-- you can run a #2, in this case, to the water line from the meter. If you choose to go to the panel then two runs of #4 are needed to the water line ot you can run a #2 and tap with #4 to each panel.

 

[kwired]

When sizing a grounding electrode conductor forget that there is a 200 or 400 (or whatever size) overcurrent device. Grounding electrode conductors are sized according to the size of the ungrounded service entrance conductors. You can bring in 350Kcmil conductors and only have a 100 amp main breaker, you still size the GEC to the conductors not the main breaker. An overhead drop or an underground lateral are not necessarily the service entrance conductors. In the OP they are not, the conductors between the meter and the service disconnects are the service entrance conductors.

If you parallel two 3/0 conductors, you do not have two 3/0 conductors you have one 335.6Kcmil conductor. That needs a 2 AWG GEC, a 500Kcmil would need a 1/0 AWG GEC.(all copper conductors)

 

[Dennis Alwon]

When sizing a grounding electrode conductor forget that there is a 200 or 400 (or whatever size) overcurrent device. Grounding electrode conductors are sized according to the size of the ungrounded service entrance conductors. You can bring in 350Kcmil conductors and only have a 100 amp main breaker, you still size the GEC to the conductors not the main breaker. An overhead drop or an underground lateral are not necessarily the service entrance conductors. In the OP they are not, the conductors between the meter and the service disconnects are the service entrance conductors.

If you parallel two 3/0 conductors, you do not have two 3/0 conductors you have one 335.6Kcmil conductor. That needs a 2 AWG GEC, a 500Kcmil would need a 1/0 AWG GEC.(all copper conductors)

This is very true as some people get confused when they use a 400 amp meter main combo unit. They usually do not have conductors but rather service bars and thus 250.66 Note #2 comes into play. The GEC in that case must be 1/0 not #2 as the case of 2- 200 amp panels with 3/0 copper conductors.

 

[jclint07]

Thanks to everyone for the replies. I apologize again for such confusion. But as I previously mentioned, I've never came across an install such as this, either as an electrician or inspector.

Kwired, so you're saying a 1/0 copper GEC would be needed, to water pipe electrode, based on the 3/0 copper service conductors installed in parallel, in the 400 amp meterbase. But technically, they are not installed in parallel because each set of service conductors, serve separate 200 amp service enclosures. Therefore, after all my confusion, I would say the #4 GEC (from water main electrode to one of the service enclosures) is correct. All that is needed is a GEC tap to the second service enclosure.

 

[kwired]

Thanks to everyone for the replies. I apologize again for such confusion. But as I previously mentioned, I've never came across an install such as this, either as an electrician or inspector.

Kwired, so you're saying a 1/0 copper GEC would be needed, to water pipe electrode, based on the 3/0 copper service conductors installed in parallel, in the 400 amp meterbase. But technically, they are not installed in parallel because each set of service conductors, serve separate 200 amp service enclosures. Therefore, after all my confusion, I would say the #4 GEC (from water main electrode to one of the service enclosures) is correct. All that is needed is a GEC tap to the second service enclosure.

Correct if indeed they are in parallel. I have never really known the answer for your situation with two separate disconnects, and I have installed many that way. Always sized GEC as if they were parallel when a full sized GEC was needed but quite often the only electrodes present were either CEE or ground rods and 4 AWG or 6 AWG is all that was needed anyway. It is not a violation to have it too big. People can present a pretty strong case either way so I never have really had a strong opinion of which way is correct.

 

[Dennis Alwon]

I disagree that 1/0 is needed. Look at Note #1 to 250.66. The sum of the service conductors would come to a #2 GEC-- IMO. If there were no service conductors as the case of a 400 amp meter main then I agree 1/0 is needed.

 

[jclint07]

Just out of curiousity... per Table 250.66 for service conductors OVER 1100KCM copper....3/0 copper would be the required GEC. But where does the 12.5% of largest service conductor, for sizing the GEC come in to play? For example, paralleled 600KCM service conductors?