UFER Ground

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chrisd

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I recently added a subpanel for a customer building a new detached garage. I convinced the customer to include a UFER ground while the slab was being poured and I grounded the panel to the UFER Ground. I also ran a #6 ground back to the main panel as an additional ground for the loadcenter. The loadcenter was grounded to the water system as well. However, during some additional construction I found out the new copper pipes connect to plastic below grade, so there really is no effective ground through the water system. Is the UFER ground adequate for a 200 amp service? The customer is readying to pour a new porch slab right next to the water ingress. Should I have him do a UFER ground there as well and connect it to the water system or pound a rod?
 
chrisd said:
Is the UFER ground adequate for a 200 amp service?
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Yes, 250.50(2005 NEC) States "All grounding electrodes as described in 250.52(A)(1) through (A)(6) that are present at each building or structure served shall be bonded together to form the grounding electrode system."

If all that is "present" is a UFER ground, then that is all you need to use. You don't need to supplement a UFER ground, only a water pipe electrode needs to be supplemented per 250.53(D)(2).

Also check out 250.32 for the grounding and bonding requirements for a separate structure.

Chris
 
Chris, Interesting that your GEC bonding conductor is #6 awg back to the main disconnect panel. With the advent of your water pipe electrode being converted to plastic, there is a conflict to 250.52(3) that requires a #4 awg connection to the UFER for an overall GES requirement. Is this what you have? rbj, Seattle
 
gndrod,
Interesting that your GEC bonding conductor is #6 awg back to the main disconnect panel.
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This is an equipment grounding conductor sized by Table 250.122. A #6 is fine for a feeder protected by a 200A OCPD.
With the advent of your water pipe electrode being converted to plastic, there is a conflict to 250.52(3) that requires a #4 awg connection to the UFER for an overall GES requirement.
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There is no such requirement in that section. That section does not apply to the grounding electrode conductor, only to the grounding electrode itself. The grounding electrode conductor is still based on the feeder conductor size and Table 250.66. If the feeder is 3/0 or smaller the #6 to the rebar is fine.
Don
 
Don,
250.66 is what I am basing my question as to having a GEC for 200amp service. Maybe I interpreted the OP's statement incorrectly. The 4-wire to the sub is the only Electrode hookup after losing the water pipe changeover to plastic. I agree if there was something I missed where " the loadcenter was grounded to the waterpipe" as the origninal GEC.
Chrisd, Was the original water pipe still intact? If so, then forget about my statement. rbj, Seattle
 
The copper water system is still intact with a #4 groundwire installed within 6 feet of ingress per local requirements. However, with the upgrade to copper any connection to the original galvanized pipe was severed. Where the water goes into the ground outside it is plastic.

Since the owner is pouring a new proch I have advised him to add a UFER ground there (as it is with 1 foot of the water ingress) and I will attach a ground wire from the UFER to the copper system to be on the safe side. If something were to happen to the garage the main structure would be witout ground and it would likely be an afterthought.

Reviewing 250.xxx (2005 NEC) now...

Thanks for the feedback everyone.
 
The original waterpipe still works, but the new porch UFER would be the best to cover all bets. Sounds like future work could happen and the old pipe could get removed.
 
rbj,
250.66 is what I am basing my question as to having a GEC for 200amp service. Maybe I interpreted the OP's statement incorrectly. The 4-wire to the sub is the only Electrode hookup after losing the water pipe changeover to plastic. I agree if there was something I missed where " the loadcenter was grounded to the waterpipe" as the origninal GEC.
Chrisd, Was the original water pipe still intact? If so, then forget about my statement.
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The original post does not specify the feeder conductor size, but there is no reason to use a conductor larger than 3/0 so Table 250.66 would only require a #6.
Don
 
gndrod said:
Don,
250.66 is what I am basing my question as to having a GEC for 200amp service. Maybe I interpreted the OP's statement incorrectly. The 4-wire to the sub is the only Electrode hookup after losing the water pipe changeover to plastic. I agree if there was something I missed where " the loadcenter was grounded to the waterpipe" as the origninal GEC.
Chrisd, Was the original water pipe still intact? If so, then forget about my statement. rbj, Seattle
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gndrod...If the original grounding electrode (water line) at the house was not intact, are you suggesting that he not replace the grounding electrode at the main house and use the Ufer at the garage for both structures?
steve
 
Not at all Steve, That is why I asked for clarification of the original pipe GEC still being intact. I am aware that a backfed 4-wire feeder is not a compliant GEC in that case.

Hi Don,
I think we are talking about a feeder and a service main in the crossfire discussion. The mention of cutting the water pipe electrode was not clear to me and I was referring to the main service disconnect GEC water pipe in question (in my mind) and the 4-wire sub supplemental UFER as not a compliant GEC if the pipe was converted to plastic. I am going to sit in the back row to listen and hope I have not been confusing this thread any more than I have. The follow-on description by Chrisd cleared that up for me. Thank you for your words of wisdom. rbj, Seattle
 
From Chrisd
" I convinced the customer to include a UFER ground while the slab was being poured"

He mentions the slab for his electrode. The concrete encased electrode would be either the:

" located within and near the bottom of a concrete foundation or footing that is in direct contact with the earth"

This does not include the slab to be used as the Concrete encased electrode.

If I misunderstood the post and he is using the footing or foundation, then disregard this post.
 
Pierre C Belarge said:
From Chrisd
" I convinced the customer to include a UFER ground while the slab was being poured"

He mentions the slab for his electrode. The concrete encased electrode would be either the:

" located within and near the bottom of a concrete foundation or footing that is in direct contact with the earth"

This does not include the slab to be used as the Concrete encased electrode.

If I misunderstood the post and he is using the footing or foundation, then disregard this post.
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Pierre...What if the concrete slab is the foundation. I've seen houses built on a slab. Some with no footers.
steve
 
Anwer to why not. I think we are talking about the same thing from a system standpoint. Without the waterpipe #4 GEC, the #6 GEC from the sub to the garage footer would be non-compliant from an overall GES requirement. The sub #6 awg is mainly an EGC fault return to the main service SPG. Am I doing a good job of confusing or does this make sense?:)
 
HI Steve,
Those monolithic slabs in fact do have a perimeter footer requirement per UBC code. What Pierre C. may be relating to is that most slab pours are not in direct contact with earth or 'hardpan' conditions. This defeats the integrity of the UFER configuration. rbj, Seattle (doing UFERs since 1972)

Note: Crushed rock is used for fill and is sometimes over a visqueen moisture barrier prior to the slab pour. Still a perimeter UFER can be in the footer to compensate for the slab 'field' barrier.
 
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grndrod,
Without the waterpipe #4 GEC, the #6 GEC from the sub to the garage footer would be non-compliant from an overall GES requirement.
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That would only be true if the feeder conductors were larger than 3/0. 3/0 is 200 amp wire so there would be no reason to use a larger conductor.
Don
 
gndrod,
I've been looking at the wrong column in Table 250.66. 2/0 and 3/0 copper does require a #4 grounding electrode conductor. Sorry.
 
I believe you are correct though about #6 relative to the Sub UFER hookup. A good exercise and I appreciate you helping me. rbj
 
gndrod,
The #6 is correct for the EGC (sized per Table 250.122) that is run with the feeders to the subpanel, but the required grounding electrode conductor (per Table 250.66) at the second building must be a #4 (assuming that the feeder conductors are 3/0 copper).
Don
 
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