Bonding of electrodes

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buck33k

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Washington state and North Carolina
A GEC sized per 250.66 connects to the rebar in the footing. On the opposite side of the building a bonding jumper of the same size connects to the water main (metal underground water pipe). Is the water main properly bonded through the many tie wired sections of rebar in the footing?

Thanks
Buck
 
What you describe is IMO NEC compliant at this time.

Bonding_Jumpers.JPG


I understand that what you are describing is not actually shown in this handbook picture but there is no specific rule prohibiting using a concrete encased electrode as you describe.
 
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I should add that in my area concrete encased electrodes must be inspected by the electrical inspector prior to the concrete pour.

During that inspection the continuity of the rebar from one side of the building to the other could be ensured.
 
Ditto, but I could still some inspectors wanting the GEC to go directly to the water pipe even though it isn't required.
 
infinity said:
Ditto, but I could still some inspectors wanting the GEC to go directly to the water pipe even though it isn't required.
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I think the wording that would allow this method would be in 250.68(B) and 250.52(A)3.The key words are effective.Sounds like two pcs of rebar with tie wire are an effective grounding path.

(B) Effective Grounding Path The connection of a grounding electrode conductor or bonding jumper to a grounding electrode shall be made in a manner that will ensure a permanent and effective grounding path. Where necessary to ensure the grounding path for a metal piping system used as a grounding electrode, effective bonding shall be provided around insulated joints and around any equipment likely to be disconnected for repairs or replacement. Bonding conductors shall be of sufficient length to permit removal of such equipment while retaining the integrity of the bond.

(3) Concrete-Encased Electrode An electrode encased by at least 50 mm (2 in.) of concrete, located within and near the bottom of a concrete foundation or footing that is in direct contact with the earth, consisting of at least 6.0 m (20 ft) of one or more bare or zinc galvanized or other electrically conductive coated steel reinforcing bars or rods of not less than 13 mm ( 1/ 2 in.) in diameter, or consisting of at least 6.0 m (20 ft) of bare copper conductor not smaller than 4 AWG. Reinforcing bars shall be permitted to be bonded together by the usual steel tie wires or other effective means.
 
There are two separate issues here.

1) Connecting the grounding electrode system together.

2) Bonding of interior metal piping to provide an effective ground fault current path.

The installation as described is totally fine for 1).

The installation as described makes me uncomfortable with respect to 2), but I don't think that there is _enforceable_ code to support this discomfort. 250.4(5) is the 'effective ground fault path' requirement, but 'low impedance' 'likely to be imposed' and 'likely to become energized' are really poorly defined. I am uncomfortable with this aspect of the installation, because if a phase conductor contacts a metal water pipe, the fault current would have to travel through the re-bar and tie wires to get back to the ground-neutral bond at the service. While re-bar and tie wires seems to make a great _grounding electrode_, and is probably just fine as a _grounding electrode conductor_, but I'm not sure how well they will fare as an _equipment grounding conductor_. Note that I've not done any sort of engineering analysis of the resistance of rebar as a conductor.

Remember that electricity does not seek 'earth', but instead seeks to return to its source. In a 'ground fault', the quality of the connection to 'earth' is almost irrelevant, but the quality of the connection back to the source will determine things like voltage rise at the ground fault location, magnitude of current flow, and OCPD operation speed.

As an additional point to think about, if you use the rebar to get you to the point where the metal water piping enters the building for your grounding electrode connection, it would seem to me that you could make your 'interior piping bond' at a much more convenient location, much closer to the service.

-Jon
 
winnie said:
The installation as described is totally fine for 1).

The installation as described makes me uncomfortable with respect to 2), but I don't think that there is _enforceable_ code to support this discomfort.
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I agree with you entirely.

I have used building steel as per your '2' but I personally would not be comfortable with using the loosely jointed rebar as described.

Perhaps a proposal is in order but what would the substantiation be?

How could I show this is a bad practice beyond saying I 'just don't like it'?
 
winnie said:
As an additional point to think about, if you use the rebar to get you to the point where the metal water piping enters the building for your grounding electrode connection, it would seem to me that you could make your 'interior piping bond' at a much more convenient location, much closer to the service.
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I don't follow you here, in most cases we can not use any part of the water line more than 5' from the point of entrance as part of the GES. (Grounding Electrode System)
 
iwire said:
I don't follow you here, in most cases we can not use any part of the water line more than 5' from the point of entrance as part of the GES. (Grounding Electrode System)
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If the water supply pipe were plastic, but the interior water piping were copper, then the water pipe could not be part of the grounding electrode system, but would still need to be bonded.

The 5' requirement is found in 250.52 if your water pipe is a grounding electrode.

The bonding requirement is found in 250.104, and has no 5' restriction.

I could see an installation where you go from service to re-bar and then re-bar to water pipe in the 5' limit for the grounding electrode requirement, and a second jumper from service to water pipe _anywhere_ for the bonding requirement.

Re-reading the code sections has simply left me more confused. The permission to jump from one electrode to another is in 250.104 for bonding; but not in 250.52 and so on for grounding...which seem to be exactly the opposite of what it should be :)

-Jon
 
Jon, I am not following you.

We can not use the interior metal water piping system beyond 5' from the entrance to connect one electrode to another.

Say I have the service panel at the same location as the water main entrance. I run from the panel to the water pipe.

Now if it happens that a connection to a concrete encased electrode is located on the other side of the house I can not connect the CEE to the nearest water line and call it a day. I will have to run a wire conductor from the CCC back to some point on the GES.
 
Totally _separate_ from any issues with connecting to grounding electrodes, interior metal water piping must be bonded. (250.104)

Bonding of interior metal water piping is not subject to the 5 foot rule. The interior metal water piping cannot be used for any sort of connection to the GEC, but if the connection is only being used to bond the pipe itself, then that connection can be _anywhere_ on the pipe.

I don't see an issue with having _two_ jumpers going to the metal water pipe, one meeting the 5 foot requirement, which is the connection _to_ the water pipe grounding electrode, and the second the connection _to_ the water pipe for interior bonding.

-Jon
 
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