UFER Ground with vapor barrier

[Npstewart]

Received a building department comment that reads as follows:

The "Single-Line Diagram" calls for #3/0 to concrete embedded electrode it appears that this building has a monolithic slab. Because of the building code Code requirement that a vapor must be installed under the entire slab thereby rendering the UFER grounding electrode inadequate. Please design another primary grounding electrode system, NEC 250.50.

I understand exactly what the person is saying but it is my understanding that per NEC 250, it is required to bond/ground to all sources available regardless. For instance, if you have a building with 8 feet of copper pipe, then it transitions to plastic pipe, you still need to connect to the copper.

I have been working in my area for a pretty long time and our area is nothing but monolithic slabs on grade (with vapor barrier) and this is the first time I have seen anything like this. I dont really know how effective a 10mm +/-vapor barrier could possibly be at insulating the slab from the ground. Especially since most vapor barriers break down (or) arent installed properly. I have seen vapor barriers after 5 years and they are extremely weak, brittle, and look like Swiss cheese.

Has anyone ran into this before?

 

[kwired]

Is the footing in direct contact with soil or is there vapor barrier between? The CEE is supposed to be in the footing which usually is in direct contact with soil. Slabs may have vapor barrier and will not matter as they are not part of the CEE. If the footing does have something insulating it from direct earth contact then you do not have a qualifying CEE and according to NEC you do not have to make a CEE, but do have to use one if it exists. Just like underground metal water pipe or structural steel, you use it if it exists, but nothing makes you add one if it doesn't exist.

 

[petersonra]

Why would anyone run a 3/0 to a CEE in the first place?

I think the comment is spot on and you need to come up with a different grounding electrode system. Pound a couple of ground rods and run some #4 to it and be done. if it makes you feel better, continue the #4 over to the rebar in the footing, but it does not qualify as a CEE IMO.

(3) Concrete-Encased Electrode. A concrete-encased
electrode shall consist of at least 6.0 m (20 ft) of either
(1) or (2):

(1) 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, installed in
one continuous 6.0 m (20 ft) length, or if in multiple
pieces connected together by the usual steel tie wires,
exothermic welding, welding, or other effective means
to create a 6.0 m (20 ft) or greater length;
or
(2) Bare copper conductor not smaller than 4 AWG

Metallic components shall be encased by at least
50 mm (2 in.) of concrete and shall be located horizontally
within that portion of a concrete foundation
or footing that is in direct contact with the earth or
within vertical foundations or structural components
or members that are in direct contact with the earth.
If multiple concrete-encased electrodes are present at
a building or structure, it shall be permissible to bond
only one into the grounding electrode system.
Informational

Note: Concrete installed with insulation, vapor
barriers, films or similar items separating the concrete
from the earth is not considered to be in ?direct contact?
with the earth.

 

[Npstewart]

Why would anyone run a 3/0 to a CEE in the first place?

This is actually a church that is similar to a franchise, they have very strict requirements that are in most cases beyond code minimum.



I actually put my foot in my mouth, part of this building is actually on a stem wall. The vapor barrier runs under the footing, but it wont run under the stem wall which IS in direct contact with the earth.

 

[mgookin]

... I dont really know how effective a 10mm +/-vapor barrier could possibly be at insulating the slab from the ground. ...

It's 6 mils minimum on the vapor barrier, unless it's been increased.

There are 1,000 mils in an inch which means 0.006" minimum thickness.
There are 25.4 mm in an inch.
11mm would be about a half inch, little less.
Not trying to be an ass. Just clarifying something that caught my eye.

As to longevity of a vapor barrier, it depends on many things. I've seen them very old where they held up as new and I've seen them not too old where they are the swiss cheese you describe. Maybe too long in the sun before placement of concrete? Poor materials? Not sure why, but I agree that the integrity of that vapor barrier over time is often questionable.

 

[GoldDigger]

I have been working in my area for a pretty long time and our area is nothing but monolithic slabs on grade (with vapor barrier) and this is the first time I have seen anything like this. I dont really know how effective a 10mm +/-vapor barrier could possibly be at insulating the slab from the ground. Especially since most vapor barriers break down (or) arent installed properly. I have seen vapor barriers after 5 years and they are extremely weak, brittle, and look like Swiss cheese.

FWIW, the usefulness of a CEE depends both on the high conductivity of the concrete (really, for this purpose it is high!) and the large surface area in contact with presumably damp earth. The presence of a vapor barrier, even with open seams, etc that allow water entry, will still reduce the surface area to the point that it will not be a good CEE. If you wrapped a plastic sleeve with a few holes in it around a rod electrode and then buried it, it would not measure out very good on a ground electrode resistance tester.
Since you are not talking about lightning protection here, the voltage withstand of the vapor barrier is not really relevant.

If you have separate rebar for the stem wall and the slab, you are only required to connect one CEE for the building if you have more than one, so choose the one that is best or most convenient to attach to and meets the NEC definition and ignore the rest. Or connect to them all if the customer specifies it for some reason beyond the NEC.