Preprufe effectively eliminates ufer ground

[ptonsparky]

FWIW, I would bond to the rebar unless they are coated. What is the most it would cost? $100?

 

[don_resqcapt19]

Yes, it does disqualify it as a grounding electrode, but the potential for it to become energized is real, I'm just playing devils advocate when the lawyers ask why you didn't bond it when you knew there was a possibility of it becoming live, it's sad that you have to think this way with every installation anymore.

Lets look at it another way. Say there is a piece of equipment in the area of the concrete floor that has a high current ground fault to its enclosure. The enclosure will be energized with a voltage that is a result of the voltage drop on the EGC. This will appear as a voltage between the equipment enclosure and the concrete. The shock hazard will be greater with the concrete rebar bonded than without it bonded. It probably doesn't make any real difference because in either case (bonded or not bonded) the concrete would most likely be able to carry enough current to provide a fatal shock if the voltage drop on the EGC is high enough.

 

[petersonra]

How would an engineer of record be granted the rights to waive code rules? Unless the proper AHJ permitted what the engineer specified, no way. Code compliance or documented variance...one or the other.

he is not waiving the rules, he is abiding by them.

(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.

All of the concrete on this project is sealed from moisture intrusion

if there is no direct earth contact (because the concrete is sealed), it is not a CEE.

 

[realolman]

I looked at the web site for this stuff and it seems to me very likely that they would NOT envelope the footer in this stuff , but the walls and floors only.

Even on the web site's diagrams it shows the preprufe above the footer>

 

[hillbilly1]

Lets look at it another way. Say there is a piece of equipment in the area of the concrete floor that has a high current ground fault to its enclosure. The enclosure will be energized with a voltage that is a result of the voltage drop on the EGC. This will appear as a voltage between the equipment enclosure and the concrete. The shock hazard will be greater with the concrete rebar bonded than without it bonded. It probably doesn't make any real difference because in either case (bonded or not bonded) the concrete would most likely be able to carry enough current to provide a fatal shock if the voltage drop on the EGC is high enough.

If it is a high current ground fault, it would have a short duration, as the OCP would trip, so the shock hazard would be very limited, you could also say the same about an adjacent piece of equipment not physically connected, but grounded all the same.

 

[Smart $]

Lets look at it another way. Say there is a piece of equipment in the area of the concrete floor that has a high current ground fault to its enclosure. The enclosure will be energized with a voltage that is a result of the voltage drop on the EGC. This will appear as a voltage between the equipment enclosure and the concrete. The shock hazard will be greater with the concrete rebar bonded than without it bonded. It probably doesn't make any real difference because in either case (bonded or not bonded) the concrete would most likely be able to carry enough current to provide a fatal shock if the voltage drop on the EGC is high enough.

But bonding the rebar in the concrete would decrease the voltage drop (think multiple paths versus one for fault current), thereby lowering the potential shock hazard.

 

[Dennis Alwon]

I would bond also, BUT I have tested rebar grounds where plastic is installed under the concrete and the readings were exceptionally high when compared to the Ground grid that was installed after construction.

What were the readings compared to a ground rod? Just curious... What was the actual reading anyway- if you can remember. :smile:

 

[Aretae]

in lieu of ufer

in lieu of ufer

But from your OP,
Perhaps you can propose an alternate solution that would allay the concerns with waterproofing of the concrete. If there are anchor bolts, bond them to the rebar and bond to the steel building frame or whatever equipment is being anchored. This will effectively bond the rebar without an additional penetration of the concrete.

We are installing ground rods and then bonding the grounding electrode conductor to the rebar, structural steel, the steel enclosures....

 

[Aretae]

Enveloping footer

Enveloping footer

Are they enveloping the footer with this stuff?

Everything below grade is in essence poured with the stuff in place first. No penetrations are allowed through the slab and all penetrations through poured walls must be sealed with this same stuff, they "weld" it to everything.

 

[Aretae]

The wrapped it all

The wrapped it all

I looked at the web site for this stuff and it seems to me very likely that they would NOT envelope the footer in this stuff , but the walls and floors only.

Even on the web site's diagrams it shows the preprufe above the footer>

Interesting, I have no idea why they completely wrapped it, but it is. It spawned the AHJ's disallowance of the ufer ground as appropriate grounding. However, to make sure, I will ask someone on site tomorrow, preferably one of the waterproofing reps. I will also see if we captured it in any of the conduit installation pictures.

 

[don_resqcapt19]

If it is a high current ground fault, it would have a short duration, as the OCP would trip, so the shock hazard would be very limited, you could also say the same about an adjacent piece of equipment not physically connected, but grounded all the same.

It should be a short time fault, and yes it applies to all equipment not just the concrete.

 

[wbalsam1]

Originally Posted by wbalsam1
How would an engineer of record be granted the rights to waive code rules? Unless the proper AHJ permitted what the engineer specified, no way. Code compliance or documented variance...one or the other.:smile:

he is not waiving the rules, he is abiding by them.....

I now understand your point. Thank you.:smile: