EMT conduits grounding and bonding

[almousam1]

Our project client has their own Engineering Standards that state:

Metallic conduit shall be grounded at both end points by bonding to a grounding conductor, a grounded metal enclosure, or to a grounded metal cable tray. This may be accomplished:


 with listed or marked grounding clamps and conductors connected externally to the conduit.


 by bonding to a grounded enclosure using integral threaded bushings or using a conduit hub which is listed or marked for grounding purposes.


 bonding to a grounding conductor using listed or marked grounding bushing. Grounding with locknuts is not acceptable.


 where non-PVC coated rigid conduit is used to protect cable entering or exiting a grounded metal cable tray, by bonding with a conduit clamp to the cable tray. A grounding bushing must be used with PVC coated conduit.


Exceptions 9.9:


Where EMT is permitted it may be grounded and bonded in accordance with the NEC.


Isolated sections of rigid metal conduit that are buried at all points at least 0.5 meters below grade are not required to be grounded. (e.g., Conduit sleeves for road crossings.)


Conduit sleeves used to enclose power cables transitioning from above grade to below grade are required to be grounded only at the above grade end.

We have done all above ceiling conduit work using EMT conduits following methodology: https://ibb.co/4P9tZDQ
However, the inspector consider the installation violating the standards for not grounding and boning each conduit in the raceway. Please help me understand further the requirement for grounding EMT conduits and what's NEC requirement for grounding and bonding EMT that mentioned in the exception?

 

[infinity]

According to the NEC it's possible that most of the bonding you have shown here is not required for EMT. What is the voltage? If there are no concentric or eccentric KO's at the panel no bonding bushings are required.

Welcome to the Forum.

 

[almousam1]

According to the NEC it's possible that most of the bonding you have shown here is not required for EMT. What is the voltage? If there are no concentric or eccentric KO's at the panel no bonding bushings are required.

Welcome to the Forum.

The voltage is 230 V.
Can you refer me to specific article?

Thank you for welcoming me, I'm happy to be a member in such great Forum.

 

[garbo]

Best practice is to run a green ground in every conduit. My old cheap skate corner cutting boss almost got electrocuted due to using EMT conduit for ground on a 480 volt circuit. he got called to look at the conduit that pulled apart.While trying to reinstall the conduit he nicked the wire and got thrown to floor with severe chest pains. After that he installed ground wires.

 

[infinity]

Sure 250.118 for 230 volts and 250.97 if over 250 volts to ground. If your KO's on the panel are full sized (meaning 1 1/8" hole) then a standard EMT connector is all that's required to bond the raceway even if the voltage was over 250 volts to ground.

250.118 Types of Equipment Grounding Conductors. The
equipment grounding conductor run with or enclosing the
circuit conductors shall be one or more or a combination of
the following:
(1) A copper, aluminum, or copper-clad aluminum conduc‐
tor. This conductor shall be solid or stranded; insulated,
covered, or bare; and in the form of a wire or a busbar of
any shape.
(2) Rigid metal conduit.
(3) Intermediate metal conduit.
(4) Electrical metallic tubing.

250.97 Bonding for Over 250 Volts. For circuits of over
250 volts to ground, the electrical continuity of metal raceways
and cables with metal sheaths that contain any conductor other
than service conductors shall be ensured by one or more of the
methods specified for services in 250.92(B), except for (B)(1).
Exception: Where oversized, concentric, or eccentric knockouts are not
encountered, or where a box or enclosure with concentric or eccentric
knockouts is listed to provide a reliable bonding connection, the follow‐
ing methods shall be permitted:
(1) Threadless couplings and connectors for cables with metal
sheaths
(2) Two locknuts, on rigid metal conduit or intermediate metal
conduit, one inside and one outside of boxes and cabinets
(3) Fittings with shoulders that seat firmly against the box or cabinet,
such as electrical metallic tubing connectors, flexible metal
conduit connectors, and cable connectors, with one locknut on
the inside of boxes and cabinets
(4) Listed fittings

 

[bwat]

Best practice is to run a green ground in every conduit. My old cheap skate corner cutting boss almost got electrocuted due to using EMT conduit for ground on a 480 volt circuit. he got called to look at the conduit that pulled apart.While trying to reinstall the conduit he nicked the wire and got thrown to floor with severe chest pains. After that he installed ground wires.

“Best” is certainly debatable. But also, how would the green ground have helped your boss in that scenario where he was shocked?

 

[hillbilly1]

“Best” is certainly debatable. But also, how would the green ground have helped your boss in that scenario where he was shocked?

I have seen where the emt was seperated by forklift damage, a fault happened in the section not connected to the panel, energizing steel racking. Even though the racking was bolted to a concrete floor, the resistance of the return path was too high to trip the ocp. Customers and employees were complaing of getting shocked. If a seperate ground was pulled, the ocp would have tripped.

 

[electrofelon]

I have seen where the emt was seperated by forklift damage, a fault happened in the section not connected to the panel, energizing steel racking. Even though the racking was bolted to a concrete floor, the resistance of the return path was too high to trip the ocp. Customers and employees were complaing of getting shocked. If a seperate ground was pulled, the ocp would have tripped.

Funny, I think just the opposite: best to NOT rely on a green wire and all those potentially improperly done wirenut connections, skipped/loose ground screws, etc and instead have a properly installed and maintained conduit system as the ground.

 

[480sparky]

There's no one, single, perfect grounding method. They all can be installed wrong. They all can be damaged to the point of being unsafe.

There's no guarantees in life.

Myself, I use the EMT. I install ground screws before I even install the boxes in place. If I need a pigtail, that gets installed as well. Once I install the EMT, I go back through it all with a screwdriver and make sure everything is tight.

 

[winnie]

Back to the OP: EMT installed with listed connectors is considered a valid equipment grounding conductor per the NEC.

This would include using standard 'set screw' connectors in a metal box with a lock nut.

The client engineering standard requires EMT to be installed to NEC standards.

The fact that you used a grounding bushing and then extended an external EGC from the last receptacle to the ground bus in the room IMHO exceeds the requirements of the NEC.

-Jon

 

[dkidd]

Our project client has their own Engineering Standards that state:



We have done all above ceiling conduit work using EMT conduits following methodology: https://ibb.co/4P9tZDQ
However, the inspector consider the installation violating the standards for not grounding and boning each conduit in the raceway. Please help me understand further the requirement for grounding EMT conduits and what's NEC requirement for grounding and bonding EMT that mentioned in the exception?

I'm not sure what you mean by "not grounding and bonding each conduit in the raceway".

In any event, it seems from the specification that the Engineer recognizes that EMT is not conduit, and allows different, Code compliant bonding and grounding.

 

[kwired]

Many comments here are leaning towards pulling a green wire in the raceway, but I think the specifications in OP are going beyond that and wanting the metal raceway bonded by something other than regular locknuts. It pretty much requires use of hubs, external bonding clamps or grounding bushings and is requiring it on both ends of raceway in most instances.

 

[480sparky]

The NEC does not prohibit 'going beyond' it's own requirements, nor places limits on how far one can go. If someone wants 15 grounding/bonding methods for each conduit run, that's perfectly legal.

If a customer wants to require the electrician to wear a pink tutu, cowboy boots a yellow banana hat and play the bagpipes during the install, they're certainly free to do so.