Equipment Grounding Conductor

Status
Not open for further replies.
G

gk351

Senior Member
Location
IL
On a job that is replacing a 4 pole ATS with a 4 pole Manual Transfer switch (MTS). The existing install had conduits that went from 1600 main breaker to ATS, and return conduits that went back to load side busbar within the same switchgear to feed two feeders via 2- 800A breakers.

We abandoned the in ground conduits, and piped in 8 4" GRC runs between the switchgear and the new MTS. The line will utilize 4 conduits, and the load in the remaining 4 conduits. We are pulling 4 parallel runs of 600kcmil, to feed line side and 4 back to the load side.

My question, we used Myers hubs to make connections between MTS and Main Switchgear. The distance between MTS And Main switchgear is 48". So do I still need to run an equipment ground in every single conduit? I believe I do, but just seems redundant mostly because of the short distance between the two cabinets.
 
16c3f3cf009deb510648d55c2f6b14a0.png


Switchgear to MTS photo


Sent from my iPhone using Tapatalk
 
gk351 said:
So do I still need to run an equipment ground in every single conduit? I believe I do, but just seems redundant mostly because of the short distance between the two cabinets.
Click to expand...

Yes, you either have to put a wire EGC in each conduit or put none in and use the conduit as the EGC.

I would not hesitate to use the conduit as the EGC, those conduits have less impedance than the wire EGC you would install.
 
iwire said:
Yes, you either have to put a wire EGC in each conduit or put none in and use the conduit as the EGC.

I would not hesitate to use the conduit as the EGC, those conduits have less impedance than the wire EGC you would install.
Click to expand...

I agree, the connection with 4" RMC and hubs would be more than sufficient to serve as the EGC especially 8 of them. :)
 
infinity said:
I agree, the connection with 4" RMC and hubs would be more than sufficient to serve as the EGC especially 8 of them. :)
Click to expand...

Exactly, look at that installation, eight RMCs, six of them tied together twice on strut racks, all coupling free and all using fully threaded connections.

I doubt you can bond those two cabinets together much more than that. :)
 
Smart $ said:
I did. I'm left wondering how qualified was the person that did the threading. :lol:
Click to expand...

:D

I noticed, I was thinking at the least I would put similar threads beside each other. Luckily I think the electrons will ignore that and oscillate very freely.
 
iwire said:
:D

I noticed, I was thinking at the least I would put similar threads beside each other. Luckily I think the electrons will ignore that and oscillate very freely.
Click to expand...
Yeah... but the nit-picky sort I am says the grounding is compromised. Probably best to run the wire-type GEC's... :happyyes:
 
The threader operators are young and the automatic release was releasing so yes a few of them got a bit long.

However, if I were to use the RMC as the EGC, I would have to effectively bond the conduits with bonding locknuts, correct?

I have always thought a Myers Hub Gave a great connection point when they are cinched down wrench tight, but threads leave little room for bonding locknut.


Sent from my iPhone using Tapatalk
 
gk351 said:
The threader operators are young and the automatic release was releasing so yes a few of them got a bit long.

However, if I were to use the RMC as the EGC, I would have to effectively bond the conduits with bonding locknuts, correct?

I have always thought a Myers Hub Gave a great connection point when they are cinched down wrench tight, but threads leave little room for bonding locknut.
Click to expand...
You mean the auto release was not releasing (at least not when it should have).

IMO, a Myers hub meets a qualification for the 250.97 exception:
(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
Click to expand...
 
iwire said:
No not all without concentric KOs or service conductors
Click to expand...

So since I'm going from the load side of my main breaker, to my MTS, and back to the load side bus that feeds my load side breakers, would this still be considered service conductors?

The knockouts were cut out by us, so we should be good using the threaded hubs and RMC as the EGC?


Sent from my iPhone using Tapatalk
 
gk351 said:
So since I'm going from the load side of my main breaker, to my MTS, and back to the load side bus that feeds my load side breakers, would this still be considered service conductors?
Click to expand...
No. The conductors are feeders because they are on the load side of the service disconnecting means.
 
gk351 said:
...
The knockouts were cut out by us, so we should be good using the threaded hubs and RMC as the EGC?
Click to expand...
Typically yes. However, as a result of the long cut threads (aka running threads), you have small diameter straight threads in the Myers hubs. As part of the listing, the hubs are investigated as an effective ground-fault path. The small straight threads in the Myers hubs may have compromised the grounding effectiveness. Sure it will have continuity not under a fault condition, but we have no way of determining there effectiveness under a true ground-fault condition. If the inspector picks up on this (and there is a good possibility he may not), he may reject the installation. Running wire type EGC's will improve your odds of passing inspection IMO.
 
Even though there is no inspection authority ( military installation), we will run ground wires just be sure!


Sent from my iPhone using Tapatalk
 
Smart $ said:
I do not see how you can possibly verify your assertion. Please enlighten me...
Click to expand...

I also concur with your thinking, as I'm not following the assertion. With a wire type EGC, there are only the initial and final terminations as discontinuity points, which could be points of failure. With a conduit system, there are all sorts of discontinuity points. Every locknut, every conduit thread, every coupling, etc. A lot more discontinuities between factory pieces of material.

In concept there may be fewer Ohms per foot in the metal of the conduit system, but if any connection is not made correctly, and goes unnoticed, you loose your ground path.
 
Smart $ said:
I do not see how you can possibly verify your assertion. Please enlighten me...
Click to expand...
Because I live my life in the real world and I think GRC screwed into a myers hub makes an excellent EGC even with imperfect threads. Besides that there is parallel paths a plenty in that install so even if the long thread was a real world problem it's already cured by the redundant fault current paths that are already present. What is going to be gained by adding one more fault path other than it will have that green insulation that makes everybody calm and think the world as a whole is a better place.
 
Status
Not open for further replies.
Top