Electrician forgot to connect ground wire....how big of deal is this?

Status
Not open for further replies.

awesomesauce

Member
Location
Colorado
Forgive the stupid question: I'm merely an "electronics guy" in need of some perspective from the experts....

Our company hired a commercial electrician to install a 480V 200A (3 phase) feed to a new piece of equipment. Electrician connected the chassis ground of the equipment to the service disconnect enclosure via the green ground screw and nothing else. So there is a 3/0 green wire (from the equipment) going to this giant screw terminal, which is then connected to the service disconnect box (and nothing else) via a long, green-annodized, 6-32 screw (and that's all). We discovered this problem when we found out that the equipment wasn't grounded - turns out, the green screw wasn't even tight (so it wasn't making connection).

The feed to this service disconnect is 3-phase, 480V, 200A, done with 4/0 wire for the phases, and there is a 10AWG green wire that bonds the service disconnect box.

My understanding from 250.122 is that the ground should be at least 6AWG copper, since there is 200A available on the supply.

I assume the green screw is completely insufficient, but how big of deal is this? Thankfully, no one got hurt, but when the electrician comes to fix it (which I assume will involve pulling a new 10AWG ground), how loudly should I be yelling?
 

awesomesauce

Member
Location
Colorado
The conduit to the service disconnect is metallic, but the cable from the disconnect to the equipment is a thick piece of SO cable.

We discovered it was ungrounded when trying to solve an electrical noise problem.

Attached is a picture. The cables leaving on the bottom left are the SO cable going to the equipment, and there is a metalic conduit off the frame to the right where the supply comes in (along with the 10AWG ground that you can see bonding the service disconnect/fuse box)
 

Attachments

  • 20161019_142749.jpg
    20161019_142749.jpg
    141.4 KB · Views: 0

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
I be confused here.
You say there is 3/0 ground wire and then you say you need to pull a new #10.

#6 as you stated is the minimum. You can use a larger one.
you cannot use #10 as it is smaller.
A #6 screw is not sufficient as you have stated already.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
If the metal raceway qualifies as an EGC then the load size EGC can be terminated directly to the enclosure. I don't see the bonding screw as compliant. This is a disconnecting means for a piece of equipment not a service, correct?
 

awesomesauce

Member
Location
Colorado
Yes, it is a disconnecting means for a piece of equipment (sorry - I'm still learning terminology and realize I was misusing the term "service disconnect")
 

kwired

Electron manager
Location
NE Nebraska
The 10 AWG grounding conductor with the supply circuit is too small, should not have caused you "open ground" issues though, possibly the loose bonding screw that you mentioned was the bigger culprit. If you had metallic conduit for the supply - it also is suitable to be used as the equipment ground, but all fittings need to be tight or it is not so effective.

The bonding screw in such a disconnect is likely at least a #10 screw, I don't think I have ever seen one smaller then #10. Whatever size it may be - if it is the one shipped with the disconnect it is listed for use in there so someone involved in testing it feels it is sufficient size.
 

Saturn_Europa

Senior Member
Location
Fishing Industry
Occupation
Electrician Limited License NC
If the metal raceway qualifies as an EGC then the load size EGC can be terminated directly to the enclosure. I don't see the bonding screw as compliant. This is a disconnecting means for a piece of equipment not a service, correct?


I agree with you that the electrician could be using the metal raceway as an EGC. But if this was his intent, why did he pull a #10 green wire? Its a little odd.
 

awesomesauce

Member
Location
Colorado
So the loose screw was fixed (obviously) - does this "fix" the problem?

How do we know if the conduit is being used as ECG (in addition to the #10 wire that was pulled)?

And even if that were a #10 green bonding screw, is that really all that is necessary to connect that 3/0 wire to ground?
 

kwired

Electron manager
Location
NE Nebraska
So the loose screw was fixed (obviously) - does this "fix" the problem?

How do we know if the conduit is being used as ECG (in addition to the #10 wire that was pulled)?

And even if that were a #10 green bonding screw, is that really all that is necessary to connect that 3/0 wire to ground?
That 3/0 ground wire only needs to be 6 AWG, but with SO cord, same size green as the other conductors is usually most common stocked item so that is why it is so large.

If metal conduit is used rules for installing that conduit require it to be electrically continuous or add bonding jumpers as needed to assure it is continuous. This usually only an issue with loose fitting parts, sections in the run that are non conductive for whatever reason, or places where low impedance is questionable or compromised. It has become somewhat common practice to pull a wire EGC in the raceway anyhow as additional assurance there is a good EGC to the final end of the run, though NEC is fine with using raceway only as the EGC. Why your guy installed a #10 EGC, I have no clue.
 

awesomesauce

Member
Location
Colorado
Ok, I get that. But assuming the conduit is serving as the EGC and the #10 wire is just "extra", is the single screw connecting the box to the equipment ground sufficient? My intuition says that is not a "low impedance" connection...
 

kwired

Electron manager
Location
NE Nebraska
Ok, I get that. But assuming the conduit is serving as the EGC and the #10 wire is just "extra", is the single screw connecting the box to the equipment ground sufficient? My intuition says that is not a "low impedance" connection...
It is tested and listed for that purpose. You must use the screw they provide and put it in the hole they designed for it.

Look carefully at the hole it threads into in the back wall of the enclosure. It is probably machined so that it has a little more thickness right there for more contact area then if it were just drilled and tapped into the regular thickness of the rest of the enclosure. That is common for a lot of similar applications.
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Ok, I get that. But assuming the conduit is serving as the EGC and the #10 wire is just "extra", is the single screw connecting the box to the equipment ground sufficient? My intuition says that is not a "low impedance" connection...
If that were a service disconnect and a 3/0 grounded conductor had been brought in and landed on that neutral buss, the #10 green bonding screw is all that would be required to bond the enclosure and any conduit connected to it. So, yes the screw is sufficient if torqued correctly.
 

kwired

Electron manager
Location
NE Nebraska
Interesting. I suppose that makes sense. It doesn't look like the terminal and screw came with the disconnect, though.
The terminal and bonding screw for the 3/0 green most likely did, the one the 10 AWG is landed in IDK for certain. Could be an optional equipment grounding lug that is listed for using in that equipment.

If it is just a lug that they mounted themselves there could be some problems depending on a few details of how it was done. One usually needs to remove paint from the contact area and if just tapping the enclosure wall there is rules on number of threads that need to be engaged into that tapped hole - off top of my head I think it is two threads - so if the enclosure is less then 1/16 inch thick and you use a screw with 32 threads per inch, it would be less then two threads engaged.
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
Equipment ground vs neutral bar

Equipment ground vs neutral bar

I think it might help the OP to point out that the point where the EGC is connected in the disconnect in the photo is actually a neutral bar converted to an EG bar by installing the factory bond screw. This is a common practice where the disconnect is not being used a service disconnect and there is no neutral involved in the application. It achieves the same result when used under these conditions. I'm not sure that it meets the letter of the code but is a very common practice and if the factory screw has been tightened correctly you would not have had an issue.
As for the #10 EGC in the supply circuit, that is obviously undersized as pointed out by others. But if the conduit qualifies as an EGC you don't need a wire type EGC at all to be compliant. Note though that this wire type EGC would be viewed as an optional EGC if the conduit qualifies as the EGC but it would still have to be sized per 250.122.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
The problem, in my opinion, is that the electrician used an insulated lug that was intended to be used for a neutral as his landing point for an equipment ground. He probably should have installed a lug for the EGC directly to the box instead. If there was a neutral in the circuit this wouldn't have happened.
 

awesomesauce

Member
Location
Colorado
Texie, you're saying that even if the #10 wire is an optional EGC (and the conduit is the "intended" EGC), the wire still has to be sized per 250.122? So it needs to either be removed or made bigger?
 
Status
Not open for further replies.
Top