Underground power 600v grounding

[Cjmccarthy]

I work for the FDOT, and we are doing a walkthrough of a project that was completed. The project is an ITS project. The power service goes to a generator site that has an Automatic transfer switch for backup power. From there it goes underground in a 2inch HDPE conduit, and we are using Quazite Pull Boxes (Concrete blend). The 2 conductors are carrying 600v along with a green ground conductor to each site. The runs are long, and the contractor must splice the conductors together in some of the pull boxes. On every other project, the contractor installed a ground rod in the pull box where a splice was present and Exothermic Welded the ground conductors to the ground rod. On the latest project, they are fighting that and saying, "Where in the FDOT spec does it say we have to do that!". The FDOT references the NEC, NESC and many other agencies for references outside their spec. My question is, is there a code I can hold them to in either the NEC or NESC?


Thank you, Chris

 

[petersonra]

What is the point of all those ground rods?

 

[Cjmccarthy]

Bob, I don't know what the point of all the ground rods are for, hence my question. I was told (years ago) that it is a requirement that at any pull box where they have to splice the conductors together, instead of splicing the ground wires together, they need to install a ground rod and Exothermic Welded the ground conductors to the ground rod.

 

[tortuga]

Who is the Authority Having Jurisdiction (AHJ) and whats an ITS project?

 

[petersonra]

Bob, I don't know what the point of all the ground rods are for, hence my question. I was told (years ago) that it is a requirement that at any pull box where they have to splice the conductors together, instead of splicing the ground wires together, they need to install a ground rod and Exothermic Welded the ground conductors to the ground rod.

I could see bonding the EGC to the lid of the box and the box itself if they are conductive, but I can't see any useful purpose in adding a ground rod at a handhole to bond to the EGC.

 

[Cjmccarthy]

Who is the Authority Having Jurisdiction (AHJ) and whats an ITS project?

Florida Department of Transportation (FDOT), the Intelligent Transportation System (ITS), is all the Cameras, Vehicle Detectors, Message Boards and more on the highways, and roadways. We have fiber optic and power going to each site. The DOT has specs and standards to go off of, but they reference different code enforcement agencies to reference when it is not covered in the FDOT standards.

 

[tortuga]

Florida Department of Transportation (FDOT), the Intelligent Transportation System (ITS), is all the Cameras, Vehicle Detectors, Message Boards and more on the highways, and roadways. We have fiber optic and power going to each site. The DOT has specs and standards to go off of, but they reference different code enforcement agencies to reference when it is not covered in the FDOT standards.

Ahh Ok I see
But who is the individual/ or office responsible for enforcing the requirements of a code or standard, or for approving equipment, materials, an installation, or a procedure for this project?

 

[Cjmccarthy]

Ahh Ok I see
But who is the individual/ or office responsible for enforcing the requirements of a code or standard, or for approving equipment, materials, an installation, or a procedure for this project?

The FDOT uses Construction Engineering & Inspection (CEI) firms to manage roadway construction including: earthwork and grading operations, drainage and utility work, aggregate base, asphalt, and concrete pavements, installation of roadway signage, striping, and ITS. Then the Department will check the work to make sure nothing was missed.

 

[Cjmccarthy]

I could see bonding the EGC to the lid of the box and the box itself if they are conductive, but I can't see any useful purpose in adding a ground rod at a handhole to bond to the EGC.

When we inspect the street lighting, there is a clear standard to bond to the ground rod at every light pole and or structure. Also any metal pull box lids.

 

[petersonra]

When we inspect the street lighting, there is a clear standard to bond to the ground rod at every light pole and or structure. Also any metal pull box lids.

The EGC that comes in with the circuit conductors should be bonded to the metal pole structure and boxes and lids and covers. I don't see that a ground rod even serves a purpose, but if the state wants one, then it should be bonded to the EGC.

 

[tortuga]

Seems like the NEC would apply not the NESC, unless there is somthing the NESC addresses thats not covered in the NEC.
The NESC is a performance code intended for the POCO that has in house engineering supervision.

The only thing I'd could add about the ground rod in the pull boxes is look into NEC 110.10, if line to dirt ground fault happened near a pull box and the nearest ground rod is a mile away the devices used to clear a fault may not work as intended.

 

[petersonra]

Seems like the NEC would apply not the NESC, unless there is somthing the NESC addresses thats not covered in the NEC.
The NESC is a performance code intended for the POCO that has in house engineering supervision.

The only thing I'd could add about the ground rod in the pull boxes is look into NEC 110.10, if line to dirt ground fault happened near a pull box and the nearest ground rod is a mile away the devices used to clear a fault may not work as intended.

The earth shall not be considered as an effective ground-fault current path. 250.4 (A)(5).

 

[tortuga]

There was a case in Seattle about 10-12 years ago, a guys dog got electrocuted on or next to a street lighting pull box.
The Seattle City Light said it was an isolated incident.
But then they found another energized vault in another neighborhood, if I recall right they had to re-do alot of street lighting after that.
There was a electrocution incident in Honolulu around the same time, also involving a pull box and street lighting, same type of problem, ground faulted wire and no effective return path.

 

[Cjmccarthy]

The EGC that comes in with the circuit conductors should be bonded to the metal pole structure and boxes and lids and covers. I don't see that a ground rod even serves a purpose, but if the state wants one, then it should be bonded to the EGC.

I am not sure the State wants one, It was just told to me as an inspector that there has to be one. But is everyone is in agreement that there is no reason for it and it is not in the NEC code book, then I don't need to push the contractor to install one.

 

[tortuga]

The The runs are long, and the contractor must splice the conductors

Like how long?
And how far are these pull boxes from the light poles?

 

[Cjmccarthy]

Like how long?
And how far are these pull boxes from the light poles?

a load center can feed multiple devices, we typically have a device within 1/2 mile, so runs can be up to 2,500ft.

 

[tortuga]

If I were doing a mid-pull box with a splice a thousand feet from a load center, and thousand to a pole I would put in a ground rod and tie into an the ECG.
If the pull box is close to the pole base I would not worry about it.

 

[Cjmccarthy]

If I were doing a mid-pull box with a splice a thousand feet from a load center, and thousand to a pole I would put in a ground rod and tie into an the ECG.
If the pull box is close to the pole base I would not worry about it.

That is the case. we have pull boxes every 500ft-800ft, so some of the pull boxes are pull through boxes and some of them have splices. There might be 5 or 6 sometime as many as 8 pull boxes between devices, depending on the run. the contractor usually will set up at one pull box and pull north to a pull box and then go back and pull south, that way they eliminate a splice. It is a 600v circuit through the pull boxes and then when it gets to a device location, it enters a stepdown transformer to bring it to the 120/240v needed for the cabinet. I see you said "If you were doing it" But I need to know if there is a NEC code I can reference?

 

[don_resqcapt19]

That is the case. we have pull boxes every 500ft-800ft, so some of the pull boxes are pull through boxes and some of them have splices. There might be 5 or 6 sometime as many as 8 pull boxes between devices, depending on the run. the contractor usually will set up at one pull box and pull north to a pull box and then go back and pull south, that way they eliminate a splice. It is a 600v circuit through the pull boxes and then when it gets to a device location, it enters a stepdown transformer to bring it to the 120/240v needed for the cabinet. I see you said "If you were doing it" But I need to know if there is a NEC code I can reference?

The code does not require the ground rod.

I have never seen ground rods installed at manholes, even on large medium voltage distribution systems. If I am doing there would not be a ground rod.

 

[tortuga]

Every medium voltage distribution system I have ever worked on has some type of grounding connection at every pole or every 500' or so.
I recently had do groundrods for a POCO transformer vault I was setting for them.
I am no expert but I'd look at that NEC 110.10