The Electrical Contractor Network

ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

Books, Tools and Test Equipment for Electrical and Construction Trades

Register Now!

Register Now!

We want your input!


2017 NEC and Related
2017 NEC
Now Available!

Recent Posts
Parking lot pole light swap....
by gfretwell
10/24/16 08:46 PM
International Wire Colour Codes
by Tjia1981
10/23/16 12:08 PM
Son of Sparky
by HotLine1
10/20/16 07:43 PM
Speaking of Plugmold ...
by gfretwell
10/17/16 02:37 PM
Broken battery charger? Check for cobwebs!
by gfretwell
10/17/16 02:30 PM
New in the Gallery:
12.5A through 0.75mm˛ flex (just out of curiosity)
Shout Box

Top Posters (30 Days)
gfretwell 14
HotLine1 7
ghost307 7
renosteinke 6
Potseal 4
Who's Online
0 registered (), 292 Guests and 4 Spiders online.
Key: Admin, Global Mod, Mod
Topic Options
Rate This Topic
#15668 - 10/24/02 05:48 PM Manhole Questions
Webmaster Offline


Registered: 10/07/00
Posts: 3142
Loc: NY, USA
I found this last night and I am a bit confused. This picture is from down inside a 6'X 8' manhole. The three feeders you see are 12.47KV and they have an equipment grounding conductor pulled with each run as one would expect to see. One the other hand the single conductors that run with this duct bank are a bit of a mystery. They run all the way back to the 12KV substation and terminate on the equipment grounding bus. I haven't been in the MV Switches on the other end but I can assume they terminate in the same manor there. What would be the purpose of running these extra grounding conductors in a medium voltage duct bank? I have run and seen run a bare copper conductor in the encasement of similar duct banks but again I am at a lose to the theory behind it. Any one have any insight?

PS: The conductors were not continuous in this man hole. They were just coiled up on the floor. But that is a subject for another thread.

- Nick

Work Gear for Electricians and the Trades

Work Gear for Electricians and the Trades
Work Gear for Electricians and the Trades
Arc Flash Clothing, Gloves, KneePads, Tool Belts, Pouches, Tool Carriers, etc. etc....

#15669 - 10/27/02 06:56 PM Re: Manhole Questions
Trumpy Offline


Registered: 07/05/02
Posts: 8532
Loc: SI,New Zealand
It would'nt be some sort of an Earth-Potential Neutral conductor, would it?
Just a long shot guess!.

P.S:What small draw-cords in them conduits,
is this the normal size used?.

[This message has been edited by Trumpy (edited 10-27-2002).]
Let's face it, these days if you're not young, you're old - Red Green grin

#15670 - 10/28/02 06:06 AM Re: Manhole Questions
electure Offline


Registered: 12/24/00
Posts: 4226
Loc: Fullerton, CA USA
When we install a slab box for a xfrmr, we install 2 ground rods, normally at the corners of the box.
It looks like these are the grounds, and although installed in an unorthodox manner, what the heck?
The pull ropes are only installed to pull in the "real" pull ropes.

#15671 - 10/28/02 04:46 PM Re: Manhole Questions
Nick Offline

Registered: 08/13/01
Posts: 603
Loc: Riverside, CA
Thanks for the replies. I answered my own question, however. I found some of the original design drawings. The "extra" ground wires go from a lineup of 12KV switchgear, which is the service for the facility, to wall mounted ground bus' in each unit substation room. This is a typical ground bus where all the local bonds and transformer grounds are connected. I suppose the original designers meant to keep all the different buildings at the same potential. I know of two that aren't though because the original contractor never connected them!
The small pull lines were left by the original contractor. The 1/4" line we installed in preparation to pull the 12KV feeder for one of the two 12KV subs we are adding here. We pulled it Friday night (all 1140 feet!). but our drawings did not call for the extra ground that the original design called for.
Hmm. This brings up a question. Although this conductor is not required in the NEC, what possible benefits or problems could it bring to the facility?

#15672 - 10/28/02 05:21 PM Re: Manhole Questions
Bjarney Offline

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
The typically small cross-sectional area of tape or drain-wire shield conductors in MV90/105 cables has a problem doing what grounding is supposed to do--limit voltage rise and permit fault current to rapidly clear overcurrent conditions.

#15673 - 10/28/02 05:47 PM Re: Manhole Questions
Nick Offline

Registered: 08/13/01
Posts: 603
Loc: Riverside, CA
This is true! However, these feeders have separate equipment grounding conductors in parallel with the shields.


ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals