Bonding buried end of metal conduit at nonmetallic adaptor

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Natfuelbilll

Senior Member
Here is the situation.

Medium voltage three phase feeder is being extended from existing manhole with three shielded cables and an insulated EGC. The feeder is to be installed in nonmetallic conduit and run into new manholes. Each new manhole has a local ground rod and bonding to installed metallic components (cable, rack, metal frame, etc.). Where splices are made in manholes the cable splice kit shield ribbon will be bonded to the EGC and the local manhole bonding.

At the last manhole the nonmetallic conduit extends out and then is adapted to metal sweep elbow and metal conduit that will exit the earth. The metal conduit will be connected to a metal box and additional metal conduit system. This first box is a pull-through box and will therefore not contain any splices.

1. Does the EGC need to be bonded to the box/conduit at the first metal box? It will be bonded at other downstream boxes where splices are to be made.

2 Does the end of the underground metal conduit need to be bonded where it meets the nonmetallic conduit? How?

Any specific NEC references are welcomed.

Thank you all Veterans for your service!
 

FionaZuppa

Senior Member
Location
AZ
Occupation
Part Time Electrician (semi retired, old) - EE retired.
#2, something like this
cch_cp_rigidlocknuts_sealinglocknuts_grounding_520.jpg

as for specific NEC #, i would have to go dig in and look, but i see no harm in bonding at all the locations you point out, unless you have to do a million of these, but i would not tap the egc if its just a pass-through, but bond down box and conduit. 250.118(4) allows the metal conduit to extent the egc, just not clear to me if you can pass the 1st metal junction and tie egc to metal downstream.
 
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Smart $

Esteemed Member
Location
Ohio
Bonding the EGC to the box in boxes where there are no splices is not required... but I do it anyway.

If you transition from underground nonmetallic to metallic at a depth greater than 18", you do not have to bond the interred end(s) of the metallic conduit section. Code actually says elbows... but I think AHJ can be persuaded for non-elbows.

However, if we are truly talking multiple manholes, I don't see the need for transition from M to NM is any one run...???
 

FionaZuppa

Senior Member
Location
AZ
Occupation
Part Time Electrician (semi retired, old) - EE retired.
Bonding the EGC to the box in boxes where there are no splices is not required... but I do it anyway.
just curious, if its insulated egc do you tap it using a clamp (removing a small section of egc insulation), or do you cut/pigtail it?
 

Smart $

Esteemed Member
Location
Ohio
The route is ~ 2000' using six manholes. NM has been chosen based on cost.
So the only place you use metal is on end runs in transition to above ground, right? Not manhole to manhole.

(Exception is for metal sweeps, but those should be in the middle of runs, not at end.)
 

Ronboz

Member
Location
NYNY
So if we only bond at one end of the rigid metal pipe , is there a touch potential safety issue at the other end of this metallic conduit ( say ~100 feet away) ?
 

Smart $

Esteemed Member
Location
Ohio
So if we only bond at one end of the rigid metal pipe , is there a touch potential safety issue at the other end of this metallic conduit ( say ~100 feet away) ?
How are you going to touch it if it is under ground? :p

Step potential safety should be only slightly different than when bonded at both ends.
 

Ronboz

Member
Location
NYNY
To clarify, would there be a touch potential problem ( above ground ) at the end of a 100 ft metallic conduit run where there is no bonding and I have a ground fault at the beginning of the 100 ft run which is properly grounded ? So, one end grounded, the other end not grounded , all above grade ?
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
To clarify, would there be a touch potential problem ( above ground ) at the end of a 100 ft metallic conduit run where there is no bonding and I have a ground fault at the beginning of the 100 ft run which is properly grounded ? So, one end grounded, the other end not grounded , all above grade ?
Would there be any touch potential problem in a similar scenario if the conduit were PVC with a green wire used for an equipment ground? Steel is a better equipment grounding conductor than any wire you can stuff in it.
 

Smart $

Esteemed Member
Location
Ohio
To clarify, would there be a touch potential problem ( above ground ) at the end of a 100 ft metallic conduit run where there is no bonding and I have a ground fault at the beginning of the 100 ft run which is properly grounded ? So, one end grounded, the other end not grounded , all above grade ?
If you have access to the far end, you're required to bond all non-current-carrying metal parts likely to be energized to the conduit... and if a separate structure, a disconnecting means and GES bond is also required.

Touch potential always exists when utilizing electricity. What is of concern is how well we mitigate the dangers. You have not provided enough information to give a quantitative answer (and even if you did, it would not be me giving the answer :D).
 
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