Rigid conduit and a bare ground wire

[Red Wiggler]

Please clarify something for me...

If I run a bare ground through a rigid conduit, I believe I am required to bond the conduit to the bare conductor to prevent parallel paths to ground and prevent a choke at the point of conductor emerging from the pipe. This would be true for a grounding electrode conductor.

But what if the bare ground is in a rigid conduit and the intent of the installation is to bring all steel parts of the building to the same potential by bonding everything together. Will the ground wires emerging from this installation still need to be bonded to the conduit by means of a special fitting or a grounding bushing? If so where can I find this in the NEC?

 

[don_resqcapt19]

The choke effect only occurs when you have a single AC conductor in a ferrous raceway. This is not the case when you install an EGC in the same raceway as the circuit conductors. There is no special bonding required when you install an bare EGC in a metal raceway, of course, the raceway itself has to be bonded some how, but that is normaly done by the lock nuts at the enclosures.

 

[Red Wiggler]

Rigid conduit and bare ground

Rigid conduit and bare ground

The issue is there is no entry into equipment with this ground wire. One end of the copper wire is emerging from a conduit and tied to a ground bar and the other end is cad-welded to building steel. Or in some case the conduit is run between building steel and the mounting framework for a motor, or the support strut that holds a controller. Everything in the building that is metal is being bonded together with this bare copper wire. The copper wire is only being protected by the rigid conduit which is the raceway between the points of termination.

 

[fmtjfw]

In that case you need to bound it at both ends. The metallic (ferrous) conduit will act as the core of a choke "coil" otherwise and limit the current rise on a fault. Also the Conduit may well be a lower resistance path than the conductor.

 

[Red Wiggler]

Bare Ground

Bare Ground

In that case you need to bound it at both ends. The metallic (ferrous) conduit will act as the core of a choke "coil" otherwise and limit the current rise on a fault. Also the Conduit may well be a lower resistance path than the conductor.

What section of the code refers to the bonding of the conduit to the bare ground conductor?

 

[ed downey]

2011 NEC 250.64(E)

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[fmtjfw]

NEC 2011

NEC 2011

250.64 Grounding Electrode Conductor Installation.
(E) Enclosures for Grounding Electrode Conductors.
Ferrous metal enclosures for grounding electrode conductors
shall be electrically continuous from the point of attachment
to cabinets or equipment to the grounding electrode
and shall be securely fastened to the ground clamp or
fitting. Nonferrous metal enclosures shall not be required to
be electrically continuous. Ferrous metal enclosures that are
not physically continuous from cabinets or equipment to
the grounding electrode shall be made electrically continuous
by bonding each end of the raceway or enclosure to the
grounding electrode conductor. Bonding methods in compliance
with 250.92(B) for installations at service equipment locations
and with 250.92(B)(2) through (B)(4) for other than
service equipment locations shall apply at each end and to all
intervening ferrous raceways, boxes, and enclosures between
the cabinets or equipment and the grounding electrode. The
bonding jumper for a grounding electrode conductor raceway
or cable armor shall be the same size as, or larger than, the
enclosed grounding electrode conductor.
...

 

[tom baker]

Some confusion here. What ground are you referring to? Or what color is it and what does it do?
Take a look at the 2011 definition of Ground.

 

[tom baker]

With grounding:
"We have met the enemy and they are us" Pogo.