250.64(E)

[dana1028]

I am resurrecting an old forum discussion [2007] in which Don made some comments about the needed bonding of the GEC when routed through other enclosures.

I have a photo from the 2011 "Electrical Grounding & Bonding" by Simmons.

Based on Don's reply to Pierre [see below], I gather the bonding within the enclosure is not necessary since all the conduits are already electrical connected [assumption - the top raceway is electrical/mechanically connected to the service cabinet].

Don's comments [2007]
Pierre,
Quote: Does it matter where the bonding occurs in the enclosure, such as at the point of entry or at a bus located inches away?
As long as the enclosure is metallic, the point of bonding between the GEC and the enclosure does not matter. If the GEC terminates on a bus, the bus would have to be bonded to the enclosure by a conductor with a an area equal to or greater than the area of the GEC. Bonding at both ends is only required when the enclosure is not electrically continuous. If you have a metal enclosure with a GEC passing through and the GEC is protected by a ferrous raceway, you could use standard locknuts on both of the raceways and a single bond to the enclosure and be in compliance with the rule in 250.64(E).

Quote: When thinking of this question, if bonding location is not important, then why are we required to bond at both ends of the enclosure?
The bonding requirement for a ferrous raceway is to make it electrically continuous. In the case of a raceway originating at a metallic enclosure, the GEC is bonded to the enclosure and to the other end of the raceway. There no code section that specifies the type of bonding that is required at the raceway to enclosure termination point. The section only refers to the Chapter 3 requirements, so standard locknuts would be permitted. If you are installing the GEC through a hole in the enclosure and the GEC is bonded to the enclosure, there is no additional bonding required.
Don

My question: I just want to make sure I am correctly understanding Don's previous comments. They sound logical, and I don't want to be making electrician's perform additional bonding if it is not required. Thanx for any feedback.

 

[infinity]

If you look at the graphic you'll see a bonding locknut used to bond the raceway to the enclosure instead of directly to the conductor itself. Mike Holt has a similar graphic depicting a bonding bushing or a bonding locknut. When I read that section I see no mention of a bonding locknut and have never understood where that permission comes from in the NEC. I agree that if the GEC is bonded somewhere to the enclosure that the bonding directly to the raceway where it enters the enclosure is redundant but the wording doesn't seem to support that interpretation since it says it needs to be bonded directly to the raceway at both ends.

IMO this section needs to be completely rewritten since it's current wording is pretty bad.

 

[don_resqcapt19]

In the graphic in post #1, I see no code reason for the grounding bushing on the top conduit or for the bonding jumper to the enclosure.

 

[Smart $]

In the graphic in post #1, I see no code reason for the grounding bushing on the top conduit or for the bonding jumper to the enclosure.

I agree. The concept is to bond metal enclosing the GEC at entry and exit points. Intermediate metal raceways and/or enclosures with solid electrical interfacing become bonded through the entry and exit bonds.

Case in point, in the graphic of post #2, there is no need for raceway bonding inside the service disconnect, as long as the raceway is solidly bonded to the disconnect enclosure by way of its termination.

 

[augie47]

I agree. The concept is to bond metal enclosing the GEC at entry and exit points. Intermediate metal raceways and/or enclosures with solid electrical interfacing become bonded through the entry and exit bonds.

Case in point, in the graphic of post #2, there is no need for raceway bonding inside the service disconnect, as long as the raceway is solidly bonded to the disconnect enclosure by way of its termination.

Humm.. a "learning moment"... I had always thought a bonding bushing was required at each end due to common practice here and my mis-reading the article. It does seem strange, however, that we don't accept "standard locknuts and bushings" for bonding on services and yet we would for bonding grounding electrodes which are subject to as high or higher fault currents.

 

[raider1]

In the graphic in post #1, I see no code reason for the grounding bushing on the top conduit or for the bonding jumper to the enclosure.

Don, I think that an argument can be made that the new wording of 250.64(E) in the 2011 NEC would require a bonding bushing on the top raceway due to the use of standard locknuts for bonding.

Here is the new wording of 250.64(E) from the 2011 NEC.

(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. If a raceway is used
as protection for a grounding electrode conductor,

Chris

 

[don_resqcapt19]

Don, I think that an argument can be made that the new wording of 250.64(E) in the 2011 NEC would require a bonding bushing on the top raceway due to the use of standard locknuts for bonding. ...

Chris, I have no idea where that wireway is. A wireway is not "service equipment" but if it is at the service equipment you could be correct. If that is the case, then both conduits would require "direct" bonding of the conduit to the wireway. I don't see the jumper from the GEC to the wireway as being the required bond, if such a bond is actually required.

 

[Smart $]

Humm.. a "learning moment"... I had always thought a bonding bushing was required at each end due to common practice here and my mis-reading the article. It does seem strange, however, that we don't accept "standard locknuts and bushings" for bonding on services and yet we would for bonding grounding electrodes which are subject to as high or higher fault currents.

The objective of a GEC is not to handle fault current, at least not the full brunt of fault currents. It will carry some fault current just by the nature of electrical phenomenon and the connection to the grounding system.

If a GEC enters a remote-from-disconnecting-means enclosure and is routed through a ferrous metal raceway to the disconnecting means enclosure, how much electrode-bound current do you want traveling through the raceway? ...the GEC? If the ferrous metal raceway is electrically continuous to the enclosures by the use of standard locknuts, what purpose does bonding serve other than redundancy?

 

[Smart $]

Chris, I have no idea where that wireway is. A wireway is not "service equipment" but if it is at the service equipment you could be correct. If that is the case, then both conduits would require "direct" bonding of the conduit to the wireway. I don't see the jumper from the GEC to the wireway as being the required bond, if such a bond is actually required.

The question I see raised is why is the conduit in the top of the wireway bonded to the GEC while the one in the bottom of the wireway not bonded to the GEC. I see the lower conduit is bonded below from the electrode end, but the requirement says each end... not somewhere in the middle. If bonding at each end of intermediate raceways and enclosures is the intent, then bonding is required to both sides of each intermediate "joint"...