Metallic Cable Tray Ground/Bond, 392-7

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tryinghard

tryinghard

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A metal frame of a building can be an electrode as described in 250-52(A)(2) but can a metal tray system that is labeled "UL approved for equipment grounding" also be an electrode when effectively grounded like the metal frame of a building?

392-7 tells me "Metallic cable trays...shall be grounded as required...in accordance with 250-96"

250-96(A) tells me "...cable trays...that are to serve as grounding conductors...shall be effectively bonded..."

Looks like an effectively bonded tray system IS the grounding conductor, or is it [can it be] the electrode like a building metal frame?

Can I terminate a properly sized GEC from a transformer to an effectively bonded tray system, and will this GEC be considered unbroken when doing so?
 
There are no code provisons that permit you to use cable tray as a grounding electrode or as an equipment grounding conductor.
 
don_resqcapt19 said:
There are no code provisons that permit you to use cable tray as a grounding electrode or as an equipment grounding conductor.
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Not sure I fully agree

Q. Must a metallic tray be grounded?

A. Metallic cable trays must be effectively bonded to ensure electrical continuity and the capacity to safely conduct any fault current likely to be imposed on them [250.96(A)]. This is accomplished by bonding the metal parts to an equipment grounding (bonding) conductor that's sized to the circuit protection device in accordance with 250.122 [392.7(A)].

Note: Metallic cable trays can serve as equipment grounding (bonding) conductors where continuous maintenance and supervision ensure that qualified persons service the installed cable tray system, and the [392.3(C) and 392.7(B)]:

Cable tray sections and fittings are identified for grounding (bonding) purposes.

Cable tray sections, fittings, and connected raceways are bonded to each other in accordance with 250.96 using bolted mechanical connectors or bonding jumpers sized in accordance with 250.102.
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http://ecmweb.com/mag/electric_stumped_code_19/
 
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tryinghard said:
A metal frame of a building can be an electrode as described in 250-52(A)(2) but can a metal tray system that is labeled "UL approved for equipment grounding" also be an electrode when effectively grounded like the metal frame of a building?

392-7 tells me "Metallic cable trays...shall be grounded as required...in accordance with 250-96"

250-96(A) tells me "...cable trays...that are to serve as grounding conductors...shall be effectively bonded..."

Looks like an effectively bonded tray system IS the grounding conductor, or is it [can it be] the electrode like a building metal frame?

Can I terminate a properly sized GEC from a transformer to an effectively bonded tray system, and will this GEC be considered unbroken when doing so?
Click to expand...
IIRC, a cable tray can be an EGC.

I don't see how it can be a GEC. I think you have to run your GEC to a GE. The cable tray is not a GE.
 
tryinghard said:
I believe CA is on 2002 but the agency I'm working for is on 2005
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Just wondering since the hyphenated article numbers disappeared after the 1999 code cycle.
 
petersonra said:
IIRC, a cable tray can be an EGC.

I don't see how it can be a GEC. I think you have to run your GEC to a GE. The cable tray is not a GE.
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Thats the way I understand 397-7(397.7 Bob :)), I am looking for varifications. What is "IIRC"?
 
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M.D.
Yes, I did not type what I was thinking in my first post. I intended to say that there are no provisions that permit the use of cable tray as the grounding electrode conductor.
 
don_resqcapt19 said:
M.D.
Yes, I did not type what I was thinking in my first post. I intended to say that there are no provisions that permit the use of cable tray as the grounding electrode conductor.
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Got it, thanks Don
 
Tryinghard,
I think you know there is a difference between a grounding conductor and an electrode conductor, much less an electrode itself. Dont have a code book handy but I wouldnt think its even technically legal. But even if it was I would say it violates the intent of the code - so if I was the inspector I would tell you no way.
 
Wait a minute I don't claim to know anything anymore :-?

"Grounding Conductor. A conductor used to connect equipment or the grounded circuit...to a grounding electrode..."

"Grounding Electrode Conductor [GEC]. The conductor used to connect the grounding electrode to the...grounded conductor..."

"Grounding Conductor, Equipment [EGC]. The conductor used to connect the...equipment...to the...grounding electrode conductor..."

And again 250.96(A) tells me "...cable trays...that are to serve as grounding conductors...shall be effectively bonded"

So I can use the tray as a "grounding conductor" and I know the tray is not listed as an electrode in 250.52.


What makes the "grounding conductor" uniquely different than the EGC and GEC?
 
Based on Mike Holts Grounding versus Bonding Part 1 of 12 I would say the "grounded conductor" is for a supplemental electrode. Mike Holt notes:
"Grounding (Earthing) Conductor. A conductor used to connect equipment to a grounding (earthing) electrode.
Author's Comment: A grounding (earthing) conductor can be used to connect a supplementary grounding (earthing) electrode to a piece of equipment [250.57] Figure 100-grounding conductor 250-54.cdr"
 
Metallic Cable Tray Ground/Bond, 392-7

In 250.96(A) the cable tray is permitted to be used as the equipment grounding conductor, with or without the use of supplementary equipment grounding conductors.
For system grounding equipment grounding conductor is required to be connected to the grounded service conductor and the grounding electrode conductor.
Equipment grounding conductor connections at the source of separately derived systems shall be made in accordance with 250.30(A)(1).
To use the building metal frame as an electrode it must meet the requirements of 250.52(A)(2).
In my opinion the effectively bonded cable tray does not meet the requirements of the grounding electrode and cannot be used as the grounding electrode to ground a transformer.
 
cripple said:
In 250.96(A) the cable tray is permitted to be used as the equipment grounding conductor, with or without the use of supplementary equipment grounding conductors.
For system grounding equipment grounding conductor is required to be connected to the grounded service conductor and the grounding electrode conductor.
Equipment grounding conductor connections at the source of separately derived systems shall be made in accordance with 250.30(A)(1).
To use the building metal frame as an electrode it must meet the requirements of 250.52(A)(2).
In my opinion the effectively bonded cable tray does not meet the requirements of the grounding electrode and cannot be used as the grounding electrode to ground a transformer.
Click to expand...

Yes I agree but an effectively bonded tray can serve as a grounding conductor 250.96(A), so the question evolves - what does one use a grounding conductor for?

Answer Post #15
 
tryinghard said:
Based on Mike Holts Grounding versus Bonding Part 1 of 12 I would say the "grounding [not grounded] conductor" is for a supplemental electrode. Mike Holt notes:
"Grounding (Earthing) Conductor. A conductor used to connect equipment to a grounding (earthing) electrode.
Author's Comment: A grounding (earthing) conductor can be used to connect a supplementary grounding (earthing) electrode to a piece of equipment [250.57] Figure 100-grounding conductor 250-54.cdr"
Click to expand...

Oops, correction in Post 15 to say grounding conductor rather than grounded
 
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