supplementary grounding,

[reyamkram]

What dose the code say about when to use supplementary grounding, do we use it when there is a possibility of vibration and damage to the conduit, ?? like in and industrial environment. lock nut and or connectors come lose, there is still a good ground fault path.

Thank you, for any information.

 

[Devin Hanes]

are you asking about a supplementary electrode? or a wire equipment ground inside a metal conduit?

 

[infinity]

250.53 uses the term supplemental grounding. It sounds like he's referring to an EGC. A wire type EGC is required in a flexible raceway that will be subject to vibration after installation.

 

[reyamkram]

are you asking about a supplementary electrode? or a wire equipment ground inside a metal conduit?

I am asking about the EGC, when installed in 10x10x2 box, with outlet mount on the cover, and a 3/4 conduit with 20 and 30 amp circuit conductors inside, the box is in a location subjected to damage and vibration, dose the same principles apply to conduit as it dose to FMT??

Thank you.

 

[Devin Hanes]

I am asking about the EGC, when installed in 10x10x2 box, with outlet mount on the cover, and a 3/4 conduit with 20 and 30 amp circuit conductors inside, the box is in a location subjected to damage and vibration, dose the same principles apply to conduit as it dose to FMT??

Thank you.

see 250.118
lengthy so not posting, unless you don't have access. but talks about LFMC, FMC needing wire with vibration and also speaks of RMC, EMT but not with vibration

FMC
348.60 Grounding and Bonding.

If used to connect equipment where flexibility is necessary to minimize the transmission of vibration from equipment or to provide flexibility for equipment that requires movement after installation, an equipment grounding conductor shall be installed.

LFMC
350.60

Above is what I believe Infinity referenced, you probably want to read this but I don't think it applies to the specific scenario you are describing unless you decide to use LFMC or FMC in there somewhere to mitigate the problems caused by vibration. I don't think you can install rigid metal conduit, IMC or EMT in a manner where you can reasonably expect it to vibrate loose required electrical bonding connections. Below are requirements I believe would be violated by my understanding of your description.

110.3

Examination, Identification, Installation, Use, and Listing (Product Certification) of Equipment.

(A) Examination. In judging equipment, considerations such as the following shall be evaluated:

(1) Suitability for installation and use...….
(2) Mechanical strength and durability,.....

110.2 Approval.

The conductors and equipment required or permitted by this Code shall be acceptable only if approved.

Article 100 Definitions

Approved.Acceptable to the authority having jurisdiction.

250.4(A)(4)and (5)

(4) Bonding of Electrically Conductive Materials and Other Equipment.

Normally non–current-carrying electrically conductive materials that are likely to become energized shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path.

250.90 General.

Bonding shall be provided where necessary to ensure electrical continuity and the capacity to conduct safely any fault current likely to be imposed.

250.96 Bonding Other Enclosures.
(A) General.

Metal raceways, cable trays, cable armor, cable sheath, enclosures, frames, fittings, and other metal non–current-carrying parts that are to serve as equipment grounding conductors, with or without the use of supplementary equipment grounding conductors, shall be bonded where necessary to ensure electrical continuity and the capacity to conduct safely any fault current likely to be imposed on them. Any nonconductive paint, enamel, or similar coating shall be removed at threads, contact points, and contact surfaces or shall be connected by means of fittings designed so as to make such removal unnecessary.

 

[Devin Hanes]

1983 ROP

Log # 1278
8- 76 - (350-5, Exception): Accept in Principle SUBMITTER: IAEI ~

RECOMMENDATION:
Add to end of present Exception: "; and the conduit is not installed in accordance with Section 350-4, Exception No. 2."

SUBSTANTIATION: This is to assure that an effective and continuous grounding path is maintained. Our field experience shows a consistent problem with loose connections and lost grounding paths where flexible metal conduit is used to wire equipment that is not fixed in one place or position. A recent experience involving electrical inspections of dozens of restaurants across different parts of the State showed this problem in each and every restaurant. This amendment would serve a dual function. First, it would assure that, in these instances, the equipment would remain grounded. Second, it would point out that, in lengths over 3 feet, flexible metal conduit must be secured.

PANEL ACTION: Accept in Principle. Add (new) Exception No. 2 to read: "When used to connect equipment where flexibility is required, a grounding conductor shall be installed." Editorial: Revise the existing exception by numbering No. i:

PANEL COMMENT: Revision provides for submitter's intent in a clearer manner. VOTE ON PANEL ACTION: AFFIRMATIVE: 13 NEGATIVE: O'Leary. EXPLANATION OF VOTE: O'LEARY: My objection to the acceptance of this change is that no consideration was given to flex leads for fixtures which are normally over 3 feet in length and in the supporting comment, in the last sentence, it points out that in lengths over 3 feet, flexible metal conduit must be secured. From a practical standpoint, this is virtually impossible in a hung ceiling where recessed fluorescent fixture