grounding through Flex

[victor9999]

Hi,

I am curently installing 1 in EMT for Fiber Optic cables. At the end of each run, we would install less than 3 ft of 1 in FLEX to a 4x4 box riveted to a Jiffy pole leading to Office furniture. My 1 in EMT is grounded at the Comms Closet
(Grounding Bus Bar).


Problem:

NEC states that FLEX is not a reliable ground. Therefore a 14 AWG ground wire should be used to bound the 1in EMT (at the last pull box) to the 4x4 box on the top of the jiffy pole.

My flex is not used between sections of Conduit. This is the last 2-3 feet of the run. The furniture has electrical wires going in through another jiffy pole and the electrical ground is provided through that path.

I am sick of having this guy on my ass so I intend to find something in writing.

There must be an exeption to FLEX when it is used in the last section of a run and is connected to a jiffy pole.

thanks for your help

 

[petersonra]

An EGC is required to be run with circuit conductors. I don't see how a fiber optic cable is a conductor.

You also have to bond metallic items likely to become energized.

IMO, the EMT can serve as the bonding means for the flex, if it turns out the flex is "likely to become energized". It may also be bonded by the connection to the jiffy pole.

 

[victor9999]

An EGC is required to be run with circuit conductors. I don't see how a fiber optic cable is a conductor.

You also have to bond metallic items likely to become energized.

IMO, the EMT can serve as the bonding means for the flex, if it turns out the flex is "likely to become energized". It may also be bonded by the connection to the jiffy pole.

Do you have the reference that states that the EGC is required only for runs with circuit conductors?

I know the Conduit requires to be grounded for safety but the flex at the end when it is Fiber optic running through it... I dont see the point. This guy gave me a paper that says: Bond conduit 121306 ALL FLEX

 

[roger]

First of all the NEC does not state "that flex is not a reliable ground".

The NEC actually recognizes it as an EGC if certain requirements are met.

250.118 Types of Equipment Grounding Conductors

The equipment grounding conductor run with or enclosing the circuit conductors shall be one or more or a combination of the following:

(5) Listed flexible metal conduit meeting all the following conditions:

a. The conduit is terminated in fittings listed for grounding.

b. The circuit conductors contained in the conduit are protected by overcurrent devices rated at 20 amperes or less.

c. The combined length of flexible metal conduit and flexible metallic tubing and liquidtight flexible metal conduit in the same ground return path does not exceed 1.8 m (6 ft).

d. Where used to connect equipment where flexibility is necessary after installation, an equipment grounding conductor shall be installed.

I would say that (b) and (c) covers your installation.

If it is a job spec, you may be out of luck though.

Roger