Elevated cable trays - when could these be considered subject to physical damage and unsupported tray cable not allowed per the NEC?

[bdn2004]

A guy at an established site (not new construction) got up in a mechanical lift doing some retrofit work, that goes on continuously at this site.
Many of the tray cables coming out of the elevated cable trays have only strain relief at the tray then onto their conduit that extends up from the equipment located on the floor. When up in the lift, for whatever reason the lift hit that section of an unsupported cable and it caused a fault. Is this typical installation an NEC violation because of the continuous maintenance and retrofit work that goes on ? On an every day basis seems the NEC exception would apply.

NEC 336.10 Exception to 7... which states:

Where not subject to physical damage, Type TC-ER shall be permitted to transition between cable trays and between cable trays and equipment or devices for distance not to exceed 1.8m (6 ft) without continuous support. The cable shall be mechanically supported where exiting the cable tray to ensure that the minimum bending radius is not exceeded.

 

[bdn2004]

No replies... I'm disappointed. I'm going to say it's my opinion that on an existing Plant site there are always hazards that you have to look out for.

They are supposed to do Job Safety Analysis (JSA's) before doing any work. If there is any chance you could hit something with your equipment- you are supposed to mitigate that hazard before you begin working. No matter what it is - cable, conduit, column, whatever.

 

[FacEngrPE]

This video has some examples of typical tray branch locations. 2020 changes series: Article 392 Cable Tray​

The description of your site above indicates it is a "supervised industrial location". The incident location required a manlift for access, so most of us would not consider it to be "subject to physical damage". The cable arrangement described seems consistent with what is allowed.

You can of course install armored type MC conduit in cable tray or conduit, but that is probably over the top.

 

[waross]

armored type MC conduit

Tough to source. May have unacceptable lead times for manufacture and delivery.

 

[bacon4life]

I wonder how theatre treat regular retrofiting of lighting? Seems like forklifts and/or mechanical lifts are powerful enough to demolish nearly any kind of protection.

 

[bdn2004]

Thanks for the replies....realize this a real life situation. I've heard that is the excuse of the offender... There's so much stuff changing all the time - that it is hardly a place not subject to physical damage and therefore a Code violation. I have some sympathy for him - operator's of the JLG's have to be very skilled to get where they go to miss everything suspended in the air and on the ground. The guy operating the lift will be hassled with drug testing and could lose his job. The company he works for will be fined, perhaps kicked off site for a while. Maybe a lawsuit. But it could lead to changing the corporate standards of wiring methods - like armored cable everywhere.

 

[waross]

Of manlifts the JLG brand is the worst. There is a time lag in the controls that makes accurate positioning impossible.
There is a trick that I taught to the instructor of a manlift course.
When precise positioning is important, get close and then stop the engine. Do your final positioning with the emergency electric hydraulic pump.
I have run a Genie Lift all day long, positioning it within 1/4 of the structure but never touching the structure. With a JLG I would be lucky to get within a foot and would still make contact from time to time.
I have some sympathy for the operator. If he survives, tell him about the emergency power trick.

 

[waross]

Anecdote alert!
The JLGs before the introduction of computer control were very good.
When JLG went to onboard processor control, they were very bad.
A friend of mine was unloading a brand new JLG at a jobsite when it lurched ahead unexpectedly due to the control lag.
The machine went over an embankment and rolled over at least once.
The operator was tethered to the basket as per regulations.
He spent a long time in hospital and came out with permanent injuries.
So someone took out a cable with a JLG?
On a JLG it could have been much worse.

 

[7anoter4]

In order to protect the cable, from cable tray up to connected equipment, you have to keep the minimum required in NEC Art.300.
In a power station -mainly in a machine room-it is recommended to run the cable from cable tray up to maximum 6 feet from the equipment in a rigid conduit-usually rigid steel conduit- and from here in a flexible conduit. The upper end of the rigid conduit will be attached to the cable tray using swivel tray clamps and grounding connectors. The conduit has to be attached firmerly to a pillar, column or other fixed object.