Cable Tray vs. Conduit

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BRV

New member
Location
Birmingham, AL
I am doing a comparison on the use of cable tray vs conduit for a natural gas facility and would like input from anyone who has done anything similar. Please let me know.
 

Smart $

Esteemed Member
Location
Ohio
BRV said:
I am doing a comparison on the use of cable tray vs conduit for a natural gas facility and would like input from anyone who has done anything similar. Please let me know.
Don't forget to weigh in considerations for into, through, and from hazardous locations.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
In most cases you will still need conduit drops from the tray to the equipment. If the equipment is lined up so a cable tray run can get close to most of it, the tray would be fine. In many cases the equipment is all spread out and by the time you run the conduit drops to the equipment in the larger size that will be required for the tray cable, you might as well have piped the whole thing.
Don
 
BRV said:
I am doing a comparison on the use of cable tray vs conduit for a natural gas facility and would like input from anyone who has done anything similar. Please let me know.
We - chemical industry - are using cable trays exclusively. Even for the equipment, control station drops from the main cable tray runs we are utilizing wirebasket, rather than conduit. Use TC-ER rated cable for 480V stuff and CLX or MC for MV installation.

No seals are required transiting from hazardous to non-classified areas.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Laszlo,
So you run sections of the wire frame tray down to the equipment? How does it stand up in a factory envrioment? Most of those products that I have seen seem to be designed for commerical use.
Don
 
don_resqcapt19 said:
Laszlo,
So you run sections of the wire frame tray down to the equipment? How does it stand up in a factory envrioment? Most of those products that I have seen seem to be designed for commerical use.
Don
Don,

The wire basket is available in different materials of construction and with different finishes. The material has to be selected for the environmental exposure. SS constuction is suitable for highly sorrosive areas. Protective finish in this case is meaningless, in my opinion, as the field fabrication will inevitably leave unfinished surface exposed, even if the installer tries diligently to restore the finish where it was cut.

Because of its load bearing capability we only use this for small to medium size power and instrumentation/control cable branch runs. The main runs remain as ladder type tray, again the material or finish is selected fro the environmental exposure.

The other use this material gets is in raised floor applications. This is mostly in control room or computer room application, though some power distribution centers may be suitable for this construction also. Load bearing is not an issue there as support is available at every 2', so even larger power cables can be properly supported.
 
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petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
BRV said:
I am doing a comparison on the use of cable tray vs conduit for a natural gas facility and would like input from anyone who has done anything similar. Please let me know.
I vote for cable tray. Makes it a whole lot easier to add/fix later on. Cost wise it is probably a wash.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
Don,

You are one of the very few people I would address this to because you have the knowledge, skill and, very importantly in this case, the resources to validate or deny what I contend. You still don’t need to agree with me on the proper use of TC-ER of course. :D

Beginning with the 1993 NEC cycle, review the development of what is now 346.10(7). After you have read the full development, I do not believe you will find one valid safety argument in the TCR/TDCs and their predecessors for the restrictions placed even today on what is now TC-ER in Section 346.10(7).

I actually happen to know a potentially valid one but the major opponents to using TC-ER as an open wiring method don’t want to use it since it would also affect their product. Those of us that are proponents have pretty much given up – we’re getting too old to fight. Maybe Laszlo would like to take up the gauntlet.

BTW I happen to believe Laszlo’s application sounds just fine.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Bob,
I will take a look at the ROPs and ROCs for that section when I have some time. My only objection to exposed cables to the equipment is based on how I see things getting treated by the plant operators. Even my rigid conduit is often damaged...I just don't see how cable and tray would stand up to the abuse that I often see. And I get paid by the hour...rigid conduit in a Classified area is very labor intensive:D
Don
 
rbalex said:
Don,


Beginning with the 1993 NEC cycle, review the development of what is now 346.10(7). After you have read the full development, I do not believe you will find one valid safety argument in the TCR/TDCs and their predecessors for the restrictions placed even today on what is now TC-ER in Section 346.10(7).

I actually happen to know a potentially valid one but the major opponents to using TC-ER as an open wiring method don?t want to use it since it would also affect their product. Those of us that are proponents have pretty much given up ? we?re getting too old to fight. Maybe Laszlo would like to take up the gauntlet.

BTW I happen to believe Laszlo?s application sounds just fine.
346.10(7) can?t find it.

But 336.10(7) is there.

We have been using this installation method for the past 30 years.

Competitive manufacturing only exist in an environment where the cost of building manufacturing facilities does not put one at a serious disadvantage. The open wiring installation has been the practice in EU for 40-50 years and has proven itself as safe. We - the US - should adopt practices that are economically advantageous and resist the ones that put additional, unnecessary burdens on us. (In many aspects this is already too late.)

It has been proven that many cables that employ a separate grounding conductor had passed the ER test without any modification. I think it was 3/#8+G or larger.

Many of the arguments against open unprotected installations are theoretical and had not proven themselves to be valid in real applications. I have seen reports where the alleged failure involved intentional destruction, actually sabotage, such as aiming a sand blaster against the cable and blasting it until bare copper was exposed.

The whole basis of saying that the installation has to withstand a certain impact force is arbitrary and it is more protectionists in its underlying motives than real concern for safety. I have seen more flex connectors pulled out of the connection point and exposing the single conductors than CGB(TC) with the same. Significantly more.
 
don_resqcapt19 said:
Bob,
I will take a look at the ROPs and ROCs for that section when I have some time. My only objection to exposed cables to the equipment is based on how I see things getting treated by the plant operators. Even my rigid conduit is often damaged...I just don't see how cable and tray would stand up to the abuse that I often see. And I get paid by the hour...rigid conduit in a Classified area is very labor intensive:D
Don
Abuse - fire them. They put their fellow workers at risk.

If that is the only reason then manufacturing will go where self discipline exist where workers treat the equipment with care. (Read also my other reply.)Then you too can go to the house and practice conduit installation in your garage...:grin:
 
don_resqcapt19 said:
Actually, not too far from me, conduit is required in the house and the garage by the local codes.
Don
Hey, knock yourself out....

The point was that insistence on installation methods thst are non-competitive eventually will cost your job too, along with the factory workers from the factory that was built somewhere else where it could be built for a more competitive price.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
weressl said:
Cable tray installation offer significant cost savings in many applications.
do you ever hang other things from them? I often see air lines and such strung along under them. I guess under them is not in them so it does not violate the wording of the code.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
weressl said:
346.10(7) can?t find it.

But 336.10(7) is there.

...
Ah yes - creeping senility on my part. I was citing from memory on that one. Thanks for the catch.
 
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