Cabling for RTD's

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Strahan

Senior Member
Location
Watsontown, PA
Guy's I need some help. I'm in the process of wiring some tanks that have RTD's installed on them. I want to run multi-conductor sheilded cable to each of them but I'm reaching a road block with the NEC. I plan on running them above the drop ceiling and then dropping them down to each RTD. I want to fasten them to the conduit drops I currently have in place for the pump motors. Type of cable that I have is Belden 9534 CMG shielded. They will not be exposed to physical damage. Is this install ok by the NEC? It's not a power circuit just resistive signal from RTD's. Thank You
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Take a look at 300.11(B). In general the code does not permit conduits to be used to support cables or other conduits.
 

Aleman

Senior Member
Location
Southern Ca, USA
The RTD's are control circuits and should be covered under Class 2 rules. There's a bunch to read up on but essentially class 2 circuits are limited power circuits so it opens
up the wiring methods and options. If you look around a large conveyor setup or a large spread out machine, breweries, water treatment plants etc you will see a lot of cabling
that is not in pipe. These are class 2 control circuits. Generally these must be separated from power circuits and there are limitations of course but what you want to do is acceptable.
I would run your cables in a raceway above the drop ceiling and then break them out and tie them to your existing pipe. All the comm cables you see strung up on the rafters in
buildings are covered under class 2 which is why they run them that way. Your RTD circuits fall under the same class. Look at the last paragraph on the link below, it gives you the
leeway to do what you want in my opinion....but disclaimer I am not an inspector. Maybe you can tie off to some piping etc instead of the pump raceways.

http://www2.iccsafe.org/states/virg...trol Signaling and Power-Limited Circuits.pdf
 

Smart $

Esteemed Member
Location
Ohio
Take a look at 300.11(B). In general the code does not permit conduits to be used to support cables or other conduits.
Aye... but isn't there something where they can if the cable is associated with the same equipment supplied by the conduits.

Found it. It's in 300.11(B)(2)

Where the raceway contains power supply conductors
for electrically controlled equipment and is used to support
Class 2 circuit conductors or cables that are solely
for the purpose of connection to the equipment control
circuits
 
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don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
The exception might apply, but would have to know a lot more about the control system and programming.
 

Strahan

Senior Member
Location
Watsontown, PA
Agree... but I'll leave that determination to Strahan unless he asks for help with it. :happyyes:

Thank you all for your help. The RTD's are used in the control circuit for the conduit that I have already run. They will be used on the control side of the current system; so I'm thinking I'm ok to tie to conduit.
 

kwired

Electron manager
Location
NE Nebraska
Thank you all for your help. The RTD's are used in the control circuit for the conduit that I have already run. They will be used on the control side of the current system; so I'm thinking I'm ok to tie to conduit.

Next step, check with equipment instructions and see what kind of separation they may want from power circuits. Though often we use shielded cable with twisted pairs for such applications and that usually limits any interference pretty well if there is trouble down the line this may be something easily eliminated from the troubleshooting check list if you have the recommended separation from power circuits.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Thank you all for your help. The RTD's are used in the control circuit for the conduit that I have already run. They will be used on the control side of the current system; so I'm thinking I'm ok to tie to conduit.
Do the RTDs actually control the starting and stopping of the motor, or do they control some type of temperature control device?

It would be my opinion that if the temperature is not the factor that controls the starting and stopping of the motor, you are not permitted to use the motor raceway as the support for the temperature sensing cables.
 

Strahan

Senior Member
Location
Watsontown, PA
Do the RTDs actually control the starting and stopping of the motor, or do they control some type of temperature control device?

It would be my opinion that if the temperature is not the factor that controls the starting and stopping of the motor, you are not permitted to use the motor raceway as the support for the temperature sensing cables.

Circulation pump that will turn on once a certain temperature is reached; so yes I think I'm ok. Now the pump can be manually operated but under automatic the temperature does play a part in controlling the pump.
 
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