Dry Contact circuit "Intrinsically Safe"?

[hurlee555]

I am currently the Electrical QC on a government project and have been searching through the NEC and different forums for an answer on this question.

Does conduit fill apply to HVAC control circuit cabling that is used only for a "dry-type" control (no voltage)?

I am assuming this will fall under NEC Sec. 504 (2011) Intrinsically Safe Systems since there is no Voltage on the cables? But section 504 does not talk about fill requirements.

The issue is our controls contractor will be pulling multiple cables through a 1" EMT conduit that I'm most certain will be over 40% fill. He states they do this all of the time and the fill requirements do not apply to cables that do not carry voltage. I understand his argument, but he nor I can find anything that says these types of circuits do not fall under the conductor/conduit fill requirements of the NEC.:?

 

[petersonra]

I am currently the Electrical QC on a government project and have been searching through the NEC and different forums for an answer on this question.

Does conduit fill apply to HVAC control circuit cabling that is used only for a "dry-type" control (no voltage)?

I am assuming this will fall under NEC Sec. 504 (2011) Intrinsically Safe Systems since there is no Voltage on the cables? But section 504 does not talk about fill requirements.

The issue is our controls contractor will be pulling multiple cables through a 1" EMT conduit that I'm most certain will be over 40% fill. He states they do this all of the time and the fill requirements do not apply to cables that do not carry voltage. I understand his argument, but he nor I can find anything that says these types of circuits do not fall under the conductor/conduit fill requirements of the NEC.:?

Article 504 is for installations in classified areas - i.e. - where there is a risk of fire/explosion.

Dry contacts are just dry contacts.

My opinion is that the circuit you are describing is not a current carrying conductor for the purposes of the NEC.

40% fill of cables is very hard to actually pull through conduits. It sounds like the conduit is mostly empty, and it sort of is, but it is a lot fuller than it might seem at first. These kind of cables are fairly fragile and long pulls of them thru conduits that are relatively full is not as easy as you might think.

 

[jewellfish]

I am currently the Electrical QC on a government project and have been searching through the NEC and different forums for an answer on this question.

Does conduit fill apply to HVAC control circuit cabling that is used only for a "dry-type" control (no voltage)?

I am assuming this will fall under NEC Sec. 504 (2011) Intrinsically Safe Systems since there is no Voltage on the cables? But section 504 does not talk about fill requirements.

The issue is our controls contractor will be pulling multiple cables through a 1" EMT conduit that I'm most certain will be over 40% fill. He states they do this all of the time and the fill requirements do not apply to cables that do not carry voltage. I understand his argument, but he nor I can find anything that says these types of circuits do not fall under the conductor/conduit fill requirements of the NEC.:?

I may be missing something here, but wiring that is connected to "dry contacts" still have voltage on them. It may be 5 volts, 24 volts, etc. but something is connected to the wire that knows when the dry contact changes states. It knows that by applying voltage through the conductors and that control voltage is not, necessarily, intrinsically safe.

 

[cadpoint]

Is it plus or is it minus?


There's a lot to be said for currect carrying conductors, it does say when!

 

[fmtjfw]

Dry contacts just means that there is no voltage always associated with the contact. This means that the voltage/current is supplied and used outside the contact. For instance a contact that is wired to a voltage source and the other side of the voltage source and the other side of the contact are available for connection, that is NOT a dry contact.

Actually pretty hard for me to explain.

BUT dry contacts are not necessarily intrinsically safe, it depends on the power source used.

"*A "dry" contact is a contact that is not initially connected to a voltage source. It could be stand-alone, such as a pressure switch mounted on a boiler.

Or, if the contact is mounted as part of an electrical unit that has a power source, then the "dry" contact has no pre-wired electrical connection to that power source. For example, a magnetic motor starter may have an extra contact that is not connected to the control circuit that starts and stops the motor. However, when the motor starts, the "dry" contact changes state, because the mechanical action of the starter moves the contact. This "dry" contact could then be wired to devices/circuits that are separate/remote from the motor starter circuits."

 

[hbiss]

I am currently the Electrical QC on a government project and have been searching through the NEC and different forums for an answer on this question.

The NEC is not a book that you can just read through and understand what it says.

Does conduit fill apply to HVAC control circuit cabling that is used only for a "dry-type" control (no voltage)?

Does conduit fill apply to low voltage HVAC control circuit cabling? Answer is no.

I am assuming this will fall under NEC Sec. 504 (2011) Intrinsically Safe Systems since there is no Voltage on the cables? But section 504 does not talk about fill requirements.

You couldn't have assumed more incorrectly. Art 725 would be the place to look.

-Hal