# downgrade Class 1 control wire to Class 2 or 3



## HARRY304E (Sep 15, 2010)

BobSteele said:


> I have an issue where I need to downgrade Class 1 control wire to Class 2 or 3 before a distribution block.
> 
> The already completed installation has a transformer panel with a 350VA transformer 120:24VAC. The hot leg goes to a 6A fuse then both legs go to a controller panel. In this panel, the hot leg goes to a fused terminal block of varying fuse sizes (0.5-2A). From the 2A fuse the 24VAC then goes out to multiple command discreet outputs.
> 
> ...


 Welcome to the forum :thumbup:

What artical in the NEC are you reading...?


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## miller_elex (Jan 25, 2008)

If it is 24VAC, fused at 4A or less, and non-critical, that would be class 2. But all your cables are Class 3 anyways.

If you are in a mech or electrical room, you are probably on the hook according to scope, to pull cable in conduit.


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## BobSteele (Mar 25, 2011)

*Control wiring*

725 and 800 along with table 11A and 11B


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## HARRY304E (Sep 15, 2010)

BobSteele said:


> 725 and 800 along with table 11A and 11B


*725.121 Power Sources for Class 2 and Class 3 Circuits.*​

*(A) Power Source. *
​The power source for a Class 2 or a​
Class 3 circuit shall be as specified in 725.121(A)(1), (A)(2),
(A)(3), (A)(4), or (A)(5):​Informational Note No. 1: Figure 725.121 illustrates the
relationships between Class 2 or Class 3 power sources,
their supply, and the Class 2 or Class 3 circuits.
Informational Note No. 2: Table 11(A) and Table 11(B) in
Chapter 9 provide the requirements for listed Class 2 and
Class 3 power sources.
(1) A listed Class 2 or Class 3 transformer
(2) A listed Class 2 or Class 3 power supply
(3) Other listed equipment marked to identify the Class 2
or Class 3 power source
_Exception No. 1 to (3): Thermocouples shall not require_
_listing as a Class 2 power source_
_Exception No. 2 to (3): Limited power circuits of listed_
_equipment where these circuits have energy levels rated at_
_or below the limits established in Chapter 9, Table 11(A)_
_and Table 11(B)._
Informational Note: Examples of other listed equipment
are as follows:
(1) A circuit card listed for use as a Class 2 or Class 3
power source where used as part of a listed assembly
(2) A current-limiting impedance, listed for the purpose,
or part of a listed product, used in conjunction with a
non–power-limited transformer or a stored energy source,
for example, storage battery, to limit the output current
(3) A thermocouple
(4) Limited voltage/current or limited impedance secondary
communications circuits of listed industrial control
equipment
(4) Listed information technology (computer) equipment
limited-power circuits.
Informational Note: One way to determine applicable requirements
for listing of information technology (computer)
equipment is to refer to UL 60950-1-2003, ​

​_Standard for Safety_​
_of Information Technology Equipment_​​

​. Typically such circuits​
are used to interconnect information technology equipment for
the purpose of exchanging information (data).​(5) Adry cell battery shall be considered an inherently limited
Class 2 power source, provided the voltage is 30 volts or
less and the capacity is equal to or less than that available
from series connected No. 6 carbon zinc cells.
*(B) Interconnection of Power Sources. *​

​Class 2 or Class 3​
power sources shall not have the output connections paralleled​​
or otherwise interconnected unless listed for such interconnection.​


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## HARRY304E (Sep 15, 2010)

Read all of 725.154 there is a lot to read there. 

*725.154 Applications of Listed Class 2, Class 3, and*
*PLTC Cables. *​​​​Class 2, Class 3, and PLTC cables shall comply
*with any of the requirements described in 725.154(A)*
*through (I)*​


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## miller_elex (Jan 25, 2008)

Harry always cuts&pastes, but you're going have to tell me what it is you're installing.... DDC? DDC has 800 and 725, but way more 725. Old pneumatic / electric hvac controls are most exclusively class 3.

Sounds like you're doing a retro-fit.


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