Class 1 or Class 2 wiring methods?

[MWh_Pro]

Hi All,

I am wondering whether I can just use Class 2 wiring methods (rather than Class 1) for a "rapid shutdown" feature for PV equipment. The behavior is described in NEC 2014, 690.12, where in the event of an emergency, there needs to be a button/switch that bring the voltage for PV output conductors down to 80V or less. I am now in the process of defining what wiring methods are best to use for the control circuits of such rapid shutdown appliances...

I like Class 2, because the wiring is affordable and can be run with communication circuits. But it seems that the functionality required of the circuit is very similar to that which is only reserved for Class 1 circuits:

"725.31: Safety Control Equipment.
(A) Remote-Control Circuits. Remote-control circuits for safety control equipment shall be classified as Class 1 if the failure of the equipment to operate introduces fire or life hazard. ..."
​

Not quite sure if a PV rapid shutdown controller qualifies as "safety control equipment", but it feels like it.

Regardless of whether Class 1 or Class 2 is used, would it be a good idea to use CI (circuit-integrity) marked wires as well?

Thanks for the help!
Dave

 

[fmtjfw]

Does the shutdown occur when the circuit containing the button is opened or closed?
what is the voltage imposed on the circuit?
What are the characteristics of the power supply to the control circuit?

 

[GoldDigger]

Depending on the Rapid Shutdown method employed (and in this case NEC only specifies results, not methods) it could be just about anything.
When micro inverters are used, it could just be the main AC service disconnect.
In the case of combiner box relays or shunt trip breakers, it could still have a wide range of options, whose design we could have a lot of fun with.


Tapatalk!

 

[MWh_Pro]

GoldDigger, fmtjfw, thanks for your input. My scheme is to use the button to cut the 24V supply to units within the array, which will open NC contactors. I agree that with microinverters, merely the absence of a grid connection will cause them to shut down (notably more elegant and simple than what I am trying to do).

Luckily, I got my NEC 2014 Handbook in the mail today, which provides a little more insight to Class 1 circuits:

(From explanation of 725.31(A))
"The remote-control circuits to safety-control devices are required to be classified as Class 1 if a failure of the safety-control circuit could cause a direct fire or life hazard. ... Generally, signalling systems such as a nurse call system do not fit this category. These systems do not have a direct link to the initiation of fire or the initiation of a life hazard but, rather, serve as the reporting or warning link of a hazard initiated by some other (indirect) cause."
​

While a malfunctioning rapid shutdown may be hazardous if a user believed that the circuit was working properly, it would not have a "direct link to the initiation of fire" since overcurrent, arc fault and ground fault devices all serve as the real means for preventing fires in PV installations.

In the absence of any more restrictions in 690.12, I think the Class 2 circuit should be A-OK. Let me know if you disagree.

Thanks,
Dave