Article 250 and LV installs

[del91574]

I've got a guy that states a residential alarm or security system (I'm guessing any alarm for that matter) is not required to be grounded.

I'm citing 250.20 A(2) as the transformer in a typical system is ungrounded at the outlet they typically plug into, albeit the HV feed is grounded.

He's stating that 250.112 (I) says no grounding needed, however the code references required in Part II and Part VIII.

I also stated that 250.162 A (1) and (2) are what modifies the requirement regarding the field wiring needing a ground, which is what changes a C1 to a
C2/C3 circuit.

His argument is saying why have a C2 or C3 circuit if there's restrictions?

I was taught and my understanding is that a system/panel was always required to be grounded, however a manufacturer's instructions supercede the
code, if they specifically tell you to not ground the system/panel, since you're installing I/A/W the manufacturer's instructions.

 

[hurk27]

I've got a guy that states a residential alarm or security system (I'm guessing any alarm for that matter) is not required to be grounded.

Unless there are requirements by the alarm manufacture he is correct, many systems are designed as low voltage un-grounded system so the system can continue to operate even if a inadvertent grounding were to occur, kind of a fail safe and is very understandable with an alarm system

I'm citing 250.20 A(2) as the transformer in a typical system is ungrounded at the outlet they typically plug into, albeit the HV feed is grounded.

250.20(A)(2) only requires that the system feeding the transformer is to be a grounded system not that the transformer is grounded when plugged in, and odd are if you have the transformer plugged into a 120 volt outlet it is being powered from a grounded system, if this was not true then we would have allot of wall warts that would be against code, phone charges included, and 250.20(A)(1) is the allowance of it to be ungrounded as the receptacle is 120 volts which doesn't exceed the 15 volt requirement

He's stating that 250.112 (I) says no grounding needed, however the code references required in Part II and Part VIII.

We have covered part II above that 250.20(A)(1) doesn't require it, and since most alarm systems operate at 24 volts 250.162(A) only applies to system with a voltage between 50 and 300 volts so again its allowed

I also stated that 250.162 A (1) and (2) are what modifies the requirement regarding the field wiring needing a ground, which is what changes a C1 to a
C2/C3 circuit.

If this alarm circuit is at 24 volts how does 250.162 apply see above. Read 250.162(A)

His argument is saying why have a C2 or C3 circuit if there's restrictions?

I have no idea each system has it's purpose

I was taught and my understanding is that a system/panel was always required to be grounded, however a manufacturer's instructions supersede the
code, if they specifically tell you to not ground the system/panel, since you're installing I/A/W the manufacturer's instructions.

Again as I said in the beginning, many systems are design by the manufacture to have the redundancy that a ungrounded system allows, and since there is no NEC requirement for a 24 volt alarm system that is fed from a 120 volt system that is grounded to be grounded, and the manufacture prohibits it in their instructions, I would say your partner is correct.