Low voltage lighting

[hardworkingstiff]

Anyone know why metal fixtures (UL label) don't have a ground screw? I assume that means you don't have to ground a 12-volt fixtures, but the transformer secondary is fused at 25 amps.

I would think 12-volts could smart.

 

[hbiss]

Re: Low voltage lighting

Because neither side of the 12 volt secondary is required to be grounded so what purpose would grounding the fixture serve?

-Hal

 

[hardworkingstiff]

Re: Low voltage lighting

Thanks Hal

 

[don_resqcapt19]

Re: Low voltage lighting

What about 250.4(B)(2)?
Don

 

[George Stolz]

Re: Low voltage lighting

Don, wouldn't 250.20(A)(1) apply to this situation? The system is 12V, and the supply conductors would be 120V. Therefore, the system would not be required to be grounded.

I think?

 

[hbiss]

Re: Low voltage lighting

It's not really clear but I too believe 250.20(A)(1)applies to the conductors on the LV secondary but Don also has a point with 250.4(B)(2)as it applies to the housings.

-Hal

 

[hurk27]

Re: Low voltage lighting

What about having more than 4 to 1 ratio transfomer?

UL requires all LV transformers to have a primary to secondary shield between the two windings. This shield is bonded to the supply circuit EGC ran with the supply conductors. this would elimate the requirment of 250.4.
250.20 only requires if the supply voltage is over 150 volts AC, or if the secondary circuit is ran as an over head. so either of these should not require a LV fixture to be grounded?

Then 411.5 (A) Clearly does not want the secondary conductors grounded. And (B) repeats the requirement for the Shield

411.5 Secondary Circuits.
(A) Grounding. Secondary circuits shall not be grounded.
(B) Isolation. The secondary circuit shall be insulated from the branch circuit by an isolating transformer.

[ May 22, 2005, 04:01 PM: Message edited by: hurk27 ]

 

[hurk27]

Re: Low voltage lighting

By hardworkingstiff:
I would think 12-volts could smart.

If we look at 725.2 we can see that voltages below 30 volts are concidered by the NEC as safe from shock hazard.

a Class 2 circuit considers safety from a fire initiation standpoint and provides acceptable protection from electric shock.

 

[kiloamp7]

Re: Low voltage lighting

If we are talking about "Capri" lighting (low voltage lighting), then isn't the 12 volts the actual load voltage? If so, I dont believe this is Class 2 circuitry & Art.725 does not apply to the load circuitry.

Isn't NEC Art.411 applicable to the load circuitry?

12V. battery in car can make some fierce fireworks. It is not just the voltage level that makes a ckt. a Class 2 ckt.

 

[pierre]

Re: Low voltage lighting

I am with George here.
250.20(A)
If it is a lighting system operating at 30 volts or less, Art 411 applies.

I do not believe one should ground the secondary side of the transformer wiring while following 250.20(A) and 250.22(4).[411.5(A) Grounding. Secondary circuits shall not be grounded. ]

 

[hurk27]

Re: Low voltage lighting

BY kiloamp7: I dont believe this is Class 2 circuitry & Art.725 does not apply to the load circuitry.

I agree, I wasn't trying to imply that 725 applyed here, I was just referanceing it to show that the NEC doesn't concider voltages below 30 volts a shock hazard.
And yes low voltage at high amprage can be a fire hazard as it is current on a conductor that causes the heat.

 

[don_resqcapt19]

Re: Low voltage lighting

I'm not saying that the secondary needs to have a grounded conductor. I'm just saying the 250.4(B) requires an EGC for this and other ungrounded systems.
Don

 

[pierre]

Re: Low voltage lighting

Don
This poses an interesting situation.
Scenario: undercabinet ligthing supplied by a class 2 transformer, which itself is supplied by a 120v circuit with an equipment ground conductor.

Does one need to install an equipment ground conductor to the under cabinet fixture if it is metallic?

 

[hurk27]

Re: Low voltage lighting

But Don Wouldn't 250.22(4) over ride this?

I do not see where a EGC ran with the secondary conductors of a ungrounded LV system would serve any purpose, there would not be any path for fault current.

I have installed hundreds of LV systems and I have never had any that had any kind of grounding terminals or a EGC included with the supplyed UL listed wires for the LV system?

 

[don_resqcapt19]

Re: Low voltage lighting

But Don Wouldn't 250.22(4) over ride this?

That section has nothing to do with equipment grounding. It covers grounded circuit conductors.

Does one need to install an equipment ground conductor to the under cabinet fixture if it is metallic?

I don't see any exceptions to 250.4(B)(2), so the code requires an EGC.

I do not see where a EGC ran with the secondary conductors of a ungrounded LV system would serve any purpose, there would not be any path for fault current.

It could clear the second fault if one ungrounded circuit conductor if faulted to one metal fixture and the other to a second fixture. If there would be any other conductive paths between the two faulted fixtures, a fire could result.
Don

 

[George Stolz]

Re: Low voltage lighting

Wouldn't it be nice to move the grounded requirements to chapter 200?

 

[George Stolz]

Re: Low voltage lighting

Originally posted by don_resqcapt19:

I do not see where a EGC ran with the secondary conductors of a ungrounded LV system would serve any purpose, there would not be any path for fault current.

It could clear the second fault if one ungrounded circuit conductor if faulted to one metal fixture and the other to a second fixture. If there would be any other conductive paths between the two faulted fixtures, a fire could result.
Don

Can you explain this further? I do not understand this scenario. Misties and fault paths sometimes are difficult to imagine.

 

[hbiss]

Re: Low voltage lighting

It could clear the second fault if one ungrounded circuit conductor if faulted to one metal fixture and the other to a second fixture. If there would be any other conductive paths between the two faulted fixtures, a fire could result.
Don

But the EGC would go back to the equipment ground on the primary side of the transformer so it would do nothing for this problem.

-Hal

 

[don_resqcapt19]

Re: Low voltage lighting

Hal,
The EGC conducting the two fixtures with the faults will result is a direct short (if the two faults are on opposite conductors) and should cause the secondary OCPD to open.
Don

 

[hbiss]

Re: Low voltage lighting

Ok, I see what you are saying.

-Hal