18th Ed. 715.422.107.2 Extra Low Voltage Lighting Question

[John-]

Hi Re the above on page 295 of the 18th Ed. regs, it states that for prevention of fire from a short circuit...

One of these areas is a device that protects against short circuit should disconnect within 0.3 seconds when a power increase of 60W (2.5A) occurs.

I have looked at a few disconnection device types Current Characteristics graphs, and i don't seem to be able to find a device that meets this. So to save a bit of time looking through more of these graphs on line, what are people using please?

Maybe the converter has some sort of protection inbuilt, it is a Robus device, so reasonably reputable i think?

I have an example at home of a SELV device supplying several 24v LED strips. The converter is rated at a max output 200w 8.4A. My design current is slightly below 5A so i put a thermal trip in rated at 5A - just to protect the 1.5mm flex cable really. But since reading the regs, and doing the math it seems the device i am using will no way comply to this 0.3s disconnection time (for prevention of fire). My device with a load of 8.3A will disconnect in about 12 seconds and this is not an inrush 2.5A / 60w so is only good for overload. This is my device: -

https://docs-emea.rs-online.com/webdocs/1225/0900766b8122539e.pdf

And I thought i was being clever by protecting the cable and the output, not clever enough i guess.


Thanks

John

 

[westward10]

Are both live conductors uninsulated?

 

[John-]

No. I assumed that only 715.422.107.1 applied to those. So are you saying then that .2 also applies to uninsulated conductors only?

 

[westward10]

Pretty certain Reg 715.422.107 only applies where both secondary conductors are uninsulated and Reg 715.422.107.2 refers to the device providing the fire risk protection as required by the first Reg. If your system is all insulated including all terminations then so long as your driver/power supply complies to a standard in Reg 715.414 then it should be fine as the driver/power supply should incorporate inherent and non inherent protection.

 

[Deleted member 72666]

If your Ib, In and Iz are in order then surely when a short circuit occurs it will meet the 0.3 second disconnection time (0.1s tn systems)

 

[John-]

If your Ib, In and Iz are in order then surely when a short circuit occurs it will meet the 0.3 second disconnection time (0.1s tn systems)

This is for extra low voltage side, not the low voltage side. The low voltage side will not be the same current, i guess by a factor of ten give or take losses and the like.