Unused cores in alarm cable...

[PhilipKS]

Morning all,

I've researched the importance of properly terminating \ earthing any unused cores in multicore 230v (in case other end becomes live, induced voltages etc)

But...

Is it is necessary when using multi-core alarm cable for low voltage (24v)?

I need to connect up a couple of photo-cell sensor pairs and not all of the cores will be used (in 8 core alarm cable). Can these just be clipped back, or should they too be terminated in choc blocs etc.?

Any thoughts much appreciated...

Thanks PhilipS

 

[electronicsuk]

I'd just clip them back. You're unlikely to see any induced voltage from the other cores carrying DC, and you shouldn't be running the cable parallel to mains AC wiring for any significant distance.

 

[PhilipKS]

Thanks! good advice on the mains routing - won't be anywhere near.

But..checked the system spec and its 24v AC ~ would that make any difference to induced voltage risk??

Clipping the cores back would be much the easiest as there is not much space in the photocell units for choc blocks etc (and there is no earth to ground the used cores in any event...)

cheers
PhilipS

 

[electronicsuk]

IMO it's still not really a problem. At the voltages and currents involved, there isn't going to be any risk of shock in the unlikely event that a small voltage does appear on the unused cores. I probably wouldn't cut the spare cores right back, though, as they may come in useful for future additions.

Even with mains wiring, it's unusual to see unused cores grounded - although they should be, more often that not they are simply isolated in terminal blocks at either end.

 

[PhilipKS]

Thanks - seems like sound advice, good enough for me!
PhilipS

 

[ban-all-sheds]

low voltage (24v)?

//www.diynot.com/wiki/electrics:voltage-bands

 

[1john]

why not double up the cores?

 

[Click-Sure]

You could connect the unused cores to -neg, but BT don't terminate unused cores/pairs and never have done.