Bonding basket/tray on a fire alarm installation??

[Moses]

So assuming this is 24V alarm, he wants to have the possibility of the tray having a 230V potential on it in the event of a fault ??????? hmmm!!

I agree that in case of a fault the tray will become live, if not bonded.

If bonded then, ADS will ensure that it is safe in case of fault.

So i would bond it.

but you are the supervisor, Mr sparky from Devon, its your decision.

 

[telectrix]

how can it become "live" if it's only carrying 24volts?

 

[benji]

Whats it going to cost to bond it to earth compared with some dick on your back all the time

 

[Engineer54]

how can it become "live" if it's only carrying 24volts?

Doesn't have to be the cables ON the basket that could make the basket live!! Seen some pretty unlikely scenario's over the years, where the so-called impossible became possible, very quickly!! lol!!!

 

[Moses]

how can it become "live" if it's only carrying 24volts?

How can anyone drive a nail in to a cable berried in-line with a socket/switch.

Tel accidents happen. A fault is not designed, its an electrical accident.

People do funny/strange things.

The tray may not become live from the 24V cables in it, but then it could, if the PSU in the panel went faulty and introduced mains on to the detector loop.

Else, some one could leave a trunking cover lying across the mains and fire trunking, a fault on the mains trunking will leave both live???

 

[devonsparky]

Cost ? Considering its a factory the size of 8 or more football pitches ................ a considerable cost to do it just to keep some gimp off of my back if it doesn't need it !!

So my preferable option is to prove to him (unless he can prove otherwise) that it doesn't have to be done !

 

[needasparks]

If the factory is that big, how is the basket supported if not from the structure of the building which would be bonded.

 

[topquark]

I agree that in case of a fault the tray will become live, if not bonded.

If bonded then, ADS will ensure that it is safe in case of fault.

So i would bond it.

but you are the supervisor, Mr sparky from Devon, its your decision.

I'm not suggesting he bond or earth it!!! Exactly the opposite. Otherwise in the event of a fault elsewhere you'll have 230V and 24VDC next to each other.

 

[Moses]

I'm not suggesting he bond or earth it!!! Exactly the opposite. Otherwise in the event of a fault elsewhere you'll have 230V and 24VDC next to each other.

If its bonded, then how will you get 230v next to 24V?

ADS will disconnect the 230V as soon aS THERE IS A FAULT.

 

[alarm man]

well first off nice to see fire alarms being installed in a quality way,doesnt happen enough,the ones ive seen are not earthed,its a how far do you go situation,do you earth a t box when you break into a circ,do you earth metal junction box's just incase the worst happens,as long as its labeled up for fire alarm use only cant see a problem

 

[Engineer54]

I find this thread quite interesting in a way!! Just goes to show the lengths some will go, too find reasons and clauses, why you don't need to do something that would have been second nature to do, just few short years ago!! lol!!

 

[alarm man]

I find this thread quite interesting in a way!! Just goes to show the lengths some will go, too find reasons and clauses, why you don't need to do something that would have been second nature to do, just few short years ago!! lol!!

to be fair e54,a good few years ago it was the norm,and all the old systems ive seen the pipe wasnt earthed,granted some might have been by default if the pipe left the panel and was continuious throughout the install,but most arnt as you will have some lengths that stop and start thru walls and ceilings etc.

 

[topquark]

If its bonded, then how will you get 230v next to 24V?

ADS will disconnect the 230V as soon aS THERE IS A FAULT.

Firstly let me make this clear, I am suggesting that it should be neither bonded nor earthed! Having got that out of the way.

In the event of a fault: I agree that if bonded, then it should not reach 230V as ADS should disconnect it ... if installed correctly (and not faulty etc). If earthed, then it will reach 230V for a, hopefully limited, duration (up to 5s if it's a fault on a compliant distribution circuit). The problem with either of these two scenarios is; they could cause enough current flow in the 24V DC system to cause the panel to register a fault/fire or both. That's the very reason that you do not run alarm system cables along side other cables. HTH.

 

[telectrix]

similar scenario is with data cabling in it's own tray/basket. never seen that earthed/bonded.

 

[topquark]

similar scenario is with data cabling in it's own tray/basket. never seen that earthed/bonded.

Yep, any tray carrying any form of signalling cable should be carefully considered in this respect. Data cabling in DP centres, E1/T1 trunks in telephony systems, security systems (less prone as they're more and more digitally based) ... the list goes on. Fibre rules!