Bonding basket/tray on a fire alarm installation??

[devonsparky]

Just wondered how you guys interpret the regs on bonding dedicated basket/tray for a fire alarm installation. As it only contains ELV is there any need ? It plays no part of the LV electrical system (230v / 400v) so doesn't have any potential to become live at dangerous voltages.

Be interested to hear some views and more importantly some clarification from the BGB !!

Cheers

 

[Deleted member 26818]

You have to consider whether the tray/basket is either an exposed conductive part, or an extraneous conductive part.
If it's one, then it requires earthing, if it's the other it requires bonding, if neither, then it doesn't require either earthing or bonding.

 

[devonsparky]

Well, it's not an exposed conductive part because there is no basic insulation to fail and introduce 230/400.

Extraneous ? Not the way I see it. There is no earth potential as the basket/tray is on the wall and the metal conduits to break glass drops are coming out of the top of the break glass at 2 meters in length.

When you have some guy onsite who looks after sub-contractors telling you that all metal work needs to be earthed/bonded, you start to doubt yourself and want to get reassurance from here!! ha ha

 

[telectrix]

i tend to agree. no need to earth/bond.

 

[Engineer54]

When you have some guy onsite who looks after sub-contractors telling you that all metal work needs to be earthed/bonded, you start to doubt yourself and want to get reassurance from here!! ha ha

If this job your working on is a spec'd contract project then it doesn't matter what you or anyone else here thinks, you MUST follow the specification instructions.

As it happens, this project has basically the very same specification, in that ALL electrical metallic containment systems shall be referenced to the buildings earthing system... Who knows what that basket/traywork maybe used to carry in the future!! lol!!!

 

[devonsparky]

Well, this is in a factory environment where we have to install fire alarm specific basket/tray away from all other services so no 230/400 services will ever be allowed near it. The guy wants to be the big man with a fuzzy understanding of the regs and I want to be able to walk in on Monday and say with confidence that unless you can show me why it needs bonding/earthing then we won't be doing it.
It is not asked for in the specification ............. the only reason is that the guy thinks everything that is metal needs to be earthed/bonded !

 

[telectrix]

so nail his steel toe-cap boots to the floor.

 

[Engineer54]

Well, this is in a factory environment where we have to install fire alarm specific basket/tray away from all other services so no 230/400 services will ever be allowed near it. The guy wants to be the big man with a fuzzy understanding of the regs and I want to be able to walk in on Monday and say with confidence that unless you can show me why it needs bonding/earthing then we won't be doing it.
It is not asked for in the specification ............. the only reason is that the guy thinks everything that is metal needs to be earthed/bonded !

If you go in on Monday morning laying down an ultimatum, you better make sure your on solid ground!! The factory could well have a policy of earth referencing all metallic electrical containment systems.... And remember, many industrial installations are subject to other more stringent regulations than BS7671...

 

[topquark]

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!!

 

[devonsparky]

If the pompous git stood still long enough I would !

I will tell him that I don't believe it needs bonding/earthing ! For a change I will look forward to a Monday morning.

 

[devonsparky]

There is no has no policy (Have checked that one)

His only argument is that its 'in the regs' that all metal work needs to be earthed/bonded. Nothing more sinister.

We all like to have reassurance ............ I'm an approved electrician / qualifying superviser so have some back up but it's always good to chat with you lot as you're all good for info and good with the banter!

 

[Deleted member 26818]

Get him to show you these Regs.

 

[trev]

Do an IR on the basket/tray against the MET while he's standing watching mate

 

[telectrix]

that ought to confuse him. (the jobsworth, not the OP)

 

[Guitarist]

Some people just like to big themselves up. Had it many times over the years as I'm sure most people have. You could always play it clever by being respectful of his decision, but wanting him to sign this ...

I, ............., do hereby accept full responsibility for any damage/injury which occurs following the bonding of ...........
I understand that .......... has recommended that this equipment not be bonded.


Signed ................

 

[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!

 

[R4BOE]

there is a good guidance on this subject in guidance note 8 starting on page 151, which basically says metallic cable and basket trays (when carrying insulated cables etc) are not an exposed conductive part and there for do not require eathing or bonding under normal cirumstances unless it is deamed as an extranous conductive part

hope this helps