Fire Alarm Circuit RCD Protection TT System

[westward10]

Ah, OK.

I had assumed it was like Flexishield and the foil shield would take out the RCD/OCPD if penetrated by a nail, etc.

It is not manufactured to BS8436.

 

[loz2754]

It is not manufactured to BS8436.

Thanks for this info westwood10. I did not realise that FP200 is not suitable for this application. Following on from your post, I did a little research. I think it has to do with the construction of the foil shield, in that it is not capable of carrying a large fault current for long enough to operate the OCPD. Every day's a school day...

 

[Steviec1]

Putting in on its own RCBO is one option if it is wired in T&E or similar so the < 50mm rule applies, though if in FP cable it should be OK without "additional" protection due to the foil shield.

If worried about spurious trips not being noticed/fixed, how about taking it off a central lights circuit?

In any case I would still prefer a 100mA delay RCD up-front so a failed RCBO is not leaving the system with no viable means of disconnection on a L-E fault.

Shouldn't fire alarms be wired from the board in fireproof cable??

 

[Phil L]

Fire alarms should be wired from the main DB directly to a isolator

 

[Lister1987]

Shouldn't fire alarms be wired from the board in fireproof cable??

Depends if you're doing a Part 1 or Part 6 system.

HMO being commercial should really be a -1 system and would require suitably fire resistant cabling from source to main panel. This can however vary with local authority.

A -6 by contrast can be either a dedicated circuit or tapped out lighting circuit, with the cabling requirements being less onerous.

It is acceptable if the unit is purpose built (and not a converted house) to have a -1 system covering communal areas and individual -6 systems in each self contained unit (interlinking is optional due to each unit having the required about of fire durability.

I'll dig out my 5839s when I get a mo and get relevant clauses.

 

[Strima]

And to bring my side of this thread to a close.

The landlord has had another FRA done and the system has been put down as LD2 D1 so he's going for a wireless system...

 

[Steviec1]

And to bring my side of this thread to a close.

The landlord has had another FRA done and the system has been put down as LD2 D1 so he's going for a wireless system...

It will still need a supply!

 

[loz2754]

Yes it will still need a supply, but a Grade D1 system can be wired to local lighting circuits and radio interlinked. And as they are self contained they will not need wiring in FP.

 

[Strima]

It will still need a supply!

Fed from a local lighting circuit which is acceptable.

I'm only getting involved with wiring the bases etc, another company is being paid to design and commission the system.

 

[Darkwood]

Ah, OK.

I had assumed it was like Flexishield and the foil shield would take out the RCD/OCPD if penetrated by a nail, etc.

Thanks for this info westwood10. I did not realise that FP200 is not suitable for this application. Following on from your post, I did a little research. I think it has to do with the construction of the foil shield, in that it is not capable of carrying a large fault current for long enough to operate the OCPD. Every day's a school day...

In many systems if FP200 is employed it uses the foil as a shield from interference and if it is a monitored addressable system in use then the foil and 'earth' core is effectively isolated from common supply earth and is separately monitored by the panel, you can easily identify where this is in place as the panel usually has separate terminal inputs for the 'earth' core and any device will be clear on connecting up the devices that the 'earth' core is not fitted to any common installation earth.

@pc1966
I assume you are simply talking domestic 230v mains linked systems here which seldom use FP200, almost all systems using FP200 are monitored and the voltage down these cables is <30v DC, shorting the cable out will either pop a F/A panel glass fuse and/or the panel will actually isolate that particular zone and flag a fault warning.