Fire Alarm Circuit RCD Protection TT System

[Strima]

Doing a board swap on a HMO property with a TT system later this week and I've been asked to add OCPD for an L1 fire alarm system.

As usual the landlord is being a little cagey with letting me know the other tradesmans details so I can confirm this but I'm on the understanding that a fire alarm must not be on an RCD protected circuit?

Is this correct for TT systems, the rod Ra is just under 200 ohms which I will be trying to get down if I can find somewhere to add an additional rod, the whole pace is concreted in.

Also what size OCPD? I'm thinking 6 amp seems to be pretty normal.

 

[telectrix]

can't see a problem with the fire alarm being on it's own dedicated RCBO. the alarm panel or it's cabling would need to be faulty to trip the RCBO. the OCPD would be sized according to the cable feeding the alarm,usually 1.5mm FP200 so a 16A would be appropriate. no problem if you want to fit a lesser device.

 

[bill01803]

Hopefully using a 100mA S type RCD as main switch so that would be enough protection and just use a MCB if not as said previously it's own dedicated RCBO.

 

[Darkwood]

I would be inclined to tap directly of the tails and provide this F/A with its own dedicated supply that is not subject to a common trip like the front end rcd of a distribution board, faults of other circuits should not impact on the supply to the fire alarm.

 

[Steviec1]

The fire alarms I have dealt with (if they are monitored) supply a signal the the monitoring company that the alarm is on battery back up after a short while

 

[Strima]

The board is going to be full RCBO but I tempted to use a 100mA S type RCD as the main switch to give it some earth fault protection.

 

[telectrix]

I would be inclined to tap directly of the tails and provide this F/A with its out dedicated supply that is not subject to a common trip like the front end rcd of a distribution board, faults of other circuits should not impact on the supply to the fire alarm.

my garage circuit is fed from a non-RCD way in a hi integrity dual RCD house board. 40A MCB feeding 6.0mm to a sub. 4 freezers and my workbench on a 32A RFC (was a 20A radial till 'er indoors decided on a hot tub and a sauna. now defunct when she realised that the leccy bill has trebled) : might one day get round to fitting a RCBO in the sub.

 

[Darkwood]

my garage circuit is fed from a non-RCD way in a hi integrity dual RCD house board. 40A MCB feeding 6.0mm to a sub. 4 freezers and my workbench on a 32A RFC (was a 20A radial till 'er indoors decided on a hot tub and a sauna. now defunct when she realised that the leccy bill has trebled) : might one day get round to fitting a RCBO in the sub.

I think your own home installation is somewhat different in the requirements of a HMO L1 F/A installation and tbh does the 6mm supply need RCD protection, surely just rcbo the garage board to ensure each freezer is independent ... but I am just teaching you to suck eggs here aint I

 

[Mike Johnson]

The board is going to be full RCBO but I tempted to use a 100mA S type RCD as the main switch to give it some earth fault protection.

Don't understand your post, it's my understanding that RCBO's give earth fault protection.

 

[Strima]

Don't understand your post, it's my understanding that RCBO's give earth fault protection.

I could have been clearer, I was distracted by a bacon butty. Rather than use 30mA RCBO for the circuit I'm considering using an MCB then having upfront 100mA S Type.

I could still go with 30mA RCBO I'm just banding ideas around in my head and randomly hitting the keyboard at the same time.

Probably having a bit of a Buzz moment...