rcbo or mcb

[danluke1640]

hi i have a 17th edition board with rcbos on one side and a main rcd on the other side with 5 mcbs.i have a boiller supply and a dedicated alarm feed and wondered if these could be 0n 20amp mcbs or do they have to go on rcbos.if the other circuits on rcbos tripped then the client would know straight away that it had tripped but the only thing that i would be worried about is that if they went on rcbos and tripped the client wouldnt know that they were off until the alarm batteries ran out and the alarm started blaring out and they had no hot water.so could i put them on mcbs?

cheers for any advice

 

[telectrix]

if the cables are buried <50mm deep, then you have to fit RCD protection.

 

[danluke1640]

the alarm feed is clipped direct but the boiler feed is run under the floor and chased up the wall to the spur so i guess that the boiler should be on a rcbo and the alarm feed can be left for a 20amp mcb.cheers for the reply

 

[GLENNSPARK]

if the cables are buried <50mm deep, then you have to fit RCD protection.

...unless run in an earthed metallic conduit......

 

[MarkieSparkie]

Without further information I would think that a 6A RCBO or MCB would be more than adequate for either circuit.
I am assuming this is a domestic installation. Is the dedicated alarm system you refer to for smoke alarms. fire alarm or security alarm?
If it's for smoke alarms you could supply this from a regularly used lighting circuit MCB (there should be a means of isolating the supply to the smoke alarms without switching off the lighting) thereby giving an indication of a tripped supply. The smoke alarms should have battery backup so short term loss of supply is not a problem.
The boiler circuit could be supplied either way, lack of hot water and/or radiator heating giving an indication of a tripped supply.

 

[danluke1640]

hi.the alarm feed is for a security alarm and is fed with a 2.5mm t&e and the boiler is also fed with a 2.5mm t&e.cheers

 

[SimpleSimon]

hi.the alarm feed is for a security alarm and is fed with a 2.5mm t&e and the boiler is also fed with a 2.5mm t&e.cheers

Just to confirm, you mean boiler not immersion heater?
As an immersion heater would need a 16A MCB not a 6A like Marty has stated. (no offence Marty just making sure).
Could you do it this way.
Turn Ring final circuit onto an appropriately rated RCBO. (assuming its currently on MCB protected by RCD.)
And in its place get a 6A MCB for the water heater.
If your alarm is clipped direct than this doesnt have to have RCD protection so long as it doesnt run into the bathroom or outside.
So yes this
And in its place

Sent from my GT-I9100 using Tapatalk

 

[Dave 85]

The question is not weather it needs RCD protection or not as he says there's a main RCD on the breakers anyway. Personally I prefer not to have a security alarm sharing an RCD because they're a pain in the arse when you cut the juice (lots of beeping and general attention seeking)