17th edition and RCD's

[Toby]

Quick question... Is a single RCD protecting everything ever acceptable now?

Long version... Mate has a flat (2 bedrooms, all on one level) with an old wire fuse consumer unit.

It has 4 circuits Lights Sockets Oven Immersion (now just a socket)

He is planning on moving out of this flat and letting it, so has asked a sparks to quote for a CU upgrade.

He has been quoted for a 6 way CU with an RCD and MCB's.

Is this going to be compliant?

I suggested before the sparks came round he would be beast getting a CU with a main switch and three RCBO's (connecting the old immersion feed to the sockets RCBO as there isn't a hot water cylinder anymore) as Regulation

314.1 says "Every installation shall be divided into circuits as necessary to avoid danger and inconvenience in the event of a fault, take account of danger that may arise from the failure of a single circuit such as a lighting circuit, reduce the possibility of unwanted tripping of RCDs etc."

Thanks!

Toby...

[Mitch]

Why upgrade? There is no requirement to retrofit to the latest wiring standard unless perhaps other major alterations are required. The sparky should have just noted on the test cert 'not in accordance with latest wiring regs', which is perfectly acceptable; sounds like sparky is short of work.... Just make sure your mate gets a completed Periodic Test Report with no serious outstanding items. The main disadvantage of ONE RCD is theres no discrimination so you lose everything if it trips, not ideal but tolerable.

S

[ARWadsworth]

Are you sure? Sparky gets a phone call saying "Can you give me a price for a new CU?" and Sparky then gives a price for a new CU.

Just make sure your mate gets a completed Periodic Test Report with

I would want to see RCBOs used, especially on such a small CU.

Adam

[John Rumm]

Rarely... if it was a secondary CU in a shed or garage it might be...

Split load or just "normal"

Not really. If its a normal CU with all the circuits on the RCD then it lacks discrimination between the lights and power circuits. If its a split load with the lights on the non RCD side, then it probably fails on the 17th edition requirements for concealed cable protection with a RCD. Although this solution may become ok under amendment 1 of the 17th edition - where you can argue that retrofitting an RCD is not required if there is no significant risk from the circuit.

Yup, for a small setup like this, and all RCBO setup seems sensible.

[Toby]

Thanks Adam, I was hoping you might see this!

Main reason for the change is to bring it up to current standards to show he has taken all the necessary steps to prevent any problems later on if someone electrocuted themselves while renting the flat.

Although RCBO's are clearly the way to go, is it still permitted to use just the one RCD in this case?

Thanks!

Toby...

[Toby]

The quote just has "Remove old fuse board Install new 6 way rcd protected consumer unit Install all new MCBS Install all circuits Test all circuits & record Issue domestic electrical installation certificate"

Which I read as just one RCD, and not a split load Having a split load with two RCD's seems bonkers anyway.

I assume the certificate here is just for the new CU, and is not a certificate he can use to show it has all been tested?

Okay, didn't know about that - although in his case there is a 240v fan in the bathroom, quite close to the bath, so I would want to see that RCD'd myself.

Thaks for the comments John!

Toby...

[ARWadsworth]

I say that some discimination is needed (you answered that correctly yourself) and RCBOs should be used. I would also go as far to say that there should be 4 RCBOs, with the old immersion having it's own one. If there is a problem with the sockets[1] and the RCBO trips then at least the tenants will have one power supply to plug their fridge/freezer into until the fault is fixed.

[1] They always trip on a Friday before a Bank Holiday - ask any landlord! 4 RCBOs would add about £100 to the cost of replacing the fusebox.

Cheers

Adam

[ARWadsworth]

It would be bonkers on a set up like yours! And that is a quote for an RCD main switch.

The certificte should be as good as a PIR certificate. I actually do the tests before changing the fuse box. If there are any nasties then at least I can warn the customer before I start to change the board.

Cheers

Adam

[John Rumm]

Sounds like it, unless he means a 17th edition style one with two RCDs

Why?

Well he will also need to do some tests on the reconnected circuits.

Which circuit is it powered from though?

[Toby]

Maybe, but it doesn't look like it, I would expect it ti say "Split load" in this case

Because he only needs three circuts, so that would mean one RCD is covering just the one MCB and the other one just 2 - surely RCBOs are the beeter choice!

Lighting, like a normal bathroom fan.

Toby...

[John Rumm]

Oh, you mean in this specific case rather than generally - sorry missed what you were saying.

Having said that, it depends on your definition of better. Two RCDs plus three MCBs is probably cheaper than three RCBOs, and marginally quicker to wire as well. That often wins for a landlord!