Is this true or a bluff?

[Valkort]

Hello

We recently had an extension done and the builder took responsibility for electrics and heating. Yesterday I connected the garden trimmer to the outdoor socket which turned out to be faulty and the RCD tripped turning off power for the entire new build area (not just sockets) which includes boiler, fridge freezer, lights etc. If something similar happens when we were out/ holiday and the power to boiler and fridge goes off, its worrying.

I asked the builder's electrician on why just the power to sockets wont trip (MCB?), which is the case for the old part of the house, instead of shutting down the whole electrics, their reply was its the new regulation which requires double RCD.

Is this true? Can someone enlighten me please?

Thanks

 

[stem]

MCB's and RCD's have totally different functions. What you describe is perfectly normal.

The MCB protects individual circuits against overloading causing damage to the cables connected to them. They are rated in amps.

The RCD is completely different device it can protect several circuits and will trip when an earth fault occurs to prevent anyone receiving an electric shock. They are rated in milliamps. Building regulations require their presence. Your trimmer must have an earth fault.

Probably the old part of your house doesn't have RCD protection. if so, that would be more worrying to me than the possibility of the boiler and fridge tripping.

 

[oldbutnotdead]

Your builder is correct. Your situation is not unique (a large number of circuits fed through 1 or 2 RCDs so an earth leakage fault will drop half the house rather than just the affected circuit).
The existing wiring doesn't have to be upgraded (to RCD protection) if it isn't being altered- the new wiring pretty much has to have RCD protection (there are some exemptions).
Best way to mitigate this is to plan in advance (have dedicated circuits for key equipment like boiler, fridge, alarm all on their own RCD or even wired to the exemptions)
Next best way is to change from MCBs to RCBOs (effectively MCB and RCD combined)- expensive but will give you segregation (so a fault on one circuit will trip that circuit but not the rest of the house)- of course if the boiler, fridge and alarm are all on the same radial/RFC then that won't help much
After that, all you can do is manage the problem- when you're going on holiday, make sure you disconnect (ie unplug or isolate) anything non-essential, especially any outside ket. After all, you can't plug a dodgy strimmer in when you're in Abroad can you?

 

[Notch7]

out of interest, Is it correct that cable in safety zones need RCD protection -unless 50mm deep or have mechanical protection.

My thinking that would prevent the opportunity of having a dedicated non RCD supply for a freezer?

And on that note: in practice how much does the 50mm depth reduce risk?

 

[AndyPRK]

could you picture of the consumer unit / fusebox in the extension

 

[flameport]

, Is it correct that cable in safety zones need RCD protection -unless 50mm deep or have mechanical protection.

All concealed cables require RCD protection.
The only way to not have RCD is to either have them more than 50mm below the surface, or in steel conduit, armoured cable or similar - a socket supplied in that way could be used for a freezer and not have RCD protection.

However from January, all socket outlets require RCD protection regardless of how they are supplied, so end of line for that idea.

My thinking that would prevent the opportunity of having a dedicated non RCD supply for a freezer?

Such things are of no value in reality.

 

[EFLImpudence]

out of interest, Is it correct that cable in safety zones need RCD protection -unless 50mm deep or have mechanical protection.

Yes, but the 50mm. limit does not mean go deeper.
That would in most buildings be contrary to Building Regulations.
The wording is not ideal. RCDs are to protect people; not circuits nor appliances.

My thinking that would prevent the opportunity of having a dedicated non RCD supply for a freezer?

All sockets must be on an RCD circuit.
There are other ways but it is probably not worth it.

And on that note: in practice how much does the 50mm depth reduce risk?

You are looking at it the wrong way round.
It means that virtually all cables concealed in the wall must be on an RCD circuit.

 

[oldbutnotdead]

out of interest, Is it correct that cable in safety zones need RCD protection -unless 50mm deep or have mechanical protection.

My thinking that would prevent the opportunity of having a dedicated non RCD supply for a freezer?

And on that note: in practice how much does the 50mm depth reduce risk?

Buried (or hidden) cables require RCD protection unless they're more then 50mm from the surface (which reduces considerably the odds of someone putting a nail through the cable). Mechanical protection would have to be something you can't put a nail through (so galvanised conduit or the like- PVC doesn't count).
If you install a radial to your freezer that is on the surface (ie clipped to the wall/skirting) you'll be fine. Perpendicular penetrations of walls/ceilings would also be fine. Any corner turning while hidden in wall/ceiling- get your conduit out
EDIT Wasn't aware of that change in regs regarding all sockets to have RCD protection- interesting.
From a segregation POV it might be worth while for some to have the freezer on its own circuit (with its own RCD so if it develops a fault to earth then you won't get a belt while opening the door)- there isn't much of value in my freezer so the main cost would be clearing up the puddle left when it thawed out

 

[Notch7]

You are looking at it the wrong way round.
It means that virtually all cables concealed in the wall must be on an RCD circuit.

The reason for my thinking is that a recent orangery job had 1 wall which is 100 x 50mm studwork with 50mm insulation in between. The electricians used copex flexible conduit and ran the cabling horizontally, not in safe zones. They said that once plastered with 12mm plasterboard +3mm skim meant that the cabling would be 50mm back and therefore didnt require to be in a safe zone.

I am in the process of building a summer house / garden office and that has 50mm celetex in between 100mm x 50mm studs. Im thinking it would be neater to keep the cabling in the safe zone vertically. Im wondering if I should fix some battens vertically and clip the cable to that. otherwise in studwork wont it be tricky to keep the cables straight?

I can see on a standard cavity wall with brick or block, the cable cant be 50mm deep -which would therefore apply to the majority of work.

 

[EFLImpudence]

The reason for my thinking is that a recent orangery job had 1 wall which is 100 x 50mm studwork with 50mm insulation in between. The electricians used copex flexible conduit and ran the cabling horizontally, not in safe zones. They said that once plastered with 12mm plasterboard +3mm skim meant that the cabling would be 50mm back and therefore didnt require to be in a safe zone.

Technically correct.

I am in the process of building a summer house / garden office and that has 50mm celetex in between 100mm x 50mm studs. Im thinking it would be neater to keep the cabling in the safe zone vertically. Im wondering if I should fix some battens vertically and clip the cable to that. otherwise in studwork wont it be tricky to keep the cables straight?

It might be tricky but not impossible.
There is the argument that loose cable (not clipped) is less likely to be damaged because it will move out of the way of the drill bit.

 

[Valkort]

Many thanks for enlightening me peeps, much appreciated

 

[securespark]

If, as I suspect, the spark left the old DB alone and fitted a new one, surely they would have fitted a split board? I know I would.

 

[ban-all-sheds]

Your builder is correct.

I'm not sure he correctly read 314.

 

[JohnW2]

However from January, all socket outlets require RCD protection regardless of how they are supplied, so end of line for that idea.

True, but for someone who really want to have, say, a freezer supplied from a non-RCD-protected supply, it will still be theoretically possible to have that, by hard-wiring it to an FCU, provided that the cable itself does not need RCD protection (as you say, if buried, then in steel conduit or wired in SWA etc.), since the requirement for all sockets to be RCD-protected does not extend to FCUs.

Kind Regards, John

 

[mattylad]

There is always a way round the regs it seems