RCD Keeps tripping on new installation

[John Rumm]

The "law" actually states very little. It cites the addition of Part P to the list of building regs and some other minor modifications to do with electricity in dwellings. It makes no mention of RCDs at all.

Part P of the building regs is also a little circumspect since it does not call up BS7671 as a mandatory set of rules to follow, but simply states that :

"0.2 A way of satisfying the fundamental principles would be to follow:

a. the technical rules described in the body of BS 7671:2001 as amended or in an equivalent standard approved by a member of the EEA; and b. guidance given in installation manuals that are consistent with BS

7671:2001, such as: i. the EE (Institution of Electrical Engineers) On-Site Guide; ii. the series of IEE Publications, Guidance Notes Nos 1 to 7."

So the basic principle established is that you will comply with the building regs (and hence the legal requirements) if you follow BS7671. That does not prevent you complying with them by following an alternative standard of equal standing - although its questionable if there actually is one.

So if you accept that the baseline for any work will be BS7671 (aka "the wiring regs"), then you need to see if they (and their supporting documents) permit and installation with only one RCD. The answer to which, is they can; but only in very limited and unlikely circumstances.

For example a dwelling with a TN supply, and all lighting circuits etc wired with cabling protected by an earthed metal shield or at >50mm depth, could be run from MCB(s) connected directly to the main switch (i.e. traditional 16th edition TN style). All sockets circuits, and all circuits present in rooms containing a bath or shower could then go on a single shared 30mA trip RCD. A small flat or bedsit might conceivably be setup like this.

However, the cost of cabling in that way will far exceed the cost of adding a 17th edition style dual RCD CU - so in practice is unlikely unless its a really cheap job with all surface wiring.

So in the real world, two or more RCDs is mandatory, since a 15th edition style "whole house" RCD would not satisfy:

314.1 (i), or (iii), or (iv) 314.2

and from the OSG:

3.6.2

[John Rumm]

True, but not relevant.

The requirement is the elimination of hazards and inconvenience - these are not limited to just electrical electrical hazards.

[Doctor Drivel]

That is right - for once. It is not mandatory to fit an RCD. You can eliminate an RCD, but need that cumbersome earth bonding in the bathroom, cable below 25mm depth in walls, etc.

The 17th does not state you need two RCD's

The 17th does not state you need two RCD's

[Doctor Drivel]

This man is senile.

[Doctor Drivel]

I noticed the self imposed "experts" never responded to this - apart from idiotic senile idiot.

[Doctor Drivel]

What hazards? The ceiling falling in? A digger hitting the power cable in the street? In the case of a power outage only battery backup will be of any use for lights.

You say "not limited to just electrical electrical hazards". How about the non electrical hazard of hypothermia. The energy is cut off by a digger hitting a cable giving an "electrical" outage and the heating is off. The people in the house could die of hypothermia. This hypothermia can be brought on by an electrical problem. What provisions for that hazard have you put in?

You are making the hazards up. I made up better hazards.

[John Rumm]

No, that alone is not enough.

If you have sockets for general purpose use, then you need an RCD

If you have electricity used in a room with a bath or shower, then you need an RCD

If you have sockets that could reasonably be expected to be used to power an appliance used outside, then you need a RCD.

Indeed, and there is no reason why it would. It expects the designer to work out the number required based on the circumstances.

That means in most properties you will need *at least* two to meet the requirements:

314.1 (i), or (iii), or (iv) 314.2

and from the OSG:

3.6.2

[Tim Watts]

It's 50mm.

[Doctor Drivel]

Where does it state that?

Not if above 2550mm from floor and out of the "zones"

If nothing outside, then no RCD.

Thank you.

[Doctor Drivel]

thanks. The only thing you have got right.

[BruceB]

Reg 411.3.3(i)

No, the RCD requirement is for the whole location, not just within the zones. 701.411.3.3

All sockets for general use (

[Tim Watts]

In the 17th - look it up.

Depends if you have supplimentary bonding. Lack of supplimentary bonding requires all circuits in the wet room be RCD protected.

Completely wrong since the 17th.

[Tim Watts]

DANGER

This thread has been DiMMed:

credits to John R)

[Tim Watts]

Oi, you owe me for a new keyboard!

[John Rumm]

[Steve Firth]

[Doctor Drivel]

It doesn't.

Yep.

Show me where it states an RCD is mandatory?

[Doctor Drivel]

Read again.

Nothing states an RCD is mandatory.

[Doctor Drivel]

This man is from Essex.

[Doctor Drivel]

This man is clearly mad.