Combined MCB/RCD

[Reynardine]

I have no RCD's. I'm assuming my MCB's ( b rated ) are there simply to protect their circuits from excess current. Since MCB's are designed to trip in x milliseconds for y milliamps, do they give me ( as a side-effect of their primary function ) any protection against electrocution ?

Why can't the industry bring enhanced MCB's to the market, that also do the job of RCD's i.e. one gadget to do both tasks?

 

[RF Lighting]

What a good idea.

They could call it an RCBO, and sell them here

 

[Reynardine]

That's terrific thank you. I had no idea these things existed !

Judging by the photo, these RCBO things ( on your link ) look fairly generic.

Can these things fit into any CU regardless of make? I can't remember the manufacturer of my CU. It's some German make beginning with 'S' .

 

[Chri5]

They do, it called an RCBO

Here's an example:-

At £40 each they are expensive, but offer an excellent alternative to having to reconfigure or replace a standard CU without an RCD split rail.

Economics start to become iffy if multiple RCBO's are required. Say the 17th ed does require all sockets in house and all bathroom circuits to be via RCD.

MCB's at £4 each + £50 for a 17w wylex split board = £120 odd (depending on volume of final ccts), if say you have kitchen cct, grd floor ring, garage, 1st floor ring and bathroom cct for RCBO's that's £200 (5 x £40) and no spare ways.

With the RCD split rail your cost is simple provision of the CU and spare positions on the RCD side can be populated at the £4 cost of a MCB

 

[Adam_151]

Overcurrent devices protect against indirect contact by EEBADS (Earthed Equipotential Bonding and Automatic Disconnection of Supply), basically if there is a fault to metalwork on a piece of equipment, current flows down the earth wire, the bonding reduces the potential between it and nearby metalwork and the MCB switches off due to teh large overcurrent.

RCDS are added in a few situations:

1) For suppimenary protetcion against direct contact for sockets that might be used outside, to give you a bit of proptection incase you have a momentry lapse in concentration and pick up a mowed over mower cable, etc When the next version of the regs comes out, it'll be that all ogeneral purpose sockets have to be protected, not just ones that can be reasonably expected to be used for outside stuff

2) often required on an electric shower, consult the maker of the shower, and basically a very good idea where you have water, electricity and people together (and doubly so if they are wet and naked!)

3) If you have a TT supply (earth from a local electrode in the ground) then the earth path is of too high an impedance for this to work and RCDs are used to sense the imbalence

4) For added protection against fire in locations such as farms, or where the nature of stored or processed materials presents an increased fire risk (paper mills and the like)

 

[photon]

If you shop around you can get MK RCBO at around £25-£30 trade/online.
Other makes I assume can be bought for similar prices.
This makes the price differance not so large as "list prices" would suggest.


They offer a far better solution than the split board arrangement currently being used in most circumstances.
(though some smaller installations probably don't require a lot of RCBO's).

Nuisance tripping is much reduced when each ring has its own RCBO rather than sharing a system RCD.
A garden / garage supply on its own RCBO rather than spurred from the ground ring avoids tripping out the kitchen when you drop the hedge trimmer into the pond

 

[jondiy]

Is this a real genuine topic, or did JohnD put you up to it

It's odd that he has'nt had his say yet!

 

[davy_owen_88]

He's too busy vomiting in disgust I'm afraid.

 

[JohnD]

Where has Reynardine been all these years?

The German CU beginning with an S is quite likely a Siemens.
I'm pretty sure I've seen them in French Bricotage sheds. Not very common over here but they may supply have some other brand names.

It is always best to fit the same brand. Although the DIN rail is common, others may not line up with the busbar whose position varies, or the opening in the front of the enclosure, and wil not have been type-tested together. A device incorrectly fitted to a busbar sometimes overheats and melts with undesirable consequences.