Square D Consumer Unit

[sherlockholmes]

Just out of interest, what's the difference between an RCCB and an RCD?

An RCCB is an RCD but not all RCDs are RCCBs.
An RCBO is an RCD but not all RCDs are RCBOs.

RCD is a generic term for these kinds of devices.

I accept one is a subset of the other, but i'm still not clear on wherein the difference lies? With an rcbo for instance it has as I understand it an mcb and rcd combined. Apologies if i'm being dense here.

 

[richchad]

Cant you get RCBO's for the board?

The board already has RCBO's fitted, it was just the switch I wanted to replace with an RCCB.

 

[richchad]

A 30mA RCD will trip when there is an imbalance of >30mA in the line and neutral currents.

A 100mA RCD will trip when there is an imbalance of >100mA in the line and neutral currents.

Which one will trip first for leakage below 100mA is a no-brainer. For leakage current above 100mA it depends on the trip characterists of the devices i.e. the speed at which the device will trip. If they are nominally equivalent, then it's unpredictable.

It was common for TT installations to be protected by a slow-operating 100mA RCD to provide discrimination between RCDs. But now all domestic circuits requiring RCD protection must be at 30mA.

Thanks for this, now I understand the ratings.

 

[richchad]

The circuit(s) require protection with a 30mA RCD. A 100mA RCD does not provide the protection required.

So, lets suppose you buy a (used or new) RCD from FleaBay.
How will you test that it will trip (or even works). Do you have an RCD tester?

Per the above, better to leave it to your spark.

PS He could just put a nice new RCD in an enclosure and connect it before the existing consumer unit. Not the best practise as it means that a single fault will plunge the entire house into darkness.

Thanks for this, so must be 30ma RCCB not 100ma.

I was a qualified electrician many years ago and this would have been a simple straight forward thing for me to change, but regs have moved on a lot since then..

I don't have a RCD tester, but my thinking was a RCCB would be better than a simple switch (unless it kept tripping of course)

The lighting changes in the bathroom are just to move a light and replace a radiator which has bonding attached and as I understood it, I can omit the bonding if I have an RCCB fitted, is this correct?

 

[1john]

Cant you get RCBO's for the board?

The board already has RCBO's fitted, it was just the switch I wanted to replace with an RCCB.

Why? If there are RCBO's on the lighting circuits, what difference will and RCD upfront make? This will make the installation more dangerous.

Perhaps you are getting RCBO's consused with MCB's, pictures of your boards would help here no end.

 

[richchad]

Cant you get RCBO's for the board?

The board already has RCBO's fitted, it was just the switch I wanted to replace with an RCCB.

Why? If there are RCBO's on the lighting circuits, what difference will and RCD upfront make? This will make the installation more dangerous.

Perhaps you are getting RCBO's consused with MCB's, pictures of your boards would help here no end.

Maybe I am getting confused, they must be MCB's then...

Without RCCB

• richchad
• 2 Mar 2011
• 1

With RCCB

• richchad
• 2 Mar 2011
• 1

 

[Spark123]

Yes, those are MCBs.
If you look for RCBOs you need the Qoe range, if you go to a wholesaler you'll have a heart attack

 

[ricicle]

QOE RCBOs are over £100 each now !

 

[richchad]

I was looking for an RCCB, what are RCBO's, do they replace MCB's?

 

[sparkwright]

You do not want an RCCB as the main switch on that lighting board because if there is a fault you will lose all the lights.

Get an RCBO for the circuit that you are working on.

Alternatively, buy an RCCB and an enclosure (box) to go with it. Interupt the circuit cable leaving the consumer unit with the RCCB. The RCCB would then provide RCD protection for that one circuit.

 

[sparkwright]

I was looking for an RCCB, what are RCBO's, do they replace MCB's?

An RCBO is a cross between an MCB and an RCD. It provides overcurrent protection and RCD protection.

An RCCB does not provide overcurrent protection.

An MCB provides overcurrent protection, but not RCD protection on it's own.

 

[richchad]

Thanks for that sparkwright, so if I change the MCB on the circuit feeding the bathroom lights to an RCBO it will give me overload and over current protection.

So then I should be able to not bother connecting the bonding on the new radiators in bathroom?

 

[Spark123]

Just out of interest, what's the difference between an RCCB and an RCD?

An RCCB is an RCD but not all RCDs are RCCBs.
An RCBO is an RCD but not all RCDs are RCBOs.

RCD is a generic term for these kinds of devices.

I accept one is a subset of the other, but i'm still not clear on wherein the difference lies? With an rcbo for instance it has as I understand it an mcb and rcd combined. Apologies if i'm being dense here.

As EFLImpudence says, RCD is just a generic term, it covers more than just RCCBs and RCBOs.
What most people call an RCD is infact an RCCB.
A RCBO is a RCCB and MCB combined.

 

[Taylortwocities]

So then I should be able to not bother connecting the bonding on the new radiators in bathroom?

You have to fulfil all of the conditions of the regs to omit the bonding:
It is not just "bung in an RCD and you'll be OK"

It is all listed in reg 701.415.2

 

[richchad]

Thanks Taylortwocities, was rather hoping it was just bung in a RCBO and all would be okay, had a look at the regs and think it would all be okay but now I think I might just keep the bonding to the rad pipes below floorboard level and leave all as it is....