Upgrading a cunsumer unit to RCD status

[Rogeranerley]

My Hager CU is some 20 years old with both the RCD and MCB slots fully occupied. I'm planning to install an illuminated wall cabinet in a new shower room. Although it will be located beyond zone 2, I understand this will need to be connected to an RDC or similar. As the cabinet is to be wired into the lighting circuit (and as an earlier installed cabinet in the main bathroom runs on the same circuit), my thoughts are to replace this circuit's 6a MCB with a single pole B type RCBO.

Those that I've seen on line show both live and neutral terminal at the top, with the buzbar connecting screw at the bottom. Also, I notice that some come with a blue (neutral) flex and a white flex already installed.

I'd be grateful for clarification on the wiring of such RCBos. Normally, an MCB has the live outward feed at the top, with the neutral running to the block on that side of the CU, but how do you connect an RCBO with or without flexes already attached?

Also, does anyone know of a 'compact' B type RCBO supplier?

Finally, I see references to A curves and B curves. Is this an alternative way of describing A and B types?

Many Thanks

 

[rjm2k]

Is the lighting circuit not protected by the existing RCD?

 

[45yearsagasman]

Post this in the electrics forum. Plumbers know FA about electrics.

 

[EFLImpudence]

Those that I've seen on line show both live and neutral terminal at the top, with the buzbar connecting screw at the bottom. Also, I notice that some come with a blue (neutral) flex and a white flex already installed.

All RCBOs have a neutral fly-lead as do RCCBs but these are fitted to the terminal.
Not all have the white functional earth fly-lead.

I'd be grateful for clarification on the wiring of such RCBos. Normally, an MCB has the live outward feed at the top, with the neutral running to the block on that side of the CU, but how do you connect an RCBO with or without flexes already attached?

The circuit L & N go to the top terminals, N fly-lead to N bar and FE fly-lead to E bar.

Also, does anyone know of a 'compact' B type RCBO supplier?

Compact (if you mean the same size as an MCB) are not common.
Not seen a Hager one but they seem to call 'normal' ones compact.

Finally, I see references to A curves and B curves. Is this an alternative way of describing A and B types?

There are no A types - only B, C and D.
You need B.

Have you the equipment to determine the RCBO will operate correctly?
It and the circuit should/must be tested.

As allude to above, if the circuit is already RCD protected you do not need an RCBO.



May I ask why you posted on the Plumbing and Central Heating section.
I'm not a plumber.

 

[Rogeranerley]

Thanks for your replies, especially on the tail connections. Am I right that the lighting circuit earth wire also goes directly to the E bar? And, is this still the case if there's no earth flyer already attached?

I don't have any testing equipment beyond a main testing screwdriver. I was assuming that all RCBO/ has an integral testing button as shown at:

http://www.gepowercontrols.com/eu/product_portfolio/residential/
residual_current_device/ercbo.html

As for 'Compact', I'd spotted a C type at Toolstation that's no bigger than an MCB and wondered if there's anything similar in the B profile as it would give a little more space in the CU.

None of my 4 lighting circuits are on the RCD side of the CU, and my thinking was to upgrade the CU by fitting RCBOs in place of the MCBs.

I'll also post this and any future thoughts on the electrical forum....sorry for not realizing this!

 

[EFLImpudence]

Am I right that the lighting circuit earth wire also goes directly to the E bar? And, is this still the case if there's no earth flyer already attached?

Yes to both.
The earth fly-lead on the RCBO is for the operation of the RCBO, not really anything to do with the circuit.

I don't have any testing equipment beyond a main testing screwdriver. I was assuming that all RCBO/ has an integral testing button as shown at:

The screwdriver is not reliable for which it is intended let alone anything else.
The test button just ensures that it 'works' but does not tell you that the times or current for safety are correct.

As for 'Compact', I'd spotted a C type at Toolstation that's no bigger than an MCB and wondered if there's anything similar in the B profile as it would give a little more space in the CU.

You should fit a B type - C may be alright but has more stringent conditions to be met - and also you should fit a Hager RCBO to a Hager board.

None of my 4 lighting circuits are on the RCD side of the CU, and my thinking was to upgrade the CU by fitting RCBOs in place of the MCBs.

Ok, that would be good.
You could move the circuit to the RCD side but as the CU is full this would entail reconfiguration of the busbar.

 

[ban-all-sheds]

I don't have any testing equipment beyond a main testing screwdriver.

If somebody said to you that they had no means of testing for gas leaks beyond a finger and some Fairy Liquid, what would you say?

 

[Taylortwocities]

If somebody said to you that they had no means of testing for gas leaks beyond a finger and some Fairy Liquid, what would you say?

What's wrong with a box of matches?

 

[securespark]

BOOMEROONI!

 

[ericmark]

All circuits in a house are designed to open protective devices within a prescribed time in the case of a short circuit or earth fault and to ensure this will happen we have to measure the loop impedance and the tripping currents and time it takes to trip in the case of a RCD these have to trip in 40ms clearly you can't measure that with a stop watch.

The loop impedance will not change so if a B type MCB is fitted and it is replaced with a B type RCBO then it will be OK. However if a B type is to be replaced with a C or D type then first one has to measure the loop impedance. Unlike earth leakage where there is a set amount allowed with the loop impedance every MCB size has a different amount some we remember like a B32 is 1.44 ohms other we need to calculate however no point saying how to work it out when you don't have the meters. Once using a RCBO the loop impedance is more to do with volt drop and it may well be that a C type can be used but first it would need testing.

Most consumer units will only take the single pole switching RCBO's which are permitted with TN supplies but not with a TT supply with the latter all pole switching is required. Using an external box to the consumer unit they can be fitted however in premisses with ordinary persons looking after the building type tested distribution units called consumer units are required so although made not sure if you can use one! In the main where the supply is TT the twin RCD consumer unit is used not the RCBO type.

I have a RCD tester and have been surprised as to how many new ones fail. In the main it is the strain of the cables which has twisted the plastic unit slightly and revealing the strain will result in RCD or RCBO working OK again however not always. So testing the RCD is really required it's not just a regulation. The test button built in tests the mechanics of the device and likely will show when strain is causing a complete failure but not when it results in the response time being too slow.

The cost of test equipment means DIY people are unlikely to test as required one way around it is to have a EICR done after the work but it means that DIY can end up more expensive than getting an electrician in to do whole job.

I am torn between saying simply not a DIY job and guiding towards a safe as possible job. I realise most will go ahead anyway mainly due to the dangerous work we come across. The problem is people fit a RCD and think they are then safe and this is just not the case. Because a consumer unit is type tested a Hager CU can only use Hager components. Most RCBO's are same width as a MCB but longer and old consumer units often don't have the room to fit them.

The Add-On RCD's only come in 2 to 4 pole and can't be used with standard consumer unit.

As with most things there are ways around the problem. Using a RCD FCU one can add RCD protection outside the consumer unit but again testing is important. Where the volt drop is low using a passive type is OK but where the volt drop could cause the RCD not to work then it needs to be an active type and with those any power cut and they will trip and need resetting. So fitting a RCD FCU right next to consumer unit you can use passive type at the bathroom may need to be active type. There are also mini consumer units designed for garage or shower which could be used.

Really you are trying to do a job for which you don't have skills or test equipment required. You have to do a risk assessment and decide is it worth the risk or are you going to abandon DIY for this job.

I also look at 20 year old and wonder if the RCD fitted is 30ma or 100ma as 20 years ago using split CU was not that common but with a TT supply using a 100ma RCD was common. The 100ma RCD is not suitable for bathroom use and if you do have a 100ma fitted then likely your on a TT supply so RCD's will need to be twin pole.

 

[amstel]

Most consumer units will only take the single pole switching RCBO's which are permitted with TN supplies but not with a TT supply with the latter all pole switching is required. can't be used with standard consumer unit.

Eric, is this the reason why apartments etc in Spain, all have DP mcb's,? because of the earthing rod system (TT).
cheers.

 

[JohnW2]

Most consumer units will only take the single pole switching RCBO's which are permitted with TN supplies but not with a TT supply with the latter all pole switching is required.

Unless I'm missing something, I don't think that is necessarily strictly true, since I'm not aware of any regulation which requires double-pole protective devices in TT installations (the only requirement of which I'm aware being that 'isolation' be DP in TT installations).

Hence, if all of the final circuits are protected by (DP) RCDs and/or (SP) RCBOs in the CU, then I think that's perfectly compliant with the regs. However, if any final circuits do not have RCD/RCBO protection within the CU, then (with TT) there is obviously a requirement for an upstream RCD (usually 100mA TD). In that case, if there were a N-E fault on a final circuit protected by a SP RCBO, the upstream RCD would also operate, taking out the entire installation, probably in violation of 314.1.

Kind Regards, John

 

[Rogeranerley]

Many thanks for all the comments and advice so far, much of which I think I understand, although my head started to ache when trying to get to grips with TT and TN supplies.

Taking a step back, I'm close to concluding that my key requirement is to run the upstairs light circuit, which takes in the bath and shower rooms, directly from the RCD side of the CU.

With no spare slots on the RCD side, I'm, minded to move the immersion circuit from there and onto the MCB-only side, thus freeing up a slot for the lighting.

The immersion is only there as a standby within an indirect gas boiler heated megaflo and has only been switched on 3 times in the last 8 years.

One problem with this idea is the present limited length of the respective cable ends. The best solution I've seen so far is to extend these using the small lever connectors illustrated at http://www.tlc-direct.co.uk/Products/WA413.html.

Would there be any problem with this approach or is there a better way?

 

[Rogeranerley]

Not sure why the lever connector page isn't showing> the product is a Wago 222-413 Lever Connector 4.0mm - 3 Pole available from http://www.tlc-direct.co.uk

 

[RF Lighting]

Would there be any problem with this approach or is there a better way?

Yes. It's none compliant with regs. Just put an RCBO on the none RCD side for the upstairs lights.

They are readily availible for your hager consumer unit.