Back boxes for Dob & Dab?

[PrenticeBoyofDerry]

It's not messing around, it's one of the several specified ways of meeting the regulation, and the only one which prevents damage to the cable when drilling.

Helps prevent!
If you really tried hard, that prevention could be breached

 

[JohnW2]

Someone presumably needs to 'mess around in the CU' to install the new sockets circuit

Good point.

I would regard that as definitely preferable to messing around with 'mechanical protection'

It's not messing around, it's one of the several specified ways of meeting the regulation, and the only one which prevents damage to the cable when drilling.

It was you, not me, who introduced the 'messing around' phrase - I would probably have used different language

I am not denying that use of adequate metal protection is a perfectly acceptable method of complying with the regulations - I was merely saying that, I would personally regard the obtaining, cutting, preparation and attachment of such protection for each and every relevant cable drop to be much less preferable (much more time-consuming, and much more of a 'fiddle') than simply swapping the MCB for an RCBO (assume one will fit), whilst I was necessarily already working within the CU.

Kind Regards, John

 

[DonutHole]

I just saw this on Screwfix, the same consumer unit as mine, but with 2 rather than 1 RCD. Presumably they wouldn't sell it if it wasn't currently legal.

http://www.screwfix.com/p/mk-sentry...ail-_-E14W05A-_-Hero1-_-MKsentry10wayrcdboard


So presumably I could buy a 2nd RCD instead of an RCBO?
http://www.screwfix.com/p/mk-sentry-2-module-80a-30ma-rcd/35907

Also the consumer unit with 2 RCD's and 10 MCB's £70, a single RCD £35. One of my 6amp MCP's is broken £5.10, would it be more logical to buy a whole new consumer unit?

I see Screwfix do free delivery over £50.

 

[PrenticeBoyofDerry]

Although you may think it be more logical to install a new dual RCD consumer unit with regards to the costing of components. The bigger picture will incur installation costs and the recommended, notification fees as well as the costs for inspection, testing and reports/certification.
This would be all relevant, if costing up and trying to make a logical informed decision on whether a swap out is the best way to go.

 

[PrenticeBoyofDerry]

Also the MK boards are not the best quality of boards, even when put up amongst the lower end/budget priced boards.
For a £70 budget, I would prefer a BG (British General) dual RCD unit.

 

[DonutHole]

Although you may think it be more logical to install a new dual RCD consumer unit with regards to the costing of components. The bigger picture will incur installation costs and the recommended, notification fees as well as the costs for inspection, testing and reports/certification.
This would be all relevant, if costing up and trying to make a logical informed decision on whether a swap out is the best way to go.

A good point 'Prentice', would it still be worth buying the new consumer unit for £70, taking out 1 RCD and 1 MCB, and keeping the rest of the consumer unit complete with 1 RCD and 9 MCB's for spares?

 

[PrenticeBoyofDerry]

would it still be worth buying the new consumer unit for £70, taking out 1 RCD and 1 MCB, and keeping the rest of the consumer unit complete with 1 RCD and 9 MCB's for spares?

To what benefit?
You would be removing the important second RCCB, I understood you were trying to introduce this added protection.
I think the best solution has been covered by introducing RCBOs to your existing board. I will admit I have not read all posts made in this topic, so may have missed something.
When considering circuit divisions under RCD protection, there are number of ways this can be achieved and number of differing models of boards that although for a just RCBOs, commonly dual RCD protection, and a combination of RCCB/RCCBs (RCD) and RCBOs.
Just having the one RCCB protecting multiple MCBs, is a backward step.

 

[Taylortwocities]

I just saw this on Screwfix, the same consumer unit as mine, but with 2 rather than 1 RCD. Presumably they wouldn't sell it if it wasn't currently legal.

You can buy a gas boiler at B&Q but it's not legal for you to install it unless you are GasSafe registered.
The 'legality' of what you buy is up to the installer. The installation needs to meet Building Regulations Part P (by implication this means BS7671).


The item on Screwfix is not the same as the one you already have. The similarity is they are both made by MK.
The dual RCD item is engineered differently, and there are extra busbars inside that your existing one does not have.

 

[mfarrow]

[I would personally regard the obtaining, cutting, preparation and attachment of such protection for each and every relevant cable drop to be much less preferable (much more time-consuming, and much more of a 'fiddle') than simply swapping the MCB for an RCBO (assume one will fit), whilst I was necessarily already working within the CU.

Last time I used steel plate it was easier than I thought, just 2 minutes on the angle grinder and 4 holes, then 10 minutes with the SDS. Plate held the cable in place so no need to clip.

I'm not familiar with MK boards but I've found it usual to have to remove the busbar to get the new unit in/out, which can take time. Plus you're working around live incoming tails on that side of the board. Also there is a risk the OP has a borrowed neutral on the landing which will lead to problems when he replaces the MCB for RCBO.

 

[JohnW2]

[I would personally regard the obtaining, cutting, preparation and attachment of such protection for each and every relevant cable drop to be much less preferable (much more time-consuming, and much more of a 'fiddle') than simply swapping the MCB for an RCBO (assume one will fit), whilst I was necessarily already working within the CU.

Last time I used steel plate it was easier than I thought, just 2 minutes on the angle grinder and 4 holes, then 10 minutes with the SDS. Plate held the cable in place so no need to clip. ... I'm not familiar with MK boards but I've found it usual to have to remove the busbar to get the new unit in/out, which can take time. Plus you're working around live incoming tails on that side of the board. Also there is a risk the OP has a borrowed neutral on the landing which will lead to problems when he replaces the MCB for RCBO.

There are, indeed, swings and roundabouts - so opinions will obviously vary. I have merely indicated which would be my personal preference in the situation we're discussing. I may be wrong, but I would suspect that most electricians would probably share my preference, rather than yours.

Kind Regards, John

 

[stillp]

I'm not convinced that even 3mm mild steel is adequate mechanical protection. I just tried drilling some with a 5mm masonry bit - took about 3 seconds per hole. It would probably be easier if buried in plaster, which would stop the drill skating around.

 

[JohnW2]

I'm not convinced that even 3mm mild steel is adequate mechanical protection. I just tried drilling some with a 5mm masonry bit - took about 3 seconds per hole. It would probably be easier if buried in plaster, which would stop the drill skating around.

That doesn't surprise me, and it's obviously another reason for not going for the 'mechanical protection' route.

However, I presume the idea is not so much that the 'protection' will defy a determined attempt to penetrate it - but, rather, that the person manning a drill (or hammer and nail) ought to become aware that (s)he has hit metal (and hopefully therefore stop attacking it!) long before it is penetrated. However, as I've said, it's certainly not an approach I would normally consider taking.

Kind Regards, John

 

[stillp]

In my experience, when drilling a wall it's not at all unusual to find a hard spot - a piece of aggregate or something - that needs a bit more time and pressure on the drill, so I wouldn't assume the lack of progress meant I'd found a mechanically protected cable.

 

[PrenticeBoyofDerry]

But when your bit starts smoking, that should be a giveaway!

 

[JohnW2]

In my experience, when drilling a wall it's not at all unusual to find a hard spot - a piece of aggregate or something - that needs a bit more time and pressure on the drill, so I wouldn't assume the lack of progress meant I'd found a mechanically protected cable.

I agree, which is one of the many reasons why I personally would not rely on 'mechanical protection' of cables (unless it were ridiculously substantial protection).

Whilst what you say is true, I have also on a number of occasions (as probably have you) encountered, and recognised, the sound and feel of a drill or nail hitting metal (the walls of my house are ridden with ancient, out-of-service conduit, and even some unused cast iron pipes) - so it does work sometimes!

Kind Regards, John