Convert a twin RCD split load consumer unit?

[Demonic]

Hi,

My new build house is fitted with a Hager VC755H1 consuer unit. It's a dual RCD fixed bus bar configuration CU with 5 protected ways on each RCD and a 100A main isolator.

For a few reasons (RCD in series with CU in detached garage, smoke alarms ([on upstairs light circuit] rendered inoperative if a different circuit trips, potential for one fault tripping numerous circuits etc) I don't really like it. So I was wondering if it can be "converted" to a consumer unit that uses RCBOs and maybe the odd MCB.

My thinking is to remove the two RCDs, purchase a replacement full bus bar and load it up with RCBOs for the majority of circuits. Ideally I would like to leave the circuit that feeds the garage CU on an MCB and have RCD protection in the garage CU, possibly via RCBOs again. However, I appreciate that this circuit might need to have RCD protection at the main CU as the cable runs through internal walls before it exits the building.

Anyhow, is the above feasible? I stress that I will be getting a qualified person to do the work but I'm trying to assess what is possible and associated cost/disruption.

Cheers,

Dom

 

[EFLImpudence]

The main reason for not fitting all RCBOs is that they cost ten times as much as MCBs.

Other than that you can do what you want as long as it is fitted competently and complies with the regulations.

What you can do for the garage circuit depends on the installation method and cable type.


However, you are probably worrying unnecessarily. RCDs are not magic.

 

[flameport]

Possible, but if spending a substantial sum on new RCBOs and a busbar, you might as well buy a whole new CU to put them in for not much more.

 

[kai]

On many modern units, you can slide the items along the din-rail, in order to make way for a single non-rcd way or two adjacent to the main switch, this is why 99 percent of consumer units nowadays have what is called a flexible busbar, which can be cut to length, to match the exact number of ways to be configured, i.e. four plus four on the RCD side, plus two high integrity ways adjacent to the main switch.

 

[Iggifer]

On many modern units, you can slide the items along the din-rail, in order to make way for a single non-rcd way or two adjacent to the main switch, this is why 99 percent of consumer units nowadays have what is called a flexible busbar, which can be cut to length, to match the exact number of ways to be configured, i.e. four plus four on the RCD side, plus two high integrity ways adjacent to the main switch.

Only if the CU has three neutral bars, and from memory, the VC755H1, which is a 5+5, only has two. I think Hager do sell an extra neutral bar as an add on, but it's not something you can do out of the box with that board

 

[PrenticeBoyofDerry]

Also you would require a split load kit, to reconfigure the wiring of the neutrals between main incomer and neutral bars and RCCBs.

Not sure how the din-rail is configured on the Hager VC755H1, but that could also be an issue, as I have experienced problems locking in the RCCBs on other type of boards.

 

[SimonH2]

Possible, but if spending a substantial sum on new RCBOs and a busbar, you might as well buy a whole new CU to put them in for not much more.

Plus the cost of either paying someone to do it (and notifying through their scheme), or paying the council for building regs - £150 for my council if you can provide some paperwork. I gather from previous threads in here, that some councils can charge up to £400. So that's a big chunk of money for changing a box, or a lot less for changing it's internals !
One of those oddities of the rules - changing the box adds a lot to the cost, even though it's probably the least technically complicated part of the job.

 

[PrenticeBoyofDerry]

One of those oddities of the rules - changing the box adds a lot to the cost, even though it's probably the least technically complicated part of the job.

Changing the box may not be that technical, but performing the required tests and understanding the results, then determining whether those results are safe and compliant, plus inspecting the existing installation and understanding where they lay within codes of BS7671.
Could well be beyond the scope of most individuals!

 

[SimonH2]

All true - but I think you missed the point. All that is required if you replace all the innards if you are doing it properly. The box it's all in is ... well ... just a box really and other than mounting it securely and not leaving big holes, replacing it is not exactly a highly technical task.
I was replying to Flameport when he said (more or less) that if you are replacing all the innards then you might as well replace the outer box as well - but that then makes it notifiable work which adds considerably more than the cost of the box.

I think that (the disjoint, for building control purposes, between being able to replace every component but not the box they are in) has been "discussed to death" before here.

 

[PrenticeBoyofDerry]

Indeed the regulation laid down by building controls and the understanding of them leads to one pulling ones hair out!
I take the view if the characteristic of the circuit and devices are being changed, then this work requires inspection,testing, certification and notification. Some may argue that part p does not actually state that, but it does suggest that all electrical work shall be carried out safely and when put into service should be safe to use.
Well to me that is not a plug-in and play situation and some technical work and the understanding of that work is required.

 

[Demonic]

Thanks for all your input.

I did say initially that I'm going to get a qualified electrician in to do this work. As someone rightly pointed out, the majority of the cost lies in the RCBOs and the labour charge, and I was going to have those anyway. So, I may as well swap the box out for one that satisfies amendment 3, load it up with RCBOs and be done with it. I'm planning on having the garage CU changed at the same time and having some garden electrics installed (few sockets and some lighting control boxes) so I'd have to have an electrician in anyway.

To be honest, I was originally tempted to do the main CU conversion myself. That's only on the basis that none of the circuit cabling would have been changed and that the installation is not even a year old (new build house). I do enjoy this sort of work; I rewired my first house and installed central heating, leaving the final testing and commissioning to qualified friends. Anyway, that idea was quickly shelved. I appreciate all the testing and certification that has to be done.

Time to trawl the web for best prices.

Thanks again.

Regards,

Dom

 

[Taylortwocities]

Time to trawl the web for best prices.

I'm going to get a qualified electrician in to do this work.

You would be much better off finding an electrician and having him supply the right materials for this job.

Any decent electrician will be getting a good trade price for materials and will beat what you could buy at.

There have been so many times that i have turned up at a job and have been presented with stuff that a customer has bought. In the majority of cases it is wrong, or it is cheap dodgy rubbish. In those cases I change my pricing to time and materials because it always takes longer. I also wash my hands of any responsibility for the customer-supplied materials.

 

[Iggifer]

That being said, if you definitely want to get it yourself. Stick with Hager

 

[SimonH2]

I take the view if the characteristic of the circuit and devices are being changed, then this work requires inspection,testing, certification...

agreed

... and notification.

disagree

Some may argue that part p does not actually state that, but it does suggest that all electrical work shall be carried out safely and when put into service should be safe to use.
Well to me that is not a plug-in and play situation and some technical work and the understanding of that work is required.

But "Part P" and building regs are different things. I'm guessing that you are a member of an approved scheme, and that you'll be bound to follow the rules of that scheme which are not the same as the law as it applies. The specific detail is that notification is only required (legally, your scheme may have other views) for addition of circuits and replacing a CU - so replacing MCBs with RCBOs is not notifiable, while changing the box at the same time is. There's no difference in the technical skills required in terms of circuit testing etc - just a difference in the legal notification requirements.

 

[EFLImpudence]

... and that you'll be bound to follow the rules of that scheme which are not the same as the law as it applies.

I have read some people saying that is the case but I cannot see how it could be.

Without a list of such unrequired notifications - which there isn't one - how can it be?

If I did a non-notifiable job (and didn't notify through scheme), the only way the scheme would know is on a random inspection of certificates at annual inspection.
If told, at such an occurrence, that I should have notified this non-notifiable work they wouldn't get very far.