Forced RCD Upgrade in CU

[musashi79uk]

All of that stuff could be installed, but it's massive overkill what is effectively a few socket outlets and a light.


Only if the problem was between L&E.
Anything between N&E will still be there and tripping is likely to still occur.
The same applies to any other circuit in your house.

So what would you suggest? I'd have preferred an IP66 box on the wall where the supply exits the house and inside it have the 6mm armoured cable connect to 6mm twin and earth with Wago connectors. That way if it was an issue, it could be terminated inside the IP66 box.

 

[ericmark]

I also looked at the picture, to my mind type AC instead of type A is not really a factor, 6 mA DC is nothing, so it will only in real terms help if there is some DC detection unit to disconnect if it exceeds 6 mA. But if rules say type A then clearly type A must be used.

As to time delay doing a hunt on internet it says "The Sentry Time Delay RCDs are clearly identified with the internationally agreed representative symbol; and the words; 'TIME DELAY'." however also found examples of time delayed RCD's without the marking, however since time delayed is to provide selectivity, they tend to be 100 mA and above. This is a Wylex type S

I can't see that square with S on the example shown with @musashi79uk example.

But it does clearly show 63 amp and a 40 amp MCB so unless DNO fuse is 60 amp then likely under rated. Using a double pole switching RCBO does seem the right move for an outbuilding supply, or as already said using SWA, much depends on the route, and the consumer unit, for me to swap a type AC for type A RCBO is easy enough. And I would have thought one could also swap a type AC for a type A RCD, and that is £24.50 (Screwfix) so seems no really problem to simply swap it. Except for the problem in the house should it trip.

I was offered a SPD in the same way when I got a new consumer unit, and for the price may as will fit it, not point in checking if really required.

 

[AndyPRK]

I assume it’s a dual RCD CU, so I wouldn’t worry about the 63A rating verses the main fuse.

 

[SUNRAY]

So what would you suggest? I'd have preferred an IP66 box on the wall where the supply exits the house and inside it have the 6mm armoured cable connect to 6mm twin and earth with Wago connectors. That way if it was an issue, it could be terminated inside the IP66 box.

SWA all the way is the best way to go. In my view avoiding any joints, especially outdoors, is the right thing to do.

Chances are RCD would be required for the T&E but not for the SWA.

However as John has stated that installation could be simplifid to a 32A MCB feeding the outbuilding then directly to the sockets and use FCU's with 3A fuses as light switches.... Personally it wouldn't be my idea of best design though.

 

[flameport]

? I'd have preferred an IP66 box on the wall where the supply exits the house and inside it have the 6mm armoured cable connect to 6mm twin and earth with Wago connectors.

You have already posted about that here: https://www.diynot.com/diy/threads/garden-office-power-supply.625812/
You could do that. There is no reason to do so. It just adds more connections and a box to put them in where none are required.

So what would you suggest?

There are many possibilities. What the electrician has quoted is probably the worst option - any problem in the garden office results in not only all of that going off leaving you in darkness, it also disconnects half of your house at the same time.
Also any problem in the house on a circuit connected to that RCD disconnects half the house and the garden office as well.

It might be possible to reconfigure the consumer unit to have a non-RCD protected MCB in it, with armoured cable from there to the garden office, and a consumer unit in there with a 20A RCBO for the sockets and a 6A RCBO for the lights.
Or add a switchfuse at the house for the armoured cable instead of connecting to the existing consumer unit.

Plenty of other choices.
Most of them are not necessarily wrong, but it's really about what is actually required for this installation and how much inconvenience you want when problems occur.

 

[SUNRAY]

I assume it’s a dual RCD CU, so I wouldn’t worry about the 63A rating verses the main fuse.

You have to be a bit carefull with that, I wouldn't expect to install 63A RCD followed by a number of large MCB's if the supply is 100A

 

[Murdochcat]

Get a better spark

And this is a prime example why dual RCD boards should not be installed.

 

[SUNRAY]

You have already posted about that here: https://www.diynot.com/diy/threads/garden-office-power-supply.625812/
You could do that. There is no reason to do so. It just adds more connections and a box to put them in where none are required.


There are many possibilities. What the electrician has quoted is probably the worst option - any problem in the garden office results in not only all of that going off leaving you in darkness, it also disconnects half of your house at the same time.
Also any problem in the house on a circuit connected to that RCD disconnects half the house and the garden office as well.

It might be possible to reconfigure the consumer unit to have a non-RCD protected MCB in it, with armoured cable from there to the garden office, and a consumer unit in there with a 20A RCBO for the sockets and a 6A RCBO for the lights.
Or add a switchfuse at the house for the armoured cable instead of connecting to the existing consumer unit.

Plenty of other choices.
Most of them are not necessarily wrong, but it's really about what is actually required for this installation and how much inconvenience you want when problems occur.

Indeed there are a whole plothora of correct ways to do this job compliantly and safely but I very much agree it is by far the best thing to keep the outbuilding and half of the house off of a common RCD. Converting the CU 'should be' well within the skillset for any electrician with a modicum of experience.

 

[AndyPRK]

And as John has said. You could avoid touching that CU all together. This would avoid it tripping and avoid non compliances.

Fit a switch fuse by meter and run swa all the way to the shed would be a
Way.

 

[musashi79uk]

And as John has said. You could avoid touching that CU all together. This would avoid it tripping and avoid non compliances.

Fit a switch fuse by meter and run swa all the way to the shed would be a
Way.

But wouldn't that still cause the house CU to trip if an earth or neutral fault was detected?

 

[AndyPRK]

No. Because it would be before that CU.

 

[musashi79uk]

Do you have a link to one please?

 

[AndyPRK]

Here is an example

You want it metal so you can gland in SWA.
You want to be able to run tails into it. So a large knock out.

It could have a fuse or mcb

Metal Clad Fused Isolator Sub Main Switch FUSE INCLUDED 63A | eBay

Fuse Carrier and 63A Fuse included. Fused Switch Unit. Modern design suitable for all installation and colour in fresh white. 100A Switch Disconnector. Maximum cable size and extensive cable entry points for easy installation.

www.ebay.co.uk

 

[SUNRAY]

Not a particularly good example but from a recent thread:

The splitter block (frequently called Henley block) half way up on the left with tails to the switched fuse etc. In this case there are separate enclosures for the RCD and fuse (both EDIT: can be in same enclosure in Andy's suggestion).

My personal preference is to have the RCD at the outbuilding but there is nothing wrong either location.

 

[AndyPRK]

The one I linked just had a main switch and fuse