New Garage Consumer Unit

Schorpio

Hi folks,

Recently bought a house with a separate (masonry) garage. Garage has power via a 3-core 6mm2 SWA, fed from the main board in the house (via MCB). However, garage is not RCD protected (house is) and there is no consumer unit/distribution board in the garage.

To rectify this, I'm going to add a small 5-bank consumer unit in the garage, with an RCD, 6A MCB for lights and 16A MCB for sockets. So far so good.

I've picked up a consumer unit online, but when it arrived I realised that it's metal. It came from the UK, so I should probably have twigged this before now (as that's what their regs demand).

In theory, this isn't a problem, but it has occurred to me that if the unit were to become live from the 'supply' side, there wouldn't be any RCD protection. I realise this is very unlikely, and that the unit itself is earthed - but the UK regs seem to specify the use of a double-insulated supply, or adding a 100mA type S RCD upstream.

Question is, should I just ditch the metal unit for a plastic one? Or proceed as I was? Or use the metal unit with the type S RCD?

drury..

RCD incommer on a garage board is bad practice

We dont use time delay RCDS here on domestic.

Anyway non-recs not allowed work on boards so can't advise further

Schorpio

https://www.boards.ie/discussion/comment/122420111#Comment_122420111

Why is an RCD incomer on a garage board bad practice? It's already fed from the main house board which houses the main isolator switch.

I'm not a fan of using a time-delay RCD either, but that's what the UK spec advises for metal CUs (but I've lived in the UK, and never remember seeing one).

drury..

https://www.boards.ie/discussion/comment/122420276#Comment_122420276

RCD incommer on a garage board is bad practise cos u lose the lighting on a socket fault

Sure , the basic UK garage boards use an rcd incommer , it doesnt make it good practice

The wiring rules state don't create a unnecessary nuisance or words to that effect.

TD RCD question already answered

Anyway this work is illegal afaik so no point assisting and you're not competent anyhow , to be blunt

Schorpio

I've no idea how you've determined my (supposed) lack of competency by just my post, but I'd strongly disagree with you there.

I'd actually suggest that the sparky who stuck his inspection date sticker to the CU in the house, whilst failing to notice that there was no RCD protection for the garage, and that the lights and sockets in the garage are all on the same circuit, might be the one who lacks competence - and he's a "registered professional".

A family member had their garage wired a few years ago, with RCD protection on only one (of two) socket circuits. No RCD protection on any of the other circuits - including an external socket and lighting. The inside of the board was a rats nest with Wagos everywhere too. That was a different "registered professional".

Regarding the single incoming RCD - inside the house has separate RCD protection for the lights (as it should). By your reasoning, the options for the garage would be either none for the lights, or a second RCD. As an ancillary building, not connected to the house and used almost exclusively during daylight hours - a single RCD incomer is fine. It's safer than none at all, which was the approach taken by the "professional" in my family member's house.

drury..

Your last paragraph

That is not my reasoning on the garage options

Im not going to design the best garage board for you , simple though it may be

The determination of competency is only a blunt assessment. I've had it done to me at interview in a roundabout way too

Schorpio

I hope your previous 999 posts here have been a lot more helpful than your 1000th one.

drury..

https://www.boards.ie/discussion/comment/122421156#Comment_122421156

It's not possible to help as only a rec can work on a board

I'm only engaging in general discussion

2011

I recommend not feeding the supply to this sub-distribution board from an RCD. As previously mentioned, a fault on any circuit connected to this board could cause the RCD to trip, resulting in a loss of all circuits. Instead, I suggest feeding the supply cable from a 32A MCB in the main distribution board. In the sub-distribution board, I would install a double pole main isolating switch, typically rated at 63A. I would install an RCBO for each final circuit in the sub-distribution board. The advantage of the DP main isolating switch is that the neutral bar will not need to be used (which tend to have terminals that are too small in small enclosures).

This solution will cost more, but it is a far better job with reduced single points of failure.

drury..

https://www.boards.ie/discussion/comment/122421923#Comment_122421923

That's the way I would populate the board anyhow

I recall risteard stating that sub-boards should also have SPDs but I don't know on that

On the subject of assessment of competency I've gone to interviews and failed practicals . Ya just have to suck it up.

Doug Mc

I think that the reasoning behind the type S RCD recommendation.

Feed sub board via time delayed RCD, then DP main switch and RCBO's on sub-board. Surge protection optional.

May cost a bit more but very safe IMO.

Only really a task for REC though.

2011

https://www.boards.ie/discussion/comment/122423508#Comment_122423508

What is the advantage of this approach (time delayed RCD)?

I would consider it bad practice to have RCD protection on a supply to a sub-distribution board such as this. Also it is not consistent with the approach to the supply of the main distribution board as this is not protected by an RCD.

Doug Mc

I agree that RCD's in series is not normally a great idea however if a Metal (Fire safe?)sub board or such a DB directly to metal structures was to be protected / fed only through a MCB then a fault on the incomer come could reach dangerous levels before supply disconnection. The addition of the time delayed RCD or possibly 100 ma variant would trip in this case while still allow discrimination so that a fault on the garage install itself would only trip the relevant 30ma RCBO.

drury..

Thats UK you've been reading TT sub-mains probably

I can't remember all the details as we don't use them here

Doug Mc

Not sure about UK but while it might be consider overkill in TNS / TNCS systems, it can offer worthwhile protection in circumstances where persons / animals are likely to be in contact with exposed metalwork at the instant of fault development. Milking parlours or Metal fabrication shops for example.

2011

https://www.boards.ie/discussion/comment/122424683#Comment_122424683

Normally the risk of the supply cable for a distribution board inadvertently making extraneous metalwork live is mitigated by providing sufficient mechanical protection to the cable. Besides the garage is not metal, according to the OP is it masonry.

As per my previous post, this approach is not consistent with the supply to the main DB as this cable has no RCD protection. In reality installing an RCD on the sub-distribution supply cable is probably resulting in a net increase in risk as a loss of supply will result in all final circuits being lost including lighting.

Normal and best practice would be not to install RCD protection on cabling supplying sub-distribution boards in a TNCS installation (which is >99% of Irish installations).

2011

https://www.boards.ie/discussion/comment/122424852#Comment_122424852

This is not an approach that is used in milking parlours. A lot of the focus on these installations is on earthing and bonding, high IP ratings, using plastic accessories (for corrosion resistance) and keeping electrical items out of reach of livestock so far as is practical.

Doug Mc

Agree on providing sufficient mechanical protection for cable as well as earthing and bonding requirements. This is especially important where dairy animals are concerned where even small stray voltages can cause an issue. I've seen instances where proximity of installation ( shed) to electric fence earth rod caused problems.

While the additional RCD may be overall, as I said, the risk of a 100ma rcd triping before the individual RCD's in the sub-board could be considered low however in truth, so is the risk of the sub-board incomer contacting exposed metalwork.

drury..

Apologies on suggesting you're reading the UK forums I thought you were the op not a spark

I googled a bit of it to refresh my memory

For TN-C-S main supply and a TT shed

I think you can earth the armour on the supply side and protect sub-main with fuse/mcb .

Armour is trimmed off at shed end and swa glanded with pvc stuffing gland

Any risk at the shed end before the 30ma final circuits is contact between the submain phase conductor and the shed earthing terminal

Whatever way you mitigate that with a TD RCD incommer in shed board ?

Afaik the usual protection method on TT main supplies was the TD RCD in a pvc board upstream of the main board

https://www.boards.ie/discussion/comment/122427830#Comment_122427830

Schorpio

https://www.boards.ie/discussion/comment/122428043#Comment_122428043

With respect mate, you have no idea which posters are, and are not, RECs.

This is an anonymous forum. You can either share whatever knowledge you have in good faith, or not. Your choice.

Trying to pre-screen posters, and only share with RECs is ridiculous. If you don't want to share - fine. Just don't post. Simple.

drury..

https://www.boards.ie/discussion/comment/122428096#Comment_122428096

Well that's complete wrong anyhow and I didn't mention RECs btw

Whatever is shared can be read by anybody

You cannot only share with RECs

But the level of discussion between sparks will be different to that between sparks and non sparks

Between sparks you may be able to have a technical discussion. When posting aimed at non sparks you're mostly explaining things

You have to screen posters and restrict what you say. The main issue you being you don't want to provide instructions to enable them to carry out works they are not legally allowed to do

drury..

The OP is basically looking for instructions and will then proceed to do the illegal work

Discussion has to avoid giving those instructions

An option is simply no discussion at all or something in-between

The latter being some technical discussion of interest and some answers directed at the op without assisting illegal work being carried out

That's the balance and it doesn't always work out

Schorpio

https://www.boards.ie/discussion/comment/122428245#Comment_122428245

I'm not going to labour the point with you, so I'll leave it at this.

I've never said whether I am, or am not qualified to do this type of work. Further, even if I was not qualified, I never said who was actually going to be carrying out the work. You're making judgment calls here with basically no information.

Outlets don't restrict the sale of electrical equipment on the basis of who you are or what you might do with it, and I'd argue they have a much greater stake than some anonymous user on a forum.

If you don't want to share, fine - don't post. Honestly, at this point your silence would be more useful. But it's not your place to police anyone sharing information on this forum.

drury..

https://www.boards.ie/discussion/comment/122428340#Comment_122428340

If you have a REC carrying out the works you wouldn't be here asking for instructions and confused about the use of TD RCDs which a REC will not be using.

My points stand . Imo I'm correct in my views on electrical discussion

And no i'm not a policeman here .

Regardless of my view of what is acceptable here anybody can post what they like subject to moderation

There probably is an argument to restrict the sale of certain goods , distribution boards etc.

I haven't given it much thought regarding its effectiveness or implementation

And as I said before the assessment of competency may seem blunt

Having failed practical assessments at interview I had to suck it up and accept I wasn't good enough on the day

Schorpio

I'm not, and never have been, confused about the use of Type S RCDs. Nothing in my previous posts would suggest that I was.

They are mandated for use in the UK on metal CUs where the incomer isn't classified as double insulated. You possibly think that the authors of the UK regs are confused about their use too. I am well aware that RCDs in series is generally not good practice. As far as I can tell, there is nothing preventing the same use case here, though it would be unusual in Ireland. Hence, I came to ask for 2 cents here.

As an aside, I don't know why you keep bringing up having failed at interview assessments. This is neither an interview nor assessment of anything.

drury..

You are incorrect on their use being mandated in UK above

Discussion is mostly irrelevant anyhow

The TD RCD wont be fitted by the REC

Doug Mc

Apologies on suggesting you're reading the UK forums I thought you were the op not a spark

I googled a bit of it to refresh my memory

For TN-C-S main supply and a TT shed

I think you can earth the armour on the supply side and protect sub-main with fuse/mcb .

Armour is trimmed off at shed end and swa glanded with pvc stuffing gland

Any risk at the shed end before the 30ma final circuits is contact between the submain phase conductor and the shed earthing terminal

Whatever way you mitigate that with a TD RCD incommer in shed board ?

Afaik the usual protection method on TT main supplies was the TD RCD in a pvc board upstream of the main board

No problem there. I completely agree that adding an RCD to the incomer would not be standard practice, I was just saying that, if for some reason, extra protection was required then adding a RCD ( actually a 100ma RCBO) in the main DB and feeding the sub from that would be a way to go. I don't know any REC's that would do it without it being a specific request but it is feasible and does offer some enhanced protection, all be it at a cost.

To the Op: I think all responses in this thread have been made with the best intent, please don't take offence. Everyone is doing there best to assist.