garage consumer unit

[ceejay]

Is it necessary to install a garage consumer unit with an rcd if the feed is coming from an rcd protected main board? i don't think it is but want to make sure. It will be running a small ring and a lighting circuit.

 

[warmgun]

Hi guys I have a similar question so thought I'd jump in on this thread.

I've been asked to install a six way fuse board in a garage. The new fuse board will be used for a combi boiler supply (boiler situated in garage), garage power and lighting and a 32 amp jacuzzi in the garden.

The house fuse board is being renewed and will be upgraded to a split load 100a rcd board. The supply is TNS

Like the above suggestion I was planning on splitting the supply tails via a henley block, feeding both the new rcd fuse board and some kind of double pole switch in an enclosure. From that double pole switch I was going to run a 10mm 3 core swa into a new rcd garage board.

Does this sound OK?

Many thanks.

 

[AndyL]

Hi guys I have a similar question so thought I'd jump in on this thread.

I've been asked to install a six way fuse board in a garage. The new fuse board will be used for a combi boiler supply (boiler situated in garage), garage power and lighting and a 32 amp jacuzzi in the garden.

The house fuse board is being renewed and will be upgraded to a split load 100a rcd board. The supply is TNS

Like the above suggestion I was planning on splitting the supply tails via a henley block, feeding both the new rcd fuse board and some kind of double pole switch in an enclosure. From that double pole switch I was going to run a 10mm 3 core swa into a new rcd garage board.

Does this sound OK?

Many thanks.

Would also need overcurrent protection for the 10mm cable to the garage

 

[warmgun]

Yeah I guess I would wouldn't I. Cheers Andy. In that case would placing a double pole MCB in the enclosue be the answer (rather than a double pole switch) If so, what rating MCB would be recommended?

 

[Taylortwocities]

In that case would placing a double pole MCB in the enclosue be the answer (rather than a double pole switch)

Hmm, double pole MCB. Why would you want to do it like that? They are used a lot in petrol stations and sur le continent but around here the usual way is to use a switch fuse. One of these, eg
Click DB750 80a Switchfuse

I'm a bit worried about your next query

what rating MCB would be recommended?

I've got a feeling that you don't understand what the switchfuse would be for. You should not be doing this if you don't know what a fuse protects.

 

[warmgun]

Hmm, double pole MCB. Why would you want to do it like that? They are used a lot in petrol stations and sur le continent but around here the usual way is to use a switch fuse. One of these, eg
Click DB750 80a Switchfuse

I'm a bit worried about your next query


I've got a feeling that you don't understand what the switchfuse would be for. You should not be doing this if you don't know what a fuse protects.

Thanks for the link, that picture helps me identify what I actually need. All I was really asking is what is the best way to protect the SWA and the then the garage cu. I'm fully aware of what an MCB protects. I've been an industrial electrician for the last 11 years. I'm just not too familiar with this house bashing malarke and what the standard is. I'm going to get it signed off by a colleague and just want to do it correctly. It's funny that people are jumping over my comments yet above you have a seasoned forum member recomending the use of an isolator instead of a switchfuse. That's not protecting the outgoing cable either.

Thanks for the advice so far guys.

So I'll do it this way then

split the tails in a henley block
feed a double pole 80amp switchfuse
run a 10mm swa from that to a 6 way RCD consumer unit
protect garage circuits with MCB's.

That's gotta be better?

Thanks again.

 

[malcolmsanford]

You don't want to be keeping that 80amp fuse for the 10mm SWA.

 

[warmgun]

No, I'll down size the fuse rating. Any advise on fuse sizing anyone?

 

[malcolmsanford]

It is really how long is a piece of string. The 32 amp Jacuzzi is your meaty load, but how often and how long is it going to be on for. The lights and boiler control is minimal, so just leaves you what is likely to be plugged into it ..................well if there is a Jacuzzi, will they be using heaters in their, bit cold getting out of a warm bathtub in February in an unheated garage, so you need to look at this.

Personally I would go for 60amps, after all you protecting the cable

 

[Taylortwocities]

I've been an industrial electrician for the last 11 years. I'm just not too familiar with this house bashing malarke and what the standard is. .

No, I'll down size the fuse rating. Any advise on fuse sizing anyone?

I don't want to get heavy about this, but......

The standard is BS7671 - the same as you use every day as an "industrial electrician"

The fuse protects the cable, the same as your day job

The size of the fuse required will emerge when you do the cable calculations for the circuit and look at the current carrying characteristics of the cable. The tables are in that BS7671 book.
This is a bit more involved than just taking out the 80amp fuse and putting a different one in.

 

[Guitarist]

As the others have already said, the fuse will be protecting the cable, so you need to work out the ccc based on length of run and installation characteristics, then fuse accordingly. For example, if it was a really long run then you may end up with a fuse not capable of supplying your load and would need to install larger cable.
Industrial electricians do this all the time so I'm sure you are familiar with the calcs.

 

[warmgun]

Thanks for the advice so far chaps.

Unfortunately I've never had to do cable calculations or installation design. That's what the on site engineer does. I'm just the contractor who makes the paperwork into a tangable form so I'm well out of practice on the theory side. I was hoping that some of your more knowledgable chaps could have maybe reeled off some of your general generic garage board install advise.

I changed the consumer unit today. I have three spare ways in the split load board and a bit of bus bar left over. My new way of thinking is that I can a run a 10mm t and e with a 10mm earth from the non rcd protected side of the board backed up on a 60 mcb. I'll then put a six way rcd protected board in the garage. (cable run is approx 10m)

This seems like a lot less work for me and will be a lot less expensive for my customer. Does is sound OK though?.....I feel like an apprentice again asking these basic questions.

 

[Taylortwocities]

I changed the consumer unit today. I have three spare ways in the split load board and a bit of bus bar left over. My new way of thinking is that I can a run a 10mm t and e with a 10mm earth from the non rcd protected side of the board backed up on a 60 mcb. .

You've raised even more doubt now.
Re your new consumer unit.

In order to comply with the requirements for DOMESTIC installations (where the wiring is almost always buried in plasterwork). ALL circuits must be protected by 30mA RCDs.
So you should at least have installed a dual RCD consumer unit or a board with all 30mA RCBOs.
There should only be special circuits that do not have RCD protection.

So, if I understand you correctly, you have installed a new consumer unit and then you'll get your mate to come and lie to the local authority by saying
1. that it is all his own work (which it isn't)
and
2. that it complies with Building regulations Part P and by implication with BS7671 (which it also doesn't).

It would be bad enough if you wre doing this in your own house but your last post indicates that you are doing this work for financial gain. :nonod:

This seems like a lot less work for me and will be a lot less expensive for my customer

​

 

[SPARTYKUS]

For what its worth, I'd use a metal CU for better protection, and mount the board a little higher up the wall than I would in a house.

Sector/Senate do a 2 way metal cu with 63A main switch for £28.80 + VAT so that's hardly expensive, especially as its quicker to install 1 item, than terminate the SWA into a metal enclosure etc, etc.

Thanks Murdoch will check that out. Sounds a good way of doing it always assumed metal CU's were too expensive for this type of scenario.

 

[warmgun]

In your eagreness to criticize me I think you have completely misunderstood my last post. I have installed a 17th edition split load rcd consumer unit (as I'm sure I mentioned in a previous post). Like most split load boards the bus bars are actually designed to be adaptable so that you can add circuits to the incoming, non RCD side next to the main switch (as per the instruction manual) Also I'd like to add that as far as I'm concerned there is nothing wrong with someone else signing of an installation if they have fully inspected it and are satisfied that it complies with bs7671 so it is far form a lie. So wind your neck in and cut me some slack.

All I'm intersted in is the safest way to carry out this job so that it fully complies with regulations.

 

[Octopus]

Also I'd like to add that as far as I'm concerned there is nothing wrong with someone else signing of an installation if they have fully inspected it and are satisfied that it complies with bs7671 so it is far form a lie.

Your mate is breaking the terms of his scheme and you are deluding yourself. Self certification means "self" i.e yourself, and not your mate.

If you have the qualifications and competance why don't you simply join a scheme?