Fitting RCB/mini consumer unit in Garage.

[diydunce]

Hi,

I currently have a garage that has a very old Fuse box containing a 15Amp and a 5Amp fuse (not MCB). This fuse box is fed from the Main Consumer Unit box using a single 2.5mm2 cable. This cable is connected to a 15Amp MCB in the main consumer unit.

I want to upgrade this fuse box in the garage with a new mini consumer unit that contains MCB's as oppose to fuses. I have seen a new mini consumer unit on the internet which has the following specification (shipped from Israel).

2 way new consumer unit 1 x 40amp 30mA trip current RCCD, 1 x 6amp MCB's and 1 X16amp MCB.
Ideal for Garage, Caravan ETC.
IEC-898 STANDAD FOR THE MCB's
IEC1008-1 FOR THE RCCD
WHEATHER RESISTANCE GRADE - IP55
MCB's AND RCCB PASSED STRICTEST INSTITUTE OF STANDARDS TESTS

The Questions that I have are:
1. If I fit this new mini consumer unit in the garage should I upgrade the MCB in the main consumer unit from its existing 15Amp?
2. What rating MCB should I upgrade to in the main consumer unit?
3. What is the maximum amount of current I can draw on this single (radial) 2.5mm2 cable that runs from the main consumer unit to the garge conusmer unit?
4. I want to connect five 13Amp double plug sockets to the new 16Amp MCB in the new Garage mini consumer unit. Do i just run a single 2.5mm twin and earth to each socket in series (radial)? I.e. I wont have to run in a RING circuit for these sockets.
5. Do I have to run 1.5mm2 cable from the new 6Amp MCB in the new mini consumer unit to each of the lights in the grage. Can I just use my 2.5MM2 cable as I have plenty of that to hand.


Regards,

 

[ban-all-sheds]

Hi,

I currently have a garage that has a very old Fuse box containing a 15Amp and a 5Amp fuse (not MCB). This fuse box is fed from the Main Consumer Unit box using a single 2.5mm2 cable. This cable is connected to a 15Amp MCB in the main consumer unit.

I want to upgrade this fuse box in the garage with a new mini consumer unit that contains MCB's as oppose to fuses. I have seen a new mini consumer unit on the internet which has the following specification (shipped from Israel).

Why get one shipped from Israel when they are available here?

2 way new consumer unit 1 x 40amp 30mA trip current RCCD, 1 x 6amp MCB's and 1 X16amp MCB.
Ideal for Garage, Caravan ETC.
IEC-898 STANDAD FOR THE MCB's
IEC1008-1 FOR THE RCCD
WHEATHER RESISTANCE GRADE - IP55
MCB's AND RCCB PASSED STRICTEST INSTITUTE OF STANDARDS TESTS

Those standards are probably OK for equipment to be used in the UK, but you should do due diligence and check, or wait for someone with a better knowledge of standards to answer here...

The Questions that I have are:
1. If I fit this new mini consumer unit in the garage should I upgrade the MCB in the main consumer unit from its existing 15Amp?

You might be able to, but you don't have to. (Unless proper discrimination is a regulation requirement - I don't think it is, but I could be wrong). You already have a situation where the protective device in the house is more likely to operate in the event of a fault than the one in the garage, your new CU won't change that.

2. What rating MCB should I upgrade to in the main consumer unit?

The maximum for a 2.5mm radial is 15, 16 or 20A, depending on how the cable is installed, how long it is and so on. You'd need to work it out yourself, or refer to the tables in the IEE On-Site Guide.

3. What is the maximum amount of current I can draw on this single (radial) 2.5mm2 cable that runs from the main consumer unit to the garge conusmer unit?

That's the same Q as #2... (assuming you mean "What is the maximum amount of current I can safely draw on this single (radial) 2.5mm2 cable?" )

4. I want to connect five 13Amp double plug sockets to the new 16Amp MCB in the new Garage mini consumer unit. Do i just run a single 2.5mm twin and earth to each socket in series (radial)? I.e. I wont have to run in a RING circuit for these sockets.

You can do that, but why don't you want a ring?

5. Do I have to run 1.5mm2 cable from the new 6Amp MCB in the new mini consumer unit to each of the lights in the grage. Can I just use my 2.5MM2 cable as I have plenty of that to hand.

You may certainly use 2.5mm cable if you want to. You may prefer 1.5mm for ease of installation into light fittings and switches.


Now it's my turn.

What mechanical protection does the 2.5mm cable have on its run to the garage?

Is the circuit supplying it RCD protected?

How far away is the garage, and what sort of earthing system does your house supply have?

 

[diydunce]

Hi,

Thanks for the reply. My answers will probably expose my knowledge of electrical wiring but here goes.

The reason for the Consumer unit from Israel was because it is seeling for about £22 including P&P which I thought was good value. Let me know if you know a better source as I am all ears.

The cable run from the consumer unit to the garage is probably about 15-20metes.
If I did want a RING circuit in the Garage would I just connect the cable in a RING to/from the 15Amp MCB in the garage. I cant connect a rING circuit to the main conusmer unit in the house as it is all buried under concrete floors. I am not sure what you mean by what earthing system does my house have?

I am not sure what you mean by what mechanical protection does the cable have to the garage. It is a buried cable that was probably put in about 25 years ago when the garage extension was built by the previous owners. The cable connects from a 15Amp MCB in the main consumer unit to a 15Amp old fuse in the Garage Fuse Box. The Garage Fuse box does have a 30Amp On/OFF switch.

The main consumer unit is about 15 years old and it is an 8-Way WYLEX fuse box with MCB's and an ON/OFF switch. I am not sure how to tell if the circuit is RCD protected.

From my answers you will probably suggest that we get an electrician in but it seems such a lot of money to change out a fuse box and run a few wires. The Garage has been working for 25 years on its existing wiring which has three single power sockets, two strip lights and a halogen security light. I just want to upgrade the system to new/extra fittings/fixtures and a new mini consumer unit. I guess I could leave it as it is but whilst I am insualting my garage I wanted to upgrade the old wiring before It all gets enclosed in plasterboard.


Cheers,

 

[ban-all-sheds]

Hi,

Thanks for the reply. My answers will probably expose my knowledge of electrical wiring but here goes.

The reason for the Consumer unit from Israel was because it is seeling for about £22 including P&P which I thought was good value. Let me know if you know a better source as I am all ears.

What make is it? Or what's the URL of the site where you saw it? On the basis of YGWYPF I'd be suspicious of a price that low, but then the UK does have a reputation as being heaven-on-earth for rip-off pricers. If it's not a make with a UK presence, then as well as earlier Q's re standards you should check how easy it is to get spare parts if you need them.

The cable run from the consumer unit to the garage is probably about 15-20metes.
If I did want a RING circuit in the Garage would I just connect the cable in a RING to/from the 15Amp MCB in the garage.

Yes.

I cant connect a rING circuit to the main conusmer unit in the house as it is all buried under concrete floors. I am not sure what you mean by what earthing system does my house have?

Sounds like the garage is integral to the house - is this the case? There are different ways that the earth is supplied to houses (probably too much detail to go into here), but if your garage is effectively just another room, then, RCD protection aside, this doesn't matter. If the garage was a separate building then it might.

I am not sure what you mean by what mechanical protection does the cable have to the garage. It is a buried cable that was probably put in about 25 years ago when the garage extension was built by the previous owners.

You aren't going to like this, but I suggest you get it inspected and tested. I've no reason to think it's dodgy, but if it was just buried in concrete then who knows how sound it is?

The main consumer unit is about 15 years old and it is an 8-Way WYLEX fuse box with MCB's and an ON/OFF switch. I am not sure how to tell if the circuit is RCD protected.

Is it a "fuse box" with conversion plug-in MCBs, or a one which always had MCBs? Does it say anything about RCD or ELCB on it? Is there a test button on or near the main switch? In any event, even if the CU does have an RCD incomer, at 15 years old it might be an old-stlye 100mA one, not regarded as up-to-scratch these days.

From my answers you will probably suggest that we get an electrician in but it seems such a lot of money to change out a fuse box and run a few wires.

You may not need an electrician to do that for you, but it might be a good idea to get one in to check that there's nothing else wrong with the installation. e.g. a 25-year old cable will probably have a smaller earth conductor than modern ones, which will affect the total earth-loop resistance, which will affect what size MCB you can safely have.

The Garage has been working for 25 years on its existing wiring which has three single power sockets, two strip lights and a halogen security light. I just want to upgrade the system to new/extra fittings/fixtures and a new mini consumer unit. I guess I could leave it as it is but whilst I am insualting my garage I wanted to upgrade the old wiring before It all gets enclosed in plasterboard.

If you are insulating your cables then their current carrying capacity is reduced. 16A on a 2.5mm cable in the garage is almost certainly going to be fine, but just to make sure - how long will the run be?

 

[diydunce]

What make is it? Or what's the URL of the site where you saw it? On the basis of YGWYPF I'd be suspicious of a price that low, but then the UK does have a reputation as being heaven-on-earth for rip-off pricers. If it's not a make with a UK presence, then as well as earlier Q's re standards you should check how easy it is to get spare parts if you need them.

I was a bit sceptical myself. Maybe I will buy one with a BS mark. here

Sounds like the garage is integral to the house - is this the case? There are different ways that the earth is supplied to houses (probably too much detail to go into here), but if your garage is effectively just
another room, then, RCD protection aside, this doesn't matter. If the garage was a separate building then it might.

The garage is attached to the house. The cable is bured under concrete floors, but it is fed through some pretty thick round conduit.

Is it a "fuse box" with conversion plug-in MCBs, or a one which always had MCBs? Does it say anything about RCD or ELCB on it? Is there a test button on or near the main switch? In any event, even if the CU does have an RCD incomer, at 15 years old it might be an old-stlye 100mA one, not regarded as up-to-scratch these days.

The CU does not have anything written on it and it contains some of the old style MCB's. The MCB's have push in circular type buttons as oppose to the new switch up/down MCB's.

f you are insulating your cables then their current carrying capacity is reduced. 16A on a 2.5mm cable in the garage is almost certainly going to be fine, but just to make sure - how long will the run be?

The total length of cable (for the five double plug sockets) from the Garage mini CU will be about 28metres if run in as a spur or about 34 metres if run in as a ring. Length of cable for lights is about 8 metres

 

[unphased_spark]

Ban

Quote:
The cable run from the consumer unit to the garage is probably about 15-20metes.
If I did want a RING circuit in the Garage would I just connect the cable in a RING to/from the 15Amp MCB in the garage.

Yes.

Only if you replace the MCB to one rated at 32A

diydunce

Is the CU replacement for the garage metal clad ? It should be, not to mention the socket outlets as well ideally.

The cable runs you mention sockets/lighting seem lengthy ?? must be a big garage

 

[diydunce]

Thanks for the reply. It is a big garage, soon to be big office.

I did wonder about teh different types of consumer unit (insualated, metalclad etc..). Can you tell me why it should be a metalclad? There are quite a few consumer units here and it is hard to know what to choose.

Could you tell me if
this consumer unit is necessary or should I go for the cheaper ones like these

this (with 16Amp/6Amp MCB)

this (with 15Amp and 5Amp MCB's)


What are metalclad sockets?

 

[plugwash]

metalclad sockets:
here

if you are converting the garage into an office you probablly don't nneed metalclad sockets or a metalclad cu but it may be an idea tu seu them

personally i would use 6mm on a 32A in the main cu (prefearablly on the non-rcd side) running to a small metalclad rcd cu with a 20A radial for sockets and a 6A ligthing cuircuit in the garage

a 40A run from the main cu with a 32A ring and a 6A lighting is possible but you would probablly need 10mm cable which may be hard to pull through the trunking

 

[unphased_spark]

diydunce

Plug is right the fact you mention it's a garage to office conversion metal clad components are no longer required incidently they provide mechanical damage protection ( heavy blows from machinery/tools)
I think 4mmsq T & E would be ok for the run from Main to Garage CU with a 32A MCB in place.

From the Garage side I would go for a 2 WAY CU incorporating a 32A 30mA RCD with either 32A or 20A (SOCKETS) 6A LIGHTING) see below...

Have a look here under product name MK, Hager, Wylex Crabtree.

2.5mmsq T & E for the ring/ radial in which case 32A MCB / 20 A MCB
1.0mmsq or 1.5mmsq T & E for lighting.

 

[ban-all-sheds]

Ban

Quote:
The cable run from the consumer unit to the garage is probably about 15-20metes.
If I did want a RING circuit in the Garage would I just connect the cable in a RING to/from the 15Amp MCB in the garage.

Yes.

Only if you replace the MCB to one rated at 32A

I didn't think it was compulsory to use a 30/32A breaker on a ring circuit.

I was starting from the basis that the garage is supplied via a length of 2.5mm, and so could not possibly support a 32A ring. AFAIK, diydunce (who's probably now confused by all the different options being proposed) could have a 16A radial or 16A ring in his garage office. At the time the only advantage of a ring that I could see was better cpc resilience, but now I'm wondering if it might also be useful if the cable is going to be buried in a thermal wall, but I haven't done the sums.

Any of the alternative options that you and plugwash have proposed involve replacing the cable from the main CU to the garage/office. To be sure, if you were doing this from scratch you wouldn't use 2.5mm, but that is what is there, and it may not be possible to replace it. It may be physically impossible to pull a new cable through the conduit (there being no guarantee that it was done properly in the first place) and even if it is it may be too small to take 6mm, or even 4mm cable.

Plan B, of course, is to not have a CU in the office at all. Instead of buying one of those, put the money towards a replacement split-load house CU, and just have a 2.5mm radial circuit on a 16A or 20A breaker (RCD side) - there's no more reason to have a CU in the office than there is to have one in any other room in the house. At a convenient point on the circuit you could put a switched FCU to power the lights, and job done. I know that would mean that the office lights would be on an RCD circuit, but in an office environment I think that a non-maintained 8W fluorescent fitting would be visually acceptable.

Perhaps some kind soul with a cable calculator on their PC could take the details of the cable run assuming it becomes 1 long radial and look at VD and thermal correction to see if diydunce can put it on a 20A breaker or not....

 

[diydunce]

Thanks for all your time in replying to my messages. I will replace the CU in teh garage with a new one and run in some new 2.5mm cable, which I think is the easiest and cheapest option for me.

I will run teh wires above the rockwool insualtion so I guess this wont decrease teh length of my cable run.

Anyone know where you can get an electrician to come round and do an inspection. I find it hard enough finding an electrician to come and do some work unless there is some decent money in it for them. How much would a simple inspection of a garage (not whole house) cost?

Cheers All

 

[unphased_spark]

Ban

Take a look in the O-S-G page 41 table 7.1

 

[ban-all-sheds]

I've never checked to see how conservative those tables are, or if they give the same results as working it out "properly".

If the latter then let's hope diydunce has not yet run his new 2.5mm cable, as it looks like he's going to need 4mm for a 43-48m radial.....

 

[diydunce]

Hi All,


- I have worked out that my main consumer unit does not have an RCD, it just has an isolator switch.
- The 2.5mm cable runs from a 15Amp MCB in the main consumer unit, under the concrete floor (through ducting), to the old fuse box in the garage. This run is about 15metres
- I have seen a consumer unit on the internet which has a 5Amp (MCB), a 15Amp (MCB) and a 25Amp (RCD). I plan to replace the old fuse box in the garage with this new unit.
- I have run in some 2.5mm cable from the fuse box in the garage (soon to be the new consumer unit) to five double 13Amp sockets. The total length of the run is 23 metres and I have run the cables on top of the rockwool insulation . NOTE: I have left a 10mm vertical gap in the insulation to run cables from the roof down to each 13Amp socket so that the cables are not buried/touching in the insulation. This new cable will connect to the 15Amp MCB in the new consumer unit.
- I have run in some 2.5mm cable from the 5Amp fuse in the new consumer unit to four lights (160W, 160W, 160W and 500W Halogen). The total length of this run is 20metres).

Can you tell me if you think this sounds OK?
Can you tell me if the 25Amp RCD on the new consumer unit is of a suitable rating.
What is the o-S-G and where can I find it?
Can you tell me what is the risk of fire. Is there a risk of fire if we have all appliances on at the same time causing the 2.5mm cable (max 24Amp) to overheat. Will the MCB/RCD shut off the power before fire could occur.?

Cheers,

 

[unphased_spark]

diydunce

I have read your last post and am not sure where you have found the CU that you intend on using, if there is a link I wouldn't mind taking a look ?
I have never seen a 25A RCD although I am prepared to be proved incorrect.
As for your cable runs the 2.5mmsq runs for the socket outlets are fine but I would suggest using a 20A MCB if this is a radial, however if you have formed a ring then a 32A breaker is a pre-requisite.
The lighting circuit should be run in either 1.0mmsq or 1.5mmsq as suggested in an earlier post and protected by a 6A MCB
I have grave doubts about the CU you have seen advertised on the internet...... remember cheapness tends to imply something other than the best .... in this case inadequate.

Going back to the run from the house CU to the garage CU if there is ducting in place can a cable be pulled through ? If so then you should think of upgrading to 4 mmsq