Wiring shed

lloydyboy

Hi I am planning to install a 2 way consumer unit in my shed for maybe 2 double sockets and a light. however i wish to run SWA cable down the garden (buried) to another shed (sometime in the future) for another 2 double sockets and light. Reading other threads here didn't realise that length of run determines size of cable. Will be running 2.5 from 32Amp mcb in house to 2 way unit in shed containing 32amp for sockets and 6amp for lights.Is this ok ? Was planning to run 2.5 from 32amp two way unit to other shed to power another 2 way unit. Is this ok ? as i said nothing major being powered in them just 1 or 2 sockets. Would appreciate any advice.

fishdog

Will be running 2.5 from 32Amp mcb in house to 2 way unit in shed containing 32amp for sockets and 6amp for lights

I am guessing that you want to protect the 2.5 with a 32A MCB from you quote above. This would not be a good idea. A 32A MCB is too large for a 2.5 cable. You can go to a 25A MCB but that would be pushing it to the limit. I would normally go for a 16 or 20A MCB on a 2.5 cable.

however i wish to run SWA cable down the garden (buried) to another shed

Correct cable type.

Reading other threads here didn't realise that length of run determines size of cable

Correct. How long is the cable run in total??

What would you say the total loading will be at a maximum??

sparkyjo

if you are running a 32 amp supply down to a cunsumer unit in a shed it is not just distance that determines the size of cable

firstly as you are running a 32 amp supply out a 2.5 cable is not rated to cover that it should be at least 6sq cable

the distance of the run will now effect if you have to up the size of cable as for volt drop and as such you would need to say how far the run is and that is from the board in your house to your board in your shed

if you come off a 20 amp breaker you could run out 4 sq

hope that helps but just be very careful that don't do something wrong and electricute yourself

and thats not being smart!

lloydyboy

Ok thanks for quick answers. There is actually a spare 20amp MCB in houseboard but i was looking at Collins diy manual and it said used a 32amp mcb in house board running 2.5 to consumer unit in shed. I know they mentioned 4mm as alternative.

So can i ask what is 2.5 and 1.5mm2 made in SWA if I have to run 4mm2 ?? I can understand if I was powering a big workshop and electric garage door etc but we are only talking double sockets that might be used for radio etc (the odd power tool maybe) and a light ? why does the cable have to be so big ?

Ok so if I run 2.5 from 20amp mcb in house to 2 way consumer unit is it ok to use the 32amp in the small unit for the sockets etc ? Is this portion of the installation ok ? as the cable is in place from the builder. How would i run another cable from this small unit to another shed. Not sure of exact distances but say maybe 50+ plus feet between sheds.

fishdog

i was looking at Collins diy manual and it said used a 32amp mcb in house board running 2.5 to consumer unit in shed.

I do not know this book. It is not written with Irish regulations so I would take it with a pinch of salt if I were you.

So can i ask what is 2.5 and 1.5mm2 made in SWA if I have to run 4mm2 ??

A 1.5mm is for a load on a 10A MCB such as lights. A 2.5mm is the minimum size for a socket circuit. A cable for a socket circuit may have to be increased to 4mm depending on a few factors mainly the load and length of run. Without knowing these 2 factors it is not possible to say what size cable to use. In general if you are not sure go for the larger cable. Some wholesalers have software that will size the cable for you given all of the relevent information.

The difference in price between a 3 x 4mm sq. SWA and a 3 x 2.mm sq. SWA would be minimal.

Ok so if I run 2.5 from 20amp mcb in house to 2 way consumer unit is it ok to use the 32amp in the small unit for the sockets etc

The 32A MCB is simply too big for the 2.5 cable. It will not operate under fault conditions, the 20A will operate first so it will do nothing.


No offence but your questions would give me the impression that you may be a little out of your depth here. If you are not 100% sure of what you are doing get a qualified electrician to assist/do the job. You are dealing with a lethal voltage!

lloydyboy

out of my depth with this maybe as haven't done it before but I am quite proficient with Electrics and I am an Electronic Engineer. Can you tell me then why one of the socket circuits in my house (which is 2400sq feet) is on a 32amp mcb ? the others are on 20amp .....if 32amp is too big for 2.5 cable....lets not forget that these standards would have come from England in the first place isn't everything BS standard ???? Didn't realise the english wiring regs were outdated compared to ours......and yes my house was wired by Northern irish sparks as the builder was from the North....I am in the south.

knipex

lloydyboy wrote: »

out of my depth with this maybe as haven't done it before but I am quite proficient with Electrics and I am an Electronic Engineer. Can you tell me then why one of the socket circuits in my house (which is 2400sq feet) is on a 32amp mcb ? the others are on 20amp .....if 32amp is too big for 2.5 cable....lets not forget that these standards would have come from England in the first place isn't everything BS standard ???? Didn't realise the english wiring regs were outdated compared to ours......and yes my house was wired by Northern irish sparks as the builder was from the North....I am in the south.

Is it a ring main or a radial circuit. For a ring main circuit both ends of the cable are put into the MCB (the cable runs in a ring from the MCB to all the sockets and back to the MCB in a ring hence the name). In theory as the cable can draw power from both ends the max current carried in the cable is actually halved to 16 amps. They are used normally in a kitchen or utility.

Irish Regs and UK regs are broadly the same but DIY manuals tend to be years out of date.

Why are you insisting on using a 32amp ?

Use a 20 AMP in your house distribution board and then in Theory you can use what you like in the shed distribution board as the 20 amp in the house will trip if the cable becomes overloaded.

The other thing to consider is you need to have the sockets in the shed protected by an RCD. If you are taking the power from an RCD protected MCB in the house board then that's OK (although I personally wouldn't put lights on an RCD protected circuit). If not then you need to put an RCD in the board in the shed or at least a combined unit.

Its quite simple really.

If you are using 2.5 cable use a 20amp MCB.
If you are using a 32 amp RCD then use 6mm cable.

If you decide to do different then no one is going to shoot you but if your panel goes on fire or if your house or shed burns down then don't blame me.

In all jobs there is a right way and a wrong way. When it comes to electricity the wrong way has a tendency to get someone killed or burned.

fishdog

I am an Electronic Engineer

The 5 volt stuff is far safer :D

lets not forget that these standards would have come from England in the first place isn't everything BS standard ????

As it happens our standards in Ireland came mostly from the Germans.

Didn't realise the english wiring regs were outdated compared to ours......

Not outdated, just different and speaking as someone that studied the English and Irish regulations ours are in general higher. For example they are allowed to have sockets that are not protected by an RCD, they are allowed to use rewirable fuses and they do not have to have a main switch fuse.

and yes my house was wired by Northern irish sparks as the builder was from the North....I am in the south.

I am not suggesting that your sparks did anything wrong.


As Knipex points out a 32A MCB can be used to protect a ring circuit wired in 2.5
Your shed would be a "radial" circuit.

lloydyboy

ok fishdog less of the insults please....I came here looking for help not a lecture on Electricity.

I bought on Ebay from an english supplier a Garage unit with 63A RCCB and 6Amp & 32Amp mcb. Do i need this for the shed ? what size cable do i run shed is only 10-15 feet from house. Do i take feed from a 20-amp mcb in house or direct from main sw in house fuseboard ?

Any help would be most appreciated as long as its not a lecture.....

davelerave

use 6sq swa for both sheds if you can .you may want the extra capacity later.get a sparkie to do connecting.

RoundyMooney

To save money, why not run 6sq. to the first shed, and 2.5 from there to the second, utilising a 20A MCB from the sub board you're installing now?

You'd be talking fair distance before voltage drop comes into the equation.

Aside: I backfed around 140amps through 35s copper today for a short period, spread over a distance of around 400m or so. Didn't even get warm, but ended up with a substantial voltage drop when the load picked up. (It was initially 65A or so).

Point being, load is critical, as distance increases.

lloydyboy

Thanks roundy didn't realise distance had that effect on voltage.

so is the garage unit OVERKILL for what i want to do ?

Stoner

this is a standard shed consumer unit arrangement based on a 6sq cable feeding the shed, 1.5sq for the lights and 2.5 for the socket.

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fishdog

ok fishdog less of the insults please....

Very sorry. Did not mean to offend.

RoundyMooney:

To save money, why not run 6sq. to the first shed, and 2.5 from there to the second, utilising a 20A MCB from the sub board you're installing now?

+1

davelerave

4sq should be minimum for any shed imo.i would loop supply onto the second in 6sq and have sub-board in each shed and 32amp at house.difference in price is small .you may want it later.

lloydyboy

ok thanks for the advice ....here's what i plan to do for time being.....use 2.5 cable that is already run out under house to shed (connect this to unused 20amp mcb) and wire up two double sockets and a light from a switched spur with a 3amp fuse....

as for the other sheds will tackle that later taking into consideration your advice on cable size etc.....

No one seems prepared to answer the question about the Small Consumer unit.....obviously if i am going to use this I should run 4 or 6sq cable to it.....wiriing up sockets and lights I have no problem with ....just the feed I had the problem with....

fishdog

No one seems prepared to answer the question about the Small Consumer unit

Apoligies, what exactly is the question about the small cnsumer unit? I will try to answer.

use 2.5 cable that is already run out under house to shed (connect this to unused 20amp mcb) and wire up two double sockets and a light from a switched spur with a 3amp fuse....

I assume the 20A MCB is in the existing distribution board and it is fed through the socket RCD? Then yes this sounds OK for the small load described if the run is short.

.....obviously if i am going to use this I should run 4 or 6sq cable to it

This would be the best thing to do even if you are not installing a consumer unit in the shed. It would reduce volt drop and give better flexability in the future.

wiriing up sockets and lights I have no problem with ....just the feed I had the problem with....

Connect the feed as Stoner's drawing shows. The best cable would be the 6 sq. then the 4 sq. and the minimum possible size would be the 2.5 sq.

lloydyboy

Fishdog explain this VOlt drop to me....are you saying that I woudln't have enough power to run say a small freezer if the run was too long and the cable not up to it ?

fishdog

Fishdog explain this VOlt drop to me

As you know the conductor of a cable has a resistance. The resistance of the cable acts like a resistor connected in series with the load, so like any resistor it has a volt drop across it.

The volt drop = the resistance of the cable (live & neutral, a fixed value) x the current flowing through the cable (may not be fixed, depends on the load)

Current ETCI wiring regulations (ET101) state that the maximum permissable volt drop to any point must be less than 5% of the supply voltage.

The volt drop of any cable can be easily worked out thanks to a table in the ETCI regulations (page 235 table A52). This table tells you the volt drop per mA per meter. Once you knowthe current being drawn and the lenght of run you can easily work out the volt drop and ensure that it is less than 5% of your supply voltage (230).

Sorry if I sound condescending, it is not my aim.

are you saying that I woudln't have enough power to run say a small freezer if the run was too long and the cable not up to it ?

Yes. I am also saying that if the volt drop is too great you will be breaking regulations and this volt drop may harm some equipment that you plug in.

Does this make sense?
I would guess that a 2.5 would be OK, but I have not seen your place, so I can not say for sure.

If you feel that there is the slightest chance that you may want to increase the load drawn on this cable, go for a larger cable with more capacity. It will not cost much more.

Davy

lloydyboy wrote: »

ok thanks for the advice ....here's what i plan to do for time being.....use 2.5 cable that is already run out under house to shed (connect this to unused 20amp mcb) and wire up two double sockets and a light from a switched spur with a 3amp fuse....

as for the other sheds will tackle that later taking into consideration your advice on cable size etc.....

You understand that it wouldn't be advisable to loop from this shed to the other sheds because its being fed with a 2.5 cable. You would have to go back to the board and bring a 4 or 6 sq tot he new add on sheds, thats if you can get back to the board. Its pointless looping a 4 or 6 sq to the new sheds when its only coming from a 2.5 supply.

lloydyboy

Davy thanks, understand that ok....so if running 6sq cable from the house should it be wired into Main SW or a 32amp mcb protected by RCD ?

The small unit i bought has a 63amp RCCB, if using this should i change this for just a MAIN SW and an RCBO on the sockets ?

Sounds like I should sell this back on Ebay and buy something else....

Davy

lloydyboy wrote: »

Davy thanks, understand that ok....so if running 6sq cable from the house should it be wired into Main SW or a 32amp mcb protected by RCD ?

The small unit i bought has a 63amp RCCB, if using this should i change this for just a MAIN SW and an RCBO on the sockets ?

Sounds like I should sell this back on Ebay and buy something else....

Put the 6sq to its own switch yes, not the main switch. The 63 is a bit big, a 32amp Rcbo would be better. Also buy the stuff from a wholesaler. They will swap it for you easier than sending it back with ebay.

Then into the shed put it into a main switch and loop out to the other shed. And put it separate circuits for the lighting and sockets as the diagram already posted.

fishdog

Also buy the stuff from a wholesaler

Exactly. Makes life much simpler.

lloydyboy

Apologies if this is like pulling teeth....when i loop out of the main sw in first shed to the next shed do i need to terminate at another small consumer unit ? you'd hardly wire 6sq directly into sockets and lights ?

Davy

lloydyboy wrote: »

Apologies if this is like pulling teeth....when i loop out of the main sw in first shed to the next shed do i need to terminate at another small consumer unit ? you'd hardly wire 6sq directly into sockets and lights ?

Do yes. Ideal into another main switch fuse. Then have 2 circuits again, one for lighting and one for sockets.

davelerave

independent fuseboards in each shed.supply looped from one to next.connect to a 32amp mcb at house (wouldn't recommend rcd protection here).the boards you have are prob ok by the sound of it

lloydyboy

what's the diff between a NEOZ sw fuse and an ordinary Main sw besides neoz being fused....???

Stoner

nothing, well a main sw is just an isolating switch, while the NEOZ sw fuse is a switch in series with a fuse, the fuse holder doubles as a holder and a switch, when you flick it down you are activating a switch as well as releasing the fuse. the older way to do it was a switch with a fuse right beside it.

Stoner

Davy wrote: »

Do yes. Ideal into another main switch fuse. Then have 2 circuits again, one for lighting and one for sockets.

the small consumer unit i showed you could be used for the second shed, and you could add an MCB along side the 10 Amps MCB to a similar unit in the first shed consumer unit to feed the second shed.

TBH I would not use the garage units you got in Ebay, I've seen them before, some even have a light built into them, a good idea but a bit limited IMO.

A second 20 Amp MCB on the first board (wired like the lighting 10 Amp MCB) would feed a 4sq cable to the second shed. and the 25 Amp unit on the sub main incomer on the second shed consumer unit could be dropped to a 20 Amp unit.

Davy

Stoner wrote: »

the small consumer unit i showed you could be used for the second shed, and you could add an MCB along side the 10 Amps MCB to a similar unit in the first shed consumer unit to feed the second shed.

A second 20 Amp MCB on the first board (wired like the lighting 10 Amp MCB) would feed a 4sq cable to the second shed. and the 25 Amp unit on the sub main incomer on the second shed consumer unit could be dropped to a 20 Amp unit.

But if it tripped in the first shed, he would lose supply in the second. The cable would already protected from the main board.

Stoner

correct sorry. Looping the feed as Davy advised so long as the cable feeding the first shed is fed from an MCB in the house fuseboard.

So just two arrangements of the consumer units shown, one for one shed and one for the other with the feed for the second shed looped off the switched side of the switched fuse on the first shed.