Pls, no 'you must get' replies, can anyone help with simple shed wiring advice

I need to do a simple wiring job on my shed. 3 double sockets (I’m thinking radially wired) and two lights with independent switches.

I wired up my last home office, but this time as the feed will come from my garage and taking advice I’ve got a small consumer unit for the job. Except, it doesn’t come with a how to guide and google is not helping.

Can anyone tell me what wires to put where please..

Can anyone tell me what wires to put where please

😕

I think not finding a ‘how to’ guide should be telling you something! There is plenty on the web about this sort of stuff – try http://www.diyfaq.org.uk/index.html or http://www.therevcounter.co.uk/trc-shed/65121-consumer-unit-for-my-shed.html

YGM

Just sent you a link to download all the regs and some Part P wiring guides.

Put a plug on the end of it and just run it off an RCD?

They’re pretty simple:

Important. If your house is PME wired at the meter consumer unit you should earth the shed via a ground stake not back to the house via the twin and earth supply cable (if that is waht you used).

Can anyone tell me what wires to put where please..

So, what wires have you got and what places can they be put?

Thanks guys for the replies. Here’s the unit…

Unless you’re proactively trying to win this year’s Darwin Award, if you have to ask questions about electrical stuff, then it’s probably best left to the professionals.

At a guess:

The Lives (brown or Red wires) from the sockets go in the top of the individual fuses on the LHS. You have two fuses, so could just use one, or maybe put lights on one and sockets on the other.

All the Neutrals (Blue or Black) go to the top right bus bar (next to the big Blue wire).

All the earths go to the Top left bus bar.

The input Live and Neutral, (from your main circuit board) go to the Switch on the RHS (on the top, marked L and N).

You take the Switched Live output (from the bottom of the RCD) and daisy chain it to the lower connection on both of the Fuses, using the copper comb thing in the plastic bag.

You need a local earth rod in the ground near the shed so the RCD works properly.

NB Before wiring it up live, I always check with a multi-meter that everything is working as expected e.g. the switch really does isolate L and N etc etc.

what they say TBH if your skill level is such that you dont even know where the live and the neutral and the earth go then really step away from the dangerous thing that can kill you and burn your house down.

Power in TOP

Power out BOTTOM- from RCD

Fuses out top to circuits

Live only to the fuses L and N to the RCD
really if you cannot work that out step away from the project

I imagine the fuse does not care which way the power flows tbh but the RCD will

Footflaps hang your head in shame and sit in the corner. You know the rules, about not actually answering the question asked. Not only have answered, but you’ve not tried to baffle anyone with hocus pocus. Now can please just mention notifiable works, building control, planning permission etc etc.
oh and OP, what footflaps said.

put lights on one and sockets on the other.

This. definitely this. The lights go on the 6A rated MCB, the sockets on the 32A. I’m thinking you might want a smaller MCB for 3 sockets, perhaps a 16A?
The live incomer goes into the terminal marked 1.
Use armoured cable for the supply and earth the shield.
I’d ringmain the sockets, rather than “spur”. 1.5mm Twin + E should do it.

Fuses out top to circuits

I wouldn’t do this. You won’t be able to isolate them.
I am not an electrical engineer.

You also need to make sure that the fuse rating is the lowest rated part of the circuit, so if using a 32A breaker, the cables must be rated above this, so that in the event of an overload, the breaker trips rather than the cable catches fire…

where abouts are you pal , if near wigsn could come round and sort it for you for a few bear tokens

I wouldn’t do this. You won’t be able to isolate them.

why not?

anyway, what footflaps said, except

The input Live and Neutral, (from your main circuit board) go to the Switch on the RHS (on the top, marked L and N).

I think that is marked “1” and “N” – the output is “2” and “N” at the bottom of RCD.

NB Before wiring it up live, I always check with a multi-meter that everything is working as expected e.g. the switch really does isolate L and N etc etc

This is worth repeating, several times. As in, wire up everything *except* the incoming mains. And then double check it all with a meter.

FWIW we’ve got an almost identical garage unit, if you’re not in a hurry I’ll try and remember to get a photo up on this thread.

edit: I am not a sparky, or an electrical engineer, although I have a background in electronics and have some practical wiring experience.

edit:

I’m thinking you might want a smaller MCB for 3 sockets, perhaps a 16A?

personally I’d just leave it at 32A, and use normal 2.5 cable. 16A is about right for radial IIRC.

1. I’d echo the replies, if you can’t figure out what and where the L N and E are then step away.

2. I’d do ‘ring’ rather than ‘radial’ circuits. I’m sure the budget would take the additional £5.17 for cable.

3. How have you extended the supply from the garage? Are the shed and garage connected?

4. Has the circuit / supply ring your taking your feed from already got an RCD? If it has then the second RCD is going to give you issues with unecessary tripping. That said, if there is no existing RCD supply then you’re better off with two RCBOs than two MCBs and an RCD (IMHO).

Has the circuit / supply ring your taking your feed from already got an RCD? If it has then the second RCD is going to give you issues with unecessary tripping.

I can’t see any possible reason for this to happen. They’ll only trip if there is the minimum difference in current between L and N which won’t be affected by any ‘extra’ RCDs upstream.

I have been told on more than one occasion (by different sparks) that multiple RCDs on a circuit / connected circuits was a no no but I’m happy for someone to put their knob on the block.

Afterall, everyday is an oportunity for learning.

why not?

I read the suggestion as being to wire from the top of the RCD (same terminal as the incomer), which would bypass the switch. I think this isn’t a good idea. Have I read it wrong or do you disagree?
I’ll bow to superior knowledge WRT breaker size. Is it worth mentioning that type b breakers aren’t motor rated? Depends what you’re plugging in of course.

As footflaps says, I can’t see any logical reason why multiple rcds on a circuit would have a problem as they just measure imbalance in current. In fact my house which was wired by an electrician has 2 with one covering the whole house and a more sensitive one covering the bathroom sockets iirc.

which was wired by an electrician

and

the bathroom sockets

😯

First step would be to get one of these;

But not one of these;

I have been told on more than one occasion (by different sparks) that multiple RCDs on a circuit / connected circuits was a no no but I’m happy for someone to put their knob on the block.

I’ve just skimmed the IET wiring regs and can’t find anything saying you can’t use two RCDs.

Hamishthecat

Shaving sockets are allowed in bathrooms, and other sockets if more than 3m from baths etc.

ff,

Thanks for your response, as I said, every day’s an oportunity.

<Nob on the block>

Two RCDs in line is ok but it is preferable not to. The fault current will trip the RCD with the quickest response time. This may be the nearest to the fault or the one at the main CU (or sometimes both). With an RCD protecting the circuit locally and not further up the line means a fault can be readily resolved on-site ie in the shed, rather than having to go back into the house. If the RCD in the house protects other circuits you might find a situation where a fault in the shed takes out all the house lights at the same time which is a) irritating and b) dangerous if you then fall down the stairs trying to find the RCD to reset it.
It’s also not necessarily the case where there is a 100mA RCD remotely and a 30mA RCD locally for the 30mA to trip before the 100mA one. Fault current can be in the 100s of amps and the actual trip current won’t make a difference. Where two RCDs are in line, the furthest up the line should be an “S” curve time delay unit which will trigger slower and thus give discrimination.

100mA RCDs don’t give shock protection, they are normally used to ensure MCBs trip with TT earthing (rods).

With regards rodding the shed there is some debate about the necessity of this with PME systems. If there is no earth potential introduced into the shed (eg metal structure, water pipes etc) then rodding is not necessary. If there is then rodding is recommended but you could also ensure that the feed to the shed has a minimum 10mm earth which would suffice as a bond.

If you choose to rod it then ensure that the earth of the feed cable IS NOT CONNECTED to the earth bar in the garage consumer unit.

</Nob on the block>

Rich.

Awesome info. Rich,tx

the bathroom sockets 😯

Hehe. Good point, i’d forgotten that. I’m not uk but I used rcds all the time I was working there to keep myself safe. Good to see sockets in bathrooms are now allowed stoatsbrother

personally I’d just leave it at 32A, and use normal 2.5 cable. 16A is about right for radial IIRC.

If you are putting in a radial feed on 2.5mm cable then that breaker shouldn’t exceed 20A as the cable limit as a radial is 26A I believe.

<Nob on the block>

Two RCDs …..

If you choose to rod it then ensure that the earth of the feed cable IS NOT CONNECTED to the earth bar in the garage consumer unit.

</Nob on the block>

Rich.

Holy smoke, a rare thing indeed! Thanks.

Continuing on the ‘everyday’ matra, so if the feed cable earth is fixed to the earth rod do you then run single earth cable between the rod and the earth bar in the CU? (I appreciate this maybe an obvious question)

The RCD tripping ‘all’ the circuits is why I always spec RCBOs rather than MCBs and RCDs.

Red to red
Black to black
and Blue to smithereens.. 😆

Continuing on the ‘everyday’ matra, so if the feed cable earth is fixed to the earth rod do you then run single earth cable between the rod and the earth bar in the CU?

Assuming the feed to the shed runs from the main consumer unit, the earth in this cable will be attached to the earth bar in the main consumer unit. This will then be protected by the house earth system (PME which utilises the power company’s neutral).

At the shed end you are having a different earthing system (TT – which uses a rod). All the sockets/lights need to use this earth, not the house earth so the feed cable’s earth in the shed must be kept separate. The rod will have an earth (known as the main earthing conductor) from it to the earth bar in the garage consumer unit. The feed earth can be insulated or cut off.

To summarize – the feed cable is earthed at the main consumer unit. The garage circuits are earthed to the rod. The feed earth should not have any connection to the rod earth.

With PME systems if the power company’s neutral breaks there is no earth apart from any earthing connections inside your house. If you feed the garage with 2.5 T+E and the only earthing is in the shed you could potentially carry the full fault current (1000 ohms ?) down a bit of 1.5mm copper. This will get very hot, very quickly and catch fire. Separating the earths prevents this. Alternatively a 10mm earth on the feed will be substantial enough to carry the fault current until the main fuse goes, preventing a fire.

(I appreciate this maybe an obvious question)

If you don’t know or not sure then it’s better to ask. People are going to work on their own electrical systems instead of using an electrician regardless of the Part P. regs. – I’m just as guilty when it comes to doing my own plumbing. I’d rather give advice so it can be done safely by an “non professional” than ignore it and have it botched.

Rich.

Having more than one RCD is nothing more than ‘overkill’ as in the event of a fault, which more likely than not will be several amps all the RCD’s will trip irrelevant of the rating, the only way to partailly discriminate is to use time delays which then contrevene the wiring regs.

Regardding the supply to the shed, common sense has to be pervail, if your shed is some distance away from your house – then yes use a TT system, if you dont live in a mansion you should be OK to use supply earth or CPC as it’s refered to, and bond the various metal work (if any) to the Earth block on the new consumer unit you install.
There are a couple of reasons why you’d use a TT to supply the shed:-

1. If there’s extranaeous metalwork – these would have to be bonded otherwise, however they would be the same potential as the earth
2. In the rear event of a large earth fault from another supply, this could be imposed on your supply – very unlikely.

I’d wire the consumer shed in 6mm swa(assuming it’s not a long run) if possible, change the 32A MCB to 16A a wire in a 2.5mm radial – unless you’re planning on using a welder and heater !

Fed from a 32A RCBO (combined RCD / MCB) from your main consumer unit.

As previously stated any external works should be carried out by a comptent pesron ie Part P approved and tested to BS7671.

As has bee

I’ve only ever had one issue with using 2 rcd’s. I was called out to a large waste depot that had tt earthing and a 3phase rcd main switch. A fault on a lighting circuit tripped the rcd but even after I fixed the fault the rcd wouldn’t reset.
Turned out that if I disconnected/removed a downstream rcbo on a separate circuit to the faulty lighting one the rcd would hold.
I then reconnected the rcbo after a couple of minutes and everything was fine
Electrical witchcraft!

Thanks for all the sensible replies chaps.

I am more than happy to wire this up, if it was a simple feed off a junction box I wouldn’t be asking.

The garage has it’s own rcd in the main house consumer unit, this was all done when we renovated the house six years ago… Wired by electricians before anyone asks.

The feed from garage to shed is no more than 2 metres.

So do I need this garage consumer box then?

When the same electricians wired an out building with similar layout to what I’m doing they did not use one.

From what you’re saying the garage is pretty much on the other side of the wall the main consumer unit is on. If this is the case, run the couple of metres to the garage in a bit of 6mm T+E from a 32A MCB. Put the garage CU on the wall. Wire LN to top of RCD and earth to earth bar.
2 MCBs in the garage CU – 16 or 20 amp for the sockets and 6 amp for the lights. Sockets in 2.5 FTE lights in 1 or 1.5mm FTE.
Ring or radial? Radial is almost certainly going to be fine. Wire it as a ring if you want but I don’t think it’s worth the extra copper. A ring can use a 32A MCB but use what you’ve got.

I think all us “experts” might have made it a more complex job than it actually is!

Rich.

Just been looking into this for my workshop. My final design is a 100ma Time delay RCD on the main switch board in the house with a 30mA RCD on the local distribution board in the workshop itself.

I found a very good guide to RCDs here: http://www.etci.ie/docs/ET214.pdf

which says, on the subject of cascading RCDs:

Connection of an RCD upstream of other RCDs is often referred to as Cascading. The normal purpose of cascading RCDs is to ensure that a residual current on a subcircuit causes only its RCD to trip and does not cause the upstream RCD to trip unless the fault is sustained beyond a certain time. This is referred to as Discrimination. General Type RCDs have maximum trip times of 300mS and 40mS for residual currents of I?N and 5 I?N respectively, but no minimum trip time is specified for such devices. Thus, if a 100mA RCD is installed upstream of a 30mA RCD, there will be no certainty as to which RCD will trip first in the event of residual currents above 100mA. Cascading of General Type RCDs is therefore not recommended. Discrimination can only be provided by ensuring that the upstream RCD has a trip time and trip level envelope which is completely outside that of the downstream RCD. This can only be assured by using an S Type RCD upstream and General types downstream.

On the subject of whether to use a local earth in an outbuilding, this all depends on the earth bonding scheme you have from your leccy supplier, see: http://www.diynot.com/wiki/Electrics%3Aearthing_supply_types_and_bonding%3Aearthing_arrangements

As far as I can work out you should just export the existing earth with the exception of TT systems where you can just a local earth spike in the out building. My house is TN-S, so I’ll just be exporting the main earth out of the workshop and using that.