Any electricians on here – advice needed

[nigel jones 5Participant @nigeljones5]

[nigel jones 5Participant @nigeljones5]

Hi. Im going to rewire the power in to my workshop. It is 30 feet from the house and I intend to do the spade work myself and get a qualified sparky to finish off and certify. My thoughts so far are to run 6mm armoured cable from house to garage. In the house I cant run the armoured cable straight to the consumer unit as it is plastic, so run it to a stand alone metal box with gland and then from this box to consumer unit with additional earth from cable sheathing/metal box. Have RCD in spare slot higher than that used in workshop so workshop trips first. Im thinking that as the whole lot will be earthed that I dont need to fit an rcd in the garage as the house rcd will cover the lot – is this correct?

[nigel jones 5Participant @nigeljones5]

Typed wrong – have MCB in spare slot in house !!

[EmgeeParticipant @emgee]

Hi Fizzy, best speak to the person who is going to certify the work for details of what is required at the point of supply and also SWA cable size and switchgear needed in the workshop. Much depends on the type of supply to your property and earthing arrangements.

Emgee

[Bob Brown 1Participant @bobbrown1]

I agree with Emgee, but failing that if you know what load you need in the workshop then that can be used as a guide, note guide, **LINK** I always go up one size rather than try for minimal. Have you thought 3 core armoured cable?

[MuzzerParticipant @muzzer]

You can terminate SWA into a plastic bulkhead (if it's physically strong enough). Something like this. You get a brass earth tag that you can connect to the main earth connection.

Lots of ex spurts on here it seems, so I'll whisper. I wouldn't count on connecting RCDs in series and the smaller one tripping out first. Partly due to existing leakage currents on the large circuit but also I don't think they work consistently enough, particularly if you get a large fault current. You shouldn't require a ground rod if you have an earth wire already but it would work too. My preference would be to have a separate consumer unit for the garage, running from a non-RCD MCB in the main box and incorporating its own local RCD or MCBOs.

One hazard in a workshop with heavy equipment is that the lighting may vanish if it shares the same single RCD and it trips out. So clearly a modern dual circuit consumer unit would be very sensible. They don't cost a lot. An alternative (simpler?) solution is battery backed emergency lighting.

Murray

[Steve WithnellParticipant @stevewithnell34426]

Whilst here are a few electrically minded folks watching – minor thread hijack. Just had my kitchen re-fitted and the electrician has fitted the power socket for the integrated dishwasher directly behind it, meaning you have to strip the appliance out of the cabinet in order to isolate the power. I've told the electrician that does not comply with the 17th edition… he says it does. Surely he cannot be right?

Apologies for the hijack…

Steve

[Neil WyattModerator @neilwyatt]

Posted by Muzzer on 10/11/2016 07:16:55:

One hazard in a workshop with heavy equipment is that the lighting may vanish if it shares the same single RCD and it trips out. So clearly a modern dual circuit consumer unit would be very sensible. They don't cost a lot. An alternative (simpler?) solution is battery backed emergency lighting.

Murray

One of my best ever buys was a little LED light with motion sensor. Comes on when I enter the workshop, goes off when I leave or if the lights go out even if its the main board that trips (or a power cut – we had one of those a few weeks go, just like the 70s!)

I have a nicad backup florescent fitting that I must get around to wiring up sometime, its old and doesn't quite deliver the full 3 hours but even three minutes would be enough.

[Andy HoldawayParticipant @andyholdaway]

Steve, your electrician is correct in that the 17th edition Regs don't state that isolation has to be provided above the worktop, only that isolation is provided that is accessible. You could argue that yours is not accessible as it is behind the appliance.

Unfortunately it is a bit of a grey area as it falls under Building Regs Part 'P', which reference back to the 17th edition. My experience is with industrial installations, so I don't get too involved with domestic work, but common sense dictates that isolation for maintenance and safety should be readily accessible.

Andy

[Bob Brown 1Participant @bobbrown1]

The normal practice is to fit a fused isolation switch that is easily accessible, not behind a washing machine, tumble dryer etc.

From on site guide 17th edition

 

1 KITCHEN – .

Appliances built into kitchen furniture (integrated appliances) should be connected to a socket-outlet

or switch fused connection unit that is accessible when the appliance is in place and in normal use.

Alternatively, where an appliance is supplied from a socket-outlet or a connection unit, these should

be controlled by an accessible double-pole switch or switched fused connection unit.

 

 

Edited By Bob Brown 1 on 10/11/2016 08:59:37

[EmgeeParticipant @emgee]

Steve, whether it complies or not it is certainly not "good practice" to position a means of isolation in such an inaccessable position.

Emgee

typo corrected

Edited By Emgee on 10/11/2016 09:09:21

[Andy HoldawayParticipant @andyholdaway]

Also remember that the On-site guide is just that,- a guide. If it doesn't refer to a particular regulation it is a recommendation only.

[its-smeeParticipant @its-smee]

Steve. … I too have had my kitchen rewired recently and the electrician also fitted the socket for the washer under the worktop. saves having to drill holes for the plug lead. but he also fitted a 20A+neon switch above the worktop for isolation. so your electrician is incorrect and needs to return and correct his work.

fizzy. you need to calculate the volt drop in the cable to the workshop based on max current & distance from the source.

http://www.calculator.net/voltage-drop-calculator.html

[AjohnwParticipant @ajohnw51620]

I may have that problem Steve and from what I can gather it does comply but probably shouldn't. Regs have to be practical which is why it would be allowed. I'm trying to figure a way around the problem.

I wired up our garage for work shop use long before doing it became a problem. Not sure it is now actually but that is off topic. What I did is added an armoured cable spur of an unused cooker connection point. That also gave me an isolator in the house. I then fitted a small consumer unit into the garage and run spurs off that for lighting and power points. That gave me separate fuses for each spur also more than enough current rating for the gear that I run.

As catenary cable kits are still available it may still be possible to run a suitable wire type along one of these in order to get power into a garage etc. In the past that could just be ordinary twin and earth.

Personally if fitted I would want an rcd at the point where the cable is connected in the house however loss of lighting might be a bit of a problem at some point. Those can also be obtained that will trip on over current. I'd hope that the rcd trip levels are sorted out by now. They are mainly aimed at preventing fires. In the early days very low trip levels caused all sorts of problems with a variety of equipment.

I think I saw earth spikes mentioned. I was talking to an electrician about these fairly recently due to the problem of getting 6mm bonding to gas pipes at the meters. Seems that the wisdom of using them is being questioned so the option may go at some point. That temps me to get one fitted soon.

John

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Edited By Ajohnw on 10/11/2016 09:42:21

[Nigel McBurney 1Participant @nigelmcburney1]

.Divide the wiring in the house,have the main consumer unit,plus a smaller unit ,the shed supply is then completely isolated from the house system. do not be mean and go for the minimum cable size is does not cost much to install a heavier cable,in future you may need more power and it takes a lot of hassle to update plus the necessary electrical inspection,I personally prefer a 3 core sheathed cable rather than rely on the the wires in the armour to do the earth. during an insurance inspection the inspector said it was a good idea to be able to cut off the power from a switch in the house as it prevents thieves using the lights and using any mains power tools to cut through security cables or locked cabinets inside the workshop ,though it would be no good if a mains alarm was fitted. for safety I use a Screwfix cheap emergency light if the power trips, it can be very dark out in the sticks.

[Rik ShawParticipant @rikshaw]

Fizzy – I'm no electrician either but my workshop was lektrifyde by a proper bloke and he used 15mm armoured cable from the house to the workshop. The work included fitting an all weather socket to the outside of the building to provide power for my arc welder.

Good luck with your install.

Rik

[Martin KyteParticipant @martinkyte99762]

Well this is what I did.

10mm SWA underground to the workshop (6mmwill be fine I always go for overkill)

Feed taken from Consumer unit in the house after the Main Breaker but before any RCD's (Split box). 10mm is current protected by MCB at this end.

Earth is exported from the house to the workshop down the earth conductor of the SWA. Armored sheath is earthed at both ends.

Trench dug 3 feet deep. Go out and buy a proper trenching shovel they are cheap and will avoid having to remove more spoil than you need to. Something like this.

https://www.machinemart.co.uk/p/trench-shovel/?da=1&TC=GS-040211875&gclid=CJnxp430ndACFcO4GwodT1IMKg

Bed of sand in bottom of trench cable on top more sand to cover. This keeps the cable away from flints and sharp stones and provides visual marker for any future digging. Back fill about 8 inches and lay in Electric Cable Warning Tape.( Plastic Yellow and Black stripey stuff) Fully back fill and returf etc.

Consumer unit fitted in workshop. RCCB feed to the lights before the RCB. That way the ring mains can trip all they like and the light won't go out. Totally overboard on the power wiring. All the machines are on 4mm twin and earth and I have 2 ring mains with metal clad double sockets giving me 16 double outlets. They are never all in use but it's more about having a socket just where you want it than anything else.

This arrangement means that the house can never trip the workshop. The workshop power can never turn the lights off. It's simple to add extra wiring if I ever need to and I can isolate the workshop from the house by turning the RCB off.

Works for me.

regards Martin

[David lawrence 3Participant @davidlawrence3]

In my last house I fitted a high up, 12 foot, cantry wire to the workshop, 6mm armoured which worked fine. the consumer unit was plastic but with the right brass fitting and earth tag all worked well, screwfix sell all this gear, I had a new kitchen a few months ago and all the dishwasher, washing machine etc were fed via fused outlets fitted under the wooden sink unit carcas, easy to find and switch off and above the floor level. as for 2 x RCD in series, one on the consumer unit one in the shed, I had that and it never worked, I always had to go down the path and reset the house rcd, the shed rcd never blow, not a good system, best of luck.

[AjohnwParticipant @ajohnw51620]

Leaves me wondering why one ever did blow David ? Simple really because they shouldn't.

There is some from memory sane info on rcd trip currents and other factors here

http://electrical.theiet.org/wiring-matters/50/rcd/

 

 

John

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Edited By Ajohnw on 10/11/2016 13:41:38

[EmgeeParticipant @emgee]

Posted by Martin Kyte on 10/11/2016 12:16:20:

Well this is what I did.

10mm SWA underground to the workshop (6mmwill be fine I always go for overkill)

Feed taken from Consumer unit in the house after the Main Breaker but before any RCD's (Split box). 10mm is current protected by MCB at this end.

..Martin, what type of device is the Main Breaker referred to above ?

Emgee

[Martin KyteParticipant @martinkyte99762]

**LINK**

It's just the Mains Isolator as above(Big switch on the input of the consumer unit). It feeds the bus bar(s) within to unit to which all the additional switch-gear is attached. The MCB's are miniture cct breakers which are essentially just re-settable fuses. All the residual current cct breaker stuff is then done at the workshop end. I did all the wiring myself and just had a local chap in to test everything and give me a certificate. I did the house too. I do suggest you talk to your local electrician prior to your work just to make sure he is happy to come and test everything when you are ready. Most blokes are perfectly happy to do this and will tell you anything you need to take particular care over. After all if he's not happy with it he aint going to pass it so it's him you really need to satisfy not the wiring regs. As far as you are concerned he is the wiring regs.

PS (RCCB feed to the lights) is a typo and should read RCBO which is a combined residual current and overload device like this

**LINK**

regards Martin

[ZebethyalParticipant @zebethyal]

This is what I did:

RCBO at the house consumer unit, 4mm Twin & earth inside the house, 4mm 3 core SWA outside.

Third core and armour both used as earth, armour connected to earth via banjos at each end of the SWA in junction box and in garage consumer unit.

SWA is further protected outside by being run inside 41mm Unistrut secured to the concrete fence posts using rawl bolts.

Inside garage, RCD protected consumer unit with one circuit for lights and one for sockets, I may look into an RCCB for the lighting circuit at some point.

Sockets are on a 4mm radial circuit using individual cables run plastic conduit and dado trunking so I can have as many sockets as I need.

Lighting is cabled using individual 1.5mm individual cables in plastic conduit, 1mm would have been good enough, but I didn't have any at the time.

Some may argue issues with SWA in Unistrut above ground attached to a fence, but the garage is prefab and therefore can be argued to be temporary, fences are also viewed as temporary structures so the associated wiring is also temporary and would be removed with the garage.

Nothing in the regulations that states you can't do this and much safer and less likely to be damaged than running on a caternary wire at 12 feet above ground and I didn't feel like digging a 3 foot deep trench through tree roots.

House can't trip the garage, but isolator in house consumer unit will cut power to garage, house is on a split load consumer unit with dual RCDs, garage can also be isolated by switching off the RCBO.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Ajohnw on 10/11/2016 09:31:38:

…

I think I saw earth spikes mentioned. I was talking to an electrician about these fairly recently due to the problem of getting 6mm bonding to gas pipes at the meters. Seems that the wisdom of using them is being questioned so the option may go at some point. That temps me to get one fitted soon.

John

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Edited By Ajohnw on 10/11/2016 09:42:21

Earth spikes have been dubious for as long as I can remember. They are all but useless as an RF Ground or lightning protection and may be inadequate in an AC power system. (I have a disused earth spike outside my garage: it's resistance to ground is appalling – about 300Ω. )

There's more to a good earth than banging spikes into the ground or clipping wires to any old pipework that happens to be handy.

I expect an electrician will put me right if I've got this wrong, but I think the big problem is what happens to an installation with two or more different earths when there's a fault.

As it's unlikely that each earth spike will have the same resistance to ground, a fault will create a potential difference between appliances that should be equally grounded. That's a shock and fire hazard especially if the earth resistance isn't low enough to blow the fuse. The modern way seems to be to bond everything together and run all the earth wires in an installation back to a common earth.

What I don't know is what comprises an "installation". I see sense of wiring everything in a house back to a common earth, but that might not apply to a separate workshop at the end of the garden. Possibly a remote building should have it's own earth? I suppose this is why electricians have qualifications!

Dave

Edited By SillyOldDuffer on 10/11/2016 15:04:40

[TrevorhParticipant @trevorh]

An Installation comprises of 1 or more items and need to be bonded together and have individual earths then all earths are taken to a common point

The size of the earth wire is also as important as the Mains and shouldn't really be less than 6mm

The spikes should be driven down until you get a good reading of less than 1 ohm, if thats not possible then you start adding spikes moving away from the building usually at 5 mtr intervals until you do get the correct reading

Usually the deeper you go the better because you are more than likely to hit wet ground or the water table

I had an electrician years ago actually say to me that if you don't get a good reading just P**s on it to drag the reading down, would have served him right if he had gotten a belt from it

[SillyOldDufferModerator @sillyoldduffer]

Posted by Trevorh on 10/11/2016 15:13:57:

…

I had an electrician years ago actually say to me that if you don't get a good reading just P**s on it to drag the reading down, would have served him right if he had gotten a belt from it

There's no way I'm going to pee on my earth spike. It's in full view of the neighbours and they already think I'm weird!

Dave

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