# Workshop electrics. What do I need?



## garywayne (6 Jan 2010)

Hi folks, I hope you all had a good christmass and new year. 

I am in the prosess of draught proofing under my stairs, but before I can finnish off I need to run cable from my consumer unit and under the floor. 

When it comes to electrics I believe that I am capable to do the job. What I don't know is, what is needed, or what ratings. 

In the shed I will have:- 
1 x Lighting circuit. ( 6 double florescent lights). 
1 or 2 x ring mains. ( With lots of sockets). 
1 x Table saw, (I believe running from a 16A MCB). 
1 x Bandsaw, ( depending on which one, pos running from a 16A MCB). 
1 x Planner\Thicknesser. 
1 x Extractor. Don't know what one. 
Power tools running from ring main. 

Sorry if I am dragging on a bit. 
What I need to know is what size MCB will I need in the consumer unit, house side, and should it be RCD protected? What size T&E cable will I need to go from the consumer unit to the Armour cable, (What size Armour cable)? I take it I will need the same T&E from the Amour cable to the shed CU? 

I think the rest is pretty straight forward. 
I will be getting a part P electrician to test and I hope pass all of the electrics once I have finished.


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## Dibs-h (6 Jan 2010)

I was under the impression that the armoured cable terminates directly in the CU - but that could be a combination of intellectual intermissions and\or not paying attention.

I'm sure some knowledgeable person will be along shortly.


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## OLD (6 Jan 2010)

In the shed I will have:- 
1 x Lighting circuit. ( 6 double florescent lights). 
1 or 2 x ring mains. ( With lots of sockets). 
1 x Table saw, (I believe running from a 16A MCB). 
1 x Bandsaw, ( depending on which one, pos running from a 16A MCB). 
1 x Planner\Thicknesser. 
1 x Extractor. Don't know what one. 



Consumer unit mcb's:- 6a lights. 1xring 32a. 2x16a dedicated 
p/t, extractor unless very powerful and all other power tools use ring main,rcd main switch required.


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## garywayne (6 Jan 2010)

Thanks for replies. 

Old. 
Thanks for your listing. Do you know what size MCB I need in the house consumer unit that supplies the shed power, and should it be RCD protected 

Dibs-h. 
If I am unable to get a bit of armour cable short enough, perhaps it will be easyer to go armour all the way.


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## Dibs-h (6 Jan 2010)

garywayne":12ca2y29 said:


> Thanks for replies.
> If I am unable to get a bit of armour cable short enough, perhaps it will be easyer to go armour all the way.



For some reason, I'm under the impression it would need to be armoured cable all the way, i.e. House CU to Outbuilding CU.


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## garywayne (6 Jan 2010)

I am going by what I have read.

"Armoured cable is expensive and has to be terminated at a special junction box at each end of its run, where it can be joined to ordinary PVC-insulated cable".


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## Dibs-h (6 Jan 2010)

garywayne":2s74idfb said:


> I am going by what I have read.
> 
> "Armoured cable is expensive and has to be terminated at a special junction box at each end of its run, where it can be joined to ordinary PVC-insulated cable".



Cool - put it down to intellectual intermission\not paying attention. Good to know. Thanks.


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## garywayne (6 Jan 2010)

Your welcome Dibs.
It's nice for me to be able to help someone for a change. :wink:


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## jlawrence (6 Jan 2010)

SWA can be terminated directly in the CU - that's what the sparky did in my old house.
I'll be renewing the powerfeed to my workshop when the weather warms up. I'll be taking T&E to a junction box then SWA from the junction box, around the garden, and finally to the CU in the workshop.


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## liam8223 (6 Jan 2010)

You must use armour cable if you are putting underground.
Twin and earth is not suitabe for just burying, and for the difference in cost to the difference in safety, armour cable should be used in all circumstances even if you are laying trunking in which to house the cables.

Metal consumer units ('distribution boards' when metal) can accept armour cable, with a suitable armour gland and earth banjo.

Plastic boxes however require a cheap and simple metal adaptable box in which to terminate the armour, then use meter tails or similar into the rcd.

In all of my buildings we use a 63A RCD main switch (3 phase).

The armour cable is not that expensive although if you have only ever bought T+E, maybe it will seem a little pricey.

HTH

Liam.


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## flying haggis (6 Jan 2010)

garywayne":1d35w89s said:


> I am going by what I have read.
> 
> "Armoured cable is expensive and has to be terminated at a special junction box at each end of its run, where it can be joined to ordinary PVC-insulated cable".



not true and I hope you realise that all of this is notifiable under part P regs


another way of supplying the shed is to split the meter tails with a henley block then via a 100A switch to a CU in the shed but the sparky you employ (so you get the certificates or you need to get the building control officer at the council to sign it off)) will tell you all the options


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## Jake (6 Jan 2010)

flying haggis":239exgrw said:


> garywayne":239exgrw said:
> 
> 
> > I am going by what I have read.
> ...



What are you saying is not true?


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## SemiSkilled (6 Jan 2010)

why don't you get some advice from the spark who will test the job?

As its to an out building the first thing to look at is the earthing arrangement some elec suplliers don't let you "export the earth"

the cable required depends on

Maximum demand

The length of the run out to the shed 

The method of installation O/H , U/G or in conduit ( there are
more!)

Try this link, get a coffee / tea .

http://wiki.diyfaq.org.uk/index.php?tit ... ty_outside

Lee


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## garywayne (7 Jan 2010)

Since my motorcycle accident 8 1/2 years ago, I seem to have quite a lot of spare time on my hands, (as no one seems to want to employ me), if the wife leaves me alone, (love her lots). 
So I like doing things myself, you know, for something to do. I have been doing my own electrics for some years. Not by guessing, but by finding out how it's done. I did forget to mention that the armour cable will be at least 500mm (18in) under ground between the house and the shed. The junction boxes at either end will be internal and above the DPC. My house earth is the most common, TN-S. The cable distance is: 
T&E 14M; SWA 8.5M; TOT = 23M max. My cabling is single phase. 
As mentioned before, once I have completed the supply to the shed, and the wiring within the shed, I will then attempt to find the appropriate relyable sparks to test and hopefully pass the completed work. 
All I need to know is: 
1. Should the MCB for the shed supply be on the RCD side of the house CU or not? (My house CU is split). 
2. What size MCB should supply the shed? Is 32Amp appropriate? 
3. What gauge T&E should I use? Is 4mm sq heavy enough? 
4. What gauge SWA?

In the shed I will have:-
1 x Lighting circuit. ( 6 double florescent lights).
1 x ring mains. ( With lots of sockets).
1 x Table saw, (I believe running from a 16A MCB).
1 x Bandsaw, ( depending on which one, pos running from a 16A MCB).
1 x Planner\Thicknesser.
1 x Extractor. Don't know what one.
Power tools running from ring main.

Old has given me the MCB sizes for the shed CU. So, I think that is all I need to know. For now anyway.

Um, just read through. If I sound a bit abrupt, I appologise. Not intended.


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## OLD (7 Jan 2010)

1. Should the MCB for the shed supply be on the RCD side of the house CU or not? (My house CU is split). 
2. What size MCB should supply the shed? Is 32Amp appropriate? 
3. What gauge T&E should I use? Is 4mm sq heavy enough? 
4. What gauge SWA? 


1. RCD side
2. 50a
3. 6sq mm
4. what comes with the 2 core cable.

The shed CU can be capable of taking the swa gland which saves a job.
Talk to the sparks about the design and termination arrange to run all wires and fix components then get him to terminate what you have agreed and sign off.


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## garywayne (7 Jan 2010)

Thanks Old. 
You have been most helpfull. Just one thing though. I am in the process of reading the link Lee suggested and it states, If I have read it correctly, that the submain should be on the RCD unprotected side of the house CU.


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## matt (7 Jan 2010)

OK, here's my setup that's been tested by my sparky mate:

Garage approx 10m run of 6mm SWA.
Terminates in adaptable metal box at the house side cos the CU's is plastic and the SWA can stress the plastic if connected directly. 6mm T&E from the adaptable box to the CU.
CU at the garage end is metal so SWA connected directly.
The CB at the house end is: 40amp and on the RCD side.
Garage circuits are 6amp and 32 amp. I also have a 16amp in there for dedicated supply for the table saw if I ever decide to connect it up. This is a bit naughty because the total exceed the CB in the house...

Think that's it...


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## garywayne (7 Jan 2010)

Thanks Matt.

I think the reason for having the shed supply on the RCD unprotected side is so that if the house RCD trips while you are oporating you saw or what ever you still have power and lighting. If you have the shed supply on the RCD side and it trips you are in the dark and posibly in your saw.


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## matt (7 Jan 2010)

Mine is on the RCD side because it protects will cut power to the SWA in the event of an accident. If my lights go off then everything will go off too. I stick with RCD protected from the house consumer unit and install some emergency lighting if necessary. One thing NOT to do is use RCD at both ends - one can interfere with the other.


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## garywayne (7 Jan 2010)

If your power to the shed goes, ie. At night, lights go out while you are opperating machinery it is possible to slip into said machinery if the house RCD is tripped. But if the shed supply is on the RCD unprotected side and the house RCD trips you will not be effected.

I haven't finnished reading the link yet, but I am under the impresion that the supply comes off a MCB which will protect the shed supply 
:? I think, then you have a RCD in the shed CU.


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## OLD (7 Jan 2010)

My suggestion protects the swa cable yours keeps lights etc on when house rcd trips .Note shed rcd trips at lower current than house so no interaction.Above is covered by discuss with sparks or is this a diy.


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## garywayne (7 Jan 2010)

Thanks Old.
This is a DIY job, but I am going to get it checked by a Part P sparks.
I am having trouble finding out how to calculate what size MCB to use in the house CU, what size T&E cable, and SWA, and what size RCD in the shed CU.
In the previous link that I mentioned before, the bloke suggests using waterproof junction boxes on the outside wall to connect the T&E to the SWA.


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## jlawrence (7 Jan 2010)

To find out what size cable you need use this calculator
Likely though you'll be fine with 6mm.


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## flying haggis (7 Jan 2010)

Jake":2bkrxi36 said:


> flying haggis":2bkrxi36 said:
> 
> 
> > garywayne":2bkrxi36 said:
> ...



armoured cable does not have to be terminated at a special junc box at each end, it can be terminated into the CU, and it is not that expensive per metre although it is more expensive than T+E.

As an aside if this cable is going under ground consider adding a conduit in the trench about 3 to 4 inches away from the SWA for cat5/6 cable for computer use


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## SemiSkilled (7 Jan 2010)

> waterproof junction boxes on the outside wall to connect the T&E to the SWA.




Why d'you want to connect t&e to the swa?

I use metal adaptable boxes, fix the gland to the box and leave the cable long enough to go through the box and connect to your consumer unit.

I'd prefer to use a henly block, into a switch fuse, SWA out to consumer unit in the garage and use individual RCBO's in the CU.

leaves the house on the original set up and if owt trips you don't take out circuits that don't have faults, ie if a dodgy drill trips the sockets you'll still have lights

You need to work out your maximum demand in the shed to size the mcb in the house, 

Talk to the spark, and its a good idea to get him to terminate the swa

Off the top of my head using a biggish saw 16A, a Dust collector 16A, some strip lights and a bit in reserve you'd need a 45 A supply
( The motors don't take a lot when they run its the starting up, oh and when you calculate power requirements for discharge lighting ie strips, you use a multiplier of 1.8
Talk to the spark as you _might _not have a big enough incoming supply 

If that 45 A sounds a lot, I had a 16A to my garage, fine, then I bought some 3 phase gear the converter needs a 32A supply :shock: 

If you buy a bigger saw or PT better to have it and not need it than to nee...........................

Lee


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## WoodnDesign (7 Jan 2010)

Hi,

I've to get my workshop wired later in the year, I'd had a price for a cable runout, in the trench I'm to dig.. CU, 2 double sockets, double 6' light and fuse..
As a turner, I could or will need those sockets in full use.
I contacted the sparks with a list of all my equipment an there ratings, and that a lathe, vac, worklamp and a powertool would be used all at once, lights and amb. filter, if not something else.. He has now gone to 10mil cable.. no idea of how many extra sockets/lights... :!: .... and about twice the first price... :shock: ....

Thanks to you all and the links, I'll have a better idea as to what will be needed and what he maybe doing or not, when you have to rely on someone to do the job due to the new P regs.. I have in the past worked and done some electrics, but for this I want to be safe...

Regards. David.


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## Jake (7 Jan 2010)

SemiSkilled":3ikxfjfa said:


> > waterproof junction boxes on the outside wall to connect the T&E to the SWA.
> 
> 
> 
> ...



Because it is (a) cheaper and (b) much more pliable for internal runs.

Edit: just checked I am wrong on (a) - at 6 and 10mm SWA is cheaper or than T&E at TLC! Even 10mm2 three core (to do a belt and braces job if exporting the earth is viable) is only 25p/m more per metre.

(b) still stands, depending on where the cable is running (though it might be irrelevant if it is a straight surface mounted run).


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## Jake (7 Jan 2010)

10mm sounds sensible to me, but if DIYing you need to start with a sensible assessment of the max current you are going to want to draw (in winter, all lights blazing, any electric heating on and your biggest machine plus extractor plus anything else that you might have on at the same time) and the actual distance the cable will run and do the voltage drop calcs properly. You also need to work out the earth loop impedance calcs to work out your earthing arrangements. 

This is not simple and you'll need to do some proper research and thinking - please do not go with a 50A breaker on 6mm cable for starters.


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## Hobbyshop (7 Jan 2010)

I am also planning a workshop build for this year and I have been researching the electrical requirements quite extensively. I have written out my conclusions which I will document here for comment. I am afraid it will be quite a long post.

BUT PLEASE NOTE THIS DISCLAIMER: I AM NOT A QUALIFIED ELECTRICIAN AND WHAT I DOCUMENT HERE IS MY INTERPRETATION OF WHAT I HAVE READ. I WILL BE SEEKING PROFESSIONAL ADVICE AS WELL BEFORE I PROCEED AND WOULD RECOMMEND THE SAME TO ANYONE ELSE.

I POST THIS SO THAT PEOPLE MAY ADD TO IT OR CORRECT IT FOR MY BENEFIT AND THE BENEFIT OF OTHERS PLANNING THIS TYPE OF WORK.

*Running new Sub-Main Cable.*
Wiring regulations were changed in 2008 and now any cable that is not suitably protected against mechanical damage must be protected by a Residual Current Device not exceeding 30mA.
Suitable protection may be provided by *earthed* metal sheathing (SWA, metal conduit or metal trunking) or by burying in a wall at a depth greater than 50mm.

So if you run your sub-main cable in SWA all the way from the existing domestic supply to a new CU in the outbuilding then the cable does not need to be RCD protected. Note that the armour must be earthed so the cable will need to be properly jointed with the appropriate glands.
If part of your sub-main is made up of T&E and this section is not protected with earthed metal conduit or trunking or buried to >50mm in a wall then the supply will need to be taken from a RCD protected side of the domestic CU with RCD protection not exceeding 30mA.

This seems to answer the question as to whether supply should be taken from a RCD protected way or from a non-protected way.

The PDF guide from here proved useful:
http://www.hager.co.uk/service/downloads/guides/17th-edition-consumer-unit-guide/5632.htm

*Size of Cable and size of Circuit Breakers.*

First it seems to be necessary to estimate the maximum power requirement. As an example in my case I am looking at a single user workshop so I assumed that only one tool would be in use at any one time but other ancillary devices would also be in use. I estimated the highest power consuming tool was likely to be a table saw and using the SIP 01332 as an example I took the power requirement for the saw to be 2.2 KW.
I estimated the total power requirement as follows:
Table Saw 2.2KW
Extraction 2.0 KW
Heating 1.0 KW
Lighting 0.5 KW
Total 5.7 KW which I rounded up to 6 KW as my estimate

Together with a known cable length, I plugged this 6 KW requirement into the calculator shown in jlawrence’s link above and got the following result:
Required Cable Size	4 mm
Voltage Drop	7.83 Volts.
Percentage Drop	3.4%
Current Load	26.0 Amps
Max Cable Load*	36.0 Amps

On this basis it seems I would be safe to install 4mm cable protected by a 32 amp MCB

However, to allow for any future unforeseen power demands I have decided to install 6mm cable.
I increased the power required incrementally in the Voltage Drop calculator until it showed me a requirement for 6mm cable, and I was then able to identify the max. allowable cable load for the 6 mm cable in my case of 44 amps.

From this I decided I would be safe to install 6 mm cable protected by a 40 amp MCB

*Workshop Circuits*
I decided to install a 32 amp ring main, a 6 amp lighting circuit and a 16amp radial circuit for the saw.
Prior to the changes in 2008 the lighting circuit would not have required RCD protection but since I intend to surface mount all cables and fittings then all the circuits will need RCD protection as they will not be protected against mechanical damage.
The PDF guide I provided a link to earlier indicates that protecting all the circuits from a single RCD would not comply with the current regulations so it seems I will need to provide split RCD protection. In my case I will probably opt for a consumer unit in the workshop with RCBOs on each circuit.

*Termination of SWA Cable*
The Steel armour has to be earthed to comply with the requirements and I found some useful information by Googling for "Terminating SWA Cable".

*Is it okay to have RCD protection at both ends of the sub-main?*
I have seen this discussed in a number of forums and from my research I have come to this conclusion:
The only concern over having a RCD at both ends of the system is how you determine which device will trip first. For example a fault on the 16 amp circuit could possibly trip the main consumer unit RCD rather than just tripping the 16amp RCBO and this would mean losing lighting as well as power, creating a potential hazard, and some inconvenience.
The regulations are written to cover much larger installations and this issue becomes a serious problem in certain circumstances. In a hospital for example you would not want the operating theatres to lose power through a trip caused by someone cutting the lawns. In a single use workshop it is a lower priority and safe protection of the sub-main cable takes priority over the inconvenience of total power loss.
Of course if your sub-main cable is properly protected against mechanical damage over it's full length then you can leave out the RCD at the supply end and eliminate the inconvenience.

Hopefully others will be able to confirm or correct my conclusions (if anyone has the patience to read it all  )


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## SemiSkilled (7 Jan 2010)

Might just be me but I prefer SWA in workshop environments as it is tough enough to withstand knocks etc, T&E is a bit fragile 

The other thing about SWA is it can carry a bit more and if you use the wire armour as the earth you get a really big cross sectional area and you can get the Zs right down and meet the specs for your breakers.

I 'spose I over spec jobs as I don't pay for the stuff :lol: 

Just today at work someone decided to swap our compressor for one twice the size, now needs a bigger supply, £230 in bits and 3/4 of a day

Lee


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## jlawrence (7 Jan 2010)

I've read that bit about less than 50mm depth needing RCD protection.
My sparky said that they almost never put lighting circuits on the RCD side.
If the 50mm depth is completely correct (I'm not saying it isn't), then every circuit in a dwelling would need RCD protection. EVERY single circuit in a house is at somepoint not buried 50mm deep - take the point at which it connects to a socket or lighting point for example.

When I replace my connection to the workshop I won't be taking it from the RCD side. Like others I don't want the lights going out if (when) I trip something in the workshop - either that or I'm going to need to look at putting an emergency light in (which may not be a bad idea really).


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## Hobbyshop (7 Jan 2010)

jlawrence":tenv0uix said:


> I've read that bit about less than 50mm depth needing RCD protection.
> My sparky said that they almost never put lighting circuits on the RCD side.
> If the 50mm depth is completely correct (I'm not saying it isn't), then every circuit in a dwelling would need RCD protection. EVERY single circuit in a house is at somepoint not buried 50mm deep - take the point at which it connects to a socket or lighting point for example.
> 
> When I replace my connection to the workshop I won't be taking it from the RCD side. Like others I don't want the lights going out if (when) I trip something in the workshop - either that or I'm going to need to look at putting an emergency light in (which may not be a bad idea really).



Yes the document in the link I gave suggests that following the 2008 changes it is likely that all domestic lighting circuits will now need RCD protection, which was not the case previously.
In my case I will have to take supply from an RCD protected way on my consumer unit anyway, so I will probably add a couple of emergency light fittings too.


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## DavidE (7 Jan 2010)

There are probably a few points that could be picked up in this thread - if you are unsure it's best getting an electrician involved. That said...

When doing load calcs you need to consider voltage drop at startup not just the continuous demand.

If steel wire armoured cable is terminated into a junction box the sheath can be stripped back as others have said and the inner cable run to wherever.

If you get a steel wire armoured cable and connect a copper core to earth you must test the continuity of the armoured sheath to earth - otherwise you have a potentially dangerous installation. As SemiSkilled said you get an equivalent earth (and better depending on the cable size) in the steel wire armour providing it is properly terminated.



jlawrence":2ijvd99h said:


> I've read that bit about less than 50mm depth needing RCD protection.
> 
> If the 50mm depth is completely correct (I'm not saying it isn't), then every circuit in a dwelling would need RCD protection. EVERY single circuit in a house is at somepoint not buried 50mm deep - take the point at which it connects to a socket or lighting point for example.



With the introduction of the 17th Edition regs (nothing to do with Part P) RCDs feature a lot so it is fair to say most circuits will require RCD protection. As an earlier poster said you in some cases you can mitigate it with other factors. However, there are other reasons they are required (not just mechanical protection). I've not got my copy of the regs with me so I'm not going to try to quote it (and it's best to get some professional help with your specific installation).

When designing circuuits with RCDs if you have two of the same trip current/time they will go together when there is a fault. You can get RCDs with higher trip currents/trip times to get proper discrimination. Of course the regs need to be checked to make sure you're doing it correctly.

As another thought to the RCD problem - if you want to keep it simple with an RCD and the lights are on it - stick an emergency light in the workshop (battery backup if the power goes off) they are quite cheap and will give you enough light to find your way out/get things back going. They'd also be good if you are in an area prone to power cuts!

Edit - Kevin you typed that at the same time as me!  

I hope this helps
David


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## matt (7 Jan 2010)

I don't get why you'd NOT want to use RCD protection for a cable carrying a high current on a high AMP fuse in a potentially vulnerable route.

I get the thing about the lights going out, but then so would everything else in the workshop so even a turning blade on a table saw, whilst still having some inertia, is no longer powered. But, on the other hand, damage to the cable or more likely a joint, or perhaps just a simple fault somewhere along the line, and you're gonna take quite a shock. 

If light really is an issue then I'd go for emergency lighting every time.

FWIW - I have had RCD's at both ends of a circuit before and one RCD tripped the other (i.e. there was no fault - it was simply the presence of the RCD).


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## DavidE (7 Jan 2010)

matt":3lzy2eei said:


> I don't get why you'd NOT want to use RCD protection for a cable carrying a high current on a high AMP fuse in a potentially vulnerable route.



Just for background infomation on what RCDs are used for...

RCDs primarily provide shock protection for humans/livestock who come into contact with the live whilst earthed. There are also used to provide fault protection should an earth fault occur on a circuit where the fuse would not blow within the stated disconnection time. This is mainly for the sake of shock from the raised voltage on the earth of the circuit and the potential fire risk.

Therefore, the size of cable and current don't really come into it. If you touch a live wire whilst earthed no fuse is going to help you. The RCDs on sockets typically trip at 30mA very quickly. A fuse won't have even blinked with that current going through you - hence why the cable/fuse size doesn't come into it.

I hope this is useful - you can get breakers called RCBOs which incorporate overload protetcion too which leads to the confusion about the purpose of an RCD.
David


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## matt (7 Jan 2010)

DavidE":3d719i35 said:


> matt":3d719i35 said:
> 
> 
> > I don't get why you'd NOT want to use RCD protection for a cable carrying a high current on a high AMP fuse in a potentially vulnerable route.
> ...



I'm not really sure I understand what you just said but if I had said:


> I don't get why you'd NOT want to use RCD protection for a cable in a potentially vulnerable route.


 Would that be a reasonable interpretation?


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## SemiSkilled (7 Jan 2010)

I used to tell apprentices ~

a fuse stops fires ~usually

an rcd stops it killing you ~ hopefully

The "Earth" makes the fuse work 

After that I'd say, " look in the On Site Guide"


Lee.


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## DavidE (7 Jan 2010)

> I'm not really sure I understand what you just said but if I had said:
> I don't get why you'd NOT want to use RCD protection for a cable in a potentially vulnerable route.Would that be a reasonable interpretation?



Sorry I was't trying to cause confusion or anything else. My main point was the amount of current a cable is carrying or it's size has nothing to do with the provision of an RCD. What Lee has just posted I guess says it more clearly.

Going back to your quote above - yes that makes sense. Although... if it is buried with warning tape or tiles and care is taken where it goes in and out of the buildings to take a good route/add ducting or otherwise that will be the primary protection. With all that it is hopefully unlikely to get damaged and if someone does get it with a spade or otherwise the fuse would protect them as the sheath would earth whatever implement they were using and then the fuse would pop on contact with a live conductor.

For that last reason that is why you should be sure that the sheath of the cable is earthed if you use one of the internal copper conductors for earth too.

Cheers
David


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## shortspark (8 Jan 2010)

Just reading through this thread I have noticed part "P" has been mentioned but noboody mentioned that this only affects certain parts of the UK.

Just to throw another comment in, anytime I have installed an SWA cable underground to feed an outbuild etc... I always install a 3 core (for single phase) and 5 core (for 3 phase) supplies and use one of the cores as an earth bonded at one end.

Hope I'm not adding to the confusion :$


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## garywayne (9 Jan 2010)

Does anyone know how to calculate the startup current of a motor. Say a 2.2kW table saw?
Also, when giving cable distance for calculating what size cable is needed, do you give distance from house CU to shed CU, OR, from house CU to shed and back to house CU?


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## garywayne (9 Jan 2010)

Hi all, I'm back again. 

Well, I can't find anything that tells me how to calculate the startup current. So how do I establish the shed current for cable size?


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## OLD (9 Jan 2010)

You have all the answers you need, calculating instantaneous start current is pointless.Time to make up your mind if you are going to do this job and say nothing or consult a spark.


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## garywayne (10 Jan 2010)

Sorry Old. I don't understand what you mean: 



> Time to make up your mind if you are going to do this job and say nothing or consult a spark.


 
Like I previously said, I like to do things myself. Once I have all the relevant facts I shall install the electrics myself, then I shall employ an electrician to check my installation, and if all is fine pass it off, (I have recently heard that electricians don't like passing electrics that they themselves have not installed. If this is true, and I am unable to find one, Will the council pass it)?


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## OLD (10 Jan 2010)

Look back at my previous answers on how to square up the sparks (you do the hard work). You can apply to install electrics as a incompetent installer with a written short description of the work and pay a fee.
CU units can be expensive look at a previous post of mine for a plastic MK one on ebay more switches than you need and a extra mcb to buy but still a good price.


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## garywayne (10 Jan 2010)

Thanks again Old. You have been most helpfull.


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## Jonesy (10 Jan 2010)

Hobbyshop":3b1qn6gw said:


> *Workshop Circuits*
> Prior to the changes in 2008 the lighting circuit would not have required RCD protection but since I intend to surface mount all cables and fittings then all the circuits will need RCD protection as they will not be protected against mechanical damage.



I believe you are referring to regulations 522.6.6, 522.6.7 and 522.6.8 - these apply to cables which are *concealed* - if the cable is clipped to the surface of the wall along the entire length of the circuit and is not concealed then they do not apply. That said there may be other regulations which would apply and require an RCD to be fitted.

The wiring regs require that cables are installed to minimise the risk of mechanical damage (522.6.1, 522.6.2) and if the wiring is at risk of medium or high severity impacts then protection is required by choosing a wiring system with suitable mechanical properties, a suitable/safe route, providing mechanical protection etc.


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## Hobbyshop (10 Jan 2010)

Jonesy":cpa90fws said:


> Hobbyshop":cpa90fws said:
> 
> 
> > *Workshop Circuits*
> ...




Thankyou for the additional information. It is appreciated.


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## shortspark (11 Jan 2010)

On the subject of start up current for your table saw I would normally consult the instructions / manual as these values would be stated. If you are using mcb's you need to make sure you have the correct Type B, C or D, not knowing the exact installation I would recommend a Type C as a minimum. The different types have different tripping characteristics, I can look up if you require.

As for Consumer Unit (or Distribution Board as we call them over here :lol: ) I have found that B&Q sometimes have special offers on which can make the CU (or DB) cheaper to buy there as a one off instead of trying an electrical wholesalers (unless your already a customer of a wholesalers). I once bought all my MK electrical fittings from B&Q for fitting out a house as it was about 10% cheaper than the wholesaler could offer me (even thought I have an account with them!!!!! :roll: )

Hope this has been of help....


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## garywayne (11 Jan 2010)

Nice one shortspark. 
I did read somewhere that I would need a C type breaker, but I can't remember where. I'll have to read through everything again. :shock: 

I would like to thank everyone for your help and patiants. I realise I can be a bit slow, (medication) at times, (most) but I am the sort of guy that needs things explained step by step. Again thank you all, you have been a tremendous help. =D>


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