10mm SWA

[n0legs]

10mm gets a big tick from me =D>
I've written previously on not skimping on the size of cable for a supply, think big is my advice.

Look at it this way.
How quickly and easily could you, or a spark change, an MCB/Fuse/DP Switch to increase a supply capacity?
How quickly could you dig out/unclip/remove and reinstall an undersized cable to increase a supply capacity?
What is the cost involved for the remedial works and initial cost of cable that is now surplus to requirements?
:wink:

 

[pike]

Thanks all. Great advice. I've been told as the twin and earth reel I've already got for getting it from the entry point to the main unit is 10mm, then 10mm is what I'll need. 16mm was also suggested by some but then they realised there's not much point because of the t&e I'm connecting it to? My own feeling is 10mm will do fine anyway how I work.

I've got the 10mm t&e already as I was rebuilding my extension and garage and it was easier to put it in then than have to mess things up later.

3 core 10mm it is!

 

[Fitzroy]

Good discussion, saves me asking the same Q in 2 months time. I'm with pike 10mm the. Thanks also to all for the input.

F.

 

[RobinBHM]

I was told when I did mine that the armour definitely should not be used as an earth, hence it should be three core not two.

Its quite common to use one of the copper cores as the cpc, although I believe it depends whether the armour is large enough, based on cable size and load. The armour still needs earthing at the supply end to act as protection

Given there isnt much extra cost in using 10mm cable instead of 6mm cable it makes sense to for for the larger cable.

In some circumstances an earth may not be exported to an outbuilding so a TT earth is created at the new location.

 

[n0legs]

Seeing as there's some confusion about armours acting as earths, I thought I would post this again.

Below is taken from a paper written by John Peckham. He updated it in 2012 for the 17th edition.
The full article can be found here http://www.gadsolutions.biz/regulations/swa-as-cpc
It is considered by many as definitive.

The use of internal cores, of both thermoplastic and thermosetting SWA cables, as a CPC and/or the use of separate parallel CPCs are not required for SWA cables to comply with BS7671 provided.

1. The operating temperature of the cable does not exceed 700C.
2. The CSA of conductor cores does not exceed 95mm2.
3. The cable is not installed in the floating section of any marina.
4. The cable is correctly selected for the correct value of R1 + R2, or Z1 + Z2, for the circuit protection device protecting the cable.
5. The cable does not connect different installations together which have separate means of earthing unless sized for the potential earth fault current.
6. The cable is not used as a combined CPC and bonding conductor on a PME
installation unless suitably sized.
7. The cables are properly terminated in correctly sized manufactures brass glands selected for the external influences prevailing.
8. Where a removable gland plate is present on the enclosure to which the cable is attached the earth ring (banjo) supplied with the gland is used and is connected to the earth terminal in the enclosure with a separate CPC. This CPC terminated in an eyelet to a bolted connection to the earth ring.
9. Any protective coating on the enclosure surface is removed under the contact surfaces of the gland and associated earth ring to expose bare metal.
10. All the wires of the armouring enter the gland and the gland nut is adequately
tightened. The cable is adequately supported up to the gland with cable cleats to prevent mechanical strain on the gland


I add,
In other posts I have mentioned "a properly designed installation". There are many factors that need consideration when installing a supply, to be honest there's many considerations to be taken into account for the majority of electrical work, but if you are in any doubt over the work at hand or you're own abilities to perform the work consult a suitably qualified person.

 

[pike]

Cable is in place, quickbit were very quick to deliver. Just got to find a decent sparky now.

The 10mm swa wasn't as difficult to work with as I imagined. So long as you can lay it the way it wants to go.

I don't have any 16 amp tools so I'm thinking I'll be ok with just one 32 amp ring main? Or should I be looking to have dedicated supplies for some tools?

I have all these induction machines:
1.5kW Table saw
1.5kW Extractor
1.1kW Planer/Thicknesser
1.5kW Bandsaw

So I'll be running one of the above and the extractor and maybe heater at any one time.

I've found I only blow the fuse on my extension at the moment if I forget and run the heater at the same time as the extractor and machine. I'm thinking as long as the consumer unit has space I could add 16 amp or dedicated later if need be?

I'll go for 6 or 8 double sockets. 4 strip lights of some kind. The shed is only 6mx3m.

Are the c type breakers only for if I run dedicated 16 amp tools?

Cheers!
Carl.

 

[n0legs]

I don't have any 16 amp tools so I'm thinking I'll be ok with just one 32 amp ring main?
I'm thinking as long as the consumer unit has space I could add 16 amp or dedicated later if need be?

I think that's the best course of action for now.
I would leave at least 2 spare ways in the CU for the addition later on of a few dedicated circuits.

Are the c type breakers only for if I run dedicated 16 amp tools?

No. They're for a situation that requires a supplying circuit to be able to absorb the sudden spike of startup/surge current without the breaker (CPD/circuit protective device) operating.
Leave the breakers at B Type or allow the electrician to do his figures to see if the installation warrants the need for C Type.
If you are considering a number of traditional fluorescent light fittings tell the "spark", he may decide a C Type breaker is more suitable for the lighting circuit.
They cost pennies, so if you do experience nuisance tripping it's not a massive issue to change them out.
Hope this helps.

 

[MikeJhn]

If you are putting in a new consumer unit (cost is minimal) in the workshop, don't bother with B type MCB,s use all C type and then you will not have to change anything, the difference in price between the two is pennies as No legs said.

I have also found an overhead socket on a fly lead I can more around/hang from the ceiling more than useful for small tools.

Mike

EDIT to add, as I said before its even safer to have twin pole MCB's rather than the normal single pole.

 

[pike]

Mike, I don't know anything about electrics and after googling twin pole I'm non the wiser. No sense me asking for something if I don't even know what it is.

Unless I have a specific requirement (which I understand) I'll probably just have to tell the sparky what I'll be doing and let him spec it.

The overhead socket is something I've heard people say is really handy a few times so I'll definitely go for that.

Cheers,
Carl.

 

[deema]

I would recommend you suggest to the sparky that you want the workshop to have its own Independant supply, if something trips in the shed it won't trip the house consumer unit and visa versa. Your family will love you for it. This will involve adding a small switch / unit beside your house consumer unit.

Next ask the sparky to provide a consumer unit in the workshop with spare ways so you can add independant circuits if and when you get machines that need more juice. Typically the cost is very little for some extra ways (prongs to hang an MCB on).

 

[pcb1962]

I need 50m of 3 core SWA. Looking around online the prices inc delivery vary:

tlc-direct.co.uk 224
quickbit.co.uk 165
jcelectrics.com 140

Can anyone who's used one of the two cheaper sellers let me know if they are reliable?

Cheers,
Carl.

Have you tried ringing TLC and asking for a price? They might take 10% off just for asking as it's a decent size order.

 

[n0legs]

Unless I have a specific requirement (which I understand) I'll probably just have to tell the sparky what I'll be doing and let him spec it.


Carl.

Carl, that's exactly the right attitude.
That's what you're paying him to do and ultimately sign off on.

 

[pike]

Thanks! Other than deciding lights I think I know what I need to get right:

- the SWA which is already done
- having space in the consumer unit for future stuff
- separate supply so shed doesn't trip house
- more sockets than I think I need and at least one up high

 

[MikeJhn]

Carl

I was only pointing out the options, IMO if you go with 10mm you should take it off the main supply in your house consumer unit to an isolation switch inside said unit, then to another consumer unit inside your shed with its own RCD, then distribute it to the individual power outlets via MCB's personally I would source twin pole MCB's, that way if you do overload anything its your shed that will trip out first not the house, I also suggest putting in an emergency light over the shed consumer unit to allow you to see once its gone dark, Oh so dark, guarantee it will trip at night when you are working on something.

Oh yes it would be best if all the MCB's in the shed are motor rated C units.

Mike

Same advice from other since I posted the above.

A twin pole MCB is a unit that has both the neutral and live switched in it instead of the neutral going to a bus bar, and the potential of having a circuit that still has an electrical potential after tripping out, the safety factor of the twin is that both the neutral and live are switched off when the MCB trips with a 3mm air gap between the poles, the unfortunate point is that some sparkies think a RCBO will do the same, it does not.

Mike

 

[pike]

Cheers. Emergency light added to the list.

 

[MikeJhn]

Forgive me if I am teaching you to suck eggs, but an emergency light should be wired into your lighting circuit, so if they go out it comes on, may be obvious, but thought it worth pointing out.

When looking at lights, don't forget that LED florescent's are available, better putting them in new rather than changing later, which I suppose I will have to do at some point. (hammer)

Mike

 

[pike]

Thanks Mike. I had read on this forum about the emergency light coming on if all else fails but well worth pointing out.

I'll talk to the sparky I have coming tomorrow about lights. Not sure where I'd fit long tubes in on my open framing roof. I don't have any plans to insulate or board it up.

 

[MikeJhn]

My florescent's are hung by chains from the beams above, could easily be rafters instead or any other roof member, you can see them here:



Mike

 

[pike]

Ok. I don't have anything like the head room you do I suspect.

 

[MikeJhn]

Many ways to divest the feline of its outer layer as they say, uplighter around the periphery of the room shining onto a white painted ceiling or roof structure, florescents attached to the ridge board, so many different ways to accommodate the essential good lighting that is most definitely needed.

Mike