Workshop/Shed wiring.

[Ed]

Hi Everyone,

I was a sparky for 10 years working to 15th edition regs a long time ago.

I know there have been harmonised colors and new regs introduced under the 17th edition and would like to ask for some up to date advice about rewiring my shed/workshop which will be single phase only.

1) My house wiring is protected by a split load C/U with combined RCD, DP isolators. I intend to run a 6.0mm cable to the shed from a spare way with a 32A protective device. Would I need an MCB or RCBO to protect the new shed circuit?

2) In the shed I'll be installing PVC dado trunking an conduit for power(ring circuit) and lighting(1-way circuit). There will also be a couple of 80 watt tubular heaters with frost stat to help reduce condensation on machinery. Are the standard Brown, Blue and Green/Yellow single, stranded wires ok for these circuits? How about switch wire identification?

3) I'll be installing a milling machine and maybe later on a lathe, which simply plug in to a standard 3 pin socket outlet. Is there a need or requirement to cross bond the machine frames or would the cpc in the flex be OK?

Edit: Forgot to mention the 6.0mm cable will connect to an MK Sentry C/U inside the shed.

TIA for your advice.

Cheers,
Ed.

 

[sparkiemike]

1. It depends, will the EFLI be low enough to automatically disconnect without a RCD under fault conditions? What type of cable are you using? Will the cable be buried less than 50mm in a wall? Will you have a consumer unit in the workshop to provide RCD protection for the socket outlets or will the outlets have RCDs integrated?
2. Yes the standard 6491X single cable is OK
3. I don't think supplementary bonding will be required, as it is not an area of increased risk and you don't seem to be suggesting bonding because you can't meet automatic disconnection times?

EDIT: If you are in England and Wales are you aware of the part P requirements?

 

[Ed]

Hi Sparkiemike,

Thanks for the quick reply.

I'll have to check the EFLI on an MCB first then upgrade to an RCBO if not within acceptable limits. Haven't done any EFLI testing for years. It was never really common practice back then to have more than one RCD in an end to end circuit. RCBO's were just coming in and were used where a main RCD was not present.

I've heard of Part P, I need to do some research/reading.

Thanks again,
Ed.

 

[PrenticeBoyofDerry]

How far away from the main house consumer unit is the shed?
How do you plan to route the cable between house and shed?
Will this cable have any form of mechanical protection?

 

[Taylortwocities]

I've heard of Part P, I need to do some research/reading.
.

Info is here //www.diynot.com/wiki/electrics:part_p:diy_electrical_work_and_the_law

BTW. This 6mm cable out to the shed. What sort of cable did you have in mind?

 

[Ed]

I've heard of Part P, I need to do some research/reading.
.

Info is here //www.diynot.com/wiki/electrics:part_p:diy_electrical_work_and_the_law

BTW. This 6mm cable out to the shed. What sort of cable did you have in mind?

Hi TW,

Thanks for the link

From the consumer unit to the house perimeter wall I was going to use 6.0mm twin and earth then have a connection from there to the shed with conduit and single/stranded.

 

[Ed]

How far away from the main house consumer unit is the shed?
How do you plan to route the cable between house and shed?
Will this cable have any form of mechanical protection?

Hi PrenticeBoy,

It's about a 10m run. The cable will be T&E in the house then switch to singles in overhead conduit as long as Part P allows it. I'm replacing more or less what's already there, although it's only a 2.5 T&E at the moment spurred from a ring circuit inside the house.

Looks as though I need to be notifying somebody for this work. Do you have to pay a fee when you make a notification? ...Scratch that, after reading through the legal requirements I see that a fee is likely.

 

[Electrifying]

Yes, you will have to pay a fee if you're doing this yourself.

A bit worrying is that there's been no mention of the earthing system and whether there are extraneous conductive parts in the shed?

 

[Ed]

The Earthing system is TNS (cable sheath).

Extraneous conductive parts. ...are you testing my aged knowledge by any chance?

There will be galvanised steel racking which I can cross bond back to the C/U in the shed and also have quite a few hand tools, but I'm not going to attach an earth strap to each of my spanners, screwdrivers and the bench vice

 

[JohnW2]

Extraneous conductive parts. ...are you testing my aged knowledge by any chance?
There will be galvanised steel racking which I can cross bond back to the C/U in the shed and also have quite a few hand tools, but I'm not going to attach an earth strap to each of my spanners, screwdrivers and the bench vice

No need for that

Extraneous-conductive-parts are conductors (like metal water/gas supply pipes, structural metal etc.) which enter a property/building and have the potential ability to introduce true earth potential (the regs say "a potential, usually earth potential") into that property/building. These are required to be bonded to the 'earth'/CPCs of the electrical installation, so that there cannot be potential differences between them and anything connected to the installation's CPCs ("exposed-conductive-parts"). Don't blame me for the terminology - I'm just the messenger! In modern paralance, the idea is to cfreate an 'equipotential zone' within the building.

Needless to say, any metal contained wholly within the building (e.g. your spanners) doesn't need bonding!! (even though you'll find some heated discussions about some aspects of that statement!)

The potential discussion about earthing systems (as opposed to bonding) is whether your shed (including bonding within it) should use the TN-S earth or be insulated from that and have its own local TT electrode.

Kind Regards, John.

 

[Ed]

Thanks John,

It seems that the 17th edition regs has not only introduced new requirements, it's made the design of electrical installation a bit of a grey area. I might forget electric and make it all steam powered!

The link provided above in this thread to the legal requirements states that Part P contradicts legislation and is open to different interpretation by LABC's. ...but that's material for another duscussion I think.

Kind Regards,
Ed.

 

[JohnW2]

Thanks John, It seems that the 17th edition regs has not only introduced new requirements, it's made the design of electrical installation a bit of a grey area. I might forget electric and make it all steam powered!

You're welcome. To be fair, for all the failings of 17th ed., once one has got one's head around the vocabulary, the aspects I was explaining come down to little more than common sense in terms of safety.

The link provided above in this thread to the legal requirements states that Part P contradicts legislation and is open to different interpretation by LABC's. ...but that's material for another duscussion I think.

Indeed. Although Part P was undoubtedly well-intentioned, it's certainly not a tidy situation, and isn't really 'working', in many senses.

Kind Regards, John.