Wiring Mains to Garage May 2007 to Nov 2009 - Finished!

[matt]

I'm about to replace the side gate the leads to the side passage between my house and garage. The current gate has a fixed frame piece across the top, making it difficult/impossible to take extra large items down the side of the house.

The electrical supply to the garage currently uses this fixed frame piece as it's route. It comes out of the eves (chalet style house with "low" side nearest the garage), along the wall a short space, across the frame, and through the garage wall.

When I replace the gate, I plan to remove the fixed frame across the top and re-route the wiring. I realise this will require part P etc, therefore, I'm after a compliant solution.

I have some armoured cable, however, it's a right pain to make it look neat with so many twists and turns - I get exhausted just thinking about working with it in such a small space. Therefore, I'm thinking I could install some conduit that runs from the eaves, down the wall, under that flags in the side passage, up the outside of the garage and through the wall. I'd have to extend the cable, therefore, would create a junction as it appears from the eaves (or, better still, inside if I can get to it), but just join extra 2.5 run through the conduit. I have a consumer unit in the garage where the supply line will terminate before being distributed via a ring.

Does this sound like a plan?

Cheers

 

[OLD]

Part p allows maintenance to a installation as long as the electrical design and safety is not compromised so if the cable conductor size is same or better its ok to replace cable . Even though the installation may be grandfatherd it would be desirable to have a rcd in the garage and this should be done at the same time and improves safety.

 

[StevieB]

Not sure on the part P aspect specifically, although as mentioned you could class it as altering an existing installation. What did concern me was your reference to 2.5, which I presume means standard 2.5mm cable.

You say you have a consumer unit in the garage - does this just feed a single ring circuit for standard 13A plugs? If it feeds more than one circuit or a ring and a lighting circuit, possibly a 16A supply for a meaty table saw then I would be concerned about the 2.5mm cable feeding the CU. If you are going to replace the span then it makes sense to futureproof it. I would consider running 4mm or possibly larger (I ran 10mm armoured to my old shed, although this was over 40 meters) for this reason.

One other thing - while running in conduit is fine, it should be buried at least 2 spade depths deep. You may not be gonig to dig up the path but if you ever sell the house etc....

As to the junction box, no problem with that so long as its correctly rated, but if possible at all I would install it inside rather than outside - makes it easier to get to and install and does not need to be waterproof.

HTH,

Steve.

 

[davy_owen_88]

Could you offer some more info on what you have currently? Length of cable run from house to garage, how far the cable runs inside your house, where the cable runs within you house (under the floors, under loft insulation, inside conduit etc.), what size fuse/MCB is it connected to and whether there is RCD protection at the house end or garage end.

Current guidelines for SWA burial is that it is buried 450mm deep, backfilled about 3/4 full then insert warning tape and then fill the remainder.

If you only have a single length of 2.5mm² t&e feeding your consumer unit I would be very concerned that it is overloaded. I would install 4mmN SWA at a very minimum, 6mm² would be better.

Try to keep as many joints inside the house as possible, and try to keep the number of joints to a minimum. Using SWA requires glands to ensure earth continuity through the armour and this requires metal boxes at both ends of the SWA run for termination purposes.

 

[matt]

Thanks for the advice.... Some more info as requested.

The supply originates from the house consumer unit, protected with a normal household ring main rated circuit breaker. It goes under the floor, up in to the kitchen behind fitted cabinets, up the wall (still behind cabinets) and through the ceiling in to the roof space (single storey side of the building). From there it emerges through the eves.

It is conceivable that I could replace the supply right back to the house consumer unit with something larger than 2.5mm. In fact, I'd route it out to the garage at ground level, simply running it under the floor, and abandon the original supply.

This being the case I'm figuring:

1. ?? size circuit breaker at the house consumer unit end.
2. Feeding 6mm supply under boards to house perimeter.
3. Continuing through conduit made of ???? dropping below ground 450mm, across the path, and up above ground again.
4. Entry through garage wall and up to garage consumer unit.

Does this sound more like it? Can someone help to fill in the question marked bits?

Thanks again.

 

[davy_owen_88]

The supply originates from the house consumer unit, protected with a normal household ring main rated circuit breaker.

32A? If so that is too high for a single length of 2.5mm² twin and earth which is rated at 27A maximum (and that is under the most favourable of conditions).

It goes under the floor, up in to the kitchen behind fitted cabinets, up the wall (still behind cabinets) and through the ceiling in to the roof space (single storey side of the building). From there it emerges through the eves.

Standard t&e isn't suitable for exposure to direct sunlight either so it's probably best that you are replacing this now before the damage gets too bad and causes some problems.

This being the case I'm figuring:

1. ?? size circuit breaker at the house consumer unit end.
2. Feeding 6mm supply under boards to house perimeter.
3. Continuing through conduit made of ???? dropping below ground 450mm, across the path, and up above ground again.
4. Entry through garage wall and up to garage consumer unit.

6mm² SWA is good for 46A when buried direct in the ground or within ducting. A 40A MCB is usually more than sufficient. Connect to the non-RCD protected side of your house CU (if you have a modern split-load board) and fit a 30mA RCD in the consumer unit in the garage - this means you don't have to go back to the house to reset it. Connect socket circuits to the RCD side and lights to the non-RCD side so that the lights will remain on if something trips the RCD in the garage (vital if you have sharp spinny things).

Standard 110mm soil pipe is fine for the burial of SWA. Placing the cable in ducting isn't necessary with SWA but it is a good idea just in case you find you need to upgrade/replace any cables at a later date. When you lay the ducting consider adding some draw-lines for telephone/cat5 cables later on.

 

[matt]

Cheers. One further question... Can I connect SWA directly to the consumer units at each end?

 

[davy_owen_88]

If they are metal-clad CU's then yes, but if they are plastic you will need to terminate them into a metal adaptable box and then use 6mm² t&e to join SWA to the CU.

Here are some links to the things you will need:

Underground warning tape

60A connector strip

SWA glands

3-core 6mm² SWA

Green & yellow sleeving

Metal adaptable box

 

[StevieB]

Matt - one minor point I hate to bring up.... This is now a rewire, not altering an existing circuit. Definately comes under Part P with all the associated hassle.

Not advising on whether you do it or not, you know your own limitations best. From your questions however I would guess you are not a professional sparky? A good place for advice (and sarcasm) is also the screwfix forum if you run into trouble a need a bit of instant(ish) advice.

Steve.

 

[martlewis]

I hope you don't mind if I just add a question to this thread... My electrical installation was already in when I bought the house. I've since rebuilt the shed much larger. Cable size, current, etc are not the concern here. My question is that the swa terminates directly inside a plastic cu in the house, the armour shield/earth connected to an earth terminal in the cu. The same at the workshop, connected inside a plastic cu. Is this in need of remedy using adaptable boxes?

Martin

 

[davy_owen_88]

Was a suitable SWA gland used or was the armour just twisted together and put directly into the earth terminal?

The main reason for using a metal adaptable box is that most plastic insulated consumer units are not substantial enough to take the stresses involved during the tightening of the glands. The glands need to be tight enough to ensure continuity and provide support to the cable to stop it moving around too much which can loosen the conductors.

 

[martlewis]

the wire is just twisted and connected to earth, no glands used, but the swa is secured to the wall with cable clips so it can't move.

 

[davy_owen_88]

Is there a core used for the earth as well as the armour or is the armour the only method of earthing the outbuilding? If the latter I would definitely suggest you fit suitable glands. Whether you terminate them into your current CU or a metal box is up to you, but using the metal adap. box leaves more space within your CU (the glands take up a fair bit of space and require room to tighten too).

If the SWA has a core for earth then you could leave it as it is as long as the armour is connected well enough to ensure a good low resistance joint.

P.S You missed out the *tap tap* part of your Signature :lol:

 

[martlewis]

The swa is 3 core with one core used to carry earth. The shielding of the cable has been cut to leave about 8 strands also earthed both ends.

Good point about the sig, shame I ran out of space!

 

[davy_owen_88]

In which case the armour is only there to provide a path for fault current should you put a spade through it - just leave it be and be careful where you dig

I would prefer to see all the armour earthed (the main reason for use of suitable glands) but as I just said, if it was installed to the correct depth and warning tape was used, there should be no problem.

 

[martlewis]

It doesn't go underground, it's attached to the side of the house and then to the underside of the decking which joins onto the workshop.

 

[davy_owen_88]

In which case, you can be as careless as you want with the spade :lol:

The regulations state that buried cables require an earthed armour or for them to be run within earthed conduit. Since your cable is not buried there is no need for the armour, let alone it being earthed.

 

[RogerS]

Folks might find this link useful

 

[matt]

Two and a half years later and I've finally replaced the side-gate and run a new supply to the garage. It'll not be the same not having the CB in the house trip when I turn the tablesaw on with something else running at the same time.

 

[wizer]

Now get on and make something, chop chop :wink: