5 mm sq Armoured ...

[T i m]

Hi again ..

Recent talk of running power to outbuildings etc reminds me that I still have to do so to my own workshop!

This has been brought fwd by the mate who has recently said that I can have whatever I want off his big roll of 2.5mm 3 core .. for nowt (done him enough favours the last of which was removing two 'made of cheese' countersunk machine screws out of the rear of his BMW bike / combo brake drum ... after he had mullered the hex heads out of them of course!).

Anyway. I have been managing with a heavy duty extension lead for the odd time I need power down there but I have provided a fairly easy path already.

There is a 'spare' 32A MCB in the CU on the RCD side.. Do I need another isolator here?

There is a run of plastic drain pipe from under the suspended floor in the house, under the concrete floor of the lean-to, under the hard standing and under the 'garden' (yard) and up to the garage.

It stops in the ground .5 m from the garage base and I have cut a 3" dia hole through the bottom of the pre cast concrete panel of the garage.

The 'idea' was to make a sort of access point from a soil / surface drain fitting (bought for +AKM-1 at a boot sale) where I could bring (Armoured) / telephone cable through from my underground pipe, though this fitting and then through some steel pipe (scaffold sized) into the garage?

In there I would fit a suitable CU / RCD etc? (I'll go back and check recent ssimilar threads)

Anyway. the 'point' here was if I was to be given enough 2.5mm armoured to do the main run x2 (eg, double the cable up) would it give me a lower voltage drop for my MIG welder some +AH4-25m away?

I also noticed when playing with some armoured yesterday that if you trim back the armouring you end up with a round PVC coated 3 core cable that is fairly flexible. Could the 'inner' bit be say continued through a wall to save having to fit a junction box (ie just fit the gland and earthing washer and carry another earth cable through (or bond them together at that point) rather than making an extra joint and going on in T&E ? (and assuming it's all dry etc)

All the best .. and thanks for your time folks .. ;-)

T i m

[Lurch]

Not really, for convenience it might be useful.

Depends what rating the MIG is, I'd have thought so though assuming a standard 13A supply is required for it.

If it's going straight through the wall into the back of a CU, then technically not, but yes I'd do it that way. I wouldn't run it as a normal t&e, i.e. up a wall etc.. ..

SJW A.C.S. Ltd.

[T i m]

[T] Ok ..

[T] Nothing fancy .. std 13A job but can be fussy if the feed is a bit 'soft'.

[T] You wouldn't? I was thinking that without the rigid wire / sheath it would be easier to run under the floorboards up the wall and into the CU and you wouldn't *need* any more protection than internal T&E?

Alternativly then, 6mm T&E (for the low resistance rather than the load) from the CU to just where the cable exits the house and goes into the underground pipe where it goes into a suitable junction box and then goes into Armoured?

I was also thinking of running a spur off the Economy7 CCT to run a storage rad down there? Would I need the same down the other end for that (Mini CU / RCD) ?

All the best ..

T i m

[Lurch]

Grey area I think! I would run them to an external box if it is a fair run from the point of entry to the CU, then a T&E from the box to the CU

Yep, spot on.

Basically, yes. ..

SJW A.C.S. Ltd.

[Harry Bloomfield]

Lurch wrote on Wednesday (25/02/2004) :

Or you could simply run the heater on its own time clock using the circuit you are proposing installing. All juice drawn between the E7 hours is charges at E7 rates.

[Lurch]

Assuming it is E7 and not cheap rate night tarriff. ..

SJW A.C.S. Ltd.

[T i m]

[T] Ok, yes about 6m CU, down wall, under hall, onder middle room to back door / underfloor pipe.

Basically?

Ok .. so I have an "Economy7" CU (another MK Sentry) with radials going to the storage rads via 16A MCB's to DP switched / fused cable outlet boxes.

I take a spare MCB and feed the workshop (T&E then Armoured etc) and into another CU [ to confirm, do I need RCD's on any of this?).

From the mini CU in the workshop I run a T&E radial to the storage rad via another switched fused cable outlet?

What if I wanted a std socket on the E7 supply (to have battery chargers coming on overnight, saving timeswitches etc) any difference to the requirement please?

All the best ..

T i m

[T i m]

[T] We do use clocks Harry on the other stuff indoors as some things might be needed during the day. For a 3KW heater I'd rather have their switch do it ;-)

[T] Well, when I took it up 10 odd years ago it was 'Economy7' .. std rate during the day (some day rates were more expensive) and about 1/3rd the cost 'at night' 13:30 to 06:30 (or summat)

Current meter reading:

Std 72248 Eco 93057

;-)

All the best ..

T i m

[Lurch]

You only need an RCD for sockets that are reasonably expected to supply portable equipment used outdoors.

Actually, you don't need another CU in the shed, just run the SWA into the workshop and straight into a metalclad switch fuse.

Yes, if there are sockets then you will need a RCD on the E7 circuit. ..

SJW A.C.S. Ltd.

[Christian McArdle]

With the workshop separated from the house, a 100mA RCD may be required for TT earthing on any type of circuit. Also, although regs only require RCDs for outdoor portable equipment rings, I'd suggest that all rings should have them for supplementary direct/indirect protection, except where explicitly not desired, such as for fridges/freezers.

In the event that a (time delayed) 100mA RCD is fitted, it is better to fit

30mA RCBOs on the individual circuits, as these are guaranteed to blow first, protecting the other circuits (such as lighting) from an unnecessary trip.

Christian.

[T i m]

[T] (I am on an old real earth feed ?)

on any type of circuit. Also, although regs only require RCDs

[T] Ok, so, My MK Sentry has an 80A, 30mA trip RCD feeding various MCB's protecting upstairs / downstairs and kitchen (and hence fridge / freezer?) rings and the electric shower. The lighting ccts are pre the RCD.

[T] So, I pull out the 30mA RCD and replace it with a 100mA RCD. I then replace most of the MCB's and replace them with 30mA RCBO's (so one nusiance tripped (30mA) RCBO won't affect any other ccts (I still wouldn't need RCBO's on the light ccts etc).

Then I take the feed to the garage through an MCB off the RCD protected side of the CU and have a 30mA CU in the garage (so if it trips it won't take any ccts out in the house)

Last question. Can I get all this new gear for my MK 'Sentry' CU? (the esisting RCD is an LN 5780)

All the best ..

T i m (now going to have a lie down ..)

>

[Christian McArdle]

No. You would pull the 30mA RCD and not replace it. All MCBs/RCBOs would be not RCD protected (except internally in the case of RCBOs). If earthing is TT, then the incoming switch isolator is replaced by a 100mA time delay RCD, but you still don't need a split load.

Yes. You should also run a new 16A MCB radial to the fridge/freezer, so it stays on when the kitchen ring RCBO trips when you're on holiday. A nuisance single trip in the lifetime of the installation would probably cost more in spoilt food than the cost of DIY installation for such a circuit.

Yes, except obviously there would be no such thing as the protected side at the house end. The workshop, being a long distance from the house, will probably require TT earthing (but extra beefy cable and a lack of structural metalwork and services may make TN earthing possible if carefully designed). Personally, I'd go for TT anyway. If I did go for TN, I'd put a local earth rod in anyway, in case the armoured cable got dug up.

Assuming TT, the far end could have two layouts: (With TN, the options are the same, but with any reference to 100mA time delay RCDs changed to simple isolator switch incomers)

1. (Cheap) A non split load consumer unit protected by a 30mA RCD incomer and MCBs.
2. (Medium) Split load consumer unit with 100mA time delay RCD incomer and

30mA split load RCD.

1. (Expensive) Non split load consumer unit with 100mA time delay RCD incomer and MCB/RCBOs as appropriate.

The expensive options gets more discrimination and better safety (i.e. lights stay on)

Yes, assuming it is a modern DIN rail unit. MK do single width RCBOs. You'll need a new full length bus bar as the old RCD will have caused the existing one to be cut. You can use the old RCD (and possibly the old bus bar fragments and neutral flyleads) in the new workshop CU, if you go for time delay with split load (2) or simple (1) options above.

Christian.

[T i m]

Hi Christian,

Firstly sorry for nearly missing your complete reply.

Secondly, although I believe I understand your reply I think there are two many variables for me to pin it down exactly so I'll recap if I may.

My house / garage.

I have a MK Senty CU with the earth supplied to me via the armoured wire on the i/c cable.

Does this make this one of the TN earthing variants?

On my MK Sentry (that I believe does have a rail type mounting but not sure what standard) I have the main switch and 3 MCB's (lights etc) then 30mA RCD and all other ccts.

I want to run power down to the concrete garage via some 20M of cable,

5m of which would be 'only' in a 2" plastic pipe some 50cm below the ground level. I intend to run all the cable in Armoured (except for the bit in the house).

Q1) Where would I need to pick-up the feed on the house CU and / or what extra would I need to do to stay within code whilst being realistic please?

Q2) What would I need to get at the other end to cover some sockets and lights in the garage.

Phase two (but probably done first) will be to do similar at Mum and dads. The difference here is that I don't think they have a RCD in the house CU and the armoured stretch is isolated by two DP fised switchboxes.

Same questions for this TN earth scenario please? (And if you tell me what would be ideal for A it will probably also apply to B?)

All the best and sorry to be a pain ...;-(

T i m

[Christian McArdle]

Yes, so you don't need a time delay RCD in the house.

Take it off an MCB on the non protected side. If you wish, remove the RCD and replace socket circuit MCBs with RCBOs.

A "garage" consumer unit would be an RCD with (usually) a 20A MCB for sockets and a 6A MCB for lighting. Should you wish to have discrimination on your RCD (i.e. are using dangerous machinery), then you should install a split load unit instead and replace (or source) the incomer with a 100mA time delay RCD instead of a switch.

I would use TT earthing in the garage/shed, if it is separate from the house. This requires a tested earth rod. You are very unlikely to be able to get hold of the equipment for testing the rod, so may wish to get an electrician in to check its impedence.

Christian.

[T i m]

Ok, the only 'machinery' I'm likely to use in the workshop is my Myford ML10 lathe, a small bench grinder, pillar drill, band saw, various electric hand drills, planers, heat gun, angle grinders and my MIG and Stick welders? (I gave you this list in case any of them fitted 'dangerous' in your context)

Is this because of a potential impedance buildup between the earth at the garage and that of the house Christian?

You are very unlikely to be able to

I assume we aren't talking DMM's here then? Is this the time I wished I'd kept my Megga ? Can you buy these 'rods' or are we just talking an particular length of 15mm copper tube etc?

All the best and thanks again for the advice .. ;-)

T i m

[Christian McArdle]

I would definitely install split load/time delay RCD incomer for that lot. You wouldn't want the lights to go pop when you are using many of those tools. If you decide to replace your house MCBs with RCBOs, then the "spare" RCD liberated can be used in the split load unit (for the "protected" side, not as the incomer), saving you a bit of cash.

You buy special earth rods and clamps. They are very cheap and just driven into the ground with a big hammer.

Christian.

[T i m]

(sri ,, new terms etc .. 'incommer' being the 'first' switch in the cct on a CU?)

I'm not likely to be using that all at the same time of course!

Well, that's true. It's not too bad in there during the day as I built some windows into the frame when I replaced the 8' square up-and-over with my 3 way steel doors. At night it can get very black when the lights go out! (not that they have in the few years I've been running the equipment above on a (heavy) extension lead (slap wrists I know). ;-(

If you decide to replace your house MCBs with RCBOs, then the "spare"

Assuming my MK 'Sentry' CU is 'Euro, DIN, (whatever) rail' that is? If I told you my existing RCD was part no LN 5780 would that help you (or anyone)? To confirm, I would only need RCBO's on the socketed runs and a time delay RCD in place of the old RCD position?

This would give me summat like :

Power in Main Switch

3 x MCB (u / d lights and cupboard under stairs light ) TD RCB ( ** new **) RCBO (downstairs ring) RCBO (upstairs ring) RCBO (kitchen) MCB (new cct to fridge freezer? Or would this be *before* the RCD?)) MCB (shower?) MCB (garage?) > 6mm T&E to junction box inside house boundary > to 2 x 2.5mm Armoured (cos it's free and to minimize voltage drop for welding ) to new CU in workshop.

Main switch MCB (lights) RCD (old 30mA from house) MCB (socket ring)

Am I close yet?

Ok, and bought from any decent electrical supplier? Do they come in different lengths and if so how do I decide what will be suitable for here (Nth London and about 6' above the water table!)

You didn't comment on what would be used for testing the rod Christian?

All the best and thanks again .. T i m

[Christian McArdle]

No. You don't need a time delay RCD (or any RCD at all) on the house consumer unit if you go for RCBOs.

All OK, except that you shouldn't have any RCDs at all (except those internal to the RCBO). You replace the cut up DIN live rail with a full length version. I'm not entirely sure about having 2 runs of 2.5mm armoured. Someone else might know whether or not to slap your wrists. Personally, I wouldn't use the two runs, but would run a new load of 6mm armoured. Keep the 2.5mm for running an outside socket or some lights.

1. Time delay RCD 100mA incomer (acts as switch)
2. 6A MCB (lights)
3. RCD (old 30mA from house)
4. 32A MCB (socket ring)

The other alternative is to put the time delay 100mA incomer as the last thing in the house CU before the garage MCB. Everything for the house goes on the unprotected side. Personally I wouldn't bother unless I was worried about earth loop impedence on the garage run. Besides, you gain 2 extra ways by not having the RCD there.

I presume you could just use a standard earth loop impedence tester, but don't know if this is officially the correct technique.

Christian.

[stefek.zaba]

It's permitted, but most be done with care. The incantation is 'conductors in parallel', and the idea is that if you do load-sharing like this, you need to make damn sure that each parallel leg is closely matched in resistance/impedance (because, if they're not balanced, the lowest resistance one gets more than the designed share of the load current, and quite possible more than it's rated for).

Not only does that mean keeping the lengths the same (not to within millimetres, of course, but within a few percent of total length), but being *very* sure that you've given the terminations of each leg the same termination resistance (so, practically: if stuffed into one hole, equal surface contact; no only-half-the-strands-making-contact problems; etc. etc.) In practice, while it can be a worthwhile saving in material cost for big-arse installations to run say two 180A-rated SWAs rather than a single 320A job, for a domestic installation it rather screams "cheapskate" and (however unjustifiably in any particular case) will make any NICEIC or similar Inspector start to take a *very* close interest in the quality of the whole installation. Sorry, Tim, but that's the way of the world!

HTH - Stefek

[Lurch]

On 1 Mar 2004 16:03:01 GMT, in uk.d-i-y [e-mail] strung together this:

Fine so far...

Yes, but the same can be said for any wiring, if it's not done properly it's wrong.

I seem to remember T i m saying that the SWA was free, and if I was in the same situation I'd probably do the same.

Not really, if you make a bad job of something an NIC inspector will look into the installation with more detail. If you do it properly and demonstrate a safe working practice then I see no reason for the NIC inspector to be looking for fault's for any reason. And anyway, why would the NIC inspector be coming round? ..

SJW A.C.S. Ltd.