Seeking Advice, Attention any Sparkies!

[Spearos]

Ok, with the addition of a pillar drill my attention has been turned to the electricity supply/arrangement in my garage. Basically I'm seeking advice on whether A) what I have is safe and B) is it adequate.

My knowledge of electricity is extremely limited so please forgive my terminology! I will try my best to explain the current 'set up'.

• 32A MCB on the consumer unit fed to a electric cooker outlet (cooker is gas, no electric cooker)via 4mm cooker cable, approx length 5m
  
• 2.5mm 3 core armoured cable from electric cooker outlet into garden, ran underground to garage. approx length 20m (interestingly this is orange in colour, quick google suggests it's intended use is traffic lights/street lights?).
  
• This joins a double socket which has a further 2 double sockets spurred from it.
  
• 2 x double 4' strips lights on a 13A plug
  
• Equipment wise I have a SIP Autoplus 196A Mig on a 13A plug, 3hp compressor and the 375w pillar drill as well as smaller items such as 2000w convector heater, angle grinder, reciprocating saw, jigsaw, cicler saw etc. Obviously only one of these items in in use at one time apart from the heater.
  

Would really appreciate any comments/suggestions as the small amount of googling I've done since this concern reared it's ugly head has not only totally confused me, it has stressed me out big time with worry!

[Superpants]

Starter for 10;

Garden/ garage circuits should be fed off a 30mA RCD. It therefore sounds to me that this needs closer looking at!

[David Sparkes]

I'm not clear what is giving you cause for concern. You say it's the addition of the pillar drill to your armory, but then tell us it's only 375 Watts.

You ask if A) what I have is safe and B) is it adequate.

The compressor is on the limit for a 13A plug, and it might give the motor a little more power if you used a fused spur wired directly into your incoming feed.

Justification is that power (loss in this case) is proportional to voltage squared, so any voltage loss forcing the current through the plug and socket really drops the power available at the motor, so you don't get maximum air output.

Remember a plug and socket has at least 6 electrical connections, wire to socket, socket to plug, plug to flex. That's for the Neutral, repeat for the Live. The connections to the fuse, and the fuse itself, will also be in the fused spur outlet so there is little point in counting those.

If you don't move the heater around you could apply the same logic to your heater connection, although it's only 2KW against the compressors 3KW.

Run both the heater and compressor together and you are getting close to the limit, but not reaching it.

Despite the name I'm not professionally qualified in this area, I'm just going on my experience. I'd say what you have is adequate. Safety requires more of a visual inspection, that covers quality of wire terminations, flex on the ground being walked on, etc, and my vision stops this side of the screen :-)

If I was to consider an upgrade it would be to add a MCB consumer unit in the garage and wire the sockets, lights, and fused spur from that.

You might be able to put the sockets on a ring rather than spur, which again reduces your voltage loss. It's a minor gain, but it's working for you every time you switch something on.

HTH.

[Spearos]

I'm not clear what is giving you cause for concern. You say it's the addition of the pillar drill to your armory, but then tell us it's only 375 Watts.

You ask if A) what I have is safe and B) is it adequate.

The compressor is on the limit for a 13A plug, and it might give the motor a little more power if you used a fused spur wired directly into your incoming feed.

Justification is that power (loss in this case) is proportional to voltage squared, so any voltage loss forcing the current through the plug and socket really drops the power available at the motor, so you don't get maximum air output.

Remember a plug and socket has at least 6 electrical connections, wire to socket, socket to plug, plug to flex. That's for the Neutral, repeat for the Live. The connections to the fuse, and the fuse itself, will also be in the fused spur outlet so there is little point in counting those.

If you don't move the heater around you could apply the same logic to your heater connection, although it's only 2KW against the compressors 3KW.

Run both the heater and compressor together and you are getting close to the limit, but not reaching it.

Despite the name I'm not professionally qualified in this area, I'm just going on my experience. I'd say what you have is adequate. Safety requires more of a visual inspection, that covers quality of wire terminations, flex on the ground being walked on, etc, and my vision stops this side of the screen :-)

If I was to consider an upgrade it would be to add a MCB consumer unit in the garage and wire the sockets, lights, and fused spur from that.

You might be able to put the sockets on a ring rather than spur, which again reduces your voltage loss. It's a minor gain, but it's working for you every time you switch something on.

HTH.

Thanks for your reply, the stress had eased somewhat! The reason for my concern wasn't because of the power of the drill, it was just that with another electric tool it got me looking at the garage, it's supply and demand as a whole.

Coincidentely, there is a friendly sparky on site today. I spoke with him and he basically has said the same as you. It appears ok in theory, but fitting a garage consumer unit and ring would be beneficial and he also suggested having an electrician inspect it.

Cheers

[Spearos]

Starter for 10;

Garden/ garage circuits should be fed off a 30mA RCD. It therefore sounds to me that this needs closer looking at!

I'm really going to show my ignorance here, but would an RCD protected consumer unit suffice? Or is it a requirement to have a dedicated RCD?

[TheRecklessEngineer]

An RCD consumer unit would suffice...but if you have a fault, it'll pop out the lights as well. Not ideal in a workshop environment.

RCD to ring main, MCB to lights.

[Hybrid_From_Hell]

Can't you do what I have ?

30 Amp supply into RCD consumer unit via amoured cable

Have Commercial RCD Trips - ie house ones trip out with big welders etc starting up

2.5 cable limits what you can safely draw, why not up to bigger amoured cable ?

then as moi :

30+ amp is split into 6 amp for lighting circuit, then other RDC "Circuits"

1 x welder / compressor

1 x Plasma

1 x 2 ring mains

etc etc

If I ping a circuit only that circuit trips out ?

Nige

[ejparrott]

In the house I have a split consumer unit, saves the worry of lights going out. you have the RCD protecting the sockets, the lights are not through the RCD. If the welder/drill/heater/compressor trips a socket, you still have lights on.

According to the central cables chart I have next to my PC, a two core, single phase cable buried in ground has a current capacity of only 29amps, so the 32A MCB supplying the cooker outlet you fed the garage off is too big. your 4mm cable from unit to cooker outlet is fine, with a rated current of 38A in clipped direct mode, or 37 if in ducts or ground, but then your 2.5mm orange cable is too small.

Thats according to the central cables current carrying capacity in ampere chart I have at work, I'm no sparky either. you can find the chart online at central cables website, where i sourced it from. My workshop has a 32A MCB, supplying a 4mm armoured cable in ground, rated at 37A capacity.

[Spearos]

Interesting... Very good point erparrott, the 32a MCB will allow more current than the 2.5mm cable is rated for so this is something that will need to be addressed. Easily put right I guess by laying 4mm SWA as HFH suggests. However this will no doubt involve some fun and games in the garden with the various 'obstacles' out there.

I'm confused about the RCDs/MCBs though

Would having an RCD garage consumer unit will negate the need for an RCD on the circuit at the house consumer unit?

It appears the 2 way RCD garage consumer units I've seen have an RCD on the supply and one MCB on each outlet - does this mean if the RCD trips then power to both MCBs/circuits will be cut? Or are they like the split house consumer units where the MCB for the lighting doesn't go through the RCD?

It seems the more I read the more I get confused!

[Cynic-al]

I'm not an electrician and haven't read 18th edition so don't take this as gospel or even good advice but things to think about;

Since 2004? lots of work undertaken in a domestic property (certainly new circuits and external circuits) should be tested and issued with a certificate under the part P regs. This can be done online by a registered tradesman or if you do the work yourself you can call the building inspector from your local council who for a fee will inspect it and provide the certificate. That said all of the electricians I have spoken to personally say don't bother, now that the HIPS have gone its unlikely to cause you a problem unless you have a fire, they prove it was the electrics and they prove you did it. Lets face it, they also recommend getting your house wiring inspected every 10 years and who does that?

So with that out the way I don't look at what I'm running, I look at what could be run, it's ok saying I don't weld and change a wheel at the same time but if the compressor kicks in whilst your welding or you have a mate over you could melt the cable. I've done it by leaving cable on the roll, entertaining in its own way

If I were you I would put a 32amp breaker in your fuse box on the none rcd protected side (stops you having to walk back to the house if you trip it), run a 4mm (should be fine for a 20m run) underground cable (i ran mine in a duct so that I can also pull other cables through), direct from the consumer unit if you can, if it has to go through the cooker switch I would take the cooker switch off and put a blanking plate on so that it can't be used, to a consumer unit in the garage. I got a steel bodied 7 way MK 16th edition unit for a fiver off ebay, then put a 32a rcd in place of the main switch (ok on MK boxes due to contactor gap, not sure about other makes). then a 6 amp breaker for the lights and 16amps for you socket rings. I would stick with type b breakers unless you get a problem.

I believe under 18th edition the house consumer units have to have atleast 2 individual rcd protected sections to get around the problem of the lights going off all over when it trips out but you can buy individual mcbs (mcbo) with the rcd built in.

[Spearos]

Of course any work I do will be reported to the building inspector! I'm surprised how long it took for someone to mention regs, it seems some people on other forums get really excited when you mention power to your garage/shed! I like the no nonsense approach of the Land rover folk!

Cynic-al I take your point on what could be ran, however the only thing that is left plugged in is the radio so I suppose that minimises the chances of multiple items being used at once.

With regards to your suggestion of getting a 7 way consumer unit etc, what would be the advantage of this over buying an RCD 2 way unit? PS like the idea with the ducting

Something to add is that on the TLC website it has 2.5mm 2 core SWA and 2.5mm 3 core SWA rated at 36A and 31A respectively. So it seems there is a bit of variance on the capacity of cable, or SWA cable at least - as mentioned previously the Central Cables website says 29A?

Now as said before I haven't a fookin clue with electric theory but if I were to have a 2 way unit in the garage with a 6A and 16A breaker, surely it would not be possible to 'pull' more than 22A through the 2.5mm cable?

[Les Brock]

I am an Electrician

There are no 18th regs only BS7671 17th edition amendment 1 - 1st Jan 2012

I would be upgrading the SWA feed(taking into acount load and volts drop) , Isolating the incoming earth from the house, putting down a local earth spike, fitting a RCD DB and making the garage a TT earthing sytem in its own right, so no tripping in the house...

Quick cable calc attached if it helps, may need confirmation tho as I have just chucked in figures you quoted above so dont take it as gospel (disclaimer )

Job done

[Hybrid_From_Hell]

<cough>

Ebay + 'Old colours armoured cable' search .....may be usefull

<cough>

Nige

[Spearos]

Well plenty there to go on with, lots to 'read up' on although I do feel I now have a good idea what would be ideal so a big thank you to everyone who's replied. Top bombing!

I like your thinking Nige, I like it a lot!!

[Cynic-al]

Probably why I've never seen the 18th kicking about then I did say I wasn't a professional

Old coloured wire sells for silly money on ebay!

I went for the 7-way as it was what I could get cheap with a metal body, the metal bodies are easier to terminate the armoured cable, the standard house type ones are made from pretty crummy plastic, if you buy a plastic one look to see if it has the right size round hole for your cable to come into. The one at my house end didn't so I put a strong terminal box below the consumer unit then just took the cable tails in. If you want to get around the regs just take your cable into a 3 pin plug and plug it in

The advantage of more switches is you can split things up more, not necessary but handy to still have a working socket when your fiddling with one circuit, being able to have outside supplies on their own switch or being able to run dedicated supplies to high power devices.

You know if your on the limit of your underground cable as the ground above it never freezes

[Spearos]

Ok I'm slowly getting a plan together, just a quick query.

I reckon I'll need to run 4mm cable for the ring main, I plan to run it in conduit and as I understand it's standard practice to use singles in conduit? Trouble is 4mm single in red seems difficult to come by so is there anything stopping me splitting red/black T&E into singles?

[ejparrott]

Why do you want to run it in red? Brown is easy to get.

We have singles and T+E in conduit at work, the latest ring main is T+E in 25mm round plastic, 'cos it was easier overall.

[Spearos]

Why do you want to run it in red?

Old colours, would then look as though it's been there since before 2004 Or am I missing something?

[ejparrott]

With the disappearance of HIPS, I would't have thought it mattered....you could buy brown/blue wire before '04 anyway?

[Spearos]

With the disappearance of HIPS, I would't have thought it mattered....you could buy brown/blue wire before '04 anyway?

Good point, however I have already secured some old colours SWA so I think I will continue with that 'theme'. As for your other comment - I didn't know that. This is all new territory for me.

However I have a good idea of the bits I need and how I'm going to install it now, the only thing that I'm unsure of is the lighting circuit. As I will be using 2 way switches for some of the lights I plan to use singles, what (if any) are the implications of me buying a bulk reel of say black cable and using that thoughout the lighting circuit, with some insulating tape of the correct colour(s) for identification?

[ejparrott]

I don't know about insulating tape, but it is quite normal to find the blue wire of a 2-core/3-core cable running to/from a light switch sleeved with brown sleeving, to indicate that its a live. To aid tracing a small amount of blue is left showing. The same was true with red/black wiring, the black would be sleeved red to show that it was sometimes live. I'd buy a reel of red and a reel of black, you'll use an awful lot more red than you think!

[Spearos]

I'm hoping to get on with this in the near future so will be ordering cable soon. Just need to get an idea of where and how I'm going to run the cables. So today I have come up with this - working bank holidays isn't so bad

The cables will be 1.5mm T&E or 1.5mm singles - with all the lights on I come up with a load of about 5.5A so a 6amp breaker will be fine as will the 1.5mm cable.

The consumer unit is a 2 way, 30Ma RCD protected item with a 40A Main switch, 1 x 6A MCB and 1 x 32A MCB.

I plan to install 3 x 2 gang sockets, wired radially in 4mm T&E ran in conduit up to joist height.

Would be good to hear any comments... But please be kind, as I've said before this is all new to me!!

[ejparrott]

I would run the main feed to the consumer unit in 4mm² cable for sure, but the feed to the lights and the feed to the sockets only need be 1.5mm², as long as the sockets are wire as a ring main.

[Spearos]

Thanks for all your comments ejparrott.

So my proposed diagram looks ok?!!

However I think I will wire the sockets on radial circuits as it'll mean less cable, less running of cable and therefore less 'moving things around' - there's a lot of stuff in my garage!