Garage - Consumer Unit.

[loyalroyal13]

I've purchased and had installed an MK IP65 Garage Unit 40A 30mA RCD+1x6A 1x16A SP MCB.

From this I have armoured cabled feeding an outdoor dual socket. This will be used to power LED lights from a transformer. The transformer and lights all work fine from a standard mains ring.

The RCD of the Garage Unit trips when the lights are connected and switched on in the new outdoor socket.

Should I really be using a 32A MCB rather than a 16A for these lights?

 

[jj4091]

Depending on the type of lights you are using(presumably through a transformer) then I would have thought you would need a 6A rather than 16 or 32 if the socket is going to be used exsclusively for the lights, if not then stick to the 16A. Does the rcd trip with another appliance plugged in, if so I would have thought the problem was the socket or cable to it.

 

[loyalroyal13]

Yes it trips with an electric drill connected as well. So it could be nothing to do with having two differing loads. A 32a in the main consumer unit and a 16a mcb in the garage unit?.

It's not easy to test the armoured cable because it's burried in conduit under a patio now

 

[JohnD]

RCDs trip if there is an earth leakage.

MCBs trip if there is a current overload or short circuit.

If you have a fault that is causing the RCD to trip it is not caused by excess loading and is nothing to do with the MCBs or the loads.

a cable can be tested even though it is buried in concrete. If it is fairly new, then unless you have been attacking it with drills or pickaxes it is not likely to be faulty.

You say the RCD trips with two different loads. It would be useful to test these loads on another RCD, either within the house or on an RCD adaptor that you can get in the Gardening tools section of your DIY shed.

I would suspect a fault at the socket first, perhaps an incorrect connection.

If you can post a pic of the inside of the CU (cover open) and of the inside of the socket (cover open) both showing the wire connections it may help suggest what the problem is. Please also show how the armour has been terminated at each end.

Did you install it yourself?

 

[loyalroyal13]

I've run both the drill and the lights transformer from the mains ring within the house and it does not trip the main consumer unit RCD.

I can take a photo of inside socket and the CU about 4.30 today, I'll upload it then. A friend actually installed it who used to do a fair bit of sparky work in the past but this one has him stumped. he suggested upgrading the MCB from 16A to 32A as a first thing to try.

 

[bernardgreen]

A friend actually installed it who used to do a fair bit of sparky work in the past but this one has him stumped. he suggested upgrading the MCB from 16A to 32A as a first thing to try.

Suggesting to upgrade to 32A suggests he is a numpty who does not have enough knowledge to design a safe installation.

Odds are he has messed up the wiring around the RCD in the garage.

Most likely the earth and neutral have been confused with each other.

He may even have not put the neutral through the RCD but taken the incomer neutral straight to the neutral bus bar. ( yes I have seen that done )

 

[loyalroyal13]

I've taken some images of the garage CU and the outside socket but I'm struggling to post them up. The images can be viewed in the following location though.

http://picasaweb.google.co.uk/AdeleandDarryl/ElectricProblems

 

[JohnD]

looking at the pic of the CU, I can't see the supply cables. where are they?

btw the termination of the armour is not correct.

 

[loyalroyal13]

I've added another photo that hopefully shows the incoming feed. When you say the termination of the armoured cable are you refering to the electrical tape around the end?

Sorry for all the noddy questions but I've been left with this situation at the moment.

http://picasaweb.google.co.uk/AdeleandDarryl/ElectricPics2

Thanks

 

[JohnD]

nope, still can't see them. can you take a pic from above, so I can see the tops of the RCD and the MCBs?

If you can hold pencil tip on the incoming cable I may see what you mean.

If you can isolate the supply in the house, and take off that plastic guard at the bottom of the enclosure, that will also help.

Also, can you stand back and take a wider view, so I can see the cables on the wall, and where they enter the enclosure? It is probably marked "warning: Isolate supply before removing this cover" or similar wording,

p.s. the armour should be terminated in a metal gland and connected to the earthing terminal in the CU. As well as earthing it, that gives the advantage that you do not have a thick and stiff armoured cable to deal with inside that small enclosure. Armoured cables are often terminated in a metal box beside the CU to make it easier, and just the cores taken through.

 

[loyalroyal13]

I've taken another look at it, and I'll try and describe it;

Armoured cable:
Live - Into 32a MCB
Neutral - Furthest right neutral on the left hand bar.
Earth - Top right earth in the picture

Live Feed:
Live - Into top right of the RCD
Neutral - Second from left neutral on the left hand bar
Earth - Furthest left on the right hand bar

There is also an earth cable that runs from the Garage CU to the Main CU as well. This is located in the second from the right on right hand bar.

Hopefully this all makes sense?

 

[Steve]

if the feeder goes straight into the neutral bar the RCD will trip all the time. It MUST go through the RCD.

 

[loyalroyal13]

Thanks to Crafty and JohnD for all your help.

It was the neutral feeder that should have been in the RCD.

Thanks, I now have working lights!!

 

[bernardgreen]

He may even have not put the neutral through the RCD but taken the incomer neutral straight to the neutral bus bar. ( yes I have seen that done )

Seen it twice now.....

 

[CallEdsFirst]

Can I just add to this that its NOT SWA, but SY cable, not mechanically protected to nearly the same extend. Instead of steel wires around the cores, you just have a steel braid, which will a) not stop a spade and b) still need to be earthed for the same reasons SWA armour is.

Not sure about the UV qualities, I'd have to dig out my data sheet, but its just a clear pvc outer sheath to the best of my knowledge.