MK garage consumer unit tripping out

[sjromaine]

Have fitted an MK garage consumer unit today. 40A/30mA RCD model with 2 MCBs, 16A + 6A. Have wired 6A to two flourescent tubes in parallel via a simple indoor metal case switch. Have dummy wired one double socket merely as a test after lighting kept tripping when switched turned on. No matter what I plug in the main RCD trips out as soon as there is load througb the socket as well. I suspect I have a feed problem. Unit is connnected to spare way on fairly old Wylex main unit in house using 6mm T&E. MCB in main unit is 32A - this is not tripping. I suspect that I may have mis-wired the incoming feed from the house CU where it arrives at the garage CU. I have it earthed to the earthing bar in the MK garage unit, top right. Live feed from house runs into the top right connection on the MK RCD. Neutral from the main CU runs into the neutral bus bar above the RCD in the garage unit. Should I be running this neutral feed directly into the RCD instead? If so where?

Cheers in advance for any answers which get me nearer the holy grail of a wired up garage!

 

[Christhescott]

Yes live and neutral supply should go into the top of the rcd mainswitch, then out of the bottom of the rcd a neutral tail should supply the neutral busbar.

 

[PrenticeBoyofDerry]

Is the RCD also operating as the main isolator for the unit?
If so, I would suggest you check the polarity of the isolator.
Does the bottom left hand terminal of the RCD/isolator terminate at the live busbar?
Does the bottom right hand terminal have a cable connecting in it to the neutral busbar?
or vice versa, that should give you a clue on how to connect the live/neutrals in the top terminals.

 

[EFLImpudence]

Is the RCD also operating as the main isolator for the unit?

OP said it was/is MK Garage Unit - so yes.

If so, I would suggest you check the polarity of the isolator.
Does the bottom left hand terminal of the RCD/isolator terminate at the live busbar?... ...or vice versa.

According to pictures on the website RCD is on the left therefore busbar on the right. So Live on right and Neutral on left of RCD.

 

[RF Lighting]

Can we have a photo of the inside of your new CU please.

 

[sjromaine]

Damn - you guys are fast. Difficult for me to produce a picture at short notice. Here it is in words!

From left to right the unit has....

40A RCD - 16A MCB - 6A MCB

RCD has 4 connections (2 at top, 2 at bottom), MCBs have 2 each.

RCD came with neutral link cable running from bottom left connection to neutral bus bar in top of unit. I have connected live feed to top right, bottom right is connected via live bus bar to both MCBs - this is as it was in the box as bought. At present top left connection is empty but I suspect this is the one for the neutral feed wire. Some of your responses seem to confirm this suspicion. Sorry I can't do a picture but obviously it's kind of dark in my garage right now

 

[sjromaine]

Prentice: at present bottom right goes to live bus bar. Bottom left to neutral link cable (supplied) and then to neutral bus bar.

 

[JohnW2]

At present top left connection is empty but I suspect this is the one for the neutral feed wire. Some of your responses seem to confirm this suspicion.

That's your problem.then. You'r neutral feed should got to the 'top left' of the RCD, not to the neutral bar.

With what you have done, the neutral current is not going through the RCD. That means that whenever there is a load, there is a misbalance of the L and N current going through the RCD (since the N current is always zero!), causing the RCD to trip.

Kind Regards, John.

 

[EFLImpudence]

At present top left connection is empty but I suspect this is the one for the neutral feed wire.

Yes it is.

If you have Neutral feed in the Neutral bar the RCD WILL trip as the Neutral 'return' current is not going through the RCD.

Edit - too slow again.

 

[sjromaine]

Thankyou so much gentlemen. I am happy that I can manage the basics of wiring something like this without actually creating anything hazardous but from time to time I just need a nudge in the right direction. If I have any further issues I'll know where to come.

I'll try this fix out tomorrow if I have some time to play around with it all.

 

[JohnW2]

I'll try this fix out tomorrow if I have some time to play around with it all.

Provided that you make sure the power is off, so that you survive the exercise, it should only take you a couple of minutes - (provided it reaches!) you literally only have to move that one cable - so that the neutral feed goes to the RCD instead of the neutral bar.

Kind Regards, John.

 

[EFLImpudence]

Just for the record -

There are actually a lot of tests that should be/have been done before switching on the installation.

Also, there are the Building Regulations.

Then, perhaps you don't have a record player.

 

[JohnW2]

There are actually a lot of tests that should be/have been done before switching on the installation.

Very true - but history cannot be changed and, as we know, the installation has already been switched on.

Kind Regards, John.

 

[sjromaine]

Couldn't resist it - so headtorch on and out I went. 10 minutes later - we have light!

You guys are STARS

 

[sjromaine]

On the subject of regs.....

I did try going the 'legit' route on this. I got quotes from two 'electricians' recommended by a third party. It turned out that both came up with the exact solution I had already researched for my wiring needs. I would have booked one of them but NEITHER could actually produce any certification after the job was completed. As this was the main driver for trying the proper route I lost interest in pursuing and went for homemade. After all our plans were all the same.

I'll not be trying to sell in the near future and so the certification isn't an absolute must. That said I am more than happy to listen to opinion on the subject. I'd not like to even pretend I am an electrician but I am a degree level scientist with a decent grounding in physics and hence know most of the whys/wherefores of electricity - especially how bloody dangerous it can be if not handled carefully.