Rcd Tripping On Dual Board

[radiohead]

hi, sorry if my post was vague.

ive connected into the current downstairs lighting mcb at the consumer unit. it goes from the unit into surface mounted, mini trunking for about 300mm then into a double pole switched fused spur (fused at 1 amp.) Because i couldn't find a switched rcd spur, it then goes into an unswitched 30ma rcd spur.

it then goes into a wifi enabled switch wired in parallel with the pirs so we can turn the lights on and off via mobile phones and alexa. lots of boxes i know but it's out of the way so we don't care.

it then goes into some more mini trunking for about 750mm into a box. behind the box is the hole to the outside.

I dont think it was vague, it was clear to me that you had wired from a non RCD protected 6a MCB in the DB to an RCD FCU....and from there to your lighting system. Sounds perfectly reasonable and safe.
As has already been stated it would appear the trip on the RCD side of the board is unrelated, occasional random tripping of RCD's is common and does not always indicate a fault. But if it is a regular thing clearly it will need investigating, firstly by carrying out an insulation resistance test on the entire installation. A quick and simple test.

 

[richy3333]

@radiohead Apologies, maybe the description for me got lost in translation or scrambled at the border ?

So from what’s been said a new circuit has been created and is run in part of the house before going outside serving garden lights? But this new circuit as it exits the CU is not RCD protected at source contrary to the new requirement? It’s the fused down and RCD protected for the bit that goes outside?

The OPs bio says he is a practicing electrician - qualified. I guess I would just have thought he knew the Regs, had a knowledge of part RCD protected CUs and also how to do an IR test? Yeah I’m confused ?

 

[Williamshoeste]

hi,

it's not a new circuit. it's an addition to an existing circuit. if you're not going to help richy333 then please post elsewhere.

 

[richy3333]

I was trying to help, but I can't if I dont understand what you are saying.

Now you say it is not a new circuit but before you said 'ive connected into the current downstairs lighting mcb at the consumer unit'. That sounds like a new circuit to me even if it is 2x cables coming out of 1x MCB. OK its a radial with a branch at the MCB but you are still effectively creating a new circuit?

Sorry if you dont like what I said in post no23. I'll duck out now, just hope some customer isn't paying for this and its in your own home.

 

[ipf]

hi,

it's not a new circuit. it's an addition to an existing circuit. if you're not going to help richy333 then please post elsewhere.

Be it new circuit or not, domestic new wiring should be RCD protected at source. The point being made in the previous post, I'm sure. (#23)
As regards the tripping.....#2 sums it up.
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I was trying to help, but I can't if I dont understand what you are saying.

Now you say it is not a new circuit but before you said 'ive connected into the current downstairs lighting mcb at the consumer unit'. That sounds like a new circuit to me even if it is 2x cables coming out of 1x MCB. OK its a radial with a branch at the MCB but you are still effectively creating a new circuit?

Still one circuit rich, just a 'Jake the Peg'.

 

[Williamshoeste]

no it’s not a new circuit. Would it make you feel better if I made a radial off an existing light? It’s still the same additional connections regardless of where they’re made in the existing circuit.

you’re allowed to add a spur by connecting to the mcb in a consumer unit effectively putting 3 cores in one mcb. Do you consider that a new circuit too? It’s exactly the same as what I’ve done with the lighting circuit.

You guys are going to be minted if adding a single light to an existing lighting circuit may mean a mcb or consumer unit replacement just to give rcd protection. Unless of course the customer says no thank you I just want an outside light by the door.

I was just after some advice from people who have had domestic experience with led drivers, rcds and split boards. I don’t need snippy comments thank you.

 

[UNG]

So the "socket side" RCD tripped is the lighting MCB you connected to on the "socket side" of the CU as well? Otherwise for a spark your description and terminology is very confusing

 

[westward10]

Whether you have extended an existing circuit or created a new circuit is debatable what isn't debatable is that your part of the circuit, all of it requires additional rcd protection. The tripping of the rcd as stated in #2 is likely to be coincidental, is it still tripping.

 

[dodger421]

641.5 For an addition or alteration to an existing installation, it shall be verified that the addition or alteration complies with the Regulations and does not impair the safety of the existing installation.

To me that means if you add a light to an existing installation you need to ensure the altered circuit complies with Regulation 411.3.4. Effectively each final circuit supplying luminaires must have additional protection by RCD. I don’t see how that can be interpreted as anything other than having RCD protection at the CU for each lighting circuit.

You’ve added RCD protection for the actual lights via the spur but, as has been pointed out, the added bit from the CU to the spur isn’t RCD protected. Your additions must comply with the Regulations and as the final circuit includes the bit from the CU to your RCD spur your additions don’t comply.

And yes, that does mean if I were to add a new light to an existing circuit in a household I’d fit either an RCBO or upgrade the CU as required. Same thing if the main earthing and bonding isn’t up to scratch, that gets fixed before any additions or alterations as required by 132.16. If the customer says no thank you I’d politely decline the job.