This is more than likely an earth leakage problem, most probable is a neutral to earth, this is normally caused by an appliance but could be wiring. Before changing wiring the fault should be identified. As suggested above check the 250 in the house first.
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I understood that. My suggested test was to see if the 250 trips that when plugged into one of the house controlled circuits. If it does it is the 250 and earth leakage problem, if not then …???
I don’t think the electrician’s suggestion will solve the problem: if it us the 250 it’ll probably trip the RCBO.
I understood it trips the new spur’s dedicated consumer unit RCCB (as well as the main CU’s) - that is nothing to do with being fed from a breaker on the main CU. (Though as HH indicated, feeding via the main CU breaker is only half the job, negating having a separate CU - it might as well have been a radial curcuit taken direct from the MCB used to feed the new CU)
I don’t think there is a fault here so much as a problem with the inrush current which unsurprisingly is tripping the RCD. When you take an RDC protected slot in a consumer unit and use it to run a separate consumer unit with a further RCD it’s no surprise that it trips. I think the electrician’s suggested solution will sort it, just not as well as separating out the circuit from the main consumer unit.
Thanks for everyone’s input here really appreciated.
Not sure which way to go now though 
Kind regards
Tony
Show him my photos and say ‘I’d like this please’. It’s really very simple.
May I ask for the advantage of this? Thanks!
I am not sure but I might not have asked the sparky to do that… It has been a few years but I can’t remember…. Argggh… I might get this checked and possibly corrected when he have him around…
Believe its all about isolating the hifi from the electrical noise generated by household appliances that share the ring with the house CU
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You might be surprised how many “certified” GFCI breakers are defective (at least here in the USA). I had to take two back before I found one that worked!
Pretty much yeah. It’s often called a ‘clean earth’
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My suggested test to identify if the 250 is faulty costs nothing and doesn’t take long…
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While I have plenty of experience doing a big rewire at home, with many cu s, I am not a qualified electrician (my sparky tested all and issued certificate).
However I am familiar with troubleshooting, so a few tips. Establish what exactly is causing the trip. Follow this one first.
Second, If the 8 way block is full, unplug first the TT and use the free socket for NAP250? At some stage early on, change out the mains lead on the NAP250.
Problem remains? Then plug back in TT and remove NDX +XPS, keeping NAP250 plugged into the block.
Go step at a time, document results from what you do; try all variations. Make sure your switch on order, is exactly the same as per when the fault occurs and switch on should be staggered.
Third, eight way block, where is that plugged in - the other half of a double socket in to which you also have the NAP250 plugged in?
Is this a quality socket (for NAP250) or el cheapo? If there is a less than satisfactory rear connection into this socket, that could cause an issue.
Unless you really know what you are doing, best to get a sparky to check by investigating the socket - or use a different socket anywhere.
Finally, I am puzzled that your electrician can’t detect any abnormal readings. Has the sparky run a full set of tests - indeed does he really know how to do the various tests on a domestic circuit, which highlight all or any issues? It’s a skill, some are better testing than others.
If you can, it may be appropriate to get an alternate sparky to test your total environment and recommend any changes.
ChrisSU makes a valid point, logically correct but I have seen it required, viz separate cu close to the meter and another cu at the other end, in this case the garage; both fitted with RCD.
A second sparky would address the validity.
Important point though, if a sparky tests your circuits - do remember to totally ‘unplug’ all electronics first.
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This wasn’t done when we first had the hifi CU installed; it was connected to the house earth of the existing fuse box. I later read about how it was better to connect the earth direct to the meter, so when we had our old house fuse box replaced by the modern unit in the picture, I had the hifi earth run to the meter. Memory is shaky of course, but it seemed to make as much, if not more of a difference than having the dedicated CU in the first place. The background noise seemed to drop away, so music can fade to absolute silence. The noise is something you don’t really realise is there until it’s not there, but the results were quite noticeable and very worthwhile.
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I cant help myself from putting my 2 pence in.
My understanding is that it’s the 100ma RCCB in the garage that’s tripping. So is the feed to the garage RCD protected? If so why would you need extra RCD protection simply swap out the RCCB for a main double pole switch and your good but my gut tells me it’s not as the RCCB or RCD in the house would trip first.
The fault is between the CCU in the garage and the following circuits so a simple insulation resistance test and RCD ramp test would find the fault. And it should be easy to find as a 100mA RCD is the maximum premitable within a domestic environment so my guess would be water pen or a freezer ( white goods ) tripping it but maybe the RCCB is over sensitive so a ramp test will find that out.
Is there anything else coming off the CCU in the garage like an outside socket or lights etc. These can all add a little leakage and turning on the hifi pushes it over the limit.
The RCCB feeds all mcbs after it so all those circuits need investigating.
Finally all MCBs and RCCB units sound the same as the switch plates are the same size and must take either 3k or 6k short circuit capacity it’s the control circuit that’s different.
A type C would be preferable for a Naim hifi as it will stop the MCB from tripping when switching on but 16,20,32 or 40amps will make no difference to the sound. So keep within the regs and stick to a 32amp type C on a ring and you will be fine.
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The eight way block containing all pieces of equipment apart from NAP250DR has a Russ Andrews Superclamp going into the other socket which is a double socket.
The NAP250DR goes into a different double socket where the other socket also has a Russ Andrews Superclamp going into it both obviously to protect against mains spikes.
Regards,
Tony
Does the tripping when the NAP250 is switched on, occur with both superclamps removed per chance?
I would remove all the Russ Andrews kit and use a normal 4way and switch on the kit one by one with a second or two in-between. See if that resolves the issue first, as it could be a faulty cap in the Russ Andrews that’s leaking to earth as they do have wacky earth arrangements.
If all ok just add extra sockets for each bit of kit or make up a fancy extension lead.
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Havent tried this but will try it. Thanks
Tony
Thanks for your advice I’ll try it.
Regards Tony