NAP 250DR causing power to trip at switch on

Check what trip thingy you have in your consumer unit. You want a Type C. Mine is a Type C 50 amp. If it’s the wrong Type it’s more likely to trip when it shouldn’t. You can change them yourself if you buy a different one, just turn the power off first. 

Thanks HH. That’s pretty much what my search is telling me but think I will get the electrician  who fitted the spur back to check and rectify.

A Type C MCB worked for me, and was suggested to me by Naim support. Before I fitted it, there was about a 50:50 chance that switching on the power amp would trip it. Since fitting it, no trips at all. 

Thanks CHRISSU. That is reassuring to know. My electrician has been informed so just trying to arrange a date to get him in.

My 555 does this nearly every time I turn it on...

Are you leaving a gap of about 15 seconds between 555PS and 250 switch on? Mine trips if I don't.

I am usually turning the power amp (300) on last so 555 is first and trips the switch on its own

An important question: by safety switch do you mean an RCD (residual current device) if there is one, or just the miniature circuit breaker (MCB)? Former will say something on it like 30mA and to test regularly by pressing a button. Modern circuits commonly have both, though a hifi dedicated spur is permissible without an RCD as long as the sockets are marked to that effect. And it can be confusing because the RCD and MCB are sometimes combined into a single device known as an RCBO (residual current circuit breaker with overcurrent protection).

if it is the RCD being tripped, that is not the inrush current of the power supply, but indicates a fault creating an leakage current which potentially could be a serious safety hazard. The fault would be whatever is being switched on, if only happening at the time of switching it is often the switch itself that is faulty, but it could be anywhere the mains goes after that. It is that that would need to be looked at, rather than the breaker that is tripping.

But if it is indeed the MCB tripping then one more suited to the inrush current would be appropriate, as suggested in another response, subject to the wiring being adequate fir the potential maximum overload current, which most likely it is but your electrician can advise if you are unsure.

It sounds as though you need to look at what sort of trip you have in the consumer unit. The 555 should not cause a trip. 

When I had a 'Geddon power supply for my LP12 it too would frequently trip the MCB when powering up. I eventually tracked this down to a very poor connection within the wall plug. Only a few strands of wire were in contact with one of the pins. Must have slipped past Naim QA somehow. Anyway, I remade the connection and problems solved. Not saying this is the cause of the fault in your case but it might be worthwhile to check the plug to see that all is OK. 

pixies posted:

Thanks CHRISSU. That is reassuring to know. My electrician has been informed so just trying to arrange a date to get him in.

You will need your electrician to agree that an MCB is acceptable rather than insisting that you must have RCD protection. Some have a rather rigid interpretation of the regulations, and may tell you that (a) an RCD is required and (b) you are a nut case for thinking that your hifi needs any such special treatment. 

nut case it is then, but I try not to admit it to too many people ????

Quick update. The trip thingy in consumer unit has been checked by electrician and has been changed from type B to type C and problem resolved! So thanks for all the positive suggestions and advice.