Is it safe to use a NAP 250 DR on a 13A circuit?

Moderated Post:  Adam, I have removed your post.  Are you fully qualified and conversant with electrical regs in Switzerland?  If so, my apologies.  But if not, best not to give advice here as it may well be contrary to regs and unsafe.

You should have no issues what so ever. The NAP250 has a 400VA transformer, this equates to a maximum of 3 1/2 amps at 120 and 2 amps at 208. 13A is more than sufficient for the NAP as well as a preamp, turntable and other accessories. If there are more than just your Hi-Fi on the spur then the load of those will determine whether you overdraw the circuit.

DUPREE posted:

You should have no issues what so ever. The NAP250 has a 400VA transformer, this equates to a maximum of 3 1/2 amps at 120 and 2 amps at 208. 13A is more than sufficient for the NAP as well as a preamp, turntable and other accessories. If there are more than just your Hi-Fi on the spur then the load of those will determine whether you overdraw the circuit.

The problem as I understand it is not the steady state current draw, its the inrush current, which is relatively high with toroidal transformers. If this coincides with the voltage phase at 0V then the current can be very high. I dont think you will damage the electronics if it trips the breaker but it could become annoying if you have to keep resetting it.

Moderated Post : See above comments

Increase the amperage of the protection switch without change the wire section is totally wrong in terms of safety and logic.

You must ask at a qualified electrician.

I think you maybe have to check the characteristic of your protection switch (are exactly classified in terms of tolerance of inrush current, e.g. type A or B or C).

Your type is A! The less tolerant (the faster in trip). But change only this is not the solution from a safety point of view because it must selected according to the general circuit breaker.

Richard will likely be on this when he comes on.  The breaker is normally sized for the guage of wire used on the circuit.  You must not arbitrarily increase the breaker to higher current rating.  If you turn on each box one-at-time and wait Maybe 20 seconds or so between boxes, you may be OK.  Nothing should be harmed if the breaker trips, but of course there will be no music.

All the above cautionary warnings are correct,  don't do this without a qualified electrician confirming.  However having a 13A breaker is not logical.     I doubt the dedicated circuit is 2.5mm,  its normal to have 4mm or larger.    The normal CB current rating for a 2.5mm T&E radial circuit is 20A,   a 2.5m T&E ring circuit is 32A,  a 4mm T&E radial is also 32A  ........  So subject to a qualified electrician confirming,  there is scope

I agree. "Overbuilding" a circuit with a higher rated breaker without properly gaged wire seems reckless to me. The breaker is protection against overload and I can't see where adding a higher rater breaker would play into any measure of sound quality. The circuit wire diameter per length is the limiting factor. If you want to increase the breaker capacity, you should also increase the wire gage to the allowable limit, otherwise you risk overheating the wire and chance of a fire.

Moderated Post:  Joe, you know why...

The circuit breaker should as said above match the wiring.. However it is inrush current that is needed to be handled which is over a tiny period of time. I understand normal circuit breakers handle 8 to 10 x rating for inrush surge, however for some high efficiency transformers / motors this is not enough. There is a variant to many circuit breakers labelled 'HM' or 'High Magnetic' and these appear to allow for greater surge currents without tripping, whilst still providing the right longer period protection for the wiring.

However I need no special consideration for my 250, but I connect to a ring circuit as opposed to a radial.

Simon

Modern MCBs  (miniature circuit breakers) and RCBOs (MCBs with built in RCD) are rated types B, C or D. The ones most commonly supplied in domestic consumer units are generally Type B unless otherwise specified. The types relate to reaction to the switch-on surge before tripping: B=3 to 5 times the rated break current, C=5-10x and D=10-20x. Most manufacturers make at least both B and C, I'm not sure if that also applies to D.

Changing the MCB type would be the correct approach to deal with very high inrush current, NOT changing the rating to a higher one than necessary, and certainly NEVER changing to a high rated one (or higher rated fuse) unless advised by a qualified electrician or you have equivalent detailed understanding and knowledge of the specific wiring: the maximum safe breaker rating cannot be determined from simply the size of wire, as it also depends very much on factors related io installation, such as how the cable is fixed (at all stages of its routing), whether it is enclosed, whether there is thermal insulation (e.g beneath the insulation in a loft), the maximum ambient temperature where it runs (e.g loft in summer), and how many cables run together. Mike-B's figures are not correct in all circumstances: e.g if alone in a conduit in an insulated wall the maxima for a radial circuit would be 18.5A for 2.5mm2, and 25 for 4mm2, assuming a maximum ambient temperature of 30C. If more than one cable together, or higher temperature likely, the figures mould be lower.

I am moved to wonder if Adam's observation re oversized cables is either hype by the electrician, or lack of detailed understanding of the reason for the minimum requirements to meet EU law (which takes the various factors into account) compared possibly to previous practice. But even if true, it would be for the electrician to advise the maximum rating that the consumer could use if they wished, and never make assumptions. (Adam, I'm not suggesting for one moment that you have done otherwise, this just a cautionary note lest anyone be tempted.)

Innocent Bystander posted:

I am moved to wonder if Adam's observation re oversized cables is either hype by the electrician, or lack of detailed understanding of the reason for the minimum requirements to meet EU law (which takes the various factors into account) compared possibly to previous practice. But even if true, it would be for the electrician to advise the maximum rating that the consumer could use if they wished, and never make assumptions. (Adam, I'm not suggesting for one moment that you have done otherwise, this just a cautionary note lest anyone be tempted.)

I think my case was a bit more specific - perhaps I wasn't that clear in my previous answers. The entire network and power cables were designed from scratch. I told my team what I wanted to acheive. Their answer was that in order maintain flexibility they will fit decent and high rated power cables throughout, at an almost no extra cost. Their explanation was that in such cases it is perfectly acceptable to overspec the cables.

For regualr circuits - regualr breakers were fitted. For special purpose circuits (ovens, airconditioning units, audio) secial breakers, rated for the sepcific use, were used. 

Thanks for clarification, Adam. And indeed there is absolutely nothing wrong with using higher rated cables than the breakers or fuses fitted - just a need to be aware of what is the safe maximum if deciding one day to change to allow higher current, 

I have edited and removed various parts of posts on this thread.  May I remind members that unless you are qualified and conversant with the specific electrical code that applies to where the OP lives then please don't go giving specific electrical installation advice, as it just makes for more work as I remove it from the forum.  Thanks.

Innocent Bystander posted:

Thanks for clarification, Adam. And indeed there is absolutely nothing wrong with using higher rated cables than the breakers or fuses fitted - just a need to be aware of what is the safe maximum if deciding one day to change to allow higher current, 

Also keep in mind that the contact resistance of a CB is the same irrespective of its rating - the contacts are the same across the same make/model range,  its only the current sensing relay that changes.   So unless the CB trips due to switch-on inrush (or whatever)  up-sizing the CB rating will not do anything.   

Thanks to everyone for their thoughts and comments. I also want to thank Richard and apologise for adding a little more load to your day.

I called the electricians today and someone will come over to advise at the beginning of next year. 

The circuit is using 4mm solid core and runs exclusively in it's own armoured conduit. The conduit is buried in concrete under the floor. Fortunately it's a really easy conduit to work with so changing wires and breakers within the scope of our regulations should be fairly easy.

In section 2.4 of the Naim Power Amplifiers Reference Manual it suggests the following.

Transformer hum is not transmitted through the speakers and has no effect on the performance of the system; however, a separate mains circuit may reduce it. Such a circuit (ideally with a 30 or 45 Amp rating) will also generally improve system performance.

Within the limits/regulations of our electrical code should I be shooting for a circuit of 30-45 Amps?

It's worth keeping in mind that It's unlikely my system will grow beyond 2-3 boxes.

Greg, the recommendations given by Naim are soley applicable to the UK.  In the UK you can have a 30A or 40A circuit because ultimately the flex etc.. to any connected electrical items is protected by the fused plug, either 3A, 5A or 13A.  On the European continent, there is no such plug fuse, so Amperage has to be kept within safe limits on the circuit itself.

That means by all means ensure the cable can carry that current but, unless there is one also at the equipment end, have as low a value of breaker as approriate for the load - this is where a breaker that can withstand a higher inrush current can be beneficial, so that is something to discuss with the electrician. For negligible cost you could start with the lowest appropriatelt rated one, and change subsequently if it proves to be inadequate. It is always a balance between maximum protection and unwanted triggering.

@Richard Dane Good point! It also explains why in the German version of the guide has no specific recommendations for circuit capacity.

[@mention:41551091830475636] In view of Richard's comments, I think you are right, start small and work up. In the new year we will be doing a second round of home automation, entailing restructuring the circuits anyway. When I spoke to them today they indicated the'd done quite a few hifi circuits so hopefully they have some good ideas. I really wasn't happy with the company that put in the original circuit.

If we have had a power cut at home, when the supply resumes, my circuit break trips out, as 3 x 250's and 2 x Supercaps etc. all drawing "start-up" current is too much. I have to turn off all components, re-set the circuit breaker, then turn on the components one by one.
I'd have thought a single 250 would be just fine.