Why Naim recommends 100A RCD isolator for Hi-Fi dedicated mains if there is only one 32A MCB in the chain?

It comes down to what we are protecting. I think the 10mm cables would be a neater fit and tighten up better in a smaller unit. I have not seen a 100A unit, though I would be concerned with a sloppy connection.

The electrician knows what he is doing.


Many thanks for the input @Gigantor

The 100A switch is physically the same size and will be a perfect fit. 100A is a better option as mentioned above for what is trying to be achieved here, ie, sound quality uplift. Of course on a normal installation a 40A main switch on a 32A mcb would meet requirements and regulations.

Dedicated mains radial completed and I’m amazed at the SQ improvements. I’m getting much more defines bass, improved clarity and better sound stage improvement. Overall a lot more enjoyable listening experience. Pound for pound the most worthy upgrade. It cost me less than £600 for a ~35m of 10mm SWA run with a new Hager Consumer Unit (CU). If you are hesitating, go for it it is a worthwhile upgrade.

Next on my list, I guess, is to get a Fraim (or perhaps Simrack) since my kit sits on a rather average TV stand and I hope I can get as much SQ improvement from that as I did from the dedicated mains.

PS I still have a quiet “hisssss” from the SN3 when the NDX 2 is in standby but I have to put my ear right next to the tweeter to hear it and it doesn’t bother me at all. Should the dedicated mains have eliminated that? The HiFi CU earth is connected directly to the eaerthing terminal at the meter not via the excising CU.

That will always be there on a Naim amp. It’s to do with a no comprise circuit design and is never noticeable when playing. They could easily get rid of it, but the consequence will then be a SQ drop, so we all accept it.

What a dedicated circuit may do is reduce the Hum you may get from the transformer - but no guarantees

Many thanks for the info @GadgetMan this interesting and good to know.

The switch might be the same size, but the CU is not rated for it. A suitably rated CU is physically larger. At least by the data sheets I read.

Warm regards,


Mitch, the actual consumer unit should be fine, as should the busbar, but the neutral conductor may possibly need upsizing if using the full rated load, but the electrician should have noticed this if needed. The advice as always is if unsure then consult either an electrician or the manufacturer.

It really is great isn’t it, and it gets better too. The sound may be a bit tight and mechanical to start with at times but it begins to loosen up and flow nicely over time. Mine took a few weeks to fully settle, and I’ve never looked back. Its probably the best value for money upgrade I’ve done.

Indeed couldn’t agree more. Thanks for the very helpful advice.

Of course non of this is posible in some countries where the base electricity bill is based on the amperage of the CU.

If I installed a 100A CU I’d being paying about $200/month just for the privilege before electricity. I’ve yet to see a circuit bigger 20A too for domestic use here.

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