Dedicated Mains Radial Problem

Lounge
1

I’m hoping someone with electrical knowledge can offer some constructive advice on an issue I’ve discovered with a dedicated radial circuit. I’ve a very low understanding of electrical circuitry so please bear with me…

Two years ago I moved into a new detached house and had the opportunity of specifying a dedicated radial for my Naim system, I’d experienced some hum in my previous property so wanted to address that and wring the best sound quality possible from my sytem.The radial install followed previous advice on the forum and the attached diagram, terminating in a two socket mains outlet in the lounge.

IMG_0116
IMG_01161314×728 145 KB

After moving in, I built and connected my system, all seemed well. I still had some hum from a NAP 250DR and a HiCap DR but less than my previous home, which was in a flat with shared mains.

Later, I had a local electrician replace the switched socket the builder had installed with unswitched. I also had an issue with the NAP250DR tripping the dedicated consumer board switch, the builder had not installed a Type C MCB so he replaced that, although I think I remember him saying he installed a 32A Type C RCD, not MCB which was readily available to him and with his logic, as there was always been an RCD in front of it, it shouldn’t make any difference. I wasn’t conversant enough to argue that point.

Recently I was at a local audio dealer, not a Naim dealer, and I mentioned the humming. He’d recently taken a loan device from a supplier ‘ IsoTek Blue Horizon Mains Noise Analyzer’ and he was good enough to let me bring it home and test my electrical sockets. This device has a standard UK 13 amp plug, you simply plug it into a socket, it plays back a sound representation of any detected noise and gives a reading of how much noise in parts of 1,000. The lower the number, obviously the better.

IMG_1662
IMG_16623024×4032 3.16 MB

I started testing various sockets with the analyser and found quite a divergence between various sockets. Predictably perhaps, sockets on the ring main around the kitchen show 200-350/1000 noise, with fridge, freezer, oven etc. etc. all plugged in. Also in the hall which is adjacent the kitchen with sockets on that side reading about the same. Those sockets are also picking up some radio interference. In the lounge, which is on the other side of the house, so furthest from the mains entry to the house and the kitchen, the readings are as low as 5-10/1000.

The dedicated radial socket is also on lounge wall adjacent to the low measuring sockets, imagine my surprise on plugging the analyser in and it reads over 750/1000 - MAX as it says on the display! Not sure why that would be, it’s obviously the opposite of what a dedicated radial should measure, to my understanding?

The builder is sending someone this week to view although as he says, they only really test electrical safety and functionality but he’s willing to try help isolate the issue. He said he will start by testing the earth on those sockets, then pulling the main house mains to isolate any crosstalk from that to the dedicated radial. Failing that being successful he said he will try but will be guessing next steps.

Many thanks if anyone can add any advice on what may be causing this as I may be able to guide him further.

2

Pictures of your “consumer unit” along with pictures of the separate “dedicated” “consumer switch” would be useful. Along with a picture of the henley block.

2 Likes
3

I am in NYC which is very different. so take what I say with a grain of salt. Even when your analysis is done and deficiency corrected, I would consider an Isotek power management unit and their power cords. I am using the Sigma. All my gear is plugged into the unit. I have found it to dramatically lower the noise floor.

1 Like
4

Here’s the main house consumer unit:

IMG_1663
IMG_16634032×3024 2.8 MB

And the radial consumer unit (apologies for the quality, it’s in an understairs cupboard):

IMG_1671
IMG_16714032×3024 3.91 MB

5

Thanks and yes, I think that’s what the dealer was leading towards. I’ll keep that thought although I’d like to address the issue in the mains first.

6

I’m not saying you shouldn’t, that seems pragmatic.

1 Like
7

Can you get a picture of the Henley block ? It should be next to the meter and main Incoming fuse.

1 Like
8

Sure, I understand @Jaybar :blush:

9

Here’s the incoming mains feed cupboard and wiring, with various blocks etc. The ‘’Hifi’ wires are marked.

IMG_1672
IMG_16724032×3024 2.53 MB

10

A dedicated line was not possible for me Plaster and concrete precluded that. Nobody wanted to do the work. Also I did not have enough outlets behind the racks. An Isotek was the only viable solution and it lowered the noise floor.

1 Like
11

Well, it looks to be wired correctly. When i say “correctly”, i mean that when the builders electrician connected to the 100A switch next to the meter, he could only connect live and neutral to the bottom of that switch(the switch was fitted by the electricity supplier and has a seal at the top) What you actually needed was for live and neutral Henley boxes before that switch. Both live and neutral to be your hifi feed and then live and neutral to the switch with the switch exit going to your main consumer board.
What you have now is actually not a dedicated hifi circuit. The issue for you is that 100A switch, that is the cause of all the noise.
I will add, that 100A switch is not a legal requirement, it’s fitted to make builders, suppliers and householders lives easier because pulling the main fuse is against the law.

1 Like
12

That seems somewhat unlikely to me! It’s just a switch, how do you suggest that it is causing noise?

2 Likes
13

Did you do this test with your HiFi equipment turned on? Try turning it off to check that you don’t have a noisy, possibly faulty piece of equipment in the system.
Do you have network or other equipment using the dedicated mains circuit? Network storage, switches etc. are best kept away from the HiFi and on a separate mains circuit.

1 Like
14

It’s the cause of the noise because the OP does not have a seperate hifi curcuit. What he actually has in effect is an extension of his main consumer unit. If the connection for the hifi circuit had been made before the switch instead of after the switch, the noise from the rest of the house wouldn’t be an issue.

1 Like
15

The OP has the usual split of the tails from the meter. One set to the house CU and the other to the dedicated radial CU. The only difference is the isolator switch between the meter tails and Henley blocks.
I can’t see that the switch is causing an issue here.

2 Likes
16

Accept my apologies please both, the switch is nothing to do with it.
Not fitting a Type C MCB along with a Type C RCD has more to do with it i think.

1 Like
17

Ross - apart from the mechanical hum from the 250 and Hicap, do you have any other issues ? I’m not sure what your ‘noise meter’ is supposed to be measuring but it may be leading you down the wrong path.

Naim mains transformers can get a bit noisy depending on what is going on, on the local mains supply, sometimes caused by things within the house which is more within your control, or externally generated which is more difficult to deal with.

I have dedicated mains which greatly improved system SQ consistency - nothing going on in the rest of the house affects the system. I have occasional issues with my 350s getting a bit vocal - nothing to do with anything in the house, it’s on the incoming mains supply and I just have to accept that.

There is a good thread here which can help you track down things which may be causing excessive mechanical hum from the transformers in some of your mains powered Naim kit.

1 Like
18

My goodness there a a lot of nonsense being advanced by the responses in this thread.

I agree with ChrisSU’s scepticism.

3 Likes
19

I also cant see anything wrong with your wiring that might be of concern. It would be good to have a clearer photo of your HiFi Consumer unit as it’s hard to read the mcb types.

The only minor comment I would make is that the Henley box for the earth doesn’t look like it’s needed. It looks like you already have two each connection on the incoming mains, so would have saved a connection. But very minor, and unlikely to be related

If you do find the time to go through the “Starting Guide to Naim/Buzz”, please report back any findings.

Screenshot 2025-07-07 at 19.52.04
Screenshot 2025-07-07 at 19.52.04964×736 89 KB

1 Like
20

They should be able to do a resistance check and Insulation check on the HiFi circuit cables which will be useful, and perhaps ask them get you a Mains Voltage reading in case of over/High voltage which will cause Humm.

1 Like