Thanks - makes sense
Loop isolator on order
I was about to suggest than… c. five or six quid from a well known online site.
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Thanks Richard - expect delivery tomorrow
My advice is pretty much in line with what James has said above, so I won’t repeat it. It’s clear from your photos that the 2 consumer units are both for general use, and one is not dedicated to the HiFi, so if you can get a third one for that, ask your electrician just to put an MCB in it rather than RCDs etc. You will need to find space for it, but it will be much smaller that the two you have now.
I notice that the 2 CUs you have both have earth cables running back to a little connector block. Ask your electrician to run the earth from any additional CU to that same block. They sometimes join them to the earth in an existing CU if it’s quicker and easier for them, but for the dedicated CU, you want to keep everything isolated as far as possible.
You may find that this makes little or no difference to your hum issue, but I suspect you will still be pleased with the uplift it gives to sound quality generally.
Thanks ChrisSU.
The sparks suggested that it might be useful to earth the hifi spurs separately.
If I recall the installation the sparks said that the earth value (?) was extremely good. It goes back to the step down transformer, which is 50 m away, which is in turn 500 m from the sub-station. I had originally asked for a separate earth, but I was talked out of it by the sparks (little knowledge being a dangerous thing on my part).
Yes I thought that might a problem , my basic Ron Smith is shared by the NAT02 and the ‘qutes.
Splitting an aerial is not a problem, providing its done correctly. But whatever is not a problem in relation to audio signal ground loops as the RF signal has no connection to -ve audio signal circuits.
To split an aerial feed correctly it should be connected through a purpose made splitter that works in the 5-1000MHz range.
Sounds like you now have an electrician who is trying to give you what you want, rather than one who clearly thinks you’re an idiot and tries to put down your suggestions. It’s been suggested on here before that you use a separate earth spike buried in your garden for the dedicated supply, but if your existing earth tests well, maybe there’s no need for that.
Thanks Mike B - I believe that was done at installation. The chaps then did not know what to about the tv hum. Do you know how long these ground loop isolator have been around?
A long long time
If your TV has optical out why not run a toslink cable from tv to NDS. You should get really good tv sound and not have worry about fixing earth loops. I find the AQ Forest optical cables are inexpensive and work a treat.
Phil
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Surprised my old dealer did not suggest them when everything was installed. C’est la vie
Sadly not Filipe … the tv is not due for an upgrade yet
Ground loop isolator arrived, plugged in = result. No hum
Now time to listen to see if there is an improved sound quality
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Good news 
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Good to hear you have a result. Cheaper and easier than a proper dedicated mains circuit, although some see that as a cheap upgrade.
Indeed ChrisSU
Radio paradise sounding good - even with those annoying pictures (well sometimes off putting)
Morning all
I have now had a few quotes back from sparks. One of them suggests that I run an earth from each of my spurs back to the dedicated consumer unit (CU). In the diagram above, that seems to be excessive. The sparks referred back to a music studio they had wired and that was one of the requirements stimulated by the studio.
Has anyone had a similar experience, or indeed put in separate earths from their unstitched plug sockets?
Thanks
Steve
I don’t understand exactly what you mean here. Each spur (pedants will insist it’s called a radial!) will be earthed back to the dedicated consumer unit in any case by the Twin and Earth cable, I hope. The earth from that CU should certainly then run directly back to the main earth point as shown in James’s diagram, not via the main house CU as sometimes done for convenience by lazy sparkies.
18th edition is now in force from the 1st Jan and all designs from the 31st December 2018 have to comply with BS7671:2108.
You may need to have the above design checked against the latest regs.