RCD fuse box

[Jimbo]

I will be replacing my old 60amp fuse box with a new RCD fuse box next week and would like to hear from anyone if I am likely to hear any benefits to my system from a new box or could it adversely affect sound quality?

Not sure if it will be an 80amp or 100amp box?

[337alant]

Jim
Did you ever read the stuff by Roy K Riches?, it has some good info on Mains equipment
PM your email address as I can send it to you

Alan

[kcc123]

I got a new RCD fuse box fitted three years ago when someone installed some solar panels to the roof of my house. I think I've heard a better sound since but not sure if it is out of my imagination.

[Reffc]

I'd look at it another way, ie how can an RCD (or a fusebox) influence SQ in any respect at all? An RCD works by constantly monitoring the supply downstream for faults to earth (ie a sudden current dumping to earth) then switches off the supply to prevent damage/electrocution. In the normal flow of things (ie no faults) it doesn't interrupt or affect mains current in any way shape or form that could be detrimental to SQ as far as I understand it. It is also mandatory since July 2008 to have any rewiring or replacement of an old fusebox done with modern RCD devices under BS 7671. I would humbly suggest that if people are noticing differences in SQ when messing with upstream mains devices (including cables/fuses) then it's either 1) circumstantial at best or 2) their kit's power supply is in some way defective, either by fault or by design. Fuses that may have somehow worn/burnt down due to a previous fault condition over time may theoretically not be passing as much current as they should, but if they're that defective, one might expect them to have already burnt out/blown. Ordinarily, it's hard to understand why a properly rated fuse should affect SQ at all as sufficient current will be available to the kit's power supply. Sorry, I'm just not "a believer" and don't believe in pixies at the bottom of the garden either ;) :D

[BilliumB]

Interesting Paul - so do you have any thoughts on grounding, and the importance a low impedance connections to earth?

Cheers. Bill

[Reffc]

In what context Bill? In context of the signal itself (ie not the current feeding the amp), then a decent ground is essential to reduce "noise" which might otherwise be inductively coupled to the signal. In terms of grounding electrical equipment, i) it is mandatory for safety for anything not double insulated and ii) reducing ground currents in connected kit and therefore reducing voltage potential between connected items of kit reduces ground loop risk and hence induced noise risk. Where one might have a ground loop in connected kit, it can sometimes be caused where the star earth of say a preamp connects to the chassis which also has a direct coupled ground to mains (safety earth) and any stray ground currents can form an effective ground loop and hum. In this case, an earth loop breaker circuit can be introduced (using a 600V, 35A rated bridge rectifier with some nominal resistance between chassis earth and signal ground like say 10 Ohms and a 100nF cap in parallel to ensure RFI rejection).

[BilliumB]

Hi Paul

I was thinking in terms of the electricity supply 'quality' and impact on sound quality. I may have misunderstood your earlier post, but got the impression that you felt that the 'quality' of the elec supply is not generally an issue for SQ. I'm considering putting some considerable effort into improving my supply earth (I'm on a TT system by the way, and fully understand the safety issues) - and hence was wondering if you felt that would be a waste of time, effort and money.

Currently Ze measured from the plug supplying my kit is 15 Ohms - but this was measured with wet ground - I'm going to take some further measurements later in the summer.

Cheers. Bill

[Reffc]

Ahhh...with you now. Yes, I do agree that supply quality can affect SQ; more so in some items of kit than others. I do think that the power supply circuit within individual items of kit counts for a lot though. I just don't see how fuses or RCDs can, that's all. We're very fortunate here in that we have mains that fluctuates very little and according to an electrician mate is "relatively clean".

[Alan D]

Bill,

Your measured Zs value of 15 Ohms is very good for TT. Your Ze will be a bit lower, Zs -(R1+R2)

Have you asked your supplier if you can have a PME conversion / TN-C-S ?

Assuming you have an overhead supply, it depends if they have earthed the neutral at the poles.


Just a quick note to anyone installing a new Consumer Unit, they should now be made of metal not plastic to conform to BS7671 Amendment 3.

Alan.

[BilliumB]

Hi Alan

Yes, I understand that 15 Ohms is good - not sure it will be as good in dry times, we'll see.

At the moment I'm wondering about adding a low impedance earth route for higher frequency signals using thick coax - TT will probably allow this, whereas safety issues might preclude it with PME. Clearly suitable bonding will be needed. Still at the planning stage at the moment (and discussing it with the electrician).

Do you have any experience with such ideas?

Cheers. Bill

[Alan D]

Hi Bill,

You may not experience too much of a rise in Ze when the soil conditions are dry. It depends on your location (ground conditions) and luck!!!

Many a time I have replaced an old TT earth rod and then measured twice the original Ze from the new rod (Doh!) then it is either more rods spaced out, or the larger diameter rods screwed together and driven down with a kango hammer drill, or copper earth matting which is very expensive.

I periodically test lightning conductor systems and this is when I notice the differences in wet / dry conditions, which can be small or large, when I compare the test results to the previous set.

Whilst I have no experience of special earthing for Hi Fi, I am also a Radio Ham and earthing of RF transmitters and antenna tuners is an interesting subject and something I have taught in the past.

You mention a low impedance earth for high frequencies. The problem is that a run of cable to an earth rod may have a low resistance to DC, but the impedence (resistance) at higher frequencies may be very high, due to the inductive reactance of the cable that the HF sees!

An electrician can give you excellent advice regarding the regulations and earthing at 50Hz, which in the radio world is near DC! It is worth bearing in mind that earthing at RF is a totally different subject matter and something that even the best electrician may have no knowledge of.



I know you don't have PME, but for anyone reading the thread WHO HAS TN-C-S / PME YOU MUST NEVER ADD AN EARTH ROD, unless you are fully aware of the precautions to take to isolate the location from the suppliers earth, as under certain fault conditions a very large fault current from the distribution network could flow through your equipment to your earth rod, with the resulting indoor firework display and melted charred remains of your prized electronics.

It is also worth noting that if you have PME and an out-building, the PME should not be exported, so you end up with the house on PME and the out-building on TT with it's own earth rod so it is not uncommon to have both earthing systems at home. They must simply be implemented by a competent person.

Sorry I have waffled and cant give you a definitive answer, I would simply recommend you just reduce your Ze / Zs to the minimum possible and drop the idea of RF earthing.

Alan

[BilliumB]

Hello again Alan

I was thinking of using thick coax as a low impedance route for higher frequencies - both core and screen connected at the earth end, with core only connected at the kit end, possibly to the outer of a suitable phono (possibly using a suitable capacitor as a safety device).

Clearly the earth connection will be critical - don't want it to act as an rf detector!

Do you think I'm wasting my time, or might it be an interesting route to go down?

By the way, where are you in Cornwall?

Cheers. Bill

[Barry]

Hello Alan,

I hope you don't mind, but I have highlighted your comments on the dangers of adding an additional earth rod to those mains installations that use TN-C-S schemes.

It is difficult for those not familiar with the various earthing schemes employed by mains distribution companies to understand why adding additional earthing can be hazardous - but it can be. The risk of such a fault condition may be unlikely, but were it to happen the consequences could be disasterous (and would make your insurance null and void).

Also you are quite correct to point out the difference between RF earthing and 50Hz mains safety earthing.

Regards
Barry

[BilliumB]

Hello Barry

Do you have any thoughts / experience of the effect (benefits or otherwise) of a 'high frequency' earth on sound quality (assuming a TT earth, with proper bonding, as highlighted earlier - so safety issues sorted)?

Cheers. Bill

[Barry]

Hello Barry

Do you have any thoughts / experience of the effect (benefits or otherwise) of a 'high frequency' earth on sound quality (assuming a TT earth, with proper bonding, as highlighted earlier - so safety issues sorted)?

Cheers. Bill

Sorry Bill, I don't have any direct experience with 'high frequency' earthing of domestic audio systems. My only experience has been with low frequency radar systems where very large earth 'mats' are used.

My only advice would be that of Alan's: aim to minimise the inductance of any connection you make to the earth spike(s). That means using a cable of large cross-section (say 10mm2) or a wide (>10mm) copper braid.

[Alan D]

Hi Bill,

I am in Indian Queens, Cornwall.

Unfortunately I have no idea if your idea will bring any sonic results. With further guidance from your electrician you could try it, but I feel it is still not straight forward and you will not know how low an impedance path you are providing at different radio frequencies.

Alan

[BilliumB]

Not really sure what frequencies I'm aiming at, just looking to provide a low impedance path to earth for noise signals - it seems to me that thick coax would be a suitable cable for higher frequencies (certainly much better than the earth core in a normal twin and earth mains supply). Anyone have any experience?

Cheers. Bill