Dedicated spur

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Naim recommend leaving the cable earth disconnected..

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really, where did you see/hear this?

enjoy

ken

I installed a dedicated spur a couple of months ago and it was well worth doing. Installing the spur is easy and everyone agrees its benificial.

However, when you start talking about dedicated earths with rods rammed into the ground, you get two very opposite sets of opinions.

The Hifi guy says go for it......lots of advantages etc etc.

Every electrician I spoke to was adamantly against it and one refused to do it. They all got very techniclal, but the essence was that the dedicated earth must be connected via a RCD and that causes other problems.

In the end I gave up and the earth from the socket goes into some sort of box in the garage which in turn is connected to a gas pipe.

All I will say is that the dedicated spur is dirt cheap and very worthwhile, so go for it.

Regards

Mick

Mick - its done and I'm well aware of the benefit of dedicated spur and earth rod having had one at the old house for some years albeit with only standard cable and 15A breaker which is often tripped by the Armageddon. I'm not sure if the cable earth is also connected.

Mick - "the earth from the socket goes into some sort of box in the garage which in turn is connected to a gas pipe" - is this in lieu of cable earth, if so does it give a better result, care to share the details of the black box?

Regards

I've yet to get to the bottom of this in terms of the regulations, but the one thing I do know is having seperate, isolated, mains earths is a potentially dangerous thing to do. If they are not tied together, there is the possibility for one to be at a different potential (voltage) from the other - this is dangerous if there is any chance of you coming into contact with both earths at the same time, since you will become part of the electrical circuit.

The human body doesn't react well to conducting large amounts of current

There is no reason whatsoever that a dedicated earth spike cannot be connected to the rest of the house earthing without an RCD, but again there are certain restrictions.

As Mick's electrician has correctly stated, it's a waste of time to use an RCD, since this only increases supply impedance, something one is trying to reduce with the dedicated supply.

If your house uses PME (Protective Multiple Earthing) I believe there are limits on the minimum conductor size for the local earth cable run, since under extreme fault conditions it could be called upon to pass the full current capability of your house fuse to earth.

The problem you've experienced is that the electrician could not obtain a low enough impedance from your local spike to meet regulations. Soil types and moisture content can have a dramatic effect on soil conductivity, but multiple spikes, buried sheets or extendable longer spikes could acheive the desired result. The deeper one can drive the spike, the more stable the conditions are likely to be, and the better the earth impedance.

I'm guessing the 'cable earth' you're referring to is the normal house earth, and in this case Naim are correct providing the local earth acheives the required performance, as it doesn't your electrician is correct in that it is pontetially unsafe to disconnect it.

If your electrician has left the local earth spike connected you will still acheive better performance than not having it, so I wouldn't worry unduly. If you really want to go the whole hog I can provide some more information on creating low impedance earths for radio use, which are applicable here. You could do the earth yourself, and just ask the electrician to test it.

Andy.

are you, and is naim, suggesting that this earth on the 6mm cable should be left unconnected at bothe ends? i cant believe this, so i have probably misunderstood something. please clarify.

thanks in advance

enjoy

ken

Blinking flaming acronyms....

Regards,
Frank.
All opinions are my own and do not reflect the opinion of any organisations I work for, except where this is stated explicitly.

Naim suggested that the cable runs earth was connected at the consumer unit to "protect the cable run" but not the outlet sockets which they recommended to be star earted to the earth rod.

Regards

If any of these becomes damaged, they will then be protected.

At the sockets that feed the system this earth should not be connected and the local, low noise, low impedance, earth is used.

As stated above, if this local earth cannot be made good enough then it's unsafe.

It will be possible though, given enough effort, to make one that will perform OK.

Andy.

RCD = Residual circiut breaker. Quick trip job to stop you being electrocuted.

Regards

Mick

... At the sockets that feed the system this earth should not be connected and the local, low noise, low impedance, earth is used.

at the socket side of the spur, what is the earth wire of the spur cable connected to? i guess to the earth terminal provided in the casing of the socket?

the whole issue of a dedicated earth for my hifi has become much more important since i went active -- the system seems to be much more sensitive to mains quality variation now -- at least thats what i suspect. the problem is whenever anyone makes some recommendation here as to the best way of achieving this dedicated star earth, someone else shoots it down. so, can someone post a "down to earth" set of instructions on how to install a dedicated star earth for ones system. chance for someone to show that they really know what they are talking about. i dont.

enjoy

ken

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at the socket side of the spur, what is the earth wire of the spur cable connected to? i guess to the earth terminal provided in the casing of the socket?

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Doesn't have to be connected to anything, providing its cut back and cannot short out to anything.

Unfortunately on most sockets the earth pins of the socket are connected to the metal backing box once screwed in place (you'll see a bus bar running to the screw holes, and a rivet through the hole) , so connecting it to the casing of the socket would connect it to the dedicated earth, which we want to avoid.

ah, so this earth wire is really an open circuit -- which to me implies there is no need to connect it to earth at the consumer unit end as it has no protective value. this means i can dispense with it completely and just arrangea completely separate earth from the spur socket.

for hifi, earth serves at least 2 purposes --(a) low impedance path to a high conductivity earth in case of a fault -- this is the safety aspect (b) a separate earth that is immune from any extraneous noise generated by whatever means by other devices connected to the supply in the house/street/area. i am not sure what properties we have to have to satisfy this requirement and still achieve the low impedance path for protection.

i can see why an electrician would be uncomfortable about leaving earth unconnected, but presumably if you can arrange your own independent one, this should be OK/safe - subject to impedance etc etc...

phew... quite useful stuff, but sometimes quite confusing because of conflicting views

enjoy

ken

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ah, so this earth wire is really an open circuit -- which to me implies there is no need to connect it to earth at the consumer unit end as it has no protective value. this means i can dispense with it completely and just arrangea completely separate earth from the spur socket.

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Not quite. By connecting the earth to the consumer unit you are providing a protective function in the event the cable should become damaged (e.g. drill through it!). The conductors are likely to short to earth, blowing the consumer unit fuse.

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for hifi, earth serves at least 2 purposes --(a) low impedance path to a high conductivity earth in case of a fault -- this is the safety aspect (b) a separate earth that is immune from any extraneous noise generated by whatever means by other devices connected to the supply in the house/street/area. i am not sure what properties we have to have to satisfy this requirement and still achieve the low impedance path for protection.

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Both properties are likely to be mutually inclusive. From a noise perspective one wants to acheive the lowest possible impedance across the widest range of frequencies. This will have a dramatic noise reducing effect in terms of screening equipment from EMC and providing a low noise reference for the system (remember mains earth is connected to the signal earth at one point in a Naim system).

It's easier to acheive the low impedance at low frequencies (the electrician will measure it at DC), at high frequencies earth cable length will become a significant problem. The shorter the earth cable between local earth spike and system the wider it's low impedance bandwidth will be.

I see no problem with using multiple spikes, connected in a star fashion to lower impedance, or using longer spikes. Ben Duncan has done some work on this subject, and there are extendable (but expensive) earth spike available from him that one can just screw an extra section onto and keep driving into the ground.

Soil properties will be much more consistent at depth, which should reduce the need to water the ground spike in dry weather - the effect of poor soil conductivity is clearly audible through the system.

Andy.

The greatest gains seem to come from step 4, which reduces the impedance of the overall house circut to eath and seems to "drain noise" out of the overall system.

but connecting the mains earth to the earth spike is quite a lot different from what andrew w is suggesting -- i.e isolate the hifi earth from mains supply earth completely. has your dealer tried this "total" isolation?? and not liked it??

enjoy

ken