Inveterate meddling #103: dedicated mains spurs
A separate spur is quite possibly the best value upgrade for your listening room there is.
The point is to supply electricity with as little added electrical noise as possible and a minimum of series impedance. We do this by connecting a spur unused for any other electrical items back to the distribution point at the main intake (the consumer unit), where the impedance is as low as possible. We then, when possible, provide a dedicated earth path for equipment which needs this connection.
Cable of 6mm2 is about optimal for a dedicated spur. This carries a current rating of 30Amps when enclosed. Some people report 10mm2 (45A rating) is worth using , but it's much more difficult to work with, and fitting it into the socket receptacles can be nigh impossible. Whether you install twin-and-earth (Romex), or three separate cables is up to you/your electrician and the route to be installed; separate cables are easier to pull round bends.
Sockets: In the UK MK "Logic+" are good, as are the old-fashioned three round-pin 15A sockets. The Logic+ type have copper bus bar for the earth connection and are available switched and unswitched.
Plugs: In the UK Crabtree plugs give very consistent results and a tight fit to most sockets; they also have screw terminals inside you can really lean on.
Try a search for "mains spur" at the
Naim forum where the issue is regularly mused over by contributors worldwide.
Fit a spur not a ring. We've built both and the spur simply sounds better, regardless of what Russ Andrew says. In fact we installed a 30A dedicated ring, then cut it into two spurs after listening to it....
How you provide outlets is up to you. A cluster of switched or unswitched sockets at the end of your spur, or one single socket into which to plug a hydra- like powercord connecting all your boxes.
If you install a cluster of sockets, make a note of the order of connection to the end of the spur. For some the order in which your kit is plugged in makes a difference, whether its power amp first, source last (Naim's preference) or the other way around.
50% of the benefit is in the dedicated earth. Whether this is legal depends on some careful reading of the IEE regs and a sympathetic electrician, and will require a RCD breaker (GFI) in the consumer unit not a fuse.
If a separate earth connection appears unfeasible - for legal or logistical reasons, especially for those of you in apartments - don't worry about it. Run the the spur's earth wire back to the main earth connection on your distribution board and stop worrying. It's still a cleaner earth than the rest of your electrical installation.
Buy a couple of different RCD breakers and try them, some report sonic differences between brands.
Connecting to the nearest copper pipe (gas/water/ central heating) is NFG as a separate earth. Separate earth means a dedicated earthing stake. The pipework is earthed - 'equipotentially-bonded' more properly - only for significant safety reasons. Using such as a functional earth can compromise this.
Earth stakes generally come in 4 feet / 1220mm lengths, about 15mm dia. copper-plated steel and take quite some driving to get home. If it does go all the way in when merely shown a hammer, screw on another length and keep going....
A single stake driven under the rosebush will give results anywhere from fantastic to totally insufficent, depending on soil type, water content, last rainfall, salts content and the compaction of the ground, so...
Your new earth must be tested to determine that it provides a suitably low resistance for functional earthing, determined by local code, bylaw or your supplier's own regulations/conditions of supply. It is for your safety, so comply; besides which, lower earth impedance is better for hifi.
Don't believe anyone who tells you a separate earth will drain away all RF interference; the few feet of wire between the boxes and the earth stake has more than sufficient inductance to give the lie to this fallacy. If you believe this kind of thing, I have an AC battery I'd like to sell you.
Mains power filters are infra dig., by the all-powerful Law of Inconvenience which holds sway over the Flat Earth. For good reason, too - they all make a mess of the music.
We'll discuss DIY earthing separately.
Play with your electricity supply and you are on your own. Do we need to say this ?
From 01 Jan 05 in the UK Electrical works such as this need to be signed-off by a suitably-qualified person or approved by your local Building control inspectorate, following the introduction of the new Approved Document Part P component of the Building Regulations. Part P documents are available as a free download here: Part P
Your insurers will take a dim view of homebrew 'modifications' that do not meet prevailing IEE regulations and any other codes in force, especially if a fire or other damage results.
Don't be tempted to 'oversize' the spur RCD/fuse. It's there to protect the spur - prevent it overheating in the case of a short - and a small fire will not endear your fringe hobby to your loved ones. In any case the sonic difference is insignificant...
Fitting a separate earth requires you understand the potential for electrocution and how equipotential bonding prevents that risk. If you don't know, ask someone who does.
If in any doubt, pay a qualified electrician and heed their advice. Compared with the cost of the kit, and the risks, it's cheap; £100-150 is typical for a fully sorted - and legal - installation.
© the twisted pair 2000
02.01.07 Part P link updated.
02.01.05 Part P update added.
17.12.01 page added.