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Identifying & Solving Mains Supply Problems

In The Mains By Ben Duncan
Published July 2003

Identifying & Solving Mains Supply Problems

Most of us never have trouble with the electricity in our studios — but as with everything we take for granted, fixing problems can be difficult when they do arise. We look at some of the main problems and solutions.

The mains (AC electrical) supply in the UK is one of the most stable, generally pure and reliable across the world. The downside of being so lucky is that unless there are blatant problems, the energy supply becomes transparent — we readily forget just how reliant we all are on its smooth continuity for musical creativity.

Why Be Troubled?

Problems with the mains supply may be easy to measure but go unrecognised, or they may be hard to measure, but have a surprising effect on the sound quality you get. What constitutes a problem depends on the sort of equipment you are using, and its sensitivity to varying degrees of imperfect mains. The complexity of all the equipment you're using may well mean that you prefer to stay focused on producing music, and never find time to look into optimising mains connections. This is fine if your problems are trivial, but what if they're not? Your money and time can be wasted buying successive pieces of equipment, and finding you're never quite getting the results you wanted, while all the time the problem is elsewhere — in the quality of your studio's mains supply.

Another scenario is that you buy 'mains-improving' equipment that achieves nothing. This may be because it's a 'snake-oil' product (meaning it will do very little under any circumstances, but having paid for it, you find yourself believing it must have enhanced something) or equally, because it's just the wrong equipment for the problem at hand. This article is intended to help you identify the sort of mains-related problems that will affect sound and what you may be able to do to rectify them.

Mains Problems With Foreign Equipment
Making equipment that works smoothly on any national AC supply is not hard, but it requires a little knowledge and also forethought. The first detail is an understanding of how mains voltages vary across the world. More than one overseas manufacturer has been fooled into thinking that the mains voltage in the UK (& Eire) has been reduced to 230V, and some are careless enough to sell products made for 220V for use EU-wide. These may be stressed or unsafe when used in the UK & Eire.

The second, more major problem is that the US supply frequency is 60Hz — compared to 50Hz in the UK, Europe and many other territories. The effect of the higher frequency is that mains transformers for use in the USA (and Canada) can use smaller magnetic cores and less turns of wire to do a given job. This gives higher-powered US-made products (where transformer cost is a substantial part of the whole) a 'triple-whammy' unfair economic advantage — of lower size, weight and cost — in the world market. It also causes endless problems for users in 50Hz territories, including Britain, Ireland, most Commonwealth, and all western-European countries. It's easy enough to provide transformers with correct voltage tappings, but unless the transformers for use in the international market are designed to operate at 50Hz, a bigger problem remains. That's because when a transformer is tightly designed down to a price so that it only just works at 60Hz, then even if the mains voltage setting is correctly set, the transformer will run hot(ter), draw a higher background 'magnetising' current, adding to studio mains pollution. The saturated core will also generate high third-harmonic noise, meaning added levels of buzz at 150Hz. Such a transformer is also likely to buzz acoustically loudly. The sole remedy is to fit a correctly made, 50Hz-rated transformer, which is not cheap. It's worth noting that this is most likely to arise as a problem with grey or illegal imports, and also with equipment that is newly imported to the UK. Established and reputable US and Japanese manufacturers are less likely to forget to design and fit transformers made for 50Hz to export products — but the buyer should still beware.

However, using a transformer at a higher frequency than it was designed for will rarely disrupt it; thus most 50Hz transformers will work fine at 60Hz. Effectively, products made to work on UK and European 50Hz mains are 120 percent overdesigned and more expensive when sold into the US, and likewise, US products can be cheaper because they've unwittingly (or not!) sold us an under-designed transformer. Naturally, because imports from 50Hz countries into the US are unlikely to heat up, buzz mechanically or generate noise, American designers remain blind to the grief/hassle that their unadjusted 60Hz products cause to the rest of the world!

Voltage Problems

One of the more common causes of studio gear misperforming is high (excessive) mains voltage. This can cause the following symptoms:

  • Acoustic buzzing from transformers. This may come and go with high voltage, and is a sign that a transformer is getting saturated (for more on this, see the box on page 232). This is harmless, in the sense that it's reversible, but upsets the proper operation of transformers.
  • Gear running hotter than it's designed to. In some cases, equipment may be failing regularly, or likewise blowing fuses.
  • 'Lifeless' or 'gutless' sound over monitors.

A series of light bulbs blowing prematurely is a tell-tale sign that voltage is higher than ideal on a regular basis. In the UK, the official 'declared' voltage is in practice 240V (although it's officially described by the EU as 230V with a different 'tolerance'). In the real world, the mains voltage at your studio's intake varies anyway with loading. In ideal circumstances — a 100-percent healthy mains source — it will centre on 240V and vary from say 235V to 246V throughout the day, as other users switch on and off. Most users are unaware of the mains' continuous and ceaseless fluctuation. Whenever the supply's loading in your immediate block, village, street, or the greater area is low (particularly late at night), the voltage will tend to rise above 240V. The maximum legally allowable is 254V, but voltages as high as 275V have been recorded.

High-voltage Problems & Solutions

You can tell how likely you are to have problems with excess voltage if you can find out how far away from your studio the nearest electrical sub-station transformer is. If you are right next door, you can expect your studio gear to be regularly subjected to mains voltages above 250V at the times of lowest public power usage.

To know for sure if the mains voltage is too high, you need to measure it. Unless you're electrically competent and have time to make lots of readings, it's safest and easiest to hire an electrician to set up some voltage monitoring (logging) at your supply's intake.

There are three ways to deal with excess voltage.

Firstly, if the supply repeatedly exceeds 254V, then your REC (Regional Electricity Company) is legally required to take steps to rectify the situation. They will be most likely to take rapid steps if the mains is seriously high, say continuously above 255V, since there would then be an element of increased fire risk, and the REC would be seen to be liable.

Some musical gear can be adapted to run on various national voltages, either by changing over plugs on the equipment itself, or by altering an adjustable power supply, as here.Some musical gear can be adapted to run on various national voltages, either by changing over plugs on the equipment itself, or by altering an adjustable power supply, as here.

Secondly, you may be lucky enough to own older equipment with mains voltage adaptors allowing fine adjustments. On such gear, you can move a plug on the rear panel to 200-210, 220-230 or 240-250 volts, for example, or sometimes the external power supply itself is adjustable (see picture below). Today, however, the problem of raised mains voltage is one that most equipment manufacturers don't even recognise. Instead, most equipment is presumed to work smoothly (without adjustment) over the 200V to 260V worst-case range of voltages that occur across the UK and Europe. As most manufacturers test their equipment in the daytime, when the supply is most heavily loaded, few will ever encounter the effects of high mains. And yet how many musicians work at night, when the voltage is at its highest?

Third, an easier approach than either of the above is to use an overall suitably rated voltage-adjusting transformer that's able to power all your studio gear. Usually we think of transformers as making big voltage changes, for example 240V down to 15V, but the purpose here is to reduce the supply voltage by just a few percent. However, in order to power a small studio, with its high current peaks, transformers of this type need to be quite large, and they're not normally available off the shelf. What's more, you may find that they reduce the voltage too much at other times of day, although the side-effects of a low voltage, as we'll see next, are less serious.

Low-voltage Problems & Solutions

The UK's 240v mains can legally fall as low as 216V. In my 19 years of product and review testing, I've found that most audio gear will work to considerably lower voltages with few or no ill effects or functional degradation. The odd exception — a tape machine here, a power amp there — will suffer problems before the legal minimum voltage is reached. Symptoms and problems include relays not closing or opening (which affects controls, mechanical functions, powering-up sequences and so on), and audio signals clipping in power amps at maybe 1dB lower than you would expect (earlier overload = lower maximum output). You might also experience hum and related noise, as regulated supplies lose their ability to regulate and smooth the equipment's DC power sources. Finally, low voltages can cause some appliances with motors to burn out, particularly fridges and freezers. This won't affect your studio, but can add a domestic thrust to the desire to get the problem rectified!

All UK studio gear should now come with a fused, moulded UK plug — if not, you should return it at once. For older gear with plugs you've fitted yourself, it's worth ensuring you upgrade to decent brands with the British safety standards kitemark.All UK studio gear should now come with a fused, moulded UK plug — if not, you should return it at once. For older gear with plugs you've fitted yourself, it's worth ensuring you upgrade to decent brands with the British safety standards kitemark.

If you suffer these problems, you should again have your supply voltage logged at the intake by an electrician, as above. If the supply is regularly going below the 216V legal limit, the REC is required to raise the supply so that it doesn't. But before notifying the REC, make sure that your voltage logging tests are taking place at the supply's intake, as near to the REC's (main) fuse as your electrician can get. This is because the voltage can drop significantly further between there and your studio.

You can avoid this drop in voltage between your house's main intake and your studio by giving your studio's electronics its own dedicated supply (a radial or spur, rather than the usual ring circuit), and reduce voltage losses by using lower-resistance wiring than usual. If your studio is located a fair distance — say 100 feet — from the supply intake, surprisingly fat wires will be required. These will be nominally rated at unfeasible-sounding high currents (maybe over 100A), but what counts is the low total resistance. In electrician's language, very high current wiring is required to meet the part of the IEE (Institution of Electrical Engineers) regulations, which cite a maximum four-percent voltage drop between the mains intake and the furthest fixed outlet, when operated at the anticipated current. However, what electricians will find hard to understand is the high current peaks that studio gear draws (see below).

Subtle Problems

It's a little recognised fact that nearly all studio gear pollutes its own mains supply. It does this mainly by drawing a peak current that's a lot higher than the average level. A particular studio — including several PCs — may consume only (say) 750W in all, which is about 3A at 240V. This is the average level, and an electrician, from theory, would expect the peak current to be about 4.2A. But in fact, it's more like three to five times bigger (depending on the quality of your local supply); 9A to 15A. You'll be pleased to know that this has no adverse safety implications, because although these high currents repeat 100 times per second, they don't persist long enough to cause any overload. However, the 'spiky' loading that the high peaks represent causes extra voltage drop as well as harmonic distortion. The latter can be seen when almost any mains waveform is inspected — the smooth peaks of a pure sine wave are absent and replaced by less tidy shapes. This is especially true of current waveforms. It means that the mains voltage that the gear is itself using includes harmonics of the mains' fundamental frequency (50Hz in UK and the EU). The added frequencies (mainly odd-numbered harmonics, at 150, 250 and 350Hz) are the primary causes of the richness and complexity of hums and buzzes.

The resulting 'squashed-peak/ clipped distortion' can also cause saturation in audio equipment's mains transformers
— leading to effects similar to excessive mains voltage. You can now see your studio afresh as a high concentration of DC supplies that creates a localised area of degraded, noisier mains — with high harmonic content. Simplistic brute-force 'solutions' to this problem, like regenerating clean mains just for the studio (as touted by some US manufacturers) don't work very well, since it is the audio gear itself that's causing the problem.

Blatant Problems

If you have the following, something is badly amiss:

  • Regular or repeated total outages (power dropouts);
  • Periods of sudden and quite deep voltage dip, noticeable as periods when lamps dim and some equipment may malfunction or stop.

Such supply 'outages', as they are known, signify a problem that could be serious — for example, something involving arc'ing, which might cause a fire. For this reason alone, your REC should be keen to rectify matters promptly. Before reporting to them though, do first make sure that neighbouring users are suffering the same problems at about the same times. If not, an electrician should instead be called in first, to check that the cause is not in your premises, past the intake point where the supplier legally hands over to you. No attempt should be made to cure problems as extreme as these above, by using any power-conditioning accessories or techniques. Doing so is like using any good tool for entirely the wrong job.

Having dealt with the most common problems, we can now look at power-conditioning products in context.

Uninterruptible Power Supplies

Also called backup power supplies, these devices will mainly prevent power interruption and also deal with deep voltage dips. While achieving this, supply quality (for audio gear) will usually be low, due to high harmonic and radio-frequency (or RF) noise levels. Ordinary mains can be purer.

As the mains can fail unexpectedly at any moment, some form of UPS can be vital for computers, other digital devices with volatile memory and hard drives, to give you a chance to save your work before the power runs out.

An important aspect of choosing any UPS is that the stated 'VA capacity' of the device needs to be about five times greater than the nominal power rating of the equipment being connected (in Watts or VoltAmperes). This is because of the high peak currents that audio gear, PCs and other technical equipment draw. If you do not make this allowance, the UPS may or may not be harmed, but the gear will certainly be 'power-starved' and may work sub-optimally.

Mains Filters

Also called 'filter blocks', 'mains cleaners' and similar trade names. The common types (if they work at all) remove noise only at radio frequencies well above audio. As you cannot hear such noises directly, nor always know whether they may be strong in the vicinity, it's often impossible to tell whether or not mains filters will achieve anything. Despite this, they are sold in some instances as if filtering is a universal cure-all. You are most likely to benefit from them if your recording room is near to any RF (radio-based) equipment that's well inside the frequency range that the filter happens to cover. This could result from a nearby broadcast aerial alongside an ambulance or other public-services station, to an FM mains-connected baby alarm in the house next door.

Mains filters commonly 'backfire' by coupling noise into the equipment, which is exactly what they're supposed to deal with! This happens because the mains earth wire that the filter's 'earth' terminal has to be connected to doesn't look like an earth to the RF signals that the filter is trying to deal with. Instead, it can look more like an aerial! Also, when several items have filters, all the RF noise that's picked up in cable shields and by metal cases is summed together, but has no particular place to go. Meanwhile, each filtering capacitor inside contributes a current leakage (including noise) from the live side, through the mains earth wiring. Worse, due to thoughtless design, the use of many items of gear with RF filters may cause any Residual Current Devices you have in your fusebox (or trip/safety switches, as you may know them) to be tripped out, preventing you using your equipment, or meaning you have to remove the RCD, and forego the safety it offers. The bottom line is that RF filters are best avoided. If they must be used, get an electrician's help (or that of another expert) to isolate the filters from the existing mains earth wiring and to connect them both separately back to the mains intake earth point, and also to a solid RF earth (there's more on RF earthing later in this article). If you have much equipment fitted with mains RF filters, this gear may have to be powered from separate circuits if you want to power it through RCDs, for personal safety in the studio.

What Is Transformer Saturation?
As the name implies, when a transformer is saturated, the magnetic core that carries energy from one side of it to the other gets choked up. The transformer can't pass as much energy as may be demanded of it, and this can make the equipment mis-perform in a range of quite subtle ways that add up to degraded musical performance. When saturation occurs, the transformer generates large amounts of third and fifth harmonics — effectively adding distortion to the mains current and voltage waveforms. This then pollutes the supply locally.

The mains transformers used in studio gear will all saturate above a certain mains voltage level. As a result of keeping costs down, the transformers in some makes saturate when the mains is only ever so slightly high. Others are able to take higher voltage levels with no problem, since the makers have spent money to make them work properly over a real-world range of conditions. Some transformer types, particularly high-quality toroidal types, saturate suddenly (at a given maximum voltage) while with others, the saturation is more gradual.

Voltage Dependent Resistors

VDRs are also called 'surge (or spike) suppressors', and similar trade names. These are commonly disc shaped, wire- or tab-ended components that can work rather like an audio limiter, limiting (ie. clipping off) spikes that occur on the mains supply. They are commonly sold in a pre-connected format hidden away inside mains filters, mains adaptors and extensions. The combination with a mains filter can be good, as the filter's inductors helps the VDR to clamp some surge voltages better. A simple type of VDR product is one mounted between Live & Neutral inside a mains plug which plugs in, but isn't connected to anything. This arrangement connects the VDR across your supply without you having to make any wiring changes. British 13A plug pins, with their large contact area and high contact pressure, are particularly suited to this, but it's a rather less stable and workable solution for the weedy pins on most other national plugs, like the European type shown below.

Identifying & Solving Mains Supply Problems

VDRs will provide some protection against outright damage from lightning and switching surges when your local supply is re-energised during a storm or after a system breakdown. But VDRs offer no protection from smaller or longer-lived excess voltages. Typically, they can reduce spikes of thousands of volts to a peak level of about 700V, but no lower. And 700V is still quite damaging, compared to the official peak value of 240V mains, which is 340V. In fact, it's only sustainable if it occurs for a few millionths of a second, just as some people can pick up a hot object without harm so long as they're very quick. As with filters, VDRs can make noise problems worse if they involve connections (from either Live or N, neutral) to the mains earth, unless the earth wiring is sturdy and also happens to be close to the mains earthing stake. VDRs are sometimes held to make sonic enhancements which don't square with levelling a few spikes. The reason is that they also perform as small capacitors that may help suppress, redirect or alter RF signal levels in the wiring. In other words, they can do the same job as an RF mains filter.

The upshot is that VDRs are mainly benign, but also only one tool in the mains enhancement armoury. They are most likely to be useful if you live in a rural area, where lightning strikes have ready access to power lines. They can also help when you're near a factory or other establishment using lots of electric tools, motors, welders, or in a tower building near the lifts, for example. These operations can create a series of spikes on the mains that the capacitance and level-limiting efforts of VDRs should at least help to curtail.

Heavy-duty VDRs may be placed at the supply intake, with a direct, very heavy-duty connection to the earth. Such 'lightning protectors' cannot protect from a direct lightning strike (nothing can), but they do give enhanced protection to rural studios if a strike occurs to the overhead mains wiring, provided it's no closer than 50 feet away.

Enhanced Mains Connectors

These may include better grades of standard connectors, particularly ones with gold-plated contact surfaces. These may seem to make little sense until you realise that most of the time (outside the mains' peak voltage points), the mains connection to your gear can be acting as an aerial for all manner of RF signals that pervade the air around us. At this point, mains plug and socket contacts have only tiny leakage and transformer-magnetising currents flowing in them, and can easily act as detectors (demodulators) of radio signals (when high current is flowing, it can break through the layer of grime and oxidised metal on the contacts, but when the current level is low, the oxidised grime's radio-detecting effect can be stronger). The detected signal then makes its way into the audio path, adding background noise. It is therefore unsurprising that some people who fit gold-plated mains plugs, which don't corrode or oxidise, report enhanced sonic clarity, depth and the like. However, if the area in which your studio is located doesn't suffer from the kind of RF problems that cleaner connections reduce, you may reasonably regard a mains plug with specially plated pins as 'snake oil'. On the other hand, if there's an AM transmitter nearby (long wave, medium wave, or short wave), such plugs could have quite an effect. Even so, if the sort of music you're involved in doesn't benefit from depth or inter-transient silences, you might hear nothing at all.

A practical approach for studios with lots of gear is as follows. When you have a major maintenance session about once a year, upgrade your cheapest mains plugs to decent domestic ones, such as MK or Duraplug types, and wipe down all the mains plug pins with Caig Labs' Dexoit, or any other decent contact enhancer. Also, when equipment is unused, it can be good to leave it plugged into a mains outlet (but switched off). This protects both the plug and socket pins from oxidation and the grime build-up that causes the radio signal/noise detection problem.

Shielded Mains Cables

These are like shielded signal leads, in principle. The braided metal shield intercepts ambient RF signals, but the mains earth wiring can let down the effectiveness of the necessary earthing at radio frequencies — unless you have a low-impedence RF earth connection (more on this in a moment). This matter affects the shielding of leads carrying audio signals less, because the signal connections have higher impedance — so good results can be had without needing such a low-impedance earth. A metal cable shield around mains wires can also create dangerous situations, for example if it gets disconnected, touches live, and pokes out of the mains plug, for example. Therefore extra work is required to sleeve the cable ends, regularly inspect cables, and so on.

The upshot is that metal-shielded mains wiring is recommended only in extreme situations (say, if your studio is next to a powerful radio transmitter), and only when professionally installed (an electrician is probably needed to help you install a low-impedance RF earth, for example).

Having said all that, a new class of shielded cable (called 'Lo-Rad') has recently been developed by Jenving in Sweden using conductive plastic, which is is designed to reduce any shock risk enough to be safe for home studio and domestic use.

Woven Mains Cables

Typically protected inside plastic tubing, cables of this type comprise several loosely and openly woven strands for the live and neutral sides, with the mains earth wire running up the centre. This arrangement may be hidden by curling and placing inside a jacket, but the hosepipe size of the resulting cable gives the game away. The process of weaving the cable is extremely tedious without special, huge jigs — manufacturers have huge, Victorian-style weaving machines — and towers that cost enormous sums. This is one reason why this sort of cable sells for such high sums (usually over £20 per metre).

The apparent benefit of these cables is that they provide a ratio of inductance to capacitance (also called 'characteristic impedance') that is quite different to the ordinary wiring that precedes and follows the short lengths you might use in a studio as gear cables. The result of this is that RF noise already on the line is filtered out and/or damped down. Also, due to the weaving (the live and neutral are broken into many strands which repeatedly cross each other at right angles, so that any mutually induced fields cancel) such cable acts as a sort of 'anti-aerial', meaning that the pickup of ambient RF is reduced.

Isolation Devices

Also known as audio-grade isolating transformers, isolation devices are specialised mains transformers which introduce no change in voltage and stop noise leaking through to the audio path through the mains connections, by 'balancing' the mains leading to audio gear, so both sides (live and neutral) are equally 'above' earth, over a wide range of frequencies. This can make a massive difference to the sound quality in a studio, and is achieved by reducing what's called 'common mode noise leakage'.

Spur Wiring

As described earlier, this involves providing your studio with a more direct, dedicated, mains connection. The beefier wiring helps reduce the voltage drop and interaction between equipment caused by the high peak current being drawn. With a home studio, the spur (which should be a dedicated supply with no loop to tempt circulating earth currents, which only add extra hums and buzzes) also reduces noise from and interaction with other appliances that are being used on the house's other circuits. It's worth pointing out, though, that unless you have electrical knowledge and can interpret the present safety regulations, an audio spur needs to be fitted by a qualified electrician.

RF Earthing

This comprises a solid and suitably deep earth stake (deep enough to stay in the ground water all year round), plated with a fairly inert metal which doesn't make a good RF detector when the groundwater corrodes it. Such stakes are hard to find. Ordinary copper-plated steel ones are not much use, as the surfaces turns to rust in a few years or months. Stainless steel stakes don't corrode, but the surface oxidation acts like a radio detector when bonded with the copper earth wire. Suitable wires (flat braids or fat conductors) provide

Though essential for electrical safety, the mains earth connection is also a common source of RF contamination.Though essential for electrical safety, the mains earth connection is also a common source of RF contamination.

low-inductance connections to the point being earthed, usually some critical, central part of the studio system, such as your mixer's metal casing. The RF earth wire and stake then provide a lower-impedance bypass for RF. To avoid safety hassles, a mains safety-approved capacitor is placed in line with the RF earth, at or near the point of connecting to the casing of the mixer (or other centrally placed metal-cased gear). This special earth wire and stake will then only pass RF noise, not mains faults currents.

For best results, the gear being earthed needs to be near to ground level, so this technique is not really applicable in studios that are several floors up, or where there's no access to the soil. For electrical safety and to avoid insurance hassles, the existing safety earth connections must all be left in place.

Earth Chokes

These are inductors (coils) placed in line with the green/yellow earth wire between your studio's power wiring and the mains supply. The idea is to prevent RF noise from other sources getting to the audio gear. This makes sense, since mains earth wiring, as already noted, isn't good at providing a good RF earth, but is good at spreading RF contamination. The choke has to be a type that will work well up to quite high radio frequencies, while also being made to handle high fault currents and have a low resistance to these, to maintain safe conditions in the unlikely event of a mains earth fault. It also has to be securely connected, and suitably placed where the earth wiring passes between clean equipment (like mixers) and dirty equipment (like PCs and the rest of the house wiring).

Mains-Frequency Regenerators

Some rotational devices, such as the motors in hi-fi turntables and older tape machines rely on the mains frequency for correct speed. Mains frequency variations are heard as pitch variations, usually as 'wow' (a slow speed variation) or as a sudden, one-time speed and pitch change. The mains frequency has to be stable and quite accurate for any national AC grid system to work. In addition, millions of mains transformers across the grid would also be upset (drawing high current and ultimately failing) if the mains frequency were to drop more than a few percent. When a national AC mains supply is under heavy load, the frequency starts to drop, and below a few percent droop, some of the load has to be 'shed'. This explains why wider-than-normal frequency variations are associated with power outages, and all occur most in countries with inadequate national mains capacity.

Since frequency is a national matter (in the UK it's controlled by National Grid plc) there's not a lot you can do if it is varying too much for your gear and ears. If it's outside the statutory one percent above and below 50Hz, then all you can do is take comfort in knowing that everyone in the country will also be affected. The answer is to use a 'frequency-regenerating conditioner', or turntable power supply, such as are made for hi-fi vinyl turntables.

Snake Oil

There are few accessories for mains-related problems which completely fail to work, but some are ill-designed while others are ill-sold, meaning they'll be sold to you when their best possible effect is well down the list of your setup's priorities. As the performance benefits of many mains-enhancing products can only be determined by trying them out, a reputable supplier will have to work on a sale-or-return basis.

It may be worth being wary of mains-conditioning products that are nicely presented with impressive packaging, but have absent or jumbled technical details. A recent example is a box that plugs into a spare power outlet, and merely consists of a large capacitor placed across the supply. The simplistic idea is that the capacitor 'absorbs' any noise on the mains. Equally, it provides power factor correction — but only for a very specific load condition! There are several problems caused by the brute-force of the approach. One of these is that a large capacitor across an AC supply causes voltage rise. This unexpected fact may lead to damaged equipment, especially if the voltage in your area is already high. Second, the cap will exhibit both resonances or power factors that cause overheating in isolation transformers, as well as creating illegally high 'power factors' — essentially 'borrowing' lots of energy off the mains supply without paying a higher tariff for doing so. Thirdly, a capacitor connected from the live side to the earth, can, as noted earlier, cause more noise-related problems than it cures.