Secondly, decide what level of protection you need.

Some types of equipment are more sensitive than others when faced with problems in the mains supply. So today's stabiliser technology aims to protect in several different ways. Make sure you know what your equipment needs protection from and the level of voltage deviation it can tolerate before malfunction and equipment damage occur.

How stable a supply does your equipment need?
Most Watford Control stabilisers will provide an output voltage to within ±0.5% of the preset output voltage, but there is a cost factor to consider. If a lower accuracy, say to within ±5%, is adequate for your equipment needs, then the input voltage range is extended by 5% beyond the figures quoted for the higher accuracy. As the cost of the stabiliser is linked to the input voltage range it has to handle, then accepting a lower accuracy may make it possible to select a more economical unit.

Will transient noise create problems?
Transient noise is present to some extent in all mains supplies. High-energy voltage spikes and surges are introduced into distribution lines by the switching of equipment, especially heavy inductive loads, or by atmospheric electrical disturbance, such as induced lightning strikes. All our stabilisers are fitted with voltage surge protection, which will "clip" surges or spikes to approximately three times the supply voltage.

But will this be sufficient for your equipment? Some systems are little affected by transients, but electronic equipment especially if microprocessor based, can be damaged and make errors as circuits malfunction. In such cases merely clipping high voltage surges will not be adequate, and full transverse mode interference protection will be needed. The wider pulse width of the "spike", the more difficult it is to attenuate. Our units are tested with a 50-microsecond spike generator, and they will consistently reduce a spike of 5000V to a harmless low frequency ripple.

How about "earth to supply interference"?
Common mode interference can also be a problem and most microprocessor-based equipment will require a supply with this earth to neutral noise factor limited to less than 0.25V peak. For this reason you may be considering installing a "clean line" from the mains distribution point, but this will not always give the required level of protection.
Line conditioning is the more positive solution, achieved by fitting an isolation transformer with the secondary neutral linked to earth. This isolation transformer eliminates the need for a dedicated line and at the point of linking neutral to earth the common mode interference is nil.

Stabilisers with added interference suppression are often referred to as "Line Voltage Conditioners" or "Power Conditioners".

Circuit Protection
There are other protective devices you will want to consider. We recommend the specifying of an input or output Circuit breaker which, in addition to giving over current protection, will trip if the output / input deviates above or below a preset level.

You may also want to consider fitting a bypass switch that will facilitate the inspection and maintenance by isolating the stabiliser and connecting your load directly to the mains supply. We can supply them either suitable for wall mounting or inbuilt to the stabiliser.