Special locations and the 17th Edition

Choosing a suitable RCD is, however, not always as easy as it may seem. Let's first consider caravan and camping sites. These days, it's very likely that a substantial proportion of the loads will be electronic - televisions, computers and even fluorescent lights with high-frequency ballasts fall into this category. Loads of this type generate pulsed DC residual currents that can prevent standard RCDs from tripping under fault conditions.

Not surprisingly, leading manufacturers of RCDs, such as Schneider Electric, have developed products to overcome this difficulty. Particularly where there is a very high proportion of electronic ballast loads, or where the loads include a lot of equipment fitted with interference filters, a good choice is likely to be the new reference Si RCDs. These also have the benefit of reduced sensitivity to the supply surges caused by lightning strikes, which may be an important benefit on those camping and caravan sites that are fed by long outdoor overhead lines.

But what of swimming pools and similar installations? In some cases, these may pose problems that are rather like those already discussed, in that the loads could include fluorescent lighting, and any pumps used may, in these energy conscious days, be fitted with variable speed drives. In these instances, the use of reference Si RCDs is recommended.

What about corrosion effects?

There is, however, another issue to be considered - that of the potentially corrosive environments. The presence of moisture, possibly loaded with salt, is a distinct possibility, and chlorine, which combines with water to produce hydrochloric acid, is commonly used to treat the water in swimming pools. RCDs used in these areas are typically enclosed in protective enclosures. This adds to cost, however, and even the best of enclosures offers no useful protection when the door is open.

There is another solution - RCDs that can withstand adverse operating conditions. Once again, Schneider Electric can offer suitable products, in the form of reference SiE RCDs. These units are specially sealed to prevent the ingress of moisture and other contaminants, and have exactly the same electrical characteristics as reference Si RCCBs. They therefore provide excellent protection with a minimum risk of nuisance trips in even the most demanding of applications.

While most electrical contractors, as well as the specifiers and designers, of electrical installations now understand that the 17th Edition of the IEE Wiring Regulations places greatly increased emphasis on the use of residual current protection, not all may yet be aware of the benefits offered by reference Si and reference SiE devices, particularly in Special Locations.

The criteria for selecting these products are, however, reasonably straightforward, as has been outlined in this brief item. Further advice is readily available from expert suppliers of circuit protection equipment such as Schneider Electric.