17th Edition Consumer Unit: What's It All About?

The term '17th Edition Consumer Unit' is now one of the most commonly used and misunderstood in the UK Electrical vernacular

. Through lack of industry conformity the term has come to mean a consumer unit supplied with two RCDs. BUT: This does not necessarily mean the consumer unit abides by 17th Edition Regulations and certainly does not mean that other consumer units are not 17th Edition compliant.

Let us first remind ourselves of what the 17th Edition Regulations actually mean in terms of circuit protection: The 17th Edition regulations state, quite simply that all circuits must be protected against earth leakage, which means in laymans terms that individuals are protected against electric shock.

This may be done by using an RCD (Residual Current Device), which protects a bank of circuits against earth leakage simultaneously or an RCBO (Residual Current Breaker with Overload protection), which protects an individual circuit.

Every installation is different depending upon a number of variables including the number of circuits, the types of device being protected on each circuit, the loads on individual circuits and of course the customers budget. For this reason all consumer units are configurable upon installation and may therefore protect against earth leakage using a combination of RCDs, RCBOs or both.

In general each of the four generic designs of UK consumer unit; Main Switch, Split Load, High Integrity and Dual RCD all meet the requirements of the 17th Edition. However, depending on the installation variables it becomes apparent that some designs offer greater compliance than others by enabling better Division of Installation or separation of circuits, which prevents nuisance tripping.

To clarify the situation the UK consumer unit manufacturer Wylex has introduced a 5 star system, akin to that used by hotels, to grade 17th Edition compliance. Ironically, the very consumer unit which has over the last two years been marketed as a 17th Edition Consumer Unit, is the one which scores lowest with only 2 stars.

The Dual RCD consumer unit was originally considered the best way to [ cheaply ] satisfy the 17th Edition Regulations, which is why they became known as 17th Edition Consumer Units. But this configuration does not allow for any separation of circuits and therefore crucially, does not allow for a separate smoke alarm circuit and makes no provision for nuisance tripping.

Under the Wylex system the only type of consumer unit which scores five stars is the older type Main Switch consumer unit as it allows for full loading of RCBOs therefore providing complete independent circuit protection against earth leakage. High Integrity and Split Load consumer units both score 4 stars as they allow for a certain amount but not complete, circuit division.

In summary, a consumer unit cannot inherently be 17th Edition and this has become a misleading if not dangerous misnomer. Only when it is installed and loaded according to the 17th Edition Regulations and having taken into account the specific installation variables can a consumer unit be considered 17th Edition.

by: Darren Gilbert

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