2008-07-22
Eaton’s Memera 2000AD consumer unit range offers a wide choice of options to meet the RCD requirements of the 17th Edition Wiring Regulations (BS 7671:2008). These include a number of new isolator-controlled dual-RCD units together with existing in-line, split-load and dual-RCD units. these offer solutions to suit different cost constraints and protection requirements.
The consumer units offer all the benefits of the Memera 2000AD range including the variable split-busbar system that allows any split between two different groups of circuits to be decided on-site. The devices include Type B, C or D miniature circuit-breakers in ratings up to 63A; instantaneous and time-delayed RCDs and Eaton’s unique ‘pod’ RCBO. This last device is available in 11 standard ratings but is capable of being field-fitted with different RCD pods to achive hundereds of different combinations of sensitivity and overcurrent rating.
Individual RCBO protection
The most effective solution is to provide individual RCBO protection of each and every final circuit (Fig.1) This solution can make use of a standard isolator-controlled in-line consumer unit. The RCBOs provide both overcurrent protection and residual current protection of each circuit. When an RCBO trips, all other circuits will be unaffected. Individual circuits feeding freezers and other critical equipment can be protected by MCBs. Unfortunately, the cost of individual RCBOs make this the most expensive option.
The Memera 2000AD range offers in-line consumer units with up to 19 outgoing ways. The unique ‘pod’ RCBO is only one 18mm module wide, in overcurrent ratings up to 63A.
Isolator-controlled dual-RCD protection
The next level of protection is to provide an isolator-controlled dual-RCD consumer unit feeding two groups of circuits, with miniature circuit-breaker protection on each outgoing way.(Fig. 2). This approach requires only two 30mA RCDs to protect the entire installation. The installation designer must divide the circuits between the two RCDs in such a way as to minimise the collateral risks, as required by Regulations 314.1&2.
The Memera 2000AD range includes 8-way, 12-way and 15-way dual-RCD consumer units with a 100A isolator feeding two busbar sections each protected by a 30mA RCD. Memera’s variable split busbar system means that the installer can decide on the number of ways to be allocated to each RCD.
Isolator-controlled dual-RCD unit with additional unprotected ways
A variant on the dual-RCD approach is to have a third group of circuits which are fed directly from the isolator (Fig. 3). These might have MCB protection, if they are feeding specific circuits that do not require RCD protection, or they might have RCBO protection of individual circuits, ensuring these do not cause unwanted failure of other circuits.
The Memera 2000AD range includes a 15-way unit (AD12HEHE3D) which offers twelve ways divided between the two 30mA RCDs plus a third busbar offering three ways fed directly from the isolator.
Conventional split-load unit with a mix of MCB and RCBO protection
A fourth approach is to use a conventional split-load consumer unit having some ways fed directly from the isolator and some via a downstream 30mA RCD (Fig. 4). The circuits which are not controlled by the RCD can then be provided with individual RCBO protection (or MCB protection only if feeding specific circuits that do not require RCD protection.) This solution strikes a balance in cost and versatililty between the consumer unit with individual RCBO protection on every outgoing way and the dual-RCD solution.
The Memera 2000AD range offers split load consumer units with 10, 14 or 17 ways and the variable split-busbar system again allows on-site definition of the split between isolator-controlled and RCD-controlled sections.
Conclusion
In general, the optimum balance between cost and functionality is the isolator-controlled, dual-RCD, split-load consumer unit. The 100A isolator acts as a main switch while two 30mA RCD’s provide residual current protection of two groups of circuits.
Consumer units are also available with single RCD incomers of 30mA sensitivity, however their use is unlikely to satisfy the requirements of Regulation 314.1&2. if used as the main board in an installation.
A guide to the RCD protection requirements of the 17th Edition and the consumer unit options can be downloaded by clicking HERE or by requesting Form No. BR00400004U
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