Main Switch Consumer Units
The simplest form of consumer unit, the Main Switch board is supplied with a 100A mains isolator only. When the 17th Edition Regulations first came into being it seemed to many that the days of the main switch board, which is supplied without RCDs, were numbered.
However, Main Switch fuse boards, when used in conjunction with a full bank of RCBOs are now being considered the single best way to satisfy 17th Edition, as this allows for complete separation of circuits thus preventing nuisance tripping.
The downside to this installation is the cost as using individual RCBOs is considerably more expensive than using RCDs with MCBs. Many homeowners however are willing to pay the extra cost for the peace of mind that RCBOs provide.
High Integrity Boards
A ‘High Integrity Consumer Unit’ is one which allows for superior separation of circuits whilst still protecting all circuits from earth leakage. It does this by using three neutral bars which allows for the use of 2 RCDs and a whole bank of RCBOs.
The user may therefore protect all ‘non-mission critical circuits like lighting and ring main on the RCDs whilst protecting all mission critical circuits independently with RCBOs. In this situation a problem with the fridge freezer will not affect the smoke alarms or, for example, the alarm system will not cut power to the tropical fish tank. High Integrity boards provide very good compliance to the 17th Edition Wiring Regulations.
Split Load Consumer Units
A split load board, in common parlance, is one which is supplied with a Main Switch and RCD. Now that we operate under 17th Edition regulations the implied loading of a split load unit is that MCBs should only be put on the RCD side while RCBOs are fitted on the main switch side.
A split load board, used in this way satisifies the 17th Edition Regulations particularly well and cost effectively as it protects all circuits against earth leakage whilst decreasing the risk of nuisance tripping on mission critical circuits through good circuit separation.
Garage Consumer Units
The term ‘Garage consumer unit’ is applied to smaller consumer units and there isn’t anything else particularly special about these consumer units. Most normal domestic environments have only a small number circuits in its garages, garden sheds and outhouses and therefore does not require the larger 10 – 36 way fuse boards used in the main household.
Garage units are normally between 2 and 5 ways depending on what is being used in the outhouse. A normal shed with lighting and a couple of sockets would use a 2 way unit whilst a workshop using a lathe and power tools might opt for a 5 way unit.
Fully Loaded Consumer Units
These consumer units typically come with 2 RCDs and a full bank of MCBs and usually have between 10 and 15 usable ways. Whilst very cost effective and fully 17th Edition compliant they do not provide very good separation of circuits.