18th Edition Mythbuster

Guide to the New 18th Edition Wiring Regulations

Guide to the New 18th Edition Wiring Regulations


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Let Cudis shine some light on the <strong>18th</strong> <strong>Edition</strong>.<br />

Do I need to install an <strong>18th</strong> <strong>Edition</strong> Consumer Unit?<br />

No. There has been no change to the design of a metal consumer unit since the 17th <strong>Edition</strong>,<br />

Amendment 3. However the installation itself and circuit protection included must comply with<br />

the current regulations.<br />

Do I need to install 100A RCD’s in split load boards?<br />

No. The use of diversity factors to determine maximum demand when designing an installation<br />

is still an accepted practice in the <strong>18th</strong> <strong>Edition</strong> (following the manufacturers guidelines). In<br />

most cases a 63A or 80A RCD would be appropriate, in cases where there is a possibility of<br />

overloading the RCD protecting the downstream circuits, then it may be more suitable to install<br />

100A RCD’s.<br />

(BS 7671 Chapter 314.1)<br />

Do I need to install Type A RCCB’s as standard?<br />

No. For general purposes, Type AC RCD’s may be used.<br />

Certain installations require the use of Type A, Type B or Type F RCD’s to protect against DC<br />

fault current which may become present on the installation. Such installations include Solar<br />

PV and Car Charging Equipment. These devices can be installed at the location of the DC<br />

installation (at the AC side) and will prevent any DC earth leakage current entering the rest of<br />

the installation.<br />

(BS 7671 Chapter 531.3.3)<br />

Do I need to install a board with RCBO’s to overcome unwanted tripping of<br />

RCD’s/RCCB’s?<br />

No. The total earth leakage of the circuits protected by an RCD should not be more than 30%<br />

of the rated residual operating current (eg. a 30mA RCD, regulation state no more than 9mA of<br />

earth leakage detected on the downstream circuits).<br />

Bearing in mind that some circuits will naturally have more protective conductor current / earth<br />

leakage eg, circuits powering power supply units (like in PC’s) or transformers like LED Drivers.<br />

Careful consideration of subdivision of circuits between the 2 protective RCD’s may be enough<br />

to combat the accumulation of fault leakage.<br />

Although installing all RCBO’s will give more flexibility in the design of installation and reduce<br />

the consequences from tripping as only individual circuits will be affected.<br />

(BS 7671 Chapter 531.3.2)<br />


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