Guidance for other trades

It’s important to touch upon this in order to ensure a safe install. After all, not all work is notifiable and homeowners, landlords, and kitchen and bathroom fitters will always carry out works to electrical installations.

Main Protective Bonding

Main protective bonding has been touched on elsewhere on this website. In the domestic world, it will be 10mm or 6mm if older. There’s a few key point to make sure your MPB is idiotproof:

Go for 10mm. Bigger is better.

Bond to metal pipework such as water and gas as it comes out of the ground, preferably before any branches and within 600m of it entering the property. A massive clue to finding where it first enters the property: ask the customer where their gas meter and water main stopcock is. Thank me later.

More bonding is better than no bonding. If you want to ‘cross bond’ in the airing cupboard or take an earth clamp to your metal mirror frame, feel free to do so.

Supplementary bonding in the bathroom

Time and time again we find supplementary bonding chopped, partially missing, or completely removed and never reinstated.

Anything that is located in the bathroom (or room containing bath or a shower) that is powered by the mains needs extra protection measures in order to reduce the risk of shock (for obvious reasons). This includes your bathroom light / heater in the bathroom / electric shower / all singing all dancing mist free electric mirror. They all require extra protection.

This can be afforded in a number of ways but the foolproof belts and braces way of providing this extra protection is with supplementary bonding. This bonding needs to string every earth core that goes to every current using accessory in the bathroom, and every conductive part you can come into contact with in the bathroom. This includes: radiators, hot and cold pipes, fancy steelwork, traywork for a suspended ceiling, etc etc. The bonding needs to be atleast 4mm.

With a bit more finesse, and possibly help from someone in the know, all circuits passing through or providing power to the bathroom needs to be protected by a 30mA RCD. With the correct main protective bonding (which should already be there), you now have the extra protection in the bathroom.


It’s interesting that this little code is well known in the electrical world, but isn’t particularly well broadcasted elsewhere. As electricians, we have to keep to zones when we install cables in the walls, such that we have a good idea of where cables are likely to be hiding once plastered over.

Not only is this good practice for us to do so, but it saves the latter embarrassment from accessing into a live cable whilst putting up great auntie Evelyn’s picture frame.

All accessories such as light switches, socket outlets, fused spurs, etc, have zones that go horizontally and vertically across the entire face of the wall.

Zones can also be found up to 100mm from the ceiling and up to 100mm from the inside corners of the room.

This is good to keep in mind, it might save you a lot of hassle!

If you require our assistance, please do get in touch on 07478159026 or use our quick and convenient help me! form

If you’ve made a serious boo-boo and have an unsafe situation on your hands, please see our Emergency Call Out Page for further guidance.

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