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Steamdrivenandy

What do I do with earth leads?

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I recently had a mains electric boiler fitted in a seatbox. The installers fitted a square black fused switch on the outside of the box, but it doesn't have a tell-tale lamp which would be useful. It also doesn't match the rest of the sockets/switchgear in the van, which are all CBE.

 

I have purchased a CBE fused switch, where the actual switch lights up red when 'on', plus the relevant support and decor frames. On opening up the existing switch I see that both the supply and the feed to the boiler have earth wires that are screwed to terminals on the switch. The CBE switch has no terminal/s for earth wires. Now I know very little about electricity and I'm wondering what I should do with the earth cables when I swap to the CBE switch?

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First check the rating of the CBE switch you have. If it is mains rated with illumination I would expect the light to be a 240V neon lamp, in which case a neutral wire would need to be connected to the switch to provide a return path for the neon lamp. If the red light is provided by a LED then the switch is probably only rated for 12V DC and should not be used for mains switching.

In general the earth continuity will need to be maintained so the two wires you have will probably need to be linked together, and then continuity checked between them and the vehicle chassis.

Without further information it is impossible to guess the setup you have so please post an image or two and we can take it from there but in the meantime for your own safety, do not change anything.

Gordon

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I'm not doing anything to it for the moment Gordon and it is a 230V fused spur switch  http://www.rainbow-conversions.co.uk/cbe-motorhome-caravan/cbe-230v-fused-spur.html but the current version has the whole switch in red, rather than just a small slit. I'm quite happy with the rest of the wiring as it came with a diagram and the terminals are all marked the same on both switches, so I can just swap them. However the earth wires foxed me.

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I presume the switch looks something like this.

CBE 230v Fused Spur.jpg

 

The current circuit will either be single pole or double pole switched as below, and I guess the new circuit will be like the bottom illustration? The outer rectangle represents the switch case/cover and needs to be earthed if made of metal but not if plastic. The earth needs to have continuity and if there is no provision for this at the switch you will need to provide a connection block to link between the common earth and the boiler case.

Single and double pole switching with and without enclosure.jpg

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The new switch is identical to your picture Gordon, single pole fused spur. I haven't disconnected the existing switch yet so can only say it's a fused spur. I have no idea what the difference is between single and double pole and why it should matter. And yes, the whole of the switch and support frames etc are plastic.    

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Single pole spur switch only disconnects the live wire, leaving the neutral return connected. A double pole spur switch disconnects both live and neutral so effectively isolating the appliance completely.

Double pole switching is something that is essential if you connect to a continental mains supply where both wires are connected to a live feed of 120V above earth giving a total of 240V between them to power the appliance. In the UK we supply 240V above earth to one wire only (live) and the neutral return wire is only a few volts above earth so does not present a hazard if touched.

Gordon.

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