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Electrical question!!


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I have just bought a 500w spotlight to replace my existing outside light. I fitted it but it doesnt work! The old light still works but when I connect the new one - nothing. I've checked the fitting is ok by putting a plug on the flex and plugging it into a socket and its fine. But it just refuses to light up on the existing lighting cable. Any ideas?

 

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Presumably the cable you have fitted the plug to has come out of a junction box ? Could the feed into this have come loose or disconnected  ? I can only imagine there is a break in supply at some point along the lighting circuit if it works with a plug on and the rcd hasn't tripped.
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A long shot, but it might be that corrosion or a bad connection in the feed is causing a big enough voltage drop with the large lamp sufficient to prevent it illuminating, whereas the previous smaller lamp drew a much lower current with consequent lower voltage drop. If you have a meter try checking the voltage at the connection.

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[quote user="Alane"]

A long shot, but it might be that corrosion or a bad connection in the feed is causing a big enough voltage drop with the large lamp sufficient to prevent it illuminating, whereas the previous smaller lamp drew a much lower current with consequent lower voltage drop. If you have a meter try checking the voltage at the connection.

[/quote]

That will only yeild any useful information if after having measured (and found) mains potential it is measured again under the load of the 500 watt fitting, this would show up any resistive volage drop as mentioned above.

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JR is correct in his post. In order to determine the voltage drop I mentioned you will need to measure the voltage before and after connecting the lamp. As this is an outside lamp I would check all potentially exposed junction boxes and connection points. Water leaks into electric connections and the associated corrosion can cause all sorts of strange effects. 

You mention that the outside connection has no earth connection. If all else fails it might be worth checking , after isolating the supply, that the two connections you have really are phase and neutral. It might just be that you have phase and earth and the neutral wire has been "lost" in the gaine.

Good luck.

 

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It would if the OP's installation is recent but we don't know that. He might have a cartridge fuse installation. It's always difficult trying to help in these situations and striking the balance between asking pages of questions and trying to make helpful suggestions.
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This is begining to sound like '20 Questions' or 'Ask me Another' isn't it [:D]

Sorry if this is repeating what others have said but from everything you've described the problem can only be one of voltage drop caused either by a bad connection, or connections, or perhaps the whole thing being wired with very thin wire incapable of passing the current required for a 500w bulb. I'm sure we've all seen horrific examples of amateur electrical installations in France!  If this were the case however I think your nose or you smoke detector might have discoverd it before now [:-))]

Another possibility is that you've got live and earth but no neutral. In this case the amount of current you could pass down the earth stake might be enough to light a small incandescent bulb but would not be enough to get the barest glimmer out of a 500w one.

What size (wattage) was the original light and did it work and why are you changing it, was it too dim [blink] [Www]

 

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The original bulb is 60w and yes it was being changed to light the area up a bit better. The installation does have breakers and RCDs so it kind of rules out the phase and earth suggestion. I quite like the voltage drop idea as its beginning to look like the only possible explanation and I will be testing it as soon I get the opportunity. Thanks everyone, I'll let you know.
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