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We have had a few table lamps blowing bulbs and, at the same time, the 3A fuse in the plug. The wiring in the house is mix of of old and new, mainly all within the last 10 years and an up to date consumer unit. This all happens on the same few sockets which are all part of the house's original socket ring main, albeit mostly new wire.

 

Now, I understand how a blowing bulb might well trip a switch in the consumer unit but can't see how it can blow the lamps's fuse whilst leaving the trip alone!

 

I have one of these and it says all is OK: https://www.toolstation.com/socket-tester/p82826

 

I should add that it can be weeks or months before it happens again and it does seem to be the blowing bulb that is the trigger to the fuse going.

 

Any ideas?

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I am not an electrician but there may be a simple reason why the fuse in the plug blows first. My understanding is that they blow at 1.66 times their rating. So a 3 amp would blow at 4.98 amps. But your lamp is plugged into the power ring main and the breaker for that may be as high as 32 amps so that will not throw. Maybe check to ensure the lamp plugs are not getting warm and consider having them PAT tested?

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sounds like dodgy bulbs. The only time I have come across this is when someone put an incorrect voltage bulb in a standard lamp. Obviously, check things like the condition of the flex, lampholder etc of the lamp. See if the same bulb works OK in a ceiling pendant.

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Not a spark but know enough to be dangerous :)

 

Bulbs when they blow can pull a large current that will exceed the rated fuse, especially if the bulb is cheap, however as you're on the ring main for the sockets youre probably not going to trip a 32amp mcb. You may even not have genuine fuses if you've bought more from sources that have been a bit uncareful - worth checking although bulbs are most likely. Ive had cheap halogens take out dimmer modules a few times now. 

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Thanks for all the replies above which are all similar. My only confusion is that the trip switches are normally very sensitive and when a bulb blows in our kitchen diner (lights ring), it invariably throws the trip switch. 

 

Is the difference that we are on a socket, not lighting circuit so the trips will need more current to trip?

 

 

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Thanks. OK, I now understand :) Thanks all. Just shitty bulbs then. Great relief. We still are not all LED but bit by bit we are getting there and then I guess these issues will (almost) go away.

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All fuses are not the same and do have different rupturing characteristics. At work we often get a 13A fused spur supplying some equipment that goes faulty and it ends up blowing the 16 or 20 fuse in the fuse board and not the plug top fuse

Circuit breakers can react faster especially where a short circuit occurs, I've had a similar experience with a 110v transformer tripping my 32A ring main breaker and not the 13A plug top because the initial surge current of the transformer energising can draw quite a bit of current.

Of course RCD's will only trip on the difference between the live and neutral current, generally 30mA.

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