Hello,

The lights would not work this evening. I found the fault was the mcb.
How common is mcb failure, what causes it, and what are the sympoms?
I've never known it to happen before.

Thanks.

nospam wrote:

The lights would not work this evening. I found the fault was the mcb.
How common is mcb failure, what causes it, and what are the sympoms?
I've never known it to happen before.

Generally it is fairly uncommon with most brands. However I have seen it
happen with some Proteus MCBs made by Geyer.

The symptoms in that case were that sometimes when you switched them on
mechanically they failed to make any electrical connection. Turning off
then back on again would often fix the problem.


--
Cheers,

John.

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| Internode Ltd - http://www.internode.co.uk |
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| John Rumm - john(at)internode(dot)co(dot)uk |
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On Mon, 01 Oct 2007 02:49:33 +0100, John Rumm
wrote:


Generally it is fairly uncommon with most brands. However I have seen it
happen with some Proteus MCBs made by Geyer.

The symptoms in that case were that sometimes when you switched them on
mechanically they failed to make any electrical connection. Turning off
then back on again would often fix the problem.

Hello again,

In this case we came home one night and the lights did not come on;
there were no other symtpoms. We looked at the mcb and it was still in
its "on" position, it had not tripped. I changed bulbs, checked
wiring, etc and found no fault so tried another mcb and that worked. I
put the old one back and it didn't, so I know it's the mcb.

It's a crabtree btw.

It's just I thought it would trip to "off" if it failed or take the
rcd with it. No buzz, no smoke, no burning smell, nothing

nospam wrote:

It's just I thought it would trip to "off" if it failed or take the
rcd with it. No buzz, no smoke, no burning smell, nothing

One possibility that can occur (although rarely) - especially if you are
close to a substation - is the fault currents that can flow may exceed
the breaking capacity of the MCBs. This can result in them failing
terminally when attempting to clear a fault.

(most MCBs can break upto 6kA, although some designed as plug-ins for
old wylex units can be as low as 3kA)



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

"John Rumm" wrote in message
...
nospam wrote:

The lights would not work this evening. I found the fault was the mcb.
How common is mcb failure, what causes it, and what are the sympoms?
I've never known it to happen before.

Generally it is fairly uncommon with most brands. However I have seen it
happen with some Proteus MCBs made by Geyer.

Sometimes they just fail. Infrequent but it happens.

Adam