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Essexboy7

Does anyone know how many times an MCB can trip before it is meant to be replaced?If there is any official publications on it can anyone point me to them?

Thanks in advance for any replies
 
It would very much depend on the size of the fault currents. MCB's should be able to withstand large numbers of marginal overload trips but if it's a 3kA mcb for example and it's operated several times on a fault current that's > 2 kA then there would be an argument for replacing it.
 
As Marvo has said depends in the fault current you would need to know the break capacity of your MCB and the PFC of the install to make an informed decision. 8ka fault current through a 6ka rated MCB is a change straight away for example as it is beyond the mcbs rated break capacity and will have most likely damaged the MCB. I have seen cases where the MCB hasn't operated but the HBC in the service head has blown as the PFC was beyond that of the MCB.
 
after 2 or 3 x theyre creamcrackered, imo

How do you come to that opinion?
for example on an older building say 30 years old how do you monitor how many times an MCB in its lifetime?

I would tend to agree with marvo. As for coding it in a Condition report i would put it as an observation and uncoded as there is no setfast number and there are a lot of variables.
 
Can't say i've ever seen that in the regs, if im wrong i appologise.

Clients exaggerate, every job you get to the powers tripped 900times, in reality its maybe 2. There's noway of policing how many times an MCB would/could/has trip(ped), so can't see why they'd be a concrete reg supporting the idea. You change it when you need to change it from a proffessional opinion...you can feel by operating the toggle whether its on its way out or not, or from the state of it by visually inspecting it.
 
8ka fault current through a 6ka rated MCB is a change straight away for example as it is beyond the mcbs rated break capacity and will have most likely damaged the MCB. I have seen cases where the MCB hasn't operated but the HBC in the service head has blown as the PFC was beyond that of the MCB.

I would expect the MCB kA rating to be higher than the PFC if it's correctly specified.

As stated you can't police how many times it's tripped but if they're 6kA or less they're cheap and basically disposable items nowadays so we tend to err on the side of caution and if damage is even suspected we replace.
 
If correctly spec'd yes but have had managers who use the reg's allowing for a lower kA rating on an MCB if the suppliers over current protection exceeds the pfc to reduce number of board changes or MCB changes when carrying PIRs in the past. I agree its not ideal but is permitted in the regs don't have the bgb with me at the mo to get the reg number.
 
Marvo if it 6Ka or M6 which is the old BS3871 MCbs replacements can be expensive or impossible to get. Prime examples are
Ottermill unavailable anywhere exept sometimes ebay
MEM Alternatice MCbs made by Eaton but single cost about ÂŁ80
square D Qoe range replacements are available from shnieder but expensice
 
just checked the spec.It is a 63amp 3 pole breaker and says it is ok for 20,000 cycles mechanical operation and 10,000 cycles electrical operation


If it was only 2 or 3 it would need replacing after you have done 3 periodics
 
Marvo if it 6Ka or M6 which is the old BS3871 MCbs replacements can be expensive or impossible to get. Prime examples are
Ottermill unavailable anywhere exept sometimes ebay
MEM Alternatice MCbs made by Eaton but single cost about ÂŁ80
square D Qoe range replacements are available from shnieder but expensice

I forgot about this and you have a valid point with regard to the UK regs. Where I am we're allowed to replace any make MCB with any other make of MCB as long as it's correctly rated and identical form factor.
 

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