Life of an MCB

[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

 

[Knobhead]

Anyone thought of looking on the ASTA web site?

 

[Engineer54]

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.

Commonsense rules.... Well at least in S Africa!! lol!!

 

[Guest111]

trust Tony to come up with the obvious answer.

 

[Marvo]

Commonsense rules.... Well at least in S Africa!! lol!!

Yeah, on this particular occasion I'd agree. I can't help thinking the restrictiveness of the UK regs on this issue would overall be less safe by encouraging the use of second hand MCB's or the use of old and suspect units beyond the time they should.

 

[scotsparky]

Would you apply the same thought process for both overload and short circuit currents for changing the mcb guys?

An overload current is very small compared to a PFC or PSC so dont worry about it. It it can handle a 10,000A PFC then it will happily handle an overload up to 5 time rated value

 

[scotsparky]

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.

marco BS3871,BsEN 60896 are interchangable and nothing wrong with using either BS 3871 has just been superceded but still valid and sometime second hand is fine i keep a load in my van.
The point i was trying to make was the cost of replacing after 2 or 3 faults.
In my opinion and experiance MCBs are failsafe and if they break will not allow a current to pass through it.

 

[SYKRAPS]

An overload current is very small compared to a PFC or PSC so dont worry about it. It it can handle a 10,000A PFC then it will happily handle an overload up to 5 time rated value

Just wondered what your reasoning was and obviously could not rely on the history that may be provided by a client as they don't know the difference in the majority of circumstances.

 

[scotsparky]

Anyone thought of looking on the ASTA web site?

American Society ofTravel Agents?? they got deals on?

 

[GLENNSPARK]

well as far as i know their rated to break a Max. fault of upto 16kA before firing...
the max. in the box on the side of them refers to the max. breaking capacity whilst still being good for continued service (6kA, 10kA etc)

 

[Engineer54]

marco BS3871,BsEN 60896 are interchangable and nothing wrong with using either BS 3871 has just been superceded but still valid and sometime second hand is fine i keep a load in my van.
The point i was trying to make was the cost of replacing after 2 or 3 faults.
In my opinion and experiance MCBs are failsafe and if they break will not allow a current to pass through it.

Not always so!! I've come across quite a few over the years, where the contacts have welded themselves together!! So they couldn't be switched off!! I will admit however, that most have been 3 phase jobbies!! lol!!

 

[Marvo]

marco BS3871,BsEN 60896 are interchangable and nothing wrong with using either BS 3871 has just been superceded but still valid and sometime second hand is fine i keep a load in my van.

To be honest I'm not familiar with the UK number designations or the in's and out's of the BS regs but I understood that your regs prohibited replacing a proteus MCB with a SquareD for example even if they're the same form factor. I heard several times on here that you must use the same make (manufacturer). Maybe I misunderstood in which case apologies in advance.

The point i was trying to make was the cost of replacing after 2 or 3 faults.
In my opinion and experiance MCBs are failsafe and if they break will not allow a current to pass through it.

Agreed if you exclude RCD's then overload protective devices are generally failsafe in nature. Once in a while we've experienced one that's overheated internally due to damage of the main contact surfaces but it's pretty rare.

 

[Marvo]

Not always so!! I've come across quite a few over the years, where the contacts have welded themselves together!! So they couldn't be switched off!! I will admit however, that most have been 3 phase jobbies!! lol!!

We've had mostly MCCB's with the symptoms, I can't remember a domestic type MCB that done this. Maybe we've just been lucky.

 

[Engineer54]

We've had mostly MCCB's with the symptoms, I can't remember a domestic type MCB that done this. Maybe we've just been lucky.

These weren't on domestic installations, mainly on commercial installs. There's not much different on basic MCCB's to that of standard MCB's. And yes in most of the cases, due to over heating of the internal contacts from loose cable terminal connections... But not all!!

 

[kingeri]

I went to a job a while ago where a ring final had been put on a 5a circuit breaker, the homeowner said it had been like that for many years and tripped out almost everyday day during that period. I inspected the breaker and it was in excellent condition and was still happily breaking overload currents.

 

[GLENNSPARK]

I went to a job a while ago where a ring final had been put on a 5a circuit breaker, the homeowner said it had been like that for many years and tripped out almost everyday day during that period. I inspected the breaker and it was in excellent condition and was still happily breaking overload currents.

and did you do a PFC on it?...this would have confirmed what it was actually breaking....