locking a mcb in the on position

[Farmelectrics]

is it allowed to lock a mcb in the on position data centre spark informs me they have mcbs locked in on so no one accidently nocks breaker off i tell him that could be dangerous as the breaker will not trip in fault condition but he tells me that thermally the breaker will still trip anyone come across this your thoughts please chaps

 

[Sintra]

Yes you can lock an MCB in the on position eg fire alarm supply etc. and yes the MCB will still trip in the event of a fault.

 

[Farmelectrics]

thanks sintra never new that it would still trip 40 and still learning new things lol

 

[Dean Williams]

if you hold the switch of an RCBO in the on position and press the manual trip, you'll see it

 

[Deleted member 26818]

If you attempt to reset a tripped MCB without clearing the fault, it will not hold in.

 

[Engineer54]

Yes you can lock an MCB in the on position eg fire alarm supply etc. and yes the MCB will still trip in the event of a fault.

Yes both MCBS and MCCB's will still trip when locked in the ON position. The switching mechanism of both, has no direct effect on the protective elements within these devices!!!

 

[Marvo]

I'm not sure about the UK regs but depending on the supply arrangement we'd need to provide another point of isolation for the equipment if the MCB or MCCB was locked in the 'on' position.

 

[Engineer54]

I'm not sure about the UK regs but depending on the supply arrangement we'd need to provide another point of isolation for the equipment if the MCB or MCCB was locked in the 'on' position.

Normally, the locking ''ON'' of MCB/MCCB's would only be found on in-house maintained plant or equipment, where the staff responsible would be in possession of the lock key. Can't really see why you would want another point of isolation to be honest, any fault would be cleared by the protective device whether it be locked ''ON'' or not. I guess ...depending on the plant, you could have a local isolator. It would be prudent to have a means of indication (indicator lamps) in such situations, and many of them do, that i've come across!!

 

[i=p/u]

No load isolator are locked on . Old ones.

Never new this either so.....

 

[Knobhead]

At the end of the day, it's no different to a locked DB, switch room or what ever. Bad practice to my mind.

 

[i=p/u]

Wernt saying that when you installing no load isolators many moons ago to protect your motors from being shut down.

 

[Knobhead]

No load isolator are locked on . Old ones.

Never new this either so.....

Since when? Most were designed so they couldn't be locked on.

You would never lock a motor isolator "ON".

 

[i=p/u]

You ever been on a big site tony? :carolers: A guy told me when at tech, some old factories would have these isolators that are locked on cause they no load isolators. = switch all load off right down to main isolator

 

[Engineer54]

Never seen a ''Locked ON'' Isolator in all the years i've been in the industry, including my years in the industrial sector. For a start, you don't install no load isolators on motor circuits, they will be rated isolators...

 

[Knobhead]

You ever been on a big site tony? :carolers: A guy told me when at tech, some old factories would have these isolators that are locked on cause they no load isolators. = switch all load off right down to main isolator

You know I have. To lock an isolator "ON" would lead to instant dismisal.
BTW It off load, not no load!

 

[Engineer54]

Getting back to the original question... I wouldn't say it's a common occurrence to lock an MCB/MCCB in the ''ON'' position, but it can have it's uses in some situations, and is certainly not against any regulations that i know about.

I don't know where this use of ''OFF LOAD'' isolators has come into it, especially on motor circuits. These type of isolators are generally only used as a means of local isolation for maintenance purposes, when working on plant etc, after a full isolation procedure has taken place and are only capable of being locked in the ''OFF'' position....