Reversed MCBs

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binky

binky

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Ok, todays testing job,  a small 12 way 3 phase board. It took me  a little while to notice all the MCBs had been inserted the wrong way around, which, if I understand MCB operation correctly means they are protecting the busbar! Question is, what code? I reckon code 1 as they are not protecting the cables, your opinions please.

 
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Check manufacturers instructions but normally on AC orientation doesn't matter. DC however can be very different.

 
I remember we had some doubts with  some Crabtree  TPN boards .     Triple pole breakers  ...I think were marked somehow ,  busbar this side  or similar , but they didn't fit that way round  ,  terminals  didn't  line up with the fingers .     Ah!   Also  the din rail catch would have been at the wrong end .    

I think it was a labeling problem. 

 
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Andy™ said:
they will work either way. same as putting a fuse in the wrong way
Click to expand...
Except they don't fit on the busbar properly - that's why I noticed it.  Now I was under the impression that an MCB will only detect  a fault  upstream of itself, which would suggest an orientation, but I suppose that's becuase only leccy going to cct flows through the MCB?

 
binky said:
Ok, todays testing job,  a small 12 way 3 phase board. It took me  a little while to notice all the MCBs had been inserted the wrong way around, which, if I understand MCB operation correctly means they are protecting the busbar! Question is, what code? I reckon code 1 as they are not protecting the cables, your opinions please.
Click to expand...


How can they be the wrong way round on AC?? the current goes both ways..

IF there is a drawing on them, or other terminal ID, then that should be observed obviously. Other than that, so long as they seem to be fitted securely, happy days..

The makers instructions should be followed though as the board was "type approved" of whatever they call it the way the makers intended.

john..

 
Back to front, what is the right way?

The feed is normally connected to the fixed contact, arcing horns (if fitted) and the arc chutes first plate so that the arc is drawn up and across the splitter plates and therefore cooling the arc. A blow out coil is used in large breakers where a heavy fault has to be cleared quickly. It draws the arc to follow the curved arcing horn and pulls it to a longer and cooler path.

 
Tony S said:
Back to front, what is the right way?

The feed is normally connected to the fixed contact, arcing horns (if fitted) and the arc chutes first plate so that the arc is drawn up and across the splitter plates and therefore cooling the arc. A blow out coil is used in large breakers where a heavy fault has to be cleared quickly. It draws the arc to follow the curved arcing horn and pulls it to a longer and cooler path.
Click to expand...


Still won't matter which way round it's installed on an A.C. circuit.

@binky think about the physics behind it. 

 
have been revising breakers - I've spent far too much time over the lasy 6 years doing domestic solar, which is so simple, these things barely merit consideration...

Thank you all.

 
Rob. said:
Still won't matter which way round it's installed on an A.C. circuit.
Click to expand...


I do know that RoB.

I inherited two 3.3kV 1600A ACB's connected back to front. It took me quite a while digging back through the records to 1965 to find out why. The motor was supposed to have a PF capacitor so both cable boxes were attached to the busbars. As per usual the job was never finished as they’d run out of funds.

 
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I draw the line when breakers are installed in both configurations on the same board. came across it on a Hager TP board. It really does my head in to see MCBs installed like that.

 
Tony S said:
I do know that RoB.

I inherited two 3.3kV 1600A ACB's connected back to front. It took me quite a while digging back through the records to 1965 to find out why. The motor was supposed to have a PF capacitor so both cable boxes were attached to the busbars. As per usual the job was never finished as they’d run out of funds.
Click to expand...


I wasn't questioning you Tony, just making sure others new. 

An I hated those motors, they seemed to go through a fad of connecting PFC caps right along side large motors. Never did they fit any monitoring. As soon as the Caps failed. Which inherently was every 3 - 4 years. The O/L protection for the motors were out by a mile. 

 

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