Melted mains circuit breaker

[Skindy]

Hi. Does anyone know why a 800A mains circuit breaker just melt? Thanks

 

[malcolmsanford]

loose connection, over loaded

 

[johnboy6083]

if its overloaded, then it sounds like its running just under its tripping current, or the conductor is too small to carry the overload current. maybe the In setting is set too high for the cable. just guessing here !

 

[SirKit Breaker]

loose connection, over loaded

That would be my guess as well. But just as an afterthought is there any signs of corrosion around its terminals?

 

[Skindy]

That makes sense. We had simeone

 

[Skindy]

No corrosion. We had someone fit a couple of months ago because it kept tripping every few weeks.

 

[Engineer54]

Did they fit a new breaker, or just refurb the old breaker?? Did those that fitted the breaker last, thoroughly test the circuit it was supplying?? Did they do load checks, before setting the breakers protection/tripping perameters?? And last but not least..... was this breaker the withdrawable type, and if it was did they check the contact resistance between breaker and switchboard contacts when the breaker was in the fully inserted position ???


Other than that, it would indeed be reasnable to suspect loose bolted connections onto bus bars or cable(s)....

 

[Dcf]

Come across a 400a main switch that was burnt out .all connections tightened by king kong I reckon.Stretched all the bolts so the connections were actually looseYou picture the result. Torque wrench required in the first place