I do not know what prevents the design engineer to select or the maintenance engineer to replace a breaker with a suitable time-current characteristic in consultation with its manufacturer so that the damage to its terminals or associated wiring of the breaker is avoided by the timely tripping of the breaker on any over load above its setting.
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- Thread starter Little Bill
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I do not know what prevents the design engineer to select or the maintenance engineer to replace a breaker with a suitable time-current characteristic in consultation with its manufacturer so that the damage to its terminals or associated wiring of the breaker is avoided by the timely tripping of the breaker on any over load above its setting.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Breakers and fuses are not built with the time-current characteristics that you seem to think exist.
The system designer needs to properly compute and estimate loading to prevent this type of issue, this is one reason for the 125% factor in circuit sizing.
However, the user needs to take some responsibility also.
No, I did not mean custom built breakers and fuses but the designer should exercise due diligence in selecting them from their general population so that the protection of the system and avoidance of failure of protective devices themselves by such as running a breaker at 115% of its operating current without its timely tripping is ensured. If selection proved wrong in the field, the breaker needs to be replaced with a correct one.
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- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Probably not.
It is likely the load needs to be reduced.
Protective device and conductors sizing need to be coordinated, if the current is excessive for the breaker, it is likely excessive for the conductors also.
Is not the tolerance band in the breaker charactreistic the culprit here?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
For the most part, breakers and fuses have been designed with thermal characteristics that coordinate with those of insulated conductors, including the tolerance band of the insulation.
spark master
Senior Member
- Location
- cyberspace
When I was young, working on an assembly line (summer job), they had problems with overloaded circuits. They placed a big fan, blowing directly on the panel. Problem solved. Back then I even thought it was a stupid idea. But it worked.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
It worked at keeping the process running. At same time it ultimately shortened the time until total failure of something.
I had customer that was tripping motor overload for an auger. Of course they needed to get the order done so it could be shipped, so they placed a guy at the motor starter, and his job was to reset it as soon as it tripped, which was every 3-5 minutes maybe.
They did call me, not sure how long they were having problems before I got called, but it took me at least 45 min to an hour before I got there.
Motor was overloaded because of high fat product and gumming up of product in the auger - simple cleaning of auger would have been best solution, and is what was done to decrease the load on the motor, but instead they kept resetting that overload as quickly as it tripped, that motor was so hot when I got there you could have put a pan on it and started cooking lunch. Was amazing it still worked. But we were also talking about only a $200-400 motor and an order that needed to ship that was worth thousands - so guess what management puts a priority on?
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