MCCB Tripped, Help Needed

You may need to attach a fast acting recording meter to see if you can capture the actual tripping event. t could be that 2 minutes into it, something happens that causes an instantaneous trip, i.e. 10x the Ir. Sometimes if there is a short circuit point, it doesn't show up until something heats up sufficiently.

Also check to see if your MCCB has trip functions for anything else, such as ground fault (Earth Leakage or Residual Current).

Dear JRaef,

There isn't have any Earth Leakage protection in the MCCB and in the control panel. Can you please describe further regarding the fast acting recording meter? Thnaks

A data logger type of meter. I say "fast acting" because some products are out there which only record events every second or more, too slow for what you need. Something like a Dranetz meter which samples 32 times per second is what you need.

dranetz-bmi data logger

Or if you have a PC available, you can use a good multimeter to capture the data and then analyze it on a PC with software at a later date.

fluke 289

Sometimes you can rent meters like this if you don't want to buy one.

Kindly check the AT (Ampere Trip) of your MCCB and also type if you are using ELCB=earth leakage circuit breaker.

Dear Sir,

I mean it is Metal Clad Circuit Breaker. If it is so , just take a megger test of the equipment, and if it has tripped , the cause may be due to vermin fault.

As the rest of the parameters as informed by you are ok.

Regards,

Ulhas Pradhan

Dear Sir,

MCCB means Mould Case Circuit Breaker, I have no idea the same as Metal Clad Circuit Breaker. By the way, how to use a megger to trip a Mould Case Circuit Breaker? Can you share it? Thanks

hi fri

You need to check first MCCB condition.this MCCB ampere rating is correct or not because of u don't mention this MCCB ampere rating.you express the this MCCB is 250AF only u never mention about AT,so u check first MCCB and replace to same ampere rating.,i thought this MCCB ampere rating is normally can't trip.i thought you using over ampere rating.

Dear All,

Please correct me if I am wrong, the ampare trip isn't determine by the Ir setting, for example, I set Ir of 250AF MCCB to 0.9. that means the MCCB will trip at 0.9x250=225A

Ir rating usually refers to inrush current ratings for electic motor applications. For instance a pump load tyipcally has a low inrush (to start) and a fan load has high inrush due to the charicaristics of different loads.

A resistive load such as a heater has very little "inrush" current. I believe the post#1 is going in the right direction, because with a heating application (expansion/contraction) could have a short that only show it's face once to a certain temperature.

Your load should be 20% less than the overcurrent device for continous loads.

And it is possible that the breaker is going bad (trips before designed rating), it happens all of the time.

Good luck!

For the MCCB to trip reasons are

1) the resistive load might be drawing more current after 2minutes.

2) cable connecting the load and the MCCB may be defective.

3) MCCB itself may be defective.

Broadly isolate the fault areas as follows.

1)Connect the spare MCCB in the circuit and see whether the MCCB trips.If the spare one does not trip,the MCCB is defective.

2) Remove termination at the load side and connect some other smaller load and see the MCCB trips, there is no problem with the load.

like this, by process of elimination we can broadly identify the area of problem.

135kw load equals approx 230 amps full load current if breaker is set at .9 you are probably tripping after element heats up internal resistance is lowered as heater reaches temperature allowing more amps.

It's more like 190 Amps you probalby forgot the sqrt of 3 (three phase) in your calculation....

cheers...

"Ir rating usually refers to inrush current ratings for electic motor applications."

In IEC terminology, Ir is the adjustable Long Time trip setting of an Electronic Trip MCCB. In NEMA terms, it would be the L of an LSI or LI breaker setting.

hai,

if load is normal , there is no electrical leakage, insulation is good.

then no need to think, replace the MCCB . then monitor.

, some times this will happen due to fauilure of mechanical action inside the MCCB tripper.

i accepted your solution,

dear i would say that always give " first aid "

1. check the thimble/ lug size , whether it is accurate or not

2. size of the cable should be checked properly

3. loose connection

4 put ir to full mode

pls go through the above

are you using any auxilliaries in the MCCB

if so , then you have to bypass all those auxilliaries and re-examined your mccb with the same load , and see the difference