MCCB and MCP

Yes, excellent ! GA to you

i had forgotten the ambient compensation .. for God's sake! i am getting senile.

can i know your mail id and company name where you are working............

I am fully aware of the perils of disclosing my mail ID is an open forum like this. However, if you want to communicate with me, kinldy do so thro this forum's mailbox. I will then definitely inform you my mail ID and my current employer.

Thank you for your answers. You have removed my confusion. Thank you once again.

P.S I have registered as per your advice.

Regards,

DG

I feel it as good to add the following points also in this moment.

MCB - Miniature Circuit Breaker - it is having a preset current rating - In India I think it is available up to 80A (have to check, whether higher rating available)

MCCB - Moulded Case Circuit Breaker - It is having current setting arrangement, by which you can set to your required rating. Also, MCCBs are available with preset factory rating like MCBs.

Other Circuit Breakers are ACB, VCB, etc. using for higher current ratings.

There are Switch Fuse Units (SFU), which are replaced by the Circuit Breakers. The Circuit Breakers are having higher breaking capacity (kA) than SFUs. So, in such required designs the breakers are preferable. But, the fuses of the SFUs are sharp in the breaking of the circuit in the exactly designed value than the breakers. So, in such other required situations we move towards the conventional fuses.

(Hope others will elaborate what I explained above)

Lots of interest in this thread. Good. However, some clarifications...

For example,

• fuses of even 300kA SC capacity are available.
• Contactors have a life of millions of operations. MCBs and MCCBs have a few thousands. Contactors are 'controlgear' devices, they have no protection function. MCBs and MCCBs are specifically protective devices, to use them to switch on and off motors is not a good idea.
• Every time a short circuit happens, the fuse blows, and needs to be replaced. The protection is as good as new. If an MCB or MCCB trips on SC, we reset it and switch on again. While the MCCB may be ok to carry rated current after O-CO-CO, there is no protection thereafter. And in a real-life situations, there is no way to know how many short circuits and what current level have happened.(with modern microprocessor relays, some memory is there, still...) The debate of Fuse vs MCCB has been happening for decades, and is never going to be over

One more point. MCP is for "motor circuit protector." It will have only magnetic trip as it depends on DOL starter for thermal protection. Smaller circuit breakers are likely used for protection of smaller control or aux circuits that require thermal and magnetic protection appropriate to the circuit size.

Sir,

I also welcome you to CR4. Additional information/clarification:

• Short circuit protection for the motor and its supply wiring is from the MCCB or MCP or fuses.
• Single phase protection is only available from devices designed specifically for this function, such as IEC style overload relays.
• Running overload protection can be supplied by a set of fuses or a MCCB if either of these are sized very close to the motor's running current. In the USA, the National Electrical Code recognizes this and provides the maximum percent you can add to the motor's Full Load Amps. In your country, this may be allowed, but I do not know your codes. In some cases, running overload protection may be supplied by internal overload protectors embedded within the motor windings. For very large motors, there will be thermal sensors embedded within the windings, that will be used to turn the power off if the motor overheats. For the very vast majority of the cases, an external unit called an overload relay and set to the motor's nameplate current, will be used to provide this running overload protection.
• During the starting period for the motor, its inrush and starting current will be much higher than its running current. For this reason, the MCCB or fuses have time/current curves to allow this relatively temporary overload. In some cases, if the motor has a particularly long starting time, additional options would exist, such as selecting overload relays with a longer time delay or even the possibility of manually bypassing the running overload protection during the starting time.
  

Note, this overload relay is essentially a resistor selected or adjusted to give a calibrated amount of heat output when the motor is running normally. If the current rises for too long, the overload relay will open the thermostat contacts that are embedded within itself, interrupting the control power to the contactor and turning off the motor. Since this is an external simulation of the conditions occurring within the motor, it is approximate at best; corrections must be made if the motor is in a warmer or colder environment than the overload relay, or if the motor has specialized service conditions.

--John M.