Fire Pump Incomer MCCB Tripping On Transition

Yep. You have a problem all right, fairly common one too.

Was there a question behind this fascinating tidbit of information?

This is a new problem for me. I thought fire pumps only had service disconnects without any current overload protection at all. If the building is already on fire then the pumps have to run. This is a separate section in the NFPA section.

Once again the great unknown here is which relevant code should be applied.

NFPA 20 Section 9 requires a disconnecting means and a non-adjustable overcurrent device, but the ratings are much higher than would ever be allowed under normal circumstances. GFIs and AFIs (Arc Fault Interrupters) are specifically not permitted, nor are sensor based devices such as undervoltage, phase loss, frequency sensitive or manual trip means permitted.

NFPA 20 also references NFPA (NEC) Section 100, 695, and others for specifics.

The goal as you say, is to run hard, strong, long, and not trip for any electrical reason.

The problem is, simply, that you are in overload when in transition. The MCCB is working correctly, saving you from a fire, injury and equipment damage.

If I were you, I'd hire an Electrical Engineer to sort the installation out.

Best you get an electrician in quick to fix this rather important motor load problem.

Still, cheaper than having a fire and the insurance company denying your claim.

OK, so why electric? Why not diesel?

You need to check the windings...

You need to check that the motor and starters et al are wired correctly....

https://www.youtube.com/watch?v=oK8OQ7BgoLY

https://www.youtube.com/watch?v=RKlabe2FqPQ

http://www.hvaceducationaustralia.com/Resources/PDF/How%20to%20test%20electric%20motors.pdf

Friends,

Wareagle is correct, particularly if this installation is governed by the NEC. He also has correctly pointed out that the local code applies.

Anyone who has answered this question from the view of this being an "ordinary" pump has missed this significant exception to the typical overcurrent protection for a motor. A fire pump motor is supposed to be able to run or attempt to run regardless of any mechanical or electrical problem that may cause it to be damaged or destroyed.

Good design will, however, include supervisory warnings or alarms to alert the appropriate people that the motor has an overload problem.

--John M.

You obviously need professional help, before you burn the building down.

If life has any value where you are, evacuate the structure until this life critical equipment has been put right and certified by a professional.

Then, if there is a fire, you won't go to jail.

You may have a bigger problem than you realize! According to NFPA 20, your overcurrent device must not trip when 600% of FLA is applied for two minutes, and must not trip at 300% of FLA when applied for at least 10 minutes.

If you're tripping at 500A then you're below the requirement of 10 minutes at 510A. Better get someone in there before your insurance underwriter figures this out.

During a fire if OL trips the whole purpose of firepump is lost. Therefore some consultants say donot include OL but the short circuit trip setting should be very high nearly 20xFLC,verify from NFPA.

Secondary overcurrent protection; i.e., Overloads (OL) for protecting the motor, are not permitted, only circuit breakers for interrupting short circuits in the wiring are allowed, and they must be sized to handle the LRA of the pump motor and FLA of all auxiliary motors and equipment loads indefinitely. From NFPA 70, Article 695.4

For fire pumps generally it should be DOL Starter,

In your case, the time setting on star delta timer is too low, this is the reason for transition tripping.

Motor overload protection is not provided for fire pumps. Better to let the pump run to failure rather than prematurely stop squirting the fire.

However, IIRC, overcurrent (and short circuit) protection would still make sense. Better not to start a second fire.

Even for ordinary motors, inverse-time circuit breaker protection is allowed to be 2.5 x FLC. In this example, 2.5 x 170 = 425 A; the next size up is probably 450 A.

I don't have NFPA 20 to hand, but it may allow even higher CB ratings. To go with that, the conductors might be upsized beyond 1.25 x FLC. [Don't remember offhand.]

On the mechanical side, pump-motor combinations can be selected to be non-overloading.

As for star-delta starting, adjusting the star time may help to minimize the transition current.

Either there is a mechanical or electrical condition causing an electrical overload,

Or;

The MCCB is faulty.

Wise money is on the first one...

Is this a new problem or it was there from beginning?.

It looks like a design problem from here.

A lot of people here must be over weight like me, because you are getting exercise by jumping to conclusions.

because the question (statement) was so poorly worded, we don't know if:

1. The "Fire Pump Incomer MCCB" he/she is referring to is just the MCCB for ONLY that fire pump, or if it is the MCCB for the entire facility, which eventually FEEDS the fire pump. That could make a BIG difference.
   
2. Where he/she is. "Rated Motor Details. 93.3KW/380 VAC/50Hz... Site voltage 405 VAC..." tells us the OP is definitely NOT in a part of the world that would be subscribing the the US codes. So without knowing what his/her code requirements are, discussions of them are exercises in futility.
3. Is the MCCB a Thermal-Magnetic MCCB, a Magnetic-Only MCCB, or even a Molded Case Switch (with no trips)?
4. What are the trips (if any) set to?
5. Is this is an open transition or a closed transition star-delta starter arrangement?
6. What is the torque-speed curve of the pump? To be able to even hazard a SWAG* on what the transition time SHOULD be set at, you have to know that the pump motor got to 80% speed minimum.
7. Is 405VAC the line voltage BEFORE a start attempt, or is representing the line voltage WHILE the motor is attempting to start?

As a general rule however, Star-Delta open transition starting runs a very serious risk of causing a transition spike that can be, in theory, as high as 2000% (20X) of the motor FLC. 99.99% of MCCBs, even if they say they have NO trips, actually will have a short circuit over ride trip factory set for 10X the frame size of the breaker. So if the fire pump is fed with even a non-automatic molded case switch with a 250A frame size, the over ride trip device will be 2500A. the motor FLA is 170A, so that theoretical transition spike can be as high as 3400A, causing the MCCB to release.

As I said, this is a VERY common problem with open transition star-delta starting schemes, especially on fire pumps. That is WHY they even make closed transition starters, but hardly anyone uses them because they are more expensive. So to save a few coins on the initial hardware cost, people will potentially sacrifice the entire facility and the lives of the people in it by going with the cheapest starter then can get away with, then wonder why they are having problems.

Then rather than pay a QUALIFIED local electrical engineer to properly investigate the problem and come up with a proper course of action, they turn to a free and anonymous web forum...

*SWAG = Scientific Wild Ass Guess

"...they turn to a free and anonymous web forum..." where the advice is worth every penny they paid for it... and it's more than they deserve.

Seriously, I think the only conclusion that anyone here would jump to would be that the OP is clueless, and that all the banter is to show just how clueless he is.

The supply voltage may be just enough to high for the startup current problem. Motors do not like over voltage conditions.

Hi Every body,

Thanks for all your inputs.

I got it fixed.

Problem I found was MCCB short time trip setting was lower than required for the motor.

Initial setting was 250A x 5= 1250 A

After referring to motor starting current curve

MCCB short time trip set @ 250 x 8= 2000A

Now Motor starting as normal and running amps 122A.

Thank you.

Ediri