possible need of special breaker

[ginogag]

i have a 50 hp 480 volt 65 or 75 fla wye/delta 2 speed motor for a commercial dough mixer . The mixer supposed to run 30 seconds in low speed ,then 30 seconds in high speed . We ran #3s thhn from the hv ge panel to feed the mcc. Every time the motor kicks into high speed the breaker trips . Im assuming there is a huge inrush of current in high speed . The motor guy said the windings were fine . Im pretty sure the contols and starters are fine because i disconnected the load from the starter and everything was working fine. Me and my partner are racking our brains for 4 months trying to figure this out. We now think we need a breaker that allows a large inrush of current at 2nd speed like a inverse time cb or an instantaneous trip breaker or just a bigger breaker period .We have a 100 amp ge breaker on there now , feeding the motor with #3s , the lenght of the run is approx. 170 feet . If i need a special breaker , should i increase the wire size, and the the breaker need a special enclosure if it doesnt fit in ge 600 amp panel . Can i get a breaker that is adjustable . I read in the code book about 800% to 1100% inrush current on certain breaker applications. Can you possibly help me my address is ginogag@optonline.net thanks

 

[480sparky]

Most breakers are time-inverse, so what you have installed is probably so.

 

[don_resqcapt19]

The code would permit a 175 amp breaker with #4 wire to feed that motor.

 

[zog]

Shoud be an easy swap out, I should have one for that application.

 

[ginogag]

The code would permit a 175 amp breaker with #4 wire to feed that motor.

where would i find that in the code exactly

 

[don_resqcapt19]

where would i find that in the code exactly

You have to wind your way through a number of code sections.
240.4(G), 430.6(A)(1), Table 430.250, 430.22(A), 430.52(C), Table 430.52, 430.52(C) exception #1, 240.6.

240.4(G) tells you that the overcurrent rules in Article 240 do not apply to motor circuits.

430.6(A)(1) tells you that the conductor is sized based on the full load current as shown in the tables. It is table 430.250 for your motor and the FLA for a 3 phase 480 volt 50hp motor is 65 amps.

430.22(A) tells you that the motor circuit conductors must have an ampacity of 125% of the table value. That requires a conductor with an ampacity of at least 81.25 amps. Using the 75?C values we find that a #4 copper has an ampacity of 85 amps.

Table 430.52 tells us we can use a inverse time breaker with a rating of 250% of the motor full load current. 250% of 65 amps is 162.5 amps. 162.5 amps is not a standard size for an OCPD per 240.6 and exception #1 to 430.52(C) says we can use the next larger standard size which is 175 amps.

 

[Cow]

Im assuming there is a huge inrush of current in high speed .

Me and my partner are racking our brains for 4 months trying to figure this out.

Don't you have an amp meter with an "inrush" setting, you'd have your answer in 30 secs?

I'm sorry but I have a hard time believing it should take anybody 4 mos. to figure out a tripping breaker problem. That sounds a little extreme.

 

[ginogag]

Don't you have an amp meter with an "inrush" setting, you'd have your answer in 30 secs?

I'm sorry but I have a hard time believing it should take anybody 4 mos. to figure out a tripping breaker problem. That sounds a little extreme.

well the owner is never around , we play phone tag , we can only work when the baking is not done, and hes very reluctant to spend money on the correct equipment, besides having other jobs to do. i didnt literally mean im ther every day for 4 months.he has another machine that mixes dough , but he wants to try to produce more to increase his production. i have an old analog amprobe ....now ill get a digital one TODAY. thanks
PS dont take things so literally ,just posing a question

 

[hurk27]

I have had this problem with motors and transformers alike, one thing I noticed is when I have increased the wire size to a load, on a service with a high available fault current rating, the inrush is also higher, it seems the wire can act as a shock absorber sort of speak, like a ballast resistor, so up-sizing the wire can sometimes add to a problem. of course with a short run this wouldn't have much effect.

Ok enough out of the box thinking

 

[mikeames]

I have had this problem with motors and transformers alike, one thing I noticed is when I have increased the wire size to a load, on a service with a high available fault current rating, the inrush is also higher, it seems the wire can act as a shock absorber sort of speak, like a ballast resistor, so up-sizing the wire can sometimes add to a problem. of course with a short run this wouldn't have much effect.

Ok enough out of the box thinking

I have had similar experiences. I agree.