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I have (2) new 50 hp motors that operate the machine I am wiring. There is a double start button, one for each motor. I can start M1 and it begins running, rotation is correct. Now I try to start M2 and immediately after pressing it's start button it trips the breaker that feeds the control circuit.

I can remove the leads from both M1 & M2 from each of their overloads and both vacuum contactor coils and the seal in circuit seems to be working after I release each start button. The instantaneous on the breaker is turned to the highest setting (650 A).

I have doubled checked all my wiring and components and all appears correct.

The breaker tripped roughly 5 to 6 times as I was trouble shooting then after trying for the last time M1 came up and ran great as did M2. For the remainder of the day any time I need to start the motors they operated just as they were intended to.

I'm thinking maybe something had M2 in a bind and the in-rush of the starting current was great enough to trip the breaker. Maybe a bearing was cold. Any ideas why this breaker is now not tripping?
 

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Sorry if this comes off sarcastic- but the best way to determine if you have a current issue, is to measure the current, no point in guess what's happening.

Put a clamp meter on it. Set it to peak hold and check inrush. Then check running amps.

Vacuum Contractors on 50hp motors? Are these medium Voltage?
 

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The breaker tripped roughly 5 to 6 times as I was trouble shooting Any ideas why this breaker is now not tripping?
MCCB's are designed to be able to interrupt a fault at their max rating twice, since your had the INST cranked up all the way it's a pretty safe bet you have exceeded that and the contacts are welded shut and/or the trip unit is toast. I highly suggest having that breaker tested. Also follow Kennys advice. Seems you have a serious issue.
 

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MCCB's are designed to be able to interrupt a fault at their max rating twice, since your had the INST cranked up all the way it's a pretty safe bet you have exceeded that and the contacts are welded shut and/or the trip unit is toast. I highly suggest having that breaker tested. Also follow Kennys advice. Seems you have a serious issue.
Really eh?

If that's the case we should just go back to fuses.
 

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Something doesn't add up here. You say your control circuit is tripping and not the circuit for the motor itself, so that to me would mean your problem is a dead short somewhere in the section of the control circuit that powers the contactor for motor #2. You should check that coil out.

What kind of control power are you using and what does a 650A breaker have to do with it? Are you actually tripping the motor circuit and incorrectly calling it the control circuit? Because if not, why would you bother pulling the motor leads off for a control power problem?
 

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Something doesn't add up here. You say your control circuit is tripping and not the circuit for the motor itself, so that to me would mean your problem is a dead short somewhere in the section of the control circuit that powers the contactor for motor #2. You should check that coil out.

What kind of control power are you using and what does a 650A breaker have to do with it? Are you actually tripping the motor circuit and incorrectly calling it the control circuit? Because if not, why would you bother pulling the motor leads off for a control power problem?
I share your confusion on this, to whit:
...and immediately after pressing it's start button it trips the breaker that feeds the control circuit.
This also confuses me.
I can remove the leads from both M1 & M2 from each of their overloads and both vacuum contactor coils and the seal in circuit seems to be working after I release each start button.
If you removed the leads from the contactor coils, how on earth is the seal-in circuit working?

All that said, are these perchance Joslyn Clark low voltage vacuum contactors? Years ago they had a MAJOR problem with the aux contacts jamming and interfering with the vacuum bottle closing properly. So it would either make them chatter and blow our control fuse, or get stuck On, which was REALLY dangerous. My company at the time was using them on our equipment, and after arguing with us for months in the face of direct physical evidence, Danaher kept insisting it was not happening and refused to address it, so we quit using them and never went back.

I was tasked with analyzing the failure at the time. What I found was that they had apparently adapted a set of aux contacts for their NEMA contactors to attach to the vacuum contactors, but the armature on the vacuum contactor modes in an arc, not straight up and down. So after only a few operations, the mechanism for the aux contacts would cause them to wear more on one side and jam. We had 50+ failures in the field, Danaher denied all claims and responsibility. I would find it hard to believe it was still that way, but maybe you have older contactors?
 

· Bilge Rat
motors and controls.........
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Are both motors at a standstill when they are started? The reason I ask is that if motor #1 spins motor #2, then motor #2 is energized while it is turning, the current required to slam it in synch with motor #1 would be huge.

Also, is the breaker a motor circuit protector or a regular breaker, and what is its rating? And is there one breaker for both motors, or a breaker for each motor?
 

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I'm kinda getting control circuit problem out of this. Maybe it was shorted out and burned itself clear. It happens.
Not so sure about a motor problem just thinking that if you knew the machine, you would know how it's supposed to sound when it's running healthy.
By stating "cold bearing" means to me that the problem vanished. I'm standing on Control circuit problem.

Let us know that current measurement, I'm thinking 45 amps or so from memory ( 480 volts current is close to HP)
 

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I'm kinda getting control circuit problem out of this. Maybe it was shorted out and burned itself clear. It happens.
Not so sure about a motor problem just thinking that if you knew the machine, you would know how it's supposed to sound when it's running healthy.
By stating "cold bearing" means to me that the problem vanished. I'm standing on Control circuit problem.

Let us know that current measurement, I'm thinking 45 amps or so from memory ( 480 volts current is close to HP)
50 hp motor should be around an FLA of 65 amps at 480 volts..
 

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Nothing. All I'm saying is if a breaker needs to be serviced after interrupting two shorts, we may as well just install fuses.
A single fault can change the operating characteristics of a breaker if it's extreme enough. Multiple trips will almost always change the operating characteristics of a breaker. You should know this.

You should also know that a building or facility owner is more likely to call in an electrician to change a fuse than reset a breaker. That's good for business. You should also be telling customers that a breaker should be replaced after multiple trips. That's also good for business (not to mention the safety aspect).

Just because fuses are old technology doesn't mean they are no good. If a breaker holds after clearing a fault, it doesn't mean it's good to go.
 

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...
You should also know that a building or facility owner is more likely to call in an electrician to change a fuse than reset a breaker. That's good for business....
And in 3 phase systems if only one fuse blows (as it usually does) and all of the 3 phase motors single phase and smoke, that's good for business too... just not the OWNER's business. A motor rewind shop I used to work with has (had?) a sign behind the counter that said;
"Please uses fuses, my kids are in college!"
 

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A single fault can change the operating characteristics of a breaker if it's extreme enough. Multiple trips will almost always change the operating characteristics of a breaker. You should know this.

You should also know that a building or facility owner is more likely to call in an electrician to change a fuse than reset a breaker. That's good for business. You should also be telling customers that a breaker should be replaced after multiple trips. That's also good for business (not to mention the safety aspect).

Just because fuses are old technology doesn't mean they are no good. If a breaker holds after clearing a fault, it doesn't mean it's good to go.
I bet you just run around swapping out $600 breakers all day eh. Tool.
 

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What ever happened to this guy?

The first time I read his post I was thinking that either the coil in M2 was shorted with a solder blob and they burned it free the 78th time they reset the breaker, or they somehow paralleled around the coil and burned the offending wire off the 77th time they reset the breaker.

But then we started talking about 600 amp "control" breakers, then fuses, now ass-hurted-ness.

I need Paul Harvey and "the REST of the story".
 
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