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Discussion Starter · #1 · (Edited)
Motor overload relay keeps tripping (Schneider LRD16 for a 3 phase motor)

Motor 10 HP but is only pulling 7A (FLA)
Inrush ampacity is around 80A for a fraction of a second

The overload relay should be ok for 10A x 125% = 12.5A yet it trips even when set at 13A

EXTRA ** Also very importantly, there's exactly two identical setups and this is happening on both of them **
 

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Motor overload relay keeps tripping

Motor 10 HP but is only pulling 7A (FLA)
Inrush ampacity is around 80A for a fraction of a second

The overload relay should be ok for 10A x 125% = 12.5A yet it trips even when set at 13A
Provide details of what your OLR is and confirm that it is a 3phase motor. Many new Solid State OL relays have other features that could be protecting you from damage that you are not aware of.
 

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guitarboyled said:
Schneider LRD16 for a 3 phase motor
Ok, so that's just a basic bimetal thermal OLR, nothing special. Those are phase loss sensitive though. So maybe you have a bad connection somewhere and no (or very low) current in one phase. Did you put an ammeter on them?
 

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Discussion Starter · #5 ·
Ok, so that's just a basic bimetal thermal OLR, nothing special. Those are phase loss sensitive though. So maybe you have a bad connection somewhere and no (or very low) current in one phase. Did you put an ammeter on them?
I believe they are Class 10 OLR

Voltage was similar on all phases but Amps where measured only on one phase

The inrush current lasted a fraction of a second and FLA was reached in approximately 2 seconds

The OLR trip when set at 11.5A and 13A but are ok when set to maximum (I would guess around 14A since it's passed the last inscription)
 

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Does the motor cycle on/off or does it run cont. If cycles may be to short of a time, heating up ols. Also need the current from all three phases
 

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Did you perform a fall of potential across the OL or measure temperature?

Look for a thermal issue?

Loose connection!
 

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Discussion Starter · #9 · (Edited)
Is your wire size correct?also what's the distance of the feeder? What is the motor connected to ? Could be field problem.
Wires are properly sized at 12 AWG,
Wires have been verified (Megger) between motor and starter
No wires seem loose


Motor (Thoshiba 10 HP, 3 Phase, 600V, Cont. Duty S.F. 1.15, FLA 9.6)
Motor is running at 7.68HP and pulling about 7A

Motor --> switch --> Fuseable starter with OLR --> Feeder

The feeder is a few inches away
 

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Discussion Starter · #10 ·
Does the motor cycle on/off or does it run cont. If cycles may be to short of a time, heating up ols. Also need the current from all three phases

The motor runs once a week for a continuous 10 min period

Also very importantly, there's exactly two identical setups and this is happening on both of them.
 

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What is the ambient temperature ata the starter
 

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We need to know the current in all 3 phases. Even if your voltage is good, that can be a false reading through the motor windings. Current can't be fooled though.

Starting Current is usually irrelevant to an OLR unless, as was suggested, the duty cycle is really high. So to that point, are you sure that your contactor is not chattering or a set point controller is not fluttering and making that contactor come on and off too fast?

One bad OLR is a fluke, 2 OLRs that appear to be bad on the exact same application is an application problem.
 

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Discussion Starter · #15 ·
We need to know the current in all 3 phases. Even if your voltage is good, that can be a false reading through the motor windings. Current can't be fooled though.

Starting Current is usually irrelevant to an OLR unless, as was suggested, the duty cycle is really high. So to that point, are you sure that your contactor is not chattering or a set point controller is not fluttering and making that contactor come on and off too fast?

One bad OLR is a fluke, 2 OLRs that appear to be bad on the exact same application is an application problem.
According to the tripping curves of the OLR manufacturer and my observations, inrush/LRA shouldn't be a problem

Both OLR trip at startup (inrush) when the set current is adjusted at 13A

Both OLR are ok when the set current is adjusted at the maximum (14A)

Will try to measure amps on all phases next time I'm on site
 

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According to the tripping curves of the OLR manufacturer and my observations, inrush/LRA shouldn't be a problem

Both OLR trip at startup (inrush) when the set current is adjusted at 13A

Both OLR are ok when the set current is adjusted at the maximum (14A)

Will try to measure amps on all phases next time I'm on site
Did you perform a fall of potential across the OL or measure temperature?

Look for a thermal issue?

Loose connection!
 

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Discussion Starter · #17 · (Edited)
Did you perform a fall of potential across the OL or measure temperature?

Look for a thermal issue?

Loose connection!
I did not perform the fall of potential test but ground seemed ok

Megger testing on all phases between motor and OLR was ok

Didn't notice any unusual heat but didn't measure any peak.

I didn't check 100% of the connection but all the ones I tested where ok
 

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So if both are doing it ? Whats common to both ?
The power supply ?
Is the supply adequate ?
Might have been enough before,
But perhaps it's recently changed,
now it's not enough .

More load on the system,
reduction in available power,
not enough to start two old cranky motors.

:eek:
 

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Discussion Starter · #19 ·
So if both are doing it ? Whats common to both ?
The power supply ?
Is the supply adequate ?
Might have been enough before,
But perhaps it's recently changed,
now it's not enough .

More load on the system,
reduction in available power,
not enough to start two old cranky motors.

:eek:
The complete install is brand new... I should add that we've also had 15A fuse blowing on one of the phase.
 

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The complete install is brand new... I should add that we've also had 15A fuse blowing on one of the phase.
Is that phase suppling the amps required ?
Or is it dipping down under load ?
This would increase the current if the voltage drops down.

Is there more load on that one phase ?
 
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