What do most of you set your motor overload setting on a VFD to? Say I have a powerflex 525. If it’s a 2 HP motor the FLA is 3.4 amps. So my overload current should be 125% of FLA. 3.4 x 1.25 = 4.25 Amps. This is correct isn’t it? Just wondering as a general question. Our new system has the Nameplate FLA and overload current the same number. Thanks for the feedback.
General Overload Question
- Thread starter icehube
- Start date
psychosunshine
Member
For variable torque loads like fans and pumps, I use 125%.
For constant torque loads for industrial applications and positive displacement pumps, I use 150%
For constant torque loads for industrial applications and positive displacement pumps, I use 150%
jraef
Member
The 125% pick-up point for overloads is 1) only in reference to motor with a 1.15 SF and 2) is baked into the algorithm (as it is with every solid state OL I have ever seen). Motor mfrs will tell you that even if a motor has a 1.15SF, when used with a VFD is us 1.0 SF.
You set the OL Protection at 100% of the motor nameplate FLA, never more than that. That’s what it tells you in the manual too.
You set the OL Protection at 100% of the motor nameplate FLA, never more than that. That’s what it tells you in the manual too.
I do wonder when l here people adding there own additional % to FLC and setting O/L. makes you wonder how many motors have burn't out, but people blame the device for not tripping. As a past Tech Sales Rep we would like everyone to "RTFM"! (most people may know what that means, but for others "Read the F*&^$# Manual"))
Last edited:
jraef
Member
Where people get that notion is actually the poor way the NEC is worded and a lack of basic understanding of the concepts, coupled with people (mostly us guys) being unwilling to RTFM.
NEC Article 430.32:
What that MEANS is that the protective device will BEGIN the process of tripping at that point, then from there it is an I^2t curve. So that point, 115 or 125%, is called the "pick up point" of the curve, and MOST of the OL relay manufacturers ALREADY build it into their design. So if YOU then use 125%, the pick-up point of the OL curve becomes 125% or 125% (152%) and sure enough, it DOES lead to the early demise of motors, much to the delight of motor mfrs. If you actually perform and RTFM on the instruction sheet of the OL relay, VFD, Soft Starter etc., it will tell you to set it AT the nameplate FLA, indicating that they have INTERNALLY already factored the 115 or 125% value. There are exceptions in many of the melting alloy older heater element based OL relays, but those are becoming illegal and will go by the wayside soon.
BTW,
When challenged by people with "sensitive ears", I tell them RTFM means Read the FACTORY Manual...
jraef
Member
Where people get that notion is actually the poor way the NEC is worded and a lack of basic understanding of the concepts, coupled with people (mostly us guys) being unwilling to RTFM.
NEC Article 430.32:
What that MEANS is that the protective device will BEGIN the process of tripping at that point, then from there it is an I^2t curve. So that point, 115 or 125%, is called the "pick-up point" of the curve, and MOST of the OL relay manufacturers ALREADY build it into their design. So if YOU then use 125% as your setting, the pick-up point of the OL curve becomes 125% of 125% (152%) and sure enough, it DOES lead to the early demise of motors, much to the delight of motor mfrs. If you actually perform and RTFM on the instruction sheet of the OL relay, VFD, Soft Starter etc., it will tell you to set it AT the nameplate FLA, indicating that they have INTERNALLY already factored the 115 or 125% value. There are exceptions in many of the melting alloy older heater element based OL relays, but those are becoming illegal and will go by the wayside soon.
BTW,
When challenged by people with "sensitive ears", I tell them RTFM means Read the FACTORY Manual...
jraef
Member
Sorry for the duplicated post, something is wrong with my edit function.
Steve Bailey
Lifetime Supporting Member + Moderator
I tell them it means Read the Friendly Manual.
janner_10
Lifetime Supporting Member
You size the MCB / Overload / Fuse (whatever you call it locally) to the VFD as per the manual, the VFD protects the motor.
You size the motor to the VFD, the MCB to the VFD. The MCB doesn't care about the motor, just the cables after it.
You size the motor to the VFD, the MCB to the VFD. The MCB doesn't care about the motor, just the cables after it.
DickDV
Member
In addition to the issues jraef has mentioned, it is important to realize that unless specifically stated otherwise, motor nameplate data is based on sinewave power. As soon as you introduce VFD or pulse power to the motor, everything changes.
That's why it is important to always enter actual nameplate data into a VFD. The drive will factor those numbers based on numerous other considerations to properly thermally protect the motor. Even then, the protection is estimated, not measured. You may very well set up all the overloads, etc. properly but if the goon squad comes along and sets a large cardboard box tight against the fan intake on a TEFC motor, the motor may well burn up before the estimated protection realizes there is any problem. or what if the fan slips off the shaft, or the forktruck operator rams the fan shroud and.....you see the problem.
If you want real thermal protection, you want measured temp, not estimated. That requires thermistors in the motor windings (p leads in the junction box) or something else that actually measures temperature in the motor windings.
Inverter duty motors often have these switches with the resulting protection circuit. Sadly, in my now-ending career the P leads were often left disconnected and the better protection forfeited because many field people don't know what they are.
That's why it is important to always enter actual nameplate data into a VFD. The drive will factor those numbers based on numerous other considerations to properly thermally protect the motor. Even then, the protection is estimated, not measured. You may very well set up all the overloads, etc. properly but if the goon squad comes along and sets a large cardboard box tight against the fan intake on a TEFC motor, the motor may well burn up before the estimated protection realizes there is any problem. or what if the fan slips off the shaft, or the forktruck operator rams the fan shroud and.....you see the problem.
If you want real thermal protection, you want measured temp, not estimated. That requires thermistors in the motor windings (p leads in the junction box) or something else that actually measures temperature in the motor windings.
Inverter duty motors often have these switches with the resulting protection circuit. Sadly, in my now-ending career the P leads were often left disconnected and the better protection forfeited because many field people don't know what they are.
Saffa
Member
+1
And pretty much every decent drive has a thermistor input. All you need is the cable from the motor to the drive. Especially important for submersible pump motors that utilize cooling jackets.
BachPhi
Member
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