We have a 10HP Exhaust Fan that was specified to have a motor starter with an integral electronic overload. This overload keeps tripping upon the motor startup, obviously due to the inrush. The time delay of monitoring amps was increased to overcome the issue but kept on tripping on startup of the that fan. We haven't measured the inrush current yet or even testing the motor if there is any issue with it. The contractor proposing to use VFD to allow the motor to have a soft start and ramp up slowly. However, the motor is supposed to be a constant speed thus I'm not sure if VFD can be used for this application. Any thought where the issue could be?
Electronic Overload Keeps Tripping
- Thread starter faresos
- Start date
- Location
- Bremerton, Washington
Check all settings on OL, some have tiny DIP switches, with class of OL, etc.
Sometimes the OL dual can be hard to read, or you need to set dial at 120% of fla.
And it may be the driven load. certainly check startup amps, running amps, fan bearings, voltage….
Sometimes the OL dual can be hard to read, or you need to set dial at 120% of fla.
And it may be the driven load. certainly check startup amps, running amps, fan bearings, voltage….
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
What is the distance and wire size back to the panel? Sounds like excessive voltage drop if adding delay to the trip.
ptonsparky
Tom
- Occupation
- EC - retired
Options included may be phase loss, current imbalance, under voltage, class 10 thru 30.
It's less than 100ft at 480V/3Phase. I don't believe there is a voltage drop for this circuit.
- Location
- Bremerton, Washington
I have installed many AB electronic OLs. The instructions are printed on the box, small to read, and mostly icons.
- Location
- Illinois
- Occupation
- retired electrician
What class of overload relay is it? There are Class 10, 20 and 30 overload relays. The Class 10 will carry the 6 x full load current for 10 seconds without tripping, the Class 20 for 20 seconds, and Class 30 for 30 seconds.
Not sure, all what I was told it has TeSys T SSOLR (Solid State OL- Square D). Not sure the maximum delay time can be set
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
I believe all the TeSys overload relays are Class 10.
ptonsparky
Tom
- Occupation
- EC - retired
Downloaded a file for it. Brief look. I'm on vacation, again, but it looks like that can be programmed for about anything.
- Location
- Illinois
- Occupation
- retired electrician
Has the system been checked for too much air flow?
ptonsparky
Tom
- Occupation
- EC - retired
A VFD could be used but it shouldn't need to be used.
Don, I'm not following you when you said if the system been checked for too much air flow? Are you referring to exhaust fan air flow? if so, I wouldn't really know. My first step told them to troubleshoot the motor and measure the inrush current and duration. I'm assuming the inrush should be around 6XFLA.
- Location
- Bremerton, Washington
The load on a fan motor is controlled by the air flow, with a discharge damper closed that is minimum load.
Some time look up affinity laws for pumps/fans. The load varies with the cube of the flow, which is why VFDS save significant $$$ with pumps and fans, instead of throttling
Some time look up affinity laws for pumps/fans. The load varies with the cube of the flow, which is why VFDS save significant $$$ with pumps and fans, instead of throttling
ptonsparky
Tom
- Occupation
- EC - retired
We are assuming a centrifugal fan.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
The TeSys T SSOL is programmable to be Class 5 through Class 30. If it is an American motor, you could change the trip class to Class 20. If it is an IEC motor, do not change it from Class 10.
But I am in Don's camp, the motor may not be able to start the fan if the dampers (if any) are wide open. Load = flow, so not flow = no load. That is often how you must start centrifugal fans / blowers if there is a large mass involved (i.e. squirrel cage). Most people don't understand this issue, because they think "closed = harder", it's exactly the opposite. So IF there is a damper, close it BEFROE starting, then open it after it gets to full speed.
Adding a VFD can help, but if you never vary the speed, it will cost you about 3% of the energy permanently. As much as I love VFDs, that's not the proper solution here.
But I am in Don's camp, the motor may not be able to start the fan if the dampers (if any) are wide open. Load = flow, so not flow = no load. That is often how you must start centrifugal fans / blowers if there is a large mass involved (i.e. squirrel cage). Most people don't understand this issue, because they think "closed = harder", it's exactly the opposite. So IF there is a damper, close it BEFROE starting, then open it after it gets to full speed.
Adding a VFD can help, but if you never vary the speed, it will cost you about 3% of the energy permanently. As much as I love VFDs, that's not the proper solution here.