Trip Class 20

[StarCat]

I installed a new Fuji IEC motor starter on an upgrade job for a 2 HP airfoil fan drive. Yes this is a high inertia load by my understanding.
Initial tests were without any problems and with the trip current on the overload set to Motor nameplate which is 6 AMPS on a 208V rated 2 HP Motor. This is a 6-9 amp overload, which intuition said to buy instead of a 3-6.
The overload is noted to trip at the 6 AMP setting after some run time and has to be set for 7 to stay on line, with only 5 real amps running current on the motor. So the device is more than one amp OFF seemingly.
The Tech Support where I bought the starter is telling me I need a " Trip Class 20 " starter for this type of load. He also says the scales on those devices are not very accurate, but in the past I have ALWAYS set them to nameplate without any issues whatsoever. He also says that if I get it dialed in it can work consistently more than likely.
So excuse my ignorance on Trip Class 20. Its now necessary these days to go out an do a bunch of reading on any electronic device you may want to install, before you order.
Any more advice on this particular Starter I would like to hear.

 

[Russs57]

I can answer the easy question.

At 600% of the overload relay setting.....class 10 trips in 10 seconds, class 20 in 20 seconds, and you guessed....class 30 in 30 seconds.

The maker of the fan would be the best one to answer what class O.L. is needed.

 

[Jraef]

The "Class" number is, to make it simple, the amount of time it will take to trip at Locked Rotor Current of 600% of the setting. So Class 10 is 10 seconds, Class 20 is 20 seconds, Class 30 is 30 seconds. This then, in the design of the motor, relates to what is referred to as the "thermal damage curve" of the motor, the combination of current and time that will create enough heat in the motor to damage the winding insulation. The 600% value is one end of the curve, the other end is typically (depending on the motor), anywhere from 115% to 125% of FLA for 2 hours, also referred to as the "pick-up point" in the OL curve. 115-117% is typical for an IEC motor, 125% is typical for a NEMA motor with a 1.15 Service Factor. 140% is allowable if you prove that the motor will not accelerate, but that's not typical. One thing to note however, MOST of the OL relay manufacturers have ALREADY factored these values into their curves, so you do NOT want to add 25% to the FLA and set the OL for that, because you are in effect setting the OL pick-up point at 125% of 125%, which is 156% and now falls within the damage curve of the motor.

For the most part, any NEMA designed off-the-shelf motor is built to take Class 20 protection, meaning its design is based on the thermal damage curve represented by being protected by that curve; in other words it is designed to handle a lot. IEC motors are all built to require Class 10 protection, as are most submersible pump motors and most hermetically sealed motors, i.e. refrigeration compressors. That's why you never see a "Service Factor" on an IEC motor, there is non; they are all essentially a 1.0 SF. The same holds true by the way for a motor run from a VFD,; even if the motor says 1.15SF, it will also say it is 1.0 if run from an inverter and requires Class 10 protection (which most VFDs now provide internally).

There is nothing inherently wrong with using a Class 10 OL on a NEMA motor, except that it MIGHT, depending on the machine design criteria, nuisance trip on you. That's what it sounds like here; the fan OEM is telling you that they were expecting that because the fan was using a NEMA motor, their acceleration profile was going to make full use of that and push the envelope of the motor's thermal damage curve (without exceeding it), as defined by a Class 20 OL curve. So by you using a Class 10 OL, you were not allowing it to fully accelerate without running out of time on the OL RELAY trip curve, not the motor's damage curve. Tweaking the setting of the OL relay was a way of compensating, but that's not the right way to do it because now if there IS a real long term OL condition, the relay may NOT trip in time to save the motor. There is a, Informational Note at the end of NEC article 430.32 (C) that states this. That's basically what you were being told,; don't mess with the setting, get the right trip curve.

 

[Russs57]

After reading the OP's post a second time I see this as a possible clue.

"The overload is noted to trip at the 6 AMP setting after some run time and has to be set for 7 to stay on line, with only 5 real amps running current on the motor."

First I would want to verify this (and have defined what is "some" run time). You could have a defective overload relay. Or your problems could be very different, like having a phase drop out. Not enough info to say. But if motor is getting up to speed and current is dropping to below FLA.....and then you are tripping after several minutes/hours.....I don't think the "class 20" thing has any bearing at that point (assuming fan isn't being cycled on/off).

Great post by Jraef so read it well.

 

[ptonsparky]

As always, good info Jraef.

FWIW, at least one brand of PP we have been purchasing have selectable 10, 20, or 30. Makes it nice. Along with phase loss and a few other settings IDR.

 

[packersparky]

Great info, JRaef. And explained clearly enough that even a dunce like me can understand. :dunce:

 

[Jraef]

As always, good info Jraef.

FWIW, at least one brand of PP we have been purchasing have selectable 10, 20, or 30. Makes it nice. Along with phase loss and a few other settings IDR.

Yeah, I'm a big fan of most of the new solid state OL relays that add these kind of features. Comes in real handy when things aren't perfect. The other feature I like for pump panels is the Under Current (load loss) detection; lets you know when the pump clogs or the impeller spins off... I had a king nut break off on a 400HP submersible down a 3,000ft well once. Dropped the bowls, never got them back. The SSOL kept tripping on Under Current and everyone assumed it was defective and called me out to replace it, until I asked if any water was coming out of the pipe. Sure enough, nothing.
:slaphead:

 

[StarCat]

Thanks

Thanks

Yeah, I'm a big fan of most of the new solid state OL relays that add these kind of features. Comes in real handy when things aren't perfect. The other feature I like for pump panels is the Under Current (load loss) detection; lets you know when the pump clogs or the impeller spins off... I had a king nut break off on a 400HP submersible down a 3,000ft well once. Dropped the bowls, never got them back. The SSOL kept tripping on Under Current and everyone assumed it was defective and called me out to replace it, until I asked if any water was coming out of the pipe. Sure enough, nothing.
:slaphead:

Thanks for all responses. So the Tech support I spoke to was not the Fan OEM but the Vendor I bought the IEC ontactor from. Possibly I am just not up on all current affairs in this range so I picked a starter that I thought would be ok based on my former experience with Electronic Overloads and not expecting problems on a small 2 HP motor application. We are not dropping a phase, and yesterday during testing I dialed the OL down and it tripped instantly. So to clarify the situation, I have a motor rated at 6 AMPS, Running 5, and requiring the OL be set at 7 to stay on line. I have not tried any lower than 7 because I cannot deal with nuisance trips which totaled 3 after the install.
Thats 2 real amps out of range. I guess what I don't get is how 5 amps becomes 7. I have never had an electronic OL do this, but also not had one on an airfoil fan.
I will consult with the FAN OEM on what they suggest. Back in former days we just bought a set of heater elements and screwed them in.
Now when installing some circuit breakers for control panels however I was alerted to the need to know about 2 different trip classes on those devices because the in line Documentation and Web pages alerted me of the NEED to do so. I am a little off put by all the seeming unnecessary complexity that has arisen in these domains. Primarily because of the time it wastes getting things set up. Also I'd rather not have to buy an entire new starter for this project, but it looks like it may be necessary. I also need to spool this fan up to about 5.5A to 5.75A under current conditions as I still need more airflow.

 

[Jraef]

When you screwed in the heater elements, they were, 99.9% of the time, Class 20 even if you didn’t know that. The widespread distribution of Class 10 OLs only took place when Europeans began taking over our market starting in the 80s, a process that is now almost complete (Allen Bradley is the last remaining US based electrical equipment mfr.).

Something else you should check on is your phase current balance. IEC overloads will “bias” the trip point if the current is not balanced between the three phases so that it trips earlier than it otherwise would. If you have a voltage imbalance or a bad connection somewhere, that would explain it. Get out your clamp-on and double check that.

 

[MTW]

With the current differential protection on IEC overloads, a 240V center tapped open delta service can exacerbate this problem. The voltages on the center tapped side will often be lower than the high leg sides, while the service is under load, from the 120V loads. And it can swing back and fourth during the day.

Some makers do offer on special order, overloads without the differential protection, but they are usually a non stock item.