I'm installing a single phase 240v motor on a 3 phase starter. I know on IEC starters you need to use all 3 phases on the overload relay to prevent tripping from phase imbalance. Now on an overload relay such as the sqd 9065sf020 will I need to do the same? From what I can tell that relay only provides thermal protection
3 phase starter single phase motor
- Thread starter fireryan
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
Yes, on that 9065 solid state OL, you have to "loop back" power through all 3 poles in order to prevent it from tripping on phase loss.
Ok thanks. I didn't know if they monitored phase lose or not
A trivial point. It's usually phase unbalance rather than phase loss.
Saturn_Europa
Senior Member
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- Fishing Industry
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- Electrician Limited License NC, QMED Electrician
Hey man, I tried this same thing with a square D motor logic SS OL relay last month. Not sure if it is the same model as yours or not.
Huge waste of time. It didn't work. I screwed around with it for a few hours before giving up. I used all three phases and it tripped right away.
Ended up using the old school bi-metallic OL.
Try it, it may work for you. But it didn't for me.
Hmm. That's strange.
Saturn_Europa
Senior Member
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- Fishing Industry
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- Electrician Limited License NC, QMED Electrician
I tried it on a single phase 115 v , 1 or 2 hp pump, looped the hot leg through all three phases like you described. Using class 10 trip it tripped in 10 seconds. Using class 20 trip it tripped in.........20 seconds.
Hopefully you will have better luck.
Post back how it goes!
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
Not on that specific relay. It does do phase current imbalance too, but in addition all three phases must be pulling at least 30% of the set current value or it trips on phase loss. It's a design flaw in my opinion and it became obvious to them after the fact when a lot of centrifugal pump control panels kept tripping out because if the pump flow was too low, the current dropped below that threshold. So they released a "special" version with a lower threshold, but you have to know of the problem to be sure to order that version in advance, it's not the standard version. Most people find out the hard way. Sq D supposedly trains their distributors to ask, but a lot of people just buy components without asking for help, not expecting to run into a weird glitch like that. Guess how I know...
I prefer solid state OL relays over bi-metal or melting alloy type now, but that specific relay has cost me money...
Are the three legs phase sensitive? Would the "spare" leg know the phase relationship of the current it is passing WRT the other two legs?
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
No. They specifically instruct you to run the single hot line (of our 120V systems) through all three poles or if it is 240V, one line through 2 poles and the other line through one. Just like what you do on an IEC bi-metal OL relay.
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- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Is your load less than 30% of the setting of the OL?
Are you measuring that with a clamp-on or guessing?
Are you measuring that with a clamp-on or guessing?
Fla of motor is 40 amps. Overload is set at 45amps
Saturn_Europa
Senior Member
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- Fishing Industry
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- Electrician Limited License NC, QMED Electrician
My OL was rated properly also. It definitely wasn't tripping on amps.
ptonsparky
Tom
- Occupation
- EC - retired
What was the actual current draw of the motor at the time?
I went to the sqd website and did some research on the 9065 ss relay. Says it monitors both phase loss and phase unbalance. Im not sure if its smart enough to realize that your running 2 of the same legs thru it? It obviously must be and is tripping itself out.
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
No, as I said, it does NOT know if you are running 3 separate phases or the same phase through all three poles, it SPECIFICALLY INSTRUCTS you to run the circuit in series through the 3 poles for single phase.
But again, WHAT IS THE CURRENT going through to the motor? Just because your motor FLA is 40A, does not mean it is actually drawing that much. The current draw is based on the actual LOAD on the motor. If it is set for 45A (probably incorrect by the way*) but the motor is drawing less than 15A, then it will trip on phase loss because that's what it does.
* the OL setting should be at the motor nameplate FLA. The NEC section stating that you can have an OL relay start protecting at 115% is not the same thing. The relay ALREADY factors the 115% into the trip curve. So if you set it at 115%, you are setting it at 115% of 115% and you can lose the motor.
Ok I set my overloads off of the 40fla@ 115%. I didn't realize that the relay figured that in so that's why it's set at 45amps. The motor gets to 21 amps before it trips out.
Saturn_Europa
Senior Member
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- Fishing Industry
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- Electrician Limited License NC, QMED Electrician
I double checked it at work today. Its a 1/2 horse , 120 volt motor. FLA is 9.8 amps.
I had the adjustable OL set for 10 amps. I had all 3 contacts wired in series with the ungrounded conductor. It tripped while pulling 7.6 amps or there about.
All empirical data is pointing to this SS OL being unsuitable for for single phase use. I certainly wont try it again.
Ill either use a Tesys T or the old bi-metallic overloads. Usually we use the bi-metallic OLs because most of the guys at my plant treat Tsys T's like they are black magic.
Tangent alert!! We had a problem with engineering staff specing out specific motor protection functions that were programmed into the Tsys T's without plant maintenance staff being notified. So we would install a pump, bump test it for rotation, correct rotation, bump test it again, then go to bring it online and the Tsys T would have it locked out for an hour. It was a bit of a learning curve to get used to the software and diagnostic tools. But now I like them. My boss on the other hand likes the old school bi-metallic OLs. Its hard to argue with decades of success.
Good luck, Ryan, but I would plan on changing out the overload.
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