Setting a thermal OL to its maximum position

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grasfulls

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Clients chiller pump has a thermal OL that "someone" has maxed out. FYI - Schneider LRD 12. Anyway, I have not looked at the installation yet, so I do not know the necessary, like what is the nameplate rating of the motor, etc, but my question does not need that right now.
What does turning the dial all of the way to its max do? I have never done it.
Also, if it is set to Manual reset, what would cause the motor to immediately begin running again when releasing the stop button?
Is the attached not set to "H"?
 

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iwire

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Turning the dial to max on this unit means it will not trip until a current level above 8 amps. How far above is anyone's guess
 

jim dungar

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Clients chiller pump has a thermal OL that "someone" has maxed out. FYI - Schneider LRD 12. Anyway, I have not looked at the installation yet, so I do not know the necessary, like what is the nameplate rating of the motor, etc, but my question does not need that right now.
What does turning the dial all of the way to its max do? I have never done it.
Also, if it is set to Manual reset, what would cause the motor to immediately begin running again when releasing the stop button?
Is the attached not set to "H"?


As mentioned earlier, raising the setting means that more current is needed to cause the relay to trip.
The dial setting is used to choose the correct left to right shift of the specific time vs current curve for this relay. Following industry standard practices, this relay will carry 6x the current on the dial for 10sec. More current means a faster trip, less current means a longer trip.

Manual/Hand mode means the relay contacts remain in the 'tripped' state until the Reset button is pushed. Automatic mode means the contacts reset as soon as the relay, and be inference the motor, cools down.

The Stop button manually trips the contacts, so in Automatic mode they would reset as soon as the stop button is released.

It may be possible that your mode setting is not in either defined position.
 

Jraef

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Clients chiller pump has a thermal OL that "someone" has maxed out. FYI - Schneider LRD 12. Anyway, I have not looked at the installation yet, so I do not know the necessary, like what is the nameplate rating of the motor, etc, but my question does not need that right now.
What does turning the dial all of the way to its max do? I have never done it.
Also, if it is set to Manual reset, what would cause the motor to immediately begin running again when releasing the stop button?
Is the attached not set to "H"?
The old rule of thumb I learned a long time ago when dial adjustable OL relays first came on the market here in the US in the late 70s, was that for every tick mark on the dial that was above the FLA of the motor, you cut the motor life in half. We don't know your motor FLA, but let's say it was 6A. There would be 3 tick marks on that relay above 6A, so your motor life will be reduced to 1/2 x 1/2 x 1/2 or 1/8 of normal expected motor life. So the effect is not immediate, but eventually you pay the piper. In this case however, they have turned it up way past the last tick mark, and these are not linear, so there is no telling what the trip level will be now, but I would extrapolate that it would likely end up at 10A in that position, so take off at least another 1/2. This means if your motor would have been expected to last for 20 years, it will not last for about 14 months.

If the OL is set to Auto, AND the dial is adjusted beyond the calibration, it's entirely possible that it will reset immediately. Cut that 14 months down to about 2, maybe less ...

Here's something else I observed here, which may explain what you are seeing. I see only two wires going into that contactor on L1 and L2. Those IEC overload relays will nuisance trip on single phase power unless you have current flowing through all three poles. So if whomever installed that had READ THE FACTORY MANUAL, they would have seen that it instructed them to exit from T2, then loop back around to L3, and connect the motor leads to L1 and L3. By not doing that, they set this up for failure, then tried to make the problem go away by cranking up the OL relay. Bad idea. That motor is not likely to last much longer, the insulation is probably deteriorated already.

That contactor on the right isn't looking too good either by the way...
 

don_resqcapt19

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The old rule of thumb I learned a long time ago when dial adjustable OL relays first came on the market here in the US in the late 70s, was that for every tick mark on the dial that was above the FLA of the motor, you cut the motor life in half. We don't know your motor FLA, but let's say it was 6A. There would be 3 tick marks on that relay above 6A, so your motor life will be reduced to 1/2 x 1/2 x 1/2 or 1/8 of normal expected motor life. ...
That, of course, assumes that the motor is actually pulling enough current to trip the overload device. If you set it all the way up, and the motor is never pulling more than nameplate it doesn't make any difference. Just like 500 amp breaker on a #12 doesn't make any difference if there is never a problem on the circuit.
 

Jraef

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That, of course, assumes that the motor is actually pulling enough current to trip the overload device. If you set it all the way up, and the motor is never pulling more than nameplate it doesn't make any difference. Just like 500 amp breaker on a #12 doesn't make any difference if there is never a problem on the circuit.
True. But if someone has turned it up like that, my experience is that they did it to make it stop doing that.
 

grasfulls

Senior Member
Who knows what trip level is

Who knows what trip level is

Turning the dial to max on this unit means it will not trip until a current level above 8 amps. How far above is anyone's guess

If it follows what appears to be an equitable distance between current settings it may be a little over 9, but like you said, who knows.
 

jim dungar

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Thanks! I will

According to Schneider Electric's FAQ website:
[h=1]The dial of a D line overload has a scale of numbers and then an ``A`` a quarter turn farther. What is the ``A`` and what happens in that setting?
A = amps The numbers represent the portion of the dial which has been calibrated at the factory. If set beyond the numbered dial positions it is unclear what might happen. The overload could fail to trip.
[/h]
 

grasfulls

Senior Member
three phase OL, SP system - nuisance tripping

three phase OL, SP system - nuisance tripping

Here's something else I observed here, which may explain what you are seeing. I see only two wires going into that contactor on L1 and L2. Those IEC overload relays will nuisance trip on single phase power unless you have current flowing through all three poles. So if whomever installed that had READ THE FACTORY MANUAL, they would have seen that it instructed them to exit from T2, then loop back around to L3, and connect the motor leads to L1 and L3. By not doing that, they set this up for failure, then tried to make the problem go away by cranking up the OL relay. Bad idea. That motor is not likely to last much longer, the insulation is probably deteriorated already.

That is interesting, I did notice it is a 3pole OL being used on SP, but I had no idea that unto itself could be an issue. I will DL the manual as I am unsure what "exit from T2, then loop back around to L3, and connect the motor leads to L1 and L3" means. Do you connect the line side to T1 and T3, outputs on L1 and L3 but also have a jumper from T2 to L3? I am sure I I read the instructions it will make more sense, thanks! My ignorance even ore obvious: What does T stand for?


That contactor on the right isn't looking too good either by the way...
Yes, but I cannot tell by the image what on earth it is being used for. I am going to the site Friday to meet while the HVAC tech is there.
 
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grasfulls

Senior Member
Current draw

Current draw

That, of course, assumes that the motor is actually pulling enough current to trip the overload device. If you set it all the way up, and the motor is never pulling more than nameplate it doesn't make any difference. Just like 500 amp breaker on a #12 doesn't make any difference if there is never a problem on the circuit.

I will check actual current draw when I go
 

grasfulls

Senior Member
Three phase starter, SP installation

Three phase starter, SP installation

.

Here's something else I observed here, which may explain what you are seeing. I see only two wires going into that contactor on L1 and L2. Those IEC overload relays will nuisance trip on single phase power unless you have current flowing through all three poles. So if whomever installed that had READ THE FACTORY MANUAL, they would have seen that it instructed them to exit from T2, then loop back around to L3, and connect the motor leads to L1 and L3. By not doing that, they set this up for failure, then tried to make the problem go away by cranking up the OL relay. Bad idea. That motor is not likely to last much longer, the insulation is probably deteriorated already.

I found a troubleshooting nuisance tripping pdf on the schneider site, this was a great note on your part, thank you.
They do show a diagram for both one wire and two wire circuits, I uploaded the image. Just so you are aware, they show the line wires for a two-wire circuit at T1 and T3, Load wires at L2 and L3, the jumper from T2 to T1. I am not negating your comment, I had no idea about this and you did. I wonder that either configuration may work. Bottom line, the starter assembly is incorrectly installed and I too am guessing they cranked the amps up to stop the nuisance tripping.
 

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jim dungar

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I found a troubleshooting nuisance tripping pdf on the schneider site, this was a great note on your part, thank you.
They do show a diagram for both one wire and two wire circuits, I uploaded the image. Just so you are aware, they show the line wires for a two-wire circuit at T1 and T3, Load wires at L2 and L3, the jumper from T2 to T1. I am not negating your comment, I had no idea about this and you did. I wonder that either configuration may work. Bottom line, the starter assembly is incorrectly installed and I too am guessing they cranked the amps up to stop the nuisance tripping.

The actual terminals do not make a difference, do whatever is easiest to wire. The issue is that current needs to flow through all three poles of the overload relay.
If this is not done, the relay is supposed to operate at a slightly lower current than the dial would indicate. They call this feature single-phase sensitivity.
 

Jraef

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The actual terminals do not make a difference, do whatever is easiest to wire. The issue is that current needs to flow through all three poles of the overload relay.
If this is not done, the relay is supposed to operate at a slightly lower current than the dial would indicate. They call this feature single-phase sensitivity.
Bingo. It makes no difference how you get there, just that current flows through all 3 sensing elements.
 

mivey

Senior Member
Bingo. It makes no difference how you get there, just that current flows through all 3 sensing elements.
Given that you need current through all three poles, I wonder why the phase angles of the currents between poles does not seem to matter. Instead of a 120d displacement for three currents you have two in-phase currents and one 180d displacement.

If there is no regard to how the flux sums, perhaps it is some kind of digital sum of an absolute value? Maybe for single-phasing conditions they don't really care about the phasing but just compare the magnitudes of the currents?

Is there no use of residual information in these devices?
 

grasfulls

Senior Member
Just as long as through all poles

Just as long as through all poles

The actual terminals do not make a difference, do whatever is easiest to wire. The issue is that current needs to flow through all three poles of the overload relay.
If this is not done, the relay is supposed to operate at a slightly lower current than the dial would indicate. They call this feature single-phase sensitivity.

So neat. It does not care about direction of flow, and as long as there is no loss as it moves through each port in a one wire system, it will see the exact same current flow, maybe a tad difference in the 2-wire connection, etc. It makes sense. I guess it is less expensive to just make one type OL and adapt it to its load versus making one-pole, two-pole, or a three-pole?
 

jim dungar

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Given that you need current through all three poles, I wonder why the phase angles of the currents between poles does not seem to matter. Instead of a 120d displacement for three currents you have two in-phase currents and one 180d displacement.

If there is no regard to how the flux sums, perhaps it is some kind of digital sum of an absolute value? Maybe for single-phasing conditions they don't really care about the phasing but just compare the magnitudes of the currents?

Is there no use of residual information in these devices?

These are not electronic, they are thermal. The bimetallic elements are part of a mechanism that is mounted to a pivot. If all three elements do not heat up at the same rate, the unequal movement on the pivot causes a 'faster trip'.

And because they are bimetallic they do have some amount of inherent 'residual information'.
 

mivey

Senior Member
These are not electronic, they are thermal. The bimetallic elements are part of a mechanism that is mounted to a pivot. If all three elements do not heat up at the same rate, the unequal movement on the pivot causes a 'faster trip'.
Aha. Well that makes sense now. Can't quite picture the mechanism as all that comes to mind is a current restraint but I'll see if I can find a diagram.
And because they are bimetallic they do have some amount of inherent 'residual information'.
I can see a thermal residual given the design but what I actually had in mind was along the lines of zero sequence or residual current. Completely off the reservation I guess.
 
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