Reset Buttons on motor starter cabinets.

[meternerd]

I'm certainly not either- that would be totally irresponsible. My notices were, in my opinion, completely necessary and as direct and succinct as I thought they could be. Just two of them. Yet still got ignored by a hugely experienced electrical guy in the case I cited. Yet, you have suggested providing notices for operators not trained in electrical matters to make a judgement about making an electrical decision? What the overload tripped because the motor has shorted turns? And resetting it causes a fire that burns the place to the ground. No, it shouldn't. But electrical fires do happen. I just don't think plant operators should be placed in the position to make, or worse, be required to make the decision to push that button. Overloads trip for a reason. The operators should not be called upon to be judge and jury and have to decide on what action to take.

OP question was if it's required by Code. Conversation evolved into whether it's a good idea. Opinions seem to be both ways. My reasoning that it's OK is that OL's usually trip due to overload. Shorted turns must be rare. I've never seen failures that didn't involve sparks, smoke and eventually a tripped breaker. Just me, though. Main reason we allow operators to do it is because there are only two electricians and both live 50 miles away in Reno. An after hours electrician callout involves 2 hours double-time minimum (per contract). The on-call operator who finds a motor not running first tries resetting the OL. If it resets and the motor starts back up, then they watch flow rate for a bit and if all is well, they go on about their business. If not, they switch to a backup pump. Electricians may go out the next day on regular time if it's a frequent trip on the same motor, but usually it isn't. Calling out an electrician, waiting an hour for him to show up and then finding no problem but paying 4 hours worth of wages is not popular with management and we don't see it as a safety issue. Real world.

 

[don_resqcapt19]

Most of our OL's are solid state from Square D. They are adjustable trip and also sense phase loss. We "dim bulbs" start with the settings based on nameplate, but often it may be OK for a while, then they rearrange valving out in the field and the load on the motor goes up due to higher flow, higher backpressure, etc. Also, dirt from piping can cause excessive drag on pump impellers. We use 700ft deep wells as a source and sandy soil will allow small grains of sand through the strainers and into the piping.
....

If you have set the overloads based on the nameplate full load current, they should not be tripping unless the motor is being overloaded. All of the things you mentioned are increasing the load on the motor. The overload tripping out when set to the motor full load is doing exactly what it should do.

 

[meternerd]

If you have set the overloads based on the nameplate full load current, they should not be tripping unless the motor is being overloaded. All of the things you mentioned are increasing the load on the motor. The overload tripping out when set to the motor full load is doing exactly what it should do.

Guess I wasn't clear...not unusual for me. SS OL's come in ranges...15 to 25A, 25 to 45A, etc. Adjustment setting for the OL is in %, not amps. The same size motor starter may run different types of motor/pump combinations. Nameplate FLA is used to size the overload RANGE, but the actual setting varies with the application. If using a 15A to 35A adjustable OL on a 25FLA motor, it's not really best to just set the OL at 50%. Doesn't work that way. Same motor/pump combo may draw different amps when pumping max flow for the particular system. We try to use standard pump sizes to reduce inventory. We set the OL at the lowest setting that prevents nuisance tripping. The pumps supply hydrostatic pressure tanks. Mostly second home owners up here. Average daily usage varies drastically. Higher during holidays and weekends. We don't want the OL's set too high because during low usage times we want the motors protected conservatively, but during high usage times they may shift the system valving around to equalize pressures and pump run times. That may require higher settings. Maybe that makes more sense. The reason we use solid state OL's is because of number of run cycles per hour. With thermal OL's, the residual heat from the starting inrush adds up until the OL trips. Doesn't happen with SS OL's

 

[kwired]

OP question was if it's required by Code. Conversation evolved into whether it's a good idea. Opinions seem to be both ways. My reasoning that it's OK is that OL's usually trip due to overload. Shorted turns must be rare. I've never seen failures that didn't involve sparks, smoke and eventually a tripped breaker. Just me, though. Main reason we allow operators to do it is because there are only two electricians and both live 50 miles away in Reno. An after hours electrician callout involves 2 hours double-time minimum (per contract). The on-call operator who finds a motor not running first tries resetting the OL. If it resets and the motor starts back up, then they watch flow rate for a bit and if all is well, they go on about their business. If not, they switch to a backup pump. Electricians may go out the next day on regular time if it's a frequent trip on the same motor, but usually it isn't. Calling out an electrician, waiting an hour for him to show up and then finding no problem but paying 4 hours worth of wages is not popular with management and we don't see it as a safety issue. Real world.

Kind of gets into a point I always try to make when this kind of conversation comes up. Most replies seem to suggest a qualified elecrical person need be on site at all times to determine why an item trips a breaker or overload before resetting it. Reality is that doesn't happen other then maybe at larger industrial sites that maybe run 24/7 and have 24/7 maintenance staff. Every one of my clients is going to have reset an item a number of times for those slight overload situations before I am ever told there was any problem, a short circuit or ground fault - maybe only one attempted reset, maybe multiple attempts before I am called.

Guess I wasn't clear...not unusual for me. SS OL's come in ranges...15 to 25A, 25 to 45A, etc. Adjustment setting for the OL is in %, not amps. The same size motor starter may run different types of motor/pump combinations. Nameplate FLA is used to size the overload RANGE, but the actual setting varies with the application. If using a 15A to 35A adjustable OL on a 25FLA motor, it's not really best to just set the OL at 50%. Doesn't work that way. Same motor/pump combo may draw different amps when pumping max flow for the particular system. We try to use standard pump sizes to reduce inventory. We set the OL at the lowest setting that prevents nuisance tripping. The pumps supply hydrostatic pressure tanks. Mostly second home owners up here. Average daily usage varies drastically. Higher during holidays and weekends. We don't want the OL's set too high because during low usage times we want the motors protected conservatively, but during high usage times they may shift the system valving around to equalize pressures and pump run times. That may require higher settings. Maybe that makes more sense. The reason we use solid state OL's is because of number of run cycles per hour. With thermal OL's, the residual heat from the starting inrush adds up until the OL trips. Doesn't happen with SS OL's

Unless I am not understanding something - it is ok to set the trip point to load conditions as long as they are within motor rating, but the general concept of motor overload protection is to protect the motor not the load, and that means a 24 amp full load motor is usually provided with an overload protector set to allow that motor to draw 24 amps plus or minus other allowable amounts based on duty, sevice factor, etc.

Thermal overloads can be selected based on frequent starts, high ambients, other heat producing factors and protect very well, but usually requires finding the correct selection table from the start. The table provided with a basic motor starter is a general use table and you really need to look at manufacturers selection information when you have other conditions that change the potential heat level that will be present. One thing I do like about thermal overloads is once they are selected (and selected properly) the user doesn't usually tamper with them where solid state or other adjustable types often get cranked up to highest possible setting by the user at some point.

 

[don_resqcapt19]

... The reason we use solid state OL's is because of number of run cycles per hour. With thermal OL's, the residual heat from the starting inrush adds up until the OL trips. Doesn't happen with SS OL's

What about that same heat build up in the motor windings?

 

[Jraef]

What about that same heat build up in the motor windings?

Most SSOLs that I am aware of deal with this issue in one of two ways; they either will simply emulate a bi-metal OL action (usually the cheaper ones do this) in terms of reset time by using a fixed value, or they track the actual motor heating effect accurately and alter the trip times and reset times based on residual motor heat and cooling modeling by comparing against standardized thermal damage curves and cooling rates based on expected NEMA motor sizes for the OL relay being used. Either way, UL requires SSOLs to have what's called "retentive thermal memory" so that the minimum cool down time cannot be overridden by cycling control power to the relay. The only way you might be able to get a faster reset time using an SSOL is if the SSOL knew that the motor tripped on a long term low level OL and is predicting a shorter wait period because the residual heat is not as bad as it might have otherwise been, something a bimetal relay cannot do.

So yes, it can happen that you can reset faster because you have a better quality thermal model of the motor with a high end SSOL, but it does depend on the nature of the OL trip event.

 

[meternerd]

OK...one last comment and I think I wanna drop out. Way off the OP subject. More complicated than we need to be discussing on a Code forum. We set the OL to a trip setting that is probably more sensitive than average. The reason is that if we have a pump motor that begins to draw more load than normal, it can mean potential damage to the pump if it's due to pump seals binding, bearings in the pump, sand in the impeller or a flow problem due to valve issues, pressure switch malfunctions, etc. We decided it's better to trip the pump on overload and force an operator to visit the station (alarms when "called but not running") rather than have a pump become damaged and require replacement. Outages are not popular with the customer. Seems to be working for us. But as I said before, most of the time we find no problem when we do an amp check of the motor, so the trip was likely due to a loss of phase trip caused by a momentary voltage sag on one phase. No safety issue for the operator to do a reset.

 

[jim dungar]

We set the OL to a trip setting that is probably more sensitive than average.

You should probably leave the motor OL alone and add a 'process' overcurrent relay to your protection scheme.

 

[kwired]

You should probably leave the motor OL alone and add a 'process' overcurrent relay to your protection scheme.

Or even some process monitor that doesn't interrupt anything just gives you indication of when a particular parameter has been exceeded, such notifications could be triggered by voltage, current, excess run time, too little run time, temperature, pressure, speed, etc. Some of those items go beyond motor protection but still give your motor and driven load better reliability.

 

[Jraef]

OK...one last comment and I think I wanna drop out. Way off the OP subject. More complicated than we need to be discussing on a Code forum. We set the OL to a trip setting that is probably more sensitive than average. The reason is that if we have a pump motor that begins to draw more load than normal, it can mean potential damage to the pump if it's due to pump seals binding, bearings in the pump, sand in the impeller or a flow problem due to valve issues, pressure switch malfunctions, etc. We decided it's better to trip the pump on overload and force an operator to visit the station (alarms when "called but not running") rather than have a pump become damaged and require replacement. Outages are not popular with the customer. Seems to be working for us. But as I said before, most of the time we find no problem when we do an amp check of the motor, so the trip was likely due to a loss of phase trip caused by a momentary voltage sag on one phase. No safety issue for the operator to do a reset.

Im glad you explained that, mainly for the benefit of others who may read this and not understand why you thought it was OK to turn up the trip settings.

This is actually not an uncommon approach on submersible pumps, in fact many pump mrs require that the OL relay trip much faster than normal, ie Class 5, otherwise the pump warranty is void or not extended. Franklin is like that; if you buy and install their Sub-Trol protection unit you get a longer warranty on the pump, and it is doing some of those type of added functions. It's mostly because of the relative extreme cost of having to pull a pump out of a deep hole. Just realize that is not the norm for other industries, most people want the motor to run and produce as much as possible without sacrificing longevity, so if the OL is set to the motor FLA, turning it up is tantamount to sentencing it to execution with an indeterminate date.

 

[meternerd]

Im glad you explained that, mainly for the benefit of others who may read this and not understand why you thought it was OK to turn up the trip settings.

This is actually not an uncommon approach on submersible pumps, in fact many pump mrs require that the OL relay trip much faster than normal, ie Class 5, otherwise the pump warranty is void or not extended. Franklin is like that; if you buy and install their Sub-Trol protection unit you get a longer warranty on the pump, and it is doing some of those type of added functions. It's mostly because of the relative extreme cost of having to pull a pump out of a deep hole. Just realize that is not the norm for other industries, most people want the motor to run and produce as much as possible without sacrificing longevity, so if the OL is set to the motor FLA, turning it up is tantamount to sentencing it to execution with an indeterminate date.

Actually, I think I said we turn DOWN the setting to make the motor OL trip sooner. That said, a lot of the settings end up close to FLA anyway, because motors are most efficient at full load, so we size the motor/pump combinations accordingly. Causes a trip, forcing investigation, and reduces the likelihood of motor/pump overheating or damage due to pumping issues. We have very few that do trip on overcurrent, though. When called about a tripped OL, we measure current and it's well with spec and below trip setting. That only leaves a single phase event. No reason not to reset the OL.

May not be the most elegant solution, but we're talking water tanks and pressure or level switch controls and motor operated valves. Not very exotic controls needed.

 

[Jraef]

I kind of recall having to provide external reset operators years ago if voltage was over 250 volts to ground, but I see no such requirement in 2014 nor do I recall this being required in recent editions. Not sure when such requirement was removed or if we were misunderstanding a requirement at that time - but I recall it being enforced by the AHJ as well - but this was like 20 years ago or so....

This first part of your post has been rattling around in the brain for a while, because I was thinking I had seen something about the requirement for a reset button as well, albeit I didn't think it had to do with voltage per se.

I think I found it. Might be different, but I thought it interesting in light of this discussion. In UL508A, they make a distinction between an enclosed device having a COVER, or a DOOR. The DOOR requires a hinge and latch(es), the COVER does not, it can come off in your hand by removing screws. If you have a COVER, your overload relay MUST have an external reset button, and there cannot be power fuses in the box. It is conversely worded that if you must open an enclosure to reset an OL relay (or breaker by the way), the enclosure must have a DOOR, not a cover.

 

[kwired]

This first part of your post has been rattling around in the brain for a while, because I was thinking I had seen something about the requirement for a reset button as well, albeit I didn't think it had to do with voltage per se.

I think I found it. Might be different, but I thought it interesting in light of this discussion. In UL508A, they make a distinction between an enclosed device having a COVER, or a DOOR. The DOOR requires a hinge and latch(es), the COVER does not, it can come off in your hand by removing screws. If you have a COVER, your overload relay MUST have an external reset button, and there cannot be power fuses in the box. It is conversely worded that if you must open an enclosure to reset an OL relay (or breaker by the way), the enclosure must have a DOOR, not a cover.

My recollection was an NEC requirement to have external reset operators for motor overloads when we used to take a large enclosure and fill it with motor controllers - with the disconnect (breakers) in an adjacent panelboard. If we were doing this in a 208-240 volt system we didn't need the external operators, but if it were over 250 to ground (or something similar was almost always on 480/277 systems anyway) we had to install external reset operators - I remember looking this up in NEC even - but has been like 20-25 years ago.

May need to get out an old code book and see what I can find on this topic.

 

[kwired]

I may have found it in 1993 NEC - but I think we maybe were not interpreting 430-133 correctly at that time, or at least not understanding the intent of the section.

This information has had changes but some of it is still in 2014 in Part XII, was in part K in 1993. A lot of wording from 1993 is mostly covered in Art 110. 150 volts to ground mentioned in 1993 430-133 has since been reduced to 50 volts.


430-133 content from 1993 was titled "Guards for Atendants" and said " Where live parts of motors or controllers operating at over 150 volts to ground are guarded against accidental contact only by location as specified in Section 430-132, and where adjustment or other attendance may be necessary during the operation of the apparatus, suitable insulating mats or platforms shall be provided so that the attendant cannot readily toush live parts unless standing on the mats or platforms.

I think this said to our inspector at the time if over 150 volts to ground - we needed to provide insulating mats or platforms or put the external reset operators in so that no body is exposed to live parts when resetting an overload device. Today is different - with all the attention to safety beyond just what is in NEC - nobody wants you opening the enclosure without removing power anyway - especially to perform a simple reset operation.

 

[meternerd]

Thoughts about the DOOR vs COVER. If a door would allow an internal OL reset, the door would obviously have to be opened first. Most MCC's I've seen have an interlock so the breaker must be off before you can open the door. So every OL trip requires a breaker operation. Breakers are not intended to be used as switches, and it's my experience that breakers do wear out and fail to reset if they're operated too many times. The other option of using the "interlock defeat mechanism" to open the door with the breaker still closed would then have you resetting an OL with power still on, so you'd be staring at an energized starter when the motor starts back up. Bad idea. Interesting discussion....don't ya just love this stuff?

 

[Beenaround]

Thank you

Thank you

I apologize for being late in returning to this thread. Our motor controls have doors with an external reset. The door can be opened without shutting the breaker handle off. Yes you do have to be in the enclosure for trouble shooting problems. Incidentally the most common problems are start/stop stations pinned off and blown control circuit fuses. Our facilty is staffed 24/7, sometimes things get crazy. Our horsepower ranges from 1/2 to 2000 H.P. Voltage range from 120 to 480(majority) 2300and 4160. The biggest problem with non qualified personnel resetting overloads is not investigating what caused the trip. The policy for LOTOTO is well written and needs to be followed.The reset buttons are staying in place and my concern was safety not turf.
Thank you for your input. The professionalism is refreshing.