I have a customer who is planning to use a PLC to provide overload protection on a 3-phase motor. In the Canadian Electrical Code this would not be allowed as an overload device has to be approved for use as an overload. Is there anything in the NEC that defines what is acceptable for use as an overload device?
NEC Overload Definition
- Thread starter nte
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arjo_reich
Member
Re: NEC Overload Definition
Article 430.31 covers overload protection requirements for motors.
I'll leave the rest up to the experts, but my gut feeling is that if the device isn't specifically listed as an overload protection device then it wouldn't be acceptable.
Article 430.31 covers overload protection requirements for motors.
I'll leave the rest up to the experts, but my gut feeling is that if the device isn't specifically listed as an overload protection device then it wouldn't be acceptable.
petersonra
Senior Member
- Location
- Northern illinois
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- engineer
Re: NEC Overload Definition
does it say anywhere it has to be listed?
the only argument I would have against it is whether it meets the requirements listed in the OL protection section.
Unless the PLC has a module dedicated for this purpose, i don't see how (except for over 1500HP motors) this would meet the requirements.
does it say anywhere it has to be listed?
the only argument I would have against it is whether it meets the requirements listed in the OL protection section.
Unless the PLC has a module dedicated for this purpose, i don't see how (except for over 1500HP motors) this would meet the requirements.
Re: NEC Overload Definition
I don't know if it is allowed, but I don't think it is a good idea. Exactly how does a PLC provide overload protection? Use an analog input to measure the current to the motor?? What happens if the wire to the input opens, or if there is a programming error so the motor doesn't stop on overload.
Steve
I don't know if it is allowed, but I don't think it is a good idea. Exactly how does a PLC provide overload protection? Use an analog input to measure the current to the motor?? What happens if the wire to the input opens, or if there is a programming error so the motor doesn't stop on overload.
Steve
petersonra
Senior Member
- Location
- Northern illinois
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- engineer
Re: NEC Overload Definition
what if someone sizes an overload unit wrong?
what if someone wires it wrong?
what if someone puts a jumper around it?
what if someone sizes an overload unit wrong?
what if someone wires it wrong?
what if someone puts a jumper around it?
- Location
- Bremerton, Washington
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- Master Electrician
Re: NEC Overload Definition
there is no defintion in art 430 of what an overload device is. I'm guessing the customer will have a CT on the motor leads, with an analog input to the PLC.
The OL setting will be done in the PLC software.
this actually is not much different from a VFD. The vfd overload trip point is set in the PLC via softare or an operator interface.
My concern would be the programming of the overload response in the PLC. OL have a certain time delay and response time.
there is no defintion in art 430 of what an overload device is. I'm guessing the customer will have a CT on the motor leads, with an analog input to the PLC.
The OL setting will be done in the PLC software.
this actually is not much different from a VFD. The vfd overload trip point is set in the PLC via softare or an operator interface.
My concern would be the programming of the overload response in the PLC. OL have a certain time delay and response time.
Re: NEC Overload Definition
What I see missing here is a reference to NRC 100.3 and (B)
Also, there are SS OL devices that have been available for some time now. Off hand C-H had (has?)a IQ MP3000 microprocessor based OLR and the IQ-500 current sensing OLR. Sme of the features that are included are I2t w/programable LR protection, inst. over current, GF underload, jam. loss of phase, unbalance reversal, no. of starts limiter, alarms, and trip indicators.
This is info that I had handy. I'm sure that there are many other similar SS motor protection devices available so don't limit yourself to these.
One thing nice about any programmable OLR is that it can be programmed more closely to the motor which gives you better protection and allows you to apply the motor more closely to its capacity w/o damage.
What I see missing here is a reference to NRC 100.3 and (B)
Also, there are SS OL devices that have been available for some time now. Off hand C-H had (has?)a IQ MP3000 microprocessor based OLR and the IQ-500 current sensing OLR. Sme of the features that are included are I2t w/programable LR protection, inst. over current, GF underload, jam. loss of phase, unbalance reversal, no. of starts limiter, alarms, and trip indicators.
This is info that I had handy. I'm sure that there are many other similar SS motor protection devices available so don't limit yourself to these.
One thing nice about any programmable OLR is that it can be programmed more closely to the motor which gives you better protection and allows you to apply the motor more closely to its capacity w/o damage.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: NEC Overload Definition
i like the adjustable trip units like the IEC units have come with for many years. much easier to have one part that covers multiple situations rather than ahving to buy the exact heater you need.
i like the adjustable trip units like the IEC units have come with for many years. much easier to have one part that covers multiple situations rather than ahving to buy the exact heater you need.
- Location
- Massachusetts
Re: NEC Overload Definition
However I certainly can not argue with the convenience of an adjustable trip unit. I had to repair a NEMA starter a few weeks ago which required a 95 mile round trip to get the right heaters.
So I run into work done by the unqualified also but we make money fixing it.
I have a hard time getting used to IEC stuff, I find it many times to be of low quality.
However I certainly can not argue with the convenience of an adjustable trip unit. I had to repair a NEMA starter a few weeks ago which required a 95 mile round trip to get the right heaters.
So I run into work done by the unqualified also but we make money fixing it.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: NEC Overload Definition
We get a lot of work for similar reasons. There are a fair number of hacks in my line of work as well.
A lot of the work is not what I consider to be especially desirable or interesting, but it's profitable, and I guess that is important in the scheme of things.
We get a lot of work for similar reasons. There are a fair number of hacks in my line of work as well.
A lot of the work is not what I consider to be especially desirable or interesting, but it's profitable, and I guess that is important in the scheme of things.
Re: NEC Overload Definition
Sorry guys it's 110.3 Examination, Identification, Installation and use of equipment,
and (B) Installation and use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.
Also, 110.2 Approval, The conductors and equipment rerquired or permitted by this code shall be acceptable only if approved.
in addition, ref. art 100, definitions, "approved" and "listed."
Sorry guys it's 110.3 Examination, Identification, Installation and use of equipment,
and (B) Installation and use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.
Also, 110.2 Approval, The conductors and equipment rerquired or permitted by this code shall be acceptable only if approved.
in addition, ref. art 100, definitions, "approved" and "listed."
james wuebker
Senior Member
- Location
- Iowa
Re: NEC Overload Definition
I have to agree with Tom & Templdl. The newer PLC's are all set by a computer and a program. You can set everything with this. Your OL protection and all your safeys. The only thing you have to do is to set it up correct for your motor and other features that you will install. If you do it correct it will work fine. Some might say to put OL's for the motors in but again if you put the incorrect ones in who's to say what might happen. PLC programming works for me on the motors and systems.
Bye now,
Jim
I have to agree with Tom & Templdl. The newer PLC's are all set by a computer and a program. You can set everything with this. Your OL protection and all your safeys. The only thing you have to do is to set it up correct for your motor and other features that you will install. If you do it correct it will work fine. Some might say to put OL's for the motors in but again if you put the incorrect ones in who's to say what might happen. PLC programming works for me on the motors and systems.
Bye now,
Jim
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