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JIC stnd for showing Motor Overloads reset or trip position?
- Thread starter AJ2002
- Start date
Why do you need to know? The second part of that question sounds suspiciously like a homework problem, but your other postings lead me to believe you are a working professional (just maybe not an EE).
Giving you the benefit of the doubt, OL contacts in control logic diagrams are always shown as NC contacts; "Normal" being that the Motor Over Load Relay has NOT tripped.
References? References? I don' need no estinkin' references...
Seriously though, JIC no longer exists, so there is no "official" reference standard that I know of other than NFPA79. But you can look at a copy of the old JIC standards from 1967
here
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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Giving you the benefit of the doubt, OL contacts in control logic diagrams are always shown as NC contacts; "Normal" being that the Motor Over Load Relay has NOT tripped.
References? References? I don' need no estinkin' references...
Seriously though, JIC no longer exists, so there is no "official" reference standard that I know of other than NFPA79. But you can look at a copy of the old JIC standards from 1967
here
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376
- Moderator
- #4
It is normal to show contacts in the normal operating position on most diagrams. N/C are shown closed and N/O are shown open. I seem to remember seeing this mandated in a standard somewhere sometime but it was so long ago that memory blurs.
There are exceptions in some drawings.
What jraef said;
"References? References? I don' need no estinkin' references..."
Bill
--------------------
"Why not the best?"
Jimmy Carter
There are exceptions in some drawings.
What jraef said;
"References? References? I don' need no estinkin' references..."
Bill
--------------------
"Why not the best?"
Jimmy Carter
- Thread starter
- #5
Jraef,
I am an EE PE, like you I use 25 years of field engineering experience building and operating power plants instead of referencing codes for issues like this. However in dealing with international clients who use the IEC standards it is easier if I reference a ANSI code to state the US conventions. US standards show reset and the IEC shows it in a tripped state.
So if some had a specific code to reference from NEMA or some other standard it would be appreciated.
Thank you for the link!
I am an EE PE, like you I use 25 years of field engineering experience building and operating power plants instead of referencing codes for issues like this. However in dealing with international clients who use the IEC standards it is easier if I reference a ANSI code to state the US conventions. US standards show reset and the IEC shows it in a tripped state.
So if some had a specific code to reference from NEMA or some other standard it would be appreciated.
Thank you for the link!
AJ2002,
I think there may be a semantics issue here. I have reviewed some internal diagrams I have and IEC standards use a NC contact element off of an Over Load Relay in the control circuit diagrams as well.
I think where you may be getting confused is in the power circuit. IEC systems often use Motor Starter Protectors that are, for lack of a better term, what we in NEMA world would consider a "Manual Motor Starter". It includes the magnetic and thermal OL trip elements, as well as the disconnect mechanism. So because it has the disconnect, it is always shown in the Open position in the power diagram, as disconnects are shown in NEMA systems as well. But the difference is, if you had a control circuit auxiliary contact on one of these IEC MSP devices instead of a traditional OL relay, it will show as a NO contact, because the integral disconnect is Open.
Because JIC ceased to exist before the widespread use of these devices, there is no direct reference standard for showing them that I know of. Technically, because you need to show the MSP as an Open device (normal, de-energized), any aux. contacts associated with them will need to be shown as NO devices as well. What I used to do was to show them as NO, then add a label that said "N.O., Held Closed".
But if you are using a standard OL Relay that is controlling a contactor coil, the aux. contacts will ne shown as NC in a control logic diagram.
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376
I think there may be a semantics issue here. I have reviewed some internal diagrams I have and IEC standards use a NC contact element off of an Over Load Relay in the control circuit diagrams as well.
I think where you may be getting confused is in the power circuit. IEC systems often use Motor Starter Protectors that are, for lack of a better term, what we in NEMA world would consider a "Manual Motor Starter". It includes the magnetic and thermal OL trip elements, as well as the disconnect mechanism. So because it has the disconnect, it is always shown in the Open position in the power diagram, as disconnects are shown in NEMA systems as well. But the difference is, if you had a control circuit auxiliary contact on one of these IEC MSP devices instead of a traditional OL relay, it will show as a NO contact, because the integral disconnect is Open.
Because JIC ceased to exist before the widespread use of these devices, there is no direct reference standard for showing them that I know of. Technically, because you need to show the MSP as an Open device (normal, de-energized), any aux. contacts associated with them will need to be shown as NO devices as well. What I used to do was to show them as NO, then add a label that said "N.O., Held Closed".
But if you are using a standard OL Relay that is controlling a contactor coil, the aux. contacts will ne shown as NC in a control logic diagram.
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376
controlsdude
Electrical
This has been bugging since I read this thread. Not trying to hijack the thread, just want some clarification.
I have seen the OL contact shown two different ways. This is over 20 years looking at prints.
1st This is the nema OL contact
Shown as a normally closed contact and shown wired on the neutral side of the motor contactor where the contactor is shown as an output of the PLC or hardwired condition.
Then the OL is shown in the 3phase as the hooked contacts before the motor contactor.
2nd This is the manual motor protectors with the tripping switch on the front of the overload
Shown as a normally open contact and shown wired on the hot side of the contactor between the PLC output and contactor.
Then the OL is shown in the 3phase as the hooked contacts and circuit breaker symbol before the contactor.
Question: Why was the Nema OL shown as a NC contact and the manual motor protector shown as a NO contact? Was the normal state of the bimetal contact NC and the manual motor protector was energized holding the NO contact? But why NC contact was on the neutral side of the contactor?
I have seen the OL contact shown two different ways. This is over 20 years looking at prints.
1st This is the nema OL contact
Shown as a normally closed contact and shown wired on the neutral side of the motor contactor where the contactor is shown as an output of the PLC or hardwired condition.
Then the OL is shown in the 3phase as the hooked contacts before the motor contactor.
2nd This is the manual motor protectors with the tripping switch on the front of the overload
Shown as a normally open contact and shown wired on the hot side of the contactor between the PLC output and contactor.
Then the OL is shown in the 3phase as the hooked contacts and circuit breaker symbol before the contactor.
Question: Why was the Nema OL shown as a NC contact and the manual motor protector shown as a NO contact? Was the normal state of the bimetal contact NC and the manual motor protector was energized holding the NO contact? But why NC contact was on the neutral side of the contactor?
controlsdude,
Read my response just above yours. I answered your exact question.
And by the way, in the power diagram, those are not "hooked contacts", that is just the symbol for a thermal sensing element. There are no moving power contact devices associated with that specific symbol.
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376
Read my response just above yours. I answered your exact question.
And by the way, in the power diagram, those are not "hooked contacts", that is just the symbol for a thermal sensing element. There are no moving power contact devices associated with that specific symbol.
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376
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