We are having an electrical debate on a simple 480 motor circuit and I?m hoping this forum can help. I have a simple 480 motor circuit with a hard wired start, hardwired stop along with a DCS start and a DCS stop. The debate is over where the DCS stop and the hard wired stop should be in the circuit. Should the hardwired stop PB be this 1st element in the stop circuit or is it permissible to have the DCS stop as the 1st element in the circuit. I personally prefer the stop to be 1st element. Several electricians seem to recall a NEC standard that specifies the hardwire stop is always the 1st element. I have not been able to find this in the code, but I may be looking in the wrong place. Any help would be greatly appreciated.
Estop / Stop push button
- Thread starter cornbread
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luckylerado
Senior Member
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- Lake of the Ozarks
I do not see any difference in putting the manual stop first or 101st since they are all in series, essentially the stop circuit needs to be the first element and that could be an unlimited number of series NC stop devices.
I am not aware of a code section that addresses this.
I am not aware of a code section that addresses this.
just the cowboy
Inactive, Email Never Verified
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- newburgh,ny
don't think it's code
don't think it's code
Control logic is different depending on the use. I have seen it so many ways over the years, a 3 wire stop /start has power first, add and e stop in front for multiple stops breaking power to all stop buttons. But I have seen limit switches the first thing and depending on their state feed stops for different sections. Back when everything was hardwired you had to lay out some of your logic depending on how many contacts where on a device. Now with PLCs' I put ALL stop devices first, if logic is false the scan usually goes right to next rung.
don't think it's code
Control logic is different depending on the use. I have seen it so many ways over the years, a 3 wire stop /start has power first, add and e stop in front for multiple stops breaking power to all stop buttons. But I have seen limit switches the first thing and depending on their state feed stops for different sections. Back when everything was hardwired you had to lay out some of your logic depending on how many contacts where on a device. Now with PLCs' I put ALL stop devices first, if logic is false the scan usually goes right to next rung.
petersonra
Senior Member
- Location
- Northern illinois
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- engineer
You won't find it in the NEC because the NEC does not require an E-Stop.
I don't think it matters any where you put the E-stop in the circuit as long as it overrides all other start/run logic and requires some action by the operator to reset it.
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
It was never in the NEC, because again, the NEC does not require anything with regard to control logic.
It WAS part of what were called the JIC standards (Joint Industrial Council), a consortium of mainly the Big 3 automakers and some other large industrials who came up with standards for making wiring diagrams so that people in different parts of the country could recognize them. That is where all of our symbols and procedures came from. The rule about the E-Stop being first in the circuit had to do with the rules saying that it had to take primary control away from everything else, so if it was always the first device, you would have to work hard at screwing up and connecting another control device around it.
But the JIC no longer exists, it was kind of absorbed into NEMA standards and then parts that were more critical, became what is called "NFPA 79", the Electrical Standard for Industrial Machinery. Not all of the old JIC conventions were carried through however, and that was one of them that is no longer there. But there are rules, so get a copy of it and read section 9.2.5.4 for all the rules on E-stops, if you think it applies to your machine.
In other words, if your installation is not "industrial", it may not apply. If your machinery has an overall listing by a 3rd party, such as UL, then you don't need to worry about it. If it's for residential use, you don't need to worry about it.
It WAS part of what were called the JIC standards (Joint Industrial Council), a consortium of mainly the Big 3 automakers and some other large industrials who came up with standards for making wiring diagrams so that people in different parts of the country could recognize them. That is where all of our symbols and procedures came from. The rule about the E-Stop being first in the circuit had to do with the rules saying that it had to take primary control away from everything else, so if it was always the first device, you would have to work hard at screwing up and connecting another control device around it.
But the JIC no longer exists, it was kind of absorbed into NEMA standards and then parts that were more critical, became what is called "NFPA 79", the Electrical Standard for Industrial Machinery. Not all of the old JIC conventions were carried through however, and that was one of them that is no longer there. But there are rules, so get a copy of it and read section 9.2.5.4 for all the rules on E-stops, if you think it applies to your machine.
In other words, if your installation is not "industrial", it may not apply. If your machinery has an overall listing by a 3rd party, such as UL, then you don't need to worry about it. If it's for residential use, you don't need to worry about it.
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