Need schematic

[rkrieger]

I know I should probably know this, but I would like someone to explain how to hookup the following circuit. A school shop wants a "power disconnect" system in which two "panic" buttons located in the shop if pushed, will dump a panel in which all circuits fed by the panel will become de-energized. OK, a tap is taken from a CT, fed through a disconnect, then into a magnetic circuit breaker, then to the dedicated panel.

There will be two E-stop locations and one location with a keyed switch to reset system. E-stops can be re-set by twisting them and pulling out. Key switch is a momentary contact and spring release.

I would appreciate a schematic showing the control circuit. The wiring of the disconnect, magnetic circuit breaker (other than the coil circuit) and the panel is not a problem. Just the control circuit of the circuit breaker.

Thanks in advance for your help.

RLK:-?

 

[e57]

Is this 'home-work'?????

 

[rkrieger]

Nice guess, but no..................

Nice guess, but no..................

Not currently enrolled in any classes. The situation is that I am on a temporary hiatus recovering from shoulder surgery. A school I consult for (I am retired teacher) asked about this situation. I was just wondering how to accomplish the control circuit wiring. Trust me, when it is time to install the system, I will contact my "electrical contractor boss" and they/we will install it. I just wanted to be prepared when I discuss it with him. I believe I am probably the oldest licensed electrical apprentice in my state. I have a lot of experience with residential, simple pipe/wire jobs, but not machine control. I just hate looking "dumb" when in discussion.

Thanks,

RLK :smile:

 

[e57]

Probably a 100 ways to do it....

The easiest simple least expensive way would be a shunt trip breaker in a locked panel, and pararalel two NC (normally closed) mushroom switches to control it.

But the way it is decribed, you would need a contactor large enouch for the panel under load, with auxilary (NC) contacts so that those contacts are closed when the contactor is. You'll need to use that to hold power to the contactor. The two (NO) panic buttons open the circuit in series breaking the contactors circuit. The momemtary (NC) key switch bypasses the aux. contact and restores power to the circuit which is held by the aux contacts, but only if the panic buttons are reset. You could do this with whatever control voltage you like AC or DC.

You should be wary of what this is controlling IMO, as some (few I can't think of now) things are an exception to belief of "OFF is better" and better left running while a person is operating it, and become more of a hazard when inadvertantly shut off. You may want to add an additional aux. contact so that when off an alarm sounds to warn people using turning machines or saws or such.

 

[ptonsparky]

Typical motor starter circuit with two E stop buttons.

All manually started loads would reenergize when contactor is reset. Could be a problem if the key is in the wrong hands.

 

[ELA]

As was stated there are many ways to perform an EPO or EMO function. It is always best to perform a risk assessment to help you determine the level of safety you should incorporate.

Here is one link to a little more information:

http://www.teal.com/products/App note AN-16.htm

 

[e57]

I'm sure someone has a graphic for this - but you should be carefull in the way the circuit is designed so that a ground fault can not inadvertantly restart - or fail to open the circuit. This can be the case if using a grounded voltage source. It's one of the few cases where you want to keep the grounded conductor (if any) as short as possible and be any part of the control circuit.

 

[Jraef]

As ELA mentioned, there are many ways to accomplish this. The best way would be to use a low voltage "Safety Relay" system with the proper safety interlocks and re-start sequences enforced.
Here's a starting point: Siemens Safety Integrated

But be forewarned, NFPA79 (which sort-of covers machine safety now) is in the process of being upgraded and harmonized with the tougher IEC standards for safety systems on machinery. If you do something now without consideration of this, you may find yourself re-doing it next year or the year after. By having a qualified safety audit done, they can (should) address these upcoming safety protocols and set you up now with a system that will be compliant in future.

 

[stickelec]

RK, I can tell from your first two posts that you are eager to be an active participant in the design meeting of which you speak. "I have been there myself", and with that in mind I offer the following:

I feel there are just too many unknowns to offer "a wiring diagram", plus I would think emergency-systems design in the public domain carries with it quite a responsibility.

I would rather respectfully submit for your consideration a different approach to your participation. As you know, long before a project moves to the "wiring diagram" phase, a lot of design work has to take place. Perhaps you could step-in as a design coordinator, you might be surprised at how favorably that would be received among your peers. Once the scope is clearly defined and documented, you could then move to the next phase.

If you then want to take a shot at designing the logic, I would encourage you to Google "Relay Ladder Logic" (or similar) and make it happen on paper. You would then, of course, want to work through the review process with other qualified professionals. Because it could be considered life-safety, I would encourage you to seek the assistance of a qualified professional well versed in the various code requirements.

If you want to pursue the development of a project scope, I would be glad to offer a list of things that might be of value.

 

[rkrieger]

Drawing coming ASAP

Drawing coming ASAP

Thank you for your thoughtful comments. I appreciate the liability concern in this day in age. I have come up with what I believe is a workable design. I will include a schematic of the design as soon as I can figure out where to go to get "free" electrical schematic symbols and then put it in this format. Because so many have "looked" at this post, I thought it would be at least, interesting for all.

Background premise: The shop in question is an Automotive Technician Training facility. There is a "sanctioning" organization called NATEF that certifies all such programs in the U.S and mandates the power disc. system. Since this is a new school, it will soon apply for NATEF endorsement and thus needed the emergency disconnect system, which by the way is very, very common in high school and post high school shop settings. I fully understand the many safety concerns with several of the "posters". In this case, NATEF wants all 120V outlets and all 220V power equipment outlets to be disconnected with the E-stops. We are using a magnetic contacter and a momentary key re-set switch to maintain control upon re-start.

Thanks to all who have responded and I will soon get the drawing up.

RLK

 

[LarryFine]

I will include a schematic of the design as soon as I can figure out where to go to get "free" electrical schematic symbols and then put it in this format.

Don't overwork yourself. If you have a scanner, just hand-draw it.

 

[dbuckley]

This is a machine tool shop, so EPO is a safety of life device. In this circumstance you need an EPO that fails safe, the series contactor arrangement being one commonly used option; a shunt trip doesn't fail safe and so is not appropriate for this application.

 

[Smart $]

...I will soon get the drawing up.

I'm thinking it'll be something like this...

 

[cadpoint]

OH

OH

1 or 3 is always hot ! Where's 4 & 5 ?

 

[K2500]

Looks like the key switch will energize the circuit momentarily regardless of PB position. Stops should be in series ahead of reset/starts, so that the PB must be reset before anything starts moving again. Move 1 between 6 & Aux and you've got it.

 

[Smart $]

Looks like the key switch will energize the circuit momentarily regardless of PB position. Stops should be in series ahead of reset/starts, so that the PB must be reset before anything starts moving again. Move 1 between 6 & Aux and you've got it.

You're right!

 

[Smart $]

1 or 3 is always hot !

See revised schematic... but even so, 3 is always hot.

Where's 4 & 5 ?

4 and 5 are just terminals, jumpered, for connecting PB's in series.

 

[nakulak]

looks to me like you need to jump 3,5 and 4,6, unless I'm missing something (you want to OR the switches, correct ?) (they are AND right now)

 

[Smart $]

looks to me like you need to jump 3,5 and 4,6, unless I'm missing something (you want to OR the switches, correct ?) (they are AND right now)

Nope! Stops are always in series. If you connected them in parallel you'd have to push both to shut down the contactor.

 

[nakulak]

that's if they are wired NC, I thought he was wiring them NO, (you are correct, they should be NC, )