# E-Stops, relays and mcc's



## scotch (Oct 17, 2013)

Well Phillcruz ...if it's your job ....that's why you get paid the "Big Bucks" to figure it all out...if it's homework....well it's a nasty world out there ...get used to figuring thing out on your own if you really want to be a "controls guy " in the industry!


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## joebanana (Dec 21, 2010)

A little context would be helpful. Clearer images would be too. That's a lot of coils, in series, without the corresponding contacts. And why three different circuits?


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## telsa (May 22, 2015)

The fine print makes it read like homework.


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## JRaef (Mar 23, 2009)

What the F????
That circuit design is ridiculous, obviously drawn by someone who has no clue. You CANNOT run relay coils in series like that! They would need to be in parallel, and still, that's NOT the way to do this.

Run away, run FAR away from this, you are getting very bogus information here.


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## John Valdes (May 17, 2007)

If those are the drawings you are supposed to work from, you have two choices.

1) Tell them it will not work as drawn and have the correct drawing that YOU made to prove it.
2) Hook it up exactly as shown. Then wait for all the finger pointing and loss of production while it gets drawn correctly and implemented correctly.


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## Electrorecycler (Apr 3, 2013)

Wow! That's a mess if I've ever seen one. And why are the safety channels jumped out?! I've never met an engineer that would pass that. Using a dual channel safety relay as a single channel estop. Just not good. Like JRaef said, the coils are done all wrong, and that's just the start! I can't even begin to tell you how wrong this is. I'd start from scratch, and consult a safety engineer. You don't want to energize this circuit without an authority signing off on it. 

CYOA! Cover your own ass!


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## tates1882 (Sep 3, 2010)

Looks like somebody didn't want to spring for the drawing software. 


Sent from my iPhone using Tapatalk


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## micromind (Aug 11, 2007)

Electrorecycler said:


> I've never met an engineer that would pass that.


I've met more than one engineer who not only would but actually DID draw stuff like this. 

Of course, they were right and I was wrong........

Until we hit the switch........


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## sparkiez (Aug 1, 2015)

Wow, so much to comment on here. I'll leave the drawings alone for now, but those coils should NOT be in series for PLC outputs. Now, lets get down to brass tax. I'll answer your theory questions.

They did NOT overdo it with relays. Typical NEMA motor starter coils draw WAY more than a control relay coil. Even if the PLC output could handle it, there is both a TOTAL current limit and an INDIVIDUAL OUTPUT current limit. When looking at these limits, you can almost never load every output to the max, so relays are used for this reason, to keep the outputs safe, and help them last longer.

Lets move on to the ESTOPS. The buckets should not be "fed" like you are mentioning. 

If you are working with an old-school hard-wired MCC, then there is a conversion factor there, but I'm not getting into that right now. If you are doing that, and no one is really sure what to do, you need to call in a professional. I have done it, and there are lots of little bits and pieces involved that will cause stuff to blow up and not function properly. Not to mention the fact that you will spend WAY more money having an outside contractor ring out wires if you guys go to moving them around and the circuits no longer work properly.

Anywho, to the ESTOP circuit. Your safety relay will control power to a 120V bus which will then feed the incoming side of the dry contacts on your control relay. If the estop circuit is broken, the safety relay will open, and all control relays will open and close as normal, but no power will go to the starters in the buckets. *NOTE/DISCLAIMER*: TO PROPERLY DESIGN THIS SYSTEM YOU WOULD NEED TO HAVE A MECHANISM TO REQUIRE THE SAFETY RELAY TO RESET AFTER THE ESTOP CIRCUIT HAS BEEN BROKEN, AND I AM OMITTING THAT HERE.

Now, to cover the last bit of your post and being able to start and stop the entire system, but be able to kill individual pieces of equipment, you will want to do this within the PLC. I don't mean to offend here, but if you are having trouble so far, you really, really don't want to try to get into the relay-logic necessary to accomplish this task, I don't have the time to spell that out for you, and I won't give you the "hack" way to do it because I'm not physically there to do a safety evaluation on the equipment.

There are many potential safety and functionality pitfalls on a project like this and I wish you the best!


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