Multiple start-stop stations

[WYERMF]

When using multiple start-stop stations to operate a single starter is it neccessary to remove the jummper on all but the last station? If so what is the reason? Some of the electricians are split on the neccessity to do so. Is there a safety factor involved that prohibits the jumpers remaining installed on all of the stations? One of the reasons argued to take all but the last jumper out was if someone were to keep the stop button depressed you could still start the motor from another station. Isn't that the point. To control from remote or multiple locations. Please give me some guidance as to how I approach this matter. I am an instructor "discussing" among instructors as to how we will teach this particular objective.

 

[busbar]

In conventional 3-wire control, normally-closed stop buttons have to be connected in series. Normally-open start butons must be paralleled. There's no other way to do it, on paper or in physical installation. That limits it to one jumper on one pair of stop/start buttons.

 

[jbartos]

Suggestion: One station, either first one or last one (more common and safe) should have a jumper and others be without their jumpers. How else to do it?

 

[resqcapt19]

If the jumper is not removed, the stop buttons will end up in parallel and the motor will stop only if the first stop button is used. For all of the other stop buttons, the jumper bewteen the starts and stops will provide a path and prevent the buttons from stopping the motor. For teaching, I strongly recommend that you actualy build the circuit both ways and see exactly what happens. You can use low voltage for these circuits for safey reasons.
Don

 

[RadarRay]

While it may not be obvious, the important PB in the multiple station arrangement is the Stop Button. Just ask any personal injury lawyer. They all better work.

 

[jbartos]

Suggestion. When it comes to multiple push button stations, the controls may or may not stop here. Namely, additional stop buttons, often called emergency stops or e-stops, may be required by safety codes.

 

[gamalla1]

i agree w/ busbar all stops n/c should be in series all start n/o paralleled. i'm assumming you are latching your n/o start pb's w/ aux. contacts from your starter.there is no other way. if you can start the motor from a remote station while pressing the stop button from the same circuit.you got a safety promblem.are you use a plc ?.

 

[busbar]

Sketch the ladder {or whatever} diagram of one starter with three pairs of start/stop buttons, or lay it out on the bench. One pair is "jumpered," but only one. Given plain-vanilla 3-wire control, one button pair can be wired with three conductors—all others need four.

What say you WYERMF?

 

[WYERMF]

I thank all of those who offered guidance to my multiple S/S station question. Yes, starts are parallel, stops are in series or the station won't serve its intended purpose. Using 2 or more stations requires the internal jumper between the n/o & n/c contacts to be removed from all but 1 station. Connecting a wire from the station w/internal jumper(connects to jumper terminal) to 1 side of the other stations n/o contacts keeps motor de-energized when stop buttons are held open. Keeping internal jumpers installed offers multiple paths for current flow when stop button held in open position. Who holds a stop button in the open position for an extended time? Experimentation shows better safe than sorry. Again thanks to all of you for your expertise and guidance.

 

[bobby69]

The easiest thing to do is to tie the stops in series and the starts in parrallel.

 

[jbartos]

Suggestion: The PLC may have a better solution for the Start and Stop pushbutton wiring, namely, all Stops in series on the PLC output and all Starts in parallel on the PLC input.

 

[jraef]

WYERMF
"Who holds a stop button in the open position for an extended time? "

Just so you know, it is a very common and acceptable practice (at least in the US) to have a Lock-Out attachment on a stop push button that depresses the button and allows a padlock to be inserted, keeping it down. These devices fulfill the OSHA requirement for "Lock-Out/Tag-Out" on machine control systems. In those cases, the stop button is depressed for any length of time. Proper design then would allow for ANY stop button on the system to be capable of being locked out in this way. This of course requires that all stop buttons be in series, but you already know that.

Even if your system does not have that device now, it is prudent engineering practice to design for common uses so that IF some day someone installs one of those devices and expects it to work based on common practice, it will. That is not to say that this future person should not bother to test, its just so that a common solution can be implemented. Since you are in a teaching role, teach it the way it should be done. Subvert the dominant paradigm... Think first, then act!

 

[RBE]

busbar

why four wires for the others it can be done with three !
or have I missed something ?

 

[busbar]

RBE--

Allen-Bradley and Cutler-Hammer likley have basic control-wiring information on line.

 

[don01]

jraef (& all)
how scary is this???????
your regs say lock out on control cct is sufficient for personal safety???
NOT WHILE MY BUTTS IN THE SLING!

Who cannot recall some story of auto starting plant (water in box -cable crimped and so on. Who has NEVER plugged a contactor for a good reason let alone a bad one ?

And then putting a plc in the ES cct ?
Please ES Circuit as JBrtos says - in the output cct so the plc is a run permisive only.

Tag out and isolation for a drive should be on the primary device - Fuses,breaker, drop link, fci and co. Then when the stuff up occurs, and it will, you have the best chance of going home

Any way down off the soap box i get BUT I WOULD APPEAL TO ALL -WATCH ISOLATION TECHNIQUES VERY CAREFULLY


regards
Don

ps I've helped clean up after and done the paper work and it aint nice

 

[DRWeig]

Hi, Group!

I gotta jump in with Don on this one. Anytime I see multiple control stations, I picture a guy putting the final torque on a sheave, then having an allen wrench fired thru his headbone when the motor unexpectedly starts up.

Give a good, close read to NEC 430-73 and Part F in general. Do your isolation. At every control and safety point, ask "Will grounding either of these terminals bypass a safety or a manual stop, or complete a manual start circuit?" Then prove otherwise or don't do it. If you're running control circuits around a plant, and you can't be sure where the drunk forklift operator will cause a ground fault, make 'em double pole if needed and break both sides of the coil with stops and safeties.

Ooch, ouch, sorry guys -- this became a pet peeve of mine when I watched a mechanic friend ride the wrong (underside) of an escalator because a) he didn't lock out the supply, and b) the wrong side of a remote start button got grounded by a dropped wrench.

Your pal and safety dude,

Old Dave

 

[sparky001]

WYERMF,
I hope you are successfully sorting the good from bad suggestions here prior to "teaching" others.
Several of the practices suggested within this thread would in certain circumstances, say a coronial enquiry would earn an individual some serious gaol time or, if attributed to a group or company, mega mega fines here in Australia.

Regards
Sparky001

 

[jbartos]

Suggestion: There cannot be 100% safety. Reading some of the above postings that suggest some very remote safety jeopardizing occurrence happened and started the load. The intent of safety is to minimize the hazard to a low level or probability that in real world the engineering, design and installation are practically safe.

 

[Janus101]

Either use 3 wire and remove jumpers indicated above, or run a 4 wire system and latch at starter end, or locally through junction boxe(s).

As far as the discussion re: safety goes: Local E-stops main purpose is to stop a motor in an advert situation. When planned work, maintenance etc shall be carried out, it is normal practise to physically lock the feeder and tag it(and enter the locking and un-locking in a log book).

Just my 2 cents.