Motor control · lesson 5 of 12
More than one station
To control one motor from several places, put every Stop in series and every Start in parallel with the seal-in. Series means any one Stop can break the rung; parallel means any one Start can complete it.
Two stations: Stops in series, Starts in parallel
Turn on JavaScript to press the buttons and run this circuit.
Do this
One motor, two pushbutton stations — say one at each end of a conveyor.
Why this works
Current has to pass through every contact in a series string, so opening any one of them stops it — that is the Stop buttons. Current needs only one path through a parallel group, so closing any one of them is enough — that is the Start buttons and the seal-in. It is the same series and parallel you learned with lamps; the series / parallel practice page drills the idea.
In the field
Adding a station to an existing starter means breaking into the Stop wire to add the new Stop in series, and landing the new Start across the existing Start terminals. The seal-in contact does not change. On a long conveyor you will often see a station at each end and a pull-cord or e-stop in series with the Stops along the length.
Questions people ask
How do you wire two start/stop stations?
All the Stop buttons in series with each other, all the Start buttons in parallel with each other and with the seal-in contact. Any Stop then breaks the circuit, and any Start completes it.
What happens if a Stop is wired in parallel by mistake?
That Stop only works if the other Stop is pressed at the same moment — on its own it does nothing, because the other one still carries the current. Each button tests fine by itself, which is why it is a hard fault to spot.
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