Today I had an electrical problem at my home not yet resolved. I will explain the problem.

The switch for water motor and switch for lamp are nearby in same board. When I turn ON the lamp switch, the lamp is glowing untill the switch for motor is OFF. When the motor switch is turned ON the lamp despite its switch turned ON stops glowing and motor is also not operating. When the motor switch is turned ON with lamp switch OFF, the motor is not operating. The performance of other electricals in home is not disturbed.

What may be the reason?

As a school boy electrical enthuiasist I suspect there may increase in ohmic resistance at wire (due to some effects) series to the parallel combination of these two switches. So lamp which has high resistance able to grab some enough voltage despite that unknown series resistance. But motor which has lower resistance cannot.

Can you explain technically?

Edit: The motor was working well for years with same electricals undisturbed. This fault occured today.

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    \$\begingroup\$ I fail to see the connection between your title and the question. That's a very wild hypothesis you've got there, and you having heard of about electricity doesn't mean that the effect you did hear about is a reasonable explanation. (How reasonable does it sound to you that a copper cable becomes a high-value resistor after a couple years?) \$\endgroup\$ Nov 10, 2019 at 14:00
  • \$\begingroup\$ @MarcusMüller Be nice. user42757 is a young enthusiast, he still has a lot to learn. To you or I his hypothesis may sound unlikely, but at least he is making an effort to work it out for himself. The title reflects his interpretation of his observations. \$\endgroup\$ Nov 10, 2019 at 14:20
  • \$\begingroup\$ @MarcusMüller because I thought that the wire series to switch combination may become thinner due to any effects like heating or due to other external effects like insects.Sorry if I am wrong \$\endgroup\$
    – user42757
    Nov 10, 2019 at 14:37
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    \$\begingroup\$ @user42757 I didn't mean to be mean to you! Don't be sorry about being wrong; that happens. The point really is that when looking for a fault, you'll have to start with the likeliest reasons; and you having learned about resistance doesn't make resistance changes more likely :) So, no, it's very likely not because your cable changed resistance, but it's very hard to infer from the rest of your description what could be the reason, and sadly, you're not – yet – experienced enough to narrow this down on your own, and it might be very dangerous to do so, anyway. \$\endgroup\$ Nov 10, 2019 at 15:18
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    \$\begingroup\$ Welcome to EE.SE! "I suspect there may increase in ohmic resistance at wire (due to some effects)" In science, that would be called a hypothesis. In engineering, you rarely have that luxury and often leads to XY problem(s). Please draw a schematic/block diagram of how it's connected. \$\endgroup\$
    – winny
    Nov 11, 2019 at 15:31

1 Answer 1


Difficult to say without seeing the switches and wiring, but I would suspect a bad connection or wiring fault somewhere. You do not say if it has always been like this or if the fault has developed recently. One of the wire terminals on the switches may be lose or corroded, or maybe at the lamp, motor or distribution board.

I would very much doubt that the wires themselves have changed in resistance unless they are damaged and badly corroded.

The solution is to ask competent electrician to examine the setup and remake the connections as necessary. You say you are "school boy electrical enthusiast" so PLEASE DO NOT TRY TO DO THIS YOURSELF if you want to eventually become an adult electrical enthusiast.

  • \$\begingroup\$ Thank you for your concern.I will consult an electrician. \$\endgroup\$
    – user42757
    Nov 10, 2019 at 14:57

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