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Debate: is it possible for a motor to have the correct 415VAC applied and NOT run?

Roland Grodkowski

Hi All,

I've had a debate recently and would like the communities thoughts, as the engineering technician who is responsible for electrical isolations and contractor working safety at my site, I have performed the necessary isolations for the contractor to work on a roof fan.

Despite ensuring safety, I still always request the contractors perform a quick voltage test before touching any wiring, however, the contractor said he doesn't need to because if the motor "running" then that means there's no voltage. We debates this for a while before I let him do his thing.

I could think of a few scenarios where a motor has had voltage there and not ran in my real life experience, yet I'd like to also know everyone's thoughts on this from the technical side.

Thank you.

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    Roland Grodkowski said:
    the contractor said he doesn't need to because if the motor "running" then that means there's no voltage.

    You mean that the other way round?

    I take it the contractor is mechanically skilled and not electrically skilled? Else why would they need you to isolate for them? How do the other technicians test for voltage, with a volt stick? Do you go on the roof and test for dead before you allow the technicians to go up there?

    Sorry for all the questions, I don't work on big sites and wondered how it all works.

    Motor seized up is always a good one.

  • 0 in reply to OlympusMons

    Yh it can happen with a few things like motor seizing, drive set to 0hz, or even being wired incorrectly in multiple ways such as the first reply.  I just wanted to see if anyone else could think of more examples.

    To answer your questions, he was an electrical contractor however the company still requires the isolation to be done for them as they don't know they site and we do, so once they have given us their work order we perform the necessary isolations. All I asked the contractor, was to do his own voltage test before touching anything just as good practice and to be on the safe side.

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  • 0 in reply to OlympusMons

    Yh it can happen with a few things like motor seizing, drive set to 0hz, or even being wired incorrectly in multiple ways such as the first reply.  I just wanted to see if anyone else could think of more examples.

    To answer your questions, he was an electrical contractor however the company still requires the isolation to be done for them as they don't know they site and we do, so once they have given us their work order we perform the necessary isolations. All I asked the contractor, was to do his own voltage test before touching anything just as good practice and to be on the safe side.

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