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Discuss 0.36kw motor with no earth in the Industrial Electrician Talk area at ElectrciansForums.co.uk.

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  1. Jako13!
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    Jako13! New EF Member

    Location:
    London
    today I was doing some maintenance work on a motor and discovered the motor had no earth at the motor terminal. The motor terminal box is plastic but surely it should still have an earth is this correct? And if so should I run a new 4 core a swa!

    The reson why I’m asking is I was told just to reconnect the motor but this just doesn’t seem correct.
    Thanks for your help in advance
     
  2. littlespark
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    littlespark Electrician's Arms

    Location:
    Scottish Borders
    If theres no earth terminal in the box, then it doesn't like its designed to have one.
    If the motor already has an SWA to it, then the armour maybe used as the earth.
    Test the continuity between metal parts of the motor and a known earth. Isolator? Structural metal?
     
  3. darkwood
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    darkwood It's all about Gmes Staff Member Trusted Advisor

    Location:
    West Yorkshire
    The mounting screws for the plastic terminal box are commonly used for an earth point and often have a stamped symbol albeit sometimes hard to see, it is highly unlikely the motor does not require an earth given a stalled motor could see its winding melt and short down to the frame.
    I would either use a earthing nut onto the gland or mount a metal through box adjacent to the motor and either flex into the motor or use a suitable flexible conduit depending on the environment, pointless wasting time and money running an extra cored SWA when quicker/cheaper solutions exist.
    The earth from the SWA should be used although this motor may possibly mounted on a earthed frame/machine which would have meant it wasn't unsafe.

    What is the motor used for and pics are nice if you can post, been a 0.36kw motor it is at the lower end but the only motors I come across that don't require earthing are usually in hand tools.
    What does the plate say and is there the square within a square on it to denote it is double insulated.
     
    • Agree Agree x 1
  4. Jako13!
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    Jako13! New EF Member

    Location:
    London
    Thanks for your reply everyone. I think it’s run in swa but all cores are yellow so abit confused I was just going to run a new 2.5mm 4 core and use one of the cores as the cpc would this be sufficient and is it good practice to bond the SWA at both ends?
     
  5. darkwood
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    darkwood It's all about Gmes Staff Member Trusted Advisor

    Location:
    West Yorkshire
    @Jako13!@Jako13!
    May I ask what experience you have here, are you an apprentice level, are you newly qualified and learning the ropes, the reason I ask is you say you were told to connect a motor up that suggests you work under the instruction of someone, are they not qualified to answer these questions?
    I am happy to help but knowing a little about a members background helps us tailor our help and/or the advise you correctly.
     
    • Winner Winner x 1
  6. Pete999
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    Pete999 Trusted Advisor

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    Been saying the same thing for a while now Mate
     
  7. Jako13!
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    Jako13! New EF Member

    Location:
    London
    @darkwood@darkwood

    I’m newly qualified but my backgrounds domestic installations.

    Thanks for your help mate
     
  8. darkwood
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    darkwood It's all about Gmes Staff Member Trusted Advisor

    Location:
    West Yorkshire
    Thanks Jako13, least we have a background, to be fair if you are dropping onto such jobs as connecting motors I would advise you to do so under professional guidance, motors can be a simple task but can get very complicated very quickly, the AM2 test only prepares you on how to make a 3ph connection and gives little insight into motor theory.

    In answer to you question, if you are running a 4 core and utilising the spare core then it would be fine to earth the armour at the supply end assuming this is not controlled by a VSD, this is the problem when doing such work, often a query will lead to more questions which could all effect the way in which you do the job, unlike domestic where one blueprint often fits the majority of the jobs out there.

    We are happy to help but you may need a little more on site guidance IMHO, the forum won't give step by step guides on doing work but we are happy to advise on queries, regulations etc, you initial query was the motor earthing then you asked about earthing the SWA which then turns the thread into a step by step guide of doing the job, if you are say self employed and have no one to give you the guidance and experience in this field of installation then I suggest you consider doing 5yrs with a company to gain it or stick to your comfort zone, guidance and experience will open a lot more doors for you down the line if you go down the self employment route or in general looking for another job.
     
    • Agree Agree x 1
  9. Marvo
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    Marvo Gender Confused Staff Member

    Location:
    South Africa
    Is the motor a part of a bigger machine? If so it might be earthed by the mounting bolts and through the chassis and main supply CPC, I've come across OEM motors that don't come with an earthing point for this reason.

    Either way running a new SWA sounds like overkill if the armour of the existing cable is capable of being the earth. Even with no designated earth termination in the motor you could still use an earth ring on the SWA gland and a fly lead to an appropriate point on the motor frame from there.
     
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