Electric Motor Earth faults - question preparing for 4th engineer oral exams

Discussion in 'Electrical Systems' started by jimmymc90, Aug 12, 2011.

  1. jimmymc90
    Joined: Apr 2011
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    Location: glasgow

    jimmymc90 Junior Member

    hi everyone,
    While I know this isnt exactly the correct forum to be posting these sort of questions, I have had some great advice from here in the past and thought I might pick your brains again.

    Im due to sit my 4th engineer orals at the end of the month and could use some help in giving me a decent way to answer these questions infront of the examiner.

    Is one earth fault ok?
    Is two earth faults ok?
    What would happen if you had 2 earth faults on two seperate motors supplied by the same board?

    I know the basic for these questions, I know that while one earth fault on a motor is not Ideal it is alot safer than having two. One earth fault would not be seriously dangerous as the fault current is low due to low voltage.

    two faults however on the same motor would put the magnetic field severely out of balance and cause major damage.

    The last question confused me a bit though, would the same thing happen if if each motor only had one fault?

    Also anyone with a decent yet basic earth lamp diagram would be a great help as the ones I have arent so good

    thanks
    James
     
  2. powerabout
    Joined: Nov 2007
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    powerabout Senior Member

    i think he is taking UK Marine engineer exams...?
     
  3. Boat Design Net Moderator
    Joined: Feb 2010
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    Boat Design Net Moderator Moderator

    This thread has been moved and retitled. A page of hostile remarks between two forum members and inappropriate picture has been removed. The more background and specificity you can provide the better chance you have of getting a reasonable answer.
     
  4. powerabout
    Joined: Nov 2007
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    powerabout Senior Member

    James
    You need to explain what type of earth fault

    line to line or line to earth etc
     
  5. Frosty

    Frosty Previous Member

    Not hostile, cynical, sarcasm,---harmless male bonding.
     
  6. Boat Design Net Moderator
    Joined: Feb 2010
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    Location: www.boatdesign.net

    Boat Design Net Moderator Moderator

    Sorry Frosty, but starting with you going on about the other member not reading the question for two posts and then retaliatory posts such as the one giving the finger and your remark that "I think you have to give oral sex to pass..." seemed to be getting too hostile and not really appropriate for the forum. I saw someone post a reply which appeared to address the question and then delete it as I assume they didn't want to be part of all that which is not good for the forum. A little "bonding" is fine but it surely seemed to be getting unfriendly between you two.
     
  7. Frosty

    Frosty Previous Member

    If some one posted a serous reply to the Question and they were put off, Im sorry for that, I didnt see that. I would like to ask he who did, to repost and I will not reply.

    I did "not" post the photo with a finger, that was piston. It was inappropriate.

    I might be a bit of a joker but hostile I don't think so, or don't mean to be.

    Does this mean I get my points back off my good friend Piston?
     
  8. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    Piston_broke immediately provided the correct answer, it should not have been removed:
    anything called a fault is not OK!
     
  9. Frosty

    Frosty Previous Member

    Thats true CDK he did, but the question was that 1 fault was OK but 2 was not due to magnetism gong astray with damage.

    Its quite clear that the question was not asked as well as it could.

    I think he is asking what if the field was grounding but there was no earth, how you would know if there was 2 faults is not clear. The case would become live but with no less performance from the motor if the casing was not earthed say bolted to concrete etc.

    The question does not make clear if the fault diagnosis is for safety or performance.
     

  10. pistnbroke
    Joined: Jan 2009
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    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    God is he still going on ..I should think the OP has had a breakdown by now ....
     
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