Recent content by Surefire

  1. S

    Why don't we use isolated supplies in our homes?

    Thanks for clearing that up Darkwood. I also believe that it's more common to get over voltage issues when the neutral is not earthed especially on three phase systems.
  2. S

    Why don't we use isolated supplies in our homes?

    Thanks for the reply and I agree with your reasoning but I'm a bit confused about your bridge comment. If there is no PD then no current should flow should it?
  3. S

    Why don't we use isolated supplies in our homes?

    I'm sure most people here know that shaver sockets have an isolating transformer inside. This means that should a person come into contact with the live conductor and earth, the risk of electrical shock is greatly reduced because the secondary side has no reference to earth. My question is a...
  4. S

    Voltage drop and current drawn

    Gentlemen I have a question for your perusal. A 3kW 230volt submersible pump is connected to a long extension cable (60 metres). Approximate current drawn is I=3000watts/230volts = 13amps (ignoring PF and efficiency). Cable is rated at 0.03 volts/amp/metre therefore the volt drop is 0.03x13x60...
  5. S

    Indicators in parallel with contactor coils

    Sorry gent's loosing it in my old age
  6. S

    Indicators in parallel with contactor coils

    Am I right in thinking it is bad practice to wire indicators in parallel with contactor coils? If so, why? Thanks
  7. S

    Poof power factor or what!

    I have a small 3 phase motor and decided to do a little power factor calculation. The motor is rated as follows: 0.18KW, delta amps=1.01A, Star amps=0.58A, full load power factor=0.76 and full load efficiency=58%. Now power factor can be calculated as follows: Power (watts) / root3 x volts x...
  8. S

    Indicator lamp connected across contactor coils

    Thanks for all the responses chaps. Just to clarify, the coils are AC. I think the most valid reason not to do this is that the lamp will not give a true indication of the contactors status i.e. if the coil goes open circuit. Where ever possible I try to use a separate auxiliary on the contactor...
  9. S

    Indicator lamp connected across contactor coils

    Someone once told me this is bad practice but I cant remember why. Could anyone remind me? Thanks
  10. S

    Three phase transformers question

    Hi All Could anyone confirm the following: A 3 phase transformer has delta wound primaries and star wound secondries. The turns ratio is 1:1. If 415v is applied to the primary, will the secondary voltage be 240v? I think it will because the secondary output voltage will be: primary line...
  11. S

    Volt drop effect on appliances

    So how about this: If I have a 230w fillament lamp ohms law says it will draw 1 amp at 230volts right? If I now plug in some long extension leads say 3 x 25mtrs I will have added 75 mtrs worth of resistance and dropped some volts. Will that extra resistance make the the lamp draw more current...
  12. S

    Volt drop effect on appliances

    The mcb would trip if only one air con unit was running so it wasn't being overloaded. Normally I would agree: less volts more current. But the less volts is caused by too much resistance in the long cables. More resistance equals less current doesn't it?
  13. S

    Volt drop effect on appliances

    Hi Guys I have a question regarding volt drop. Some time ago a company I worked for installed wall mounted aircon units around their workshop. They wired them into an existing 2.5mm ring main circuit which was in singles in a truncking. During operation some of the units would cause the...
    • Surefire
    • Thread
    • appliances aus cause current effect resistance units volt drop volts
    • Replies: 7
    • Forum: Australia

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