Search results | Page 9

Search results

  1. G

    Understanding Zs values

    Good maths, but why are you telling me about the maximum lengths of cables in regard to voltage drop, when the question is concerning maximum Zs values?
  2. G

    Understanding Zs values

    In BS7671 Table 41.3, page 58 states: The Zs for a 32A type B CB to trip in 0.4s is 1.37 ohms The On-Site-Guide, Table B6, page 125 states: The Zs for a 32A type B CB to trip in 0.4s is 1.1 ohms Is this the table that is wrong?
  3. G

    Understanding Zs values

    Thank you, that is the table I was looking for. So that was the table that came with my OSG. I have two copies of the OSG and I have lost the correction table from both :( They do not make that table easy to find do they. Thank you!
  4. G

    Power Keeps Cutting Out After New Fuse Box Installed

    Hi I am training to become an electrician. I am just putting this out there for some more experienced electricians to maybe comment on. The op said the switch controls a florescent tube, could it be that, it is the inductor in the tube causing the RCD to trip. I am wondering if it has...
  5. G

    Understanding Zs values

    Can anyone help me understand Zs values. In the On-Site-Guide page 60 Table 7.1 under the heading Maximum cable length, it states if Zs < 0.35 ohms for a TN-C-S system you can have a cable length of 107m In BS7671 page 58 Table 41.3 it states the Maximum Zs for a 32A CB to operate within...
  6. G

    Understanding Earth/Shock

    I just do not understand :( I kind of understand, I think, The larger the CSA of a conductor the less the resistance. So are you saying that I have to treat the entire earth as its CSA? If so then it all makes slightly more sense to me.
  7. G

    Understanding Earth/Shock

    Thank you. I do understand that people do get killed by electricity, I just didn't understand why. So is it because we our systems that causes the lethal situation?
  8. G

    Understanding Earth/Shock

    So it is the various different paths back to the transformer that I am not factoring in?
  9. G

    Understanding Earth/Shock

    you say the resistance between your body and earth. But the current still has to get back to the transformer. Why have you not factored in the resistance of the earth to the transformer?
  10. G

    Understanding Earth/Shock

    Is the part I am not getting is that the current flow uses metal underground pipes to get back to the transformer?
  11. G

    Understanding Earth/Shock

    If i am on the 2nd floor or in a loft, how can I get much of a shock? The resistance path is through my body, through the building structure then through the earth to the transformer. That is a massive resistance
  12. G

    Understanding Earth/Shock

    well wikipedia says resistance of the soil is between 10 - 1000 ohms per meter, so lets say 500 ohms, smack in the middle. Say the transformer is 100 meters away. Ohms law current = volts / resistance, so 500 ohms x 100 meters = 50,000 ohms. I = 230 / 50,000 = 0.0046A 0.0046 amps is not much...
  13. G

    Understanding Earth/Shock

    Hi I am studying to become an electrician. There are a few things I do not fully understand regarding shocks and earth and I cannot find the answers to some of my questions. Can anyone help me understand the following points regarding a standard TN system. 1) If you are in a loft or a 2nd...
  14. G

    Help with CPC size

    Can anyone confirm if the value of t should be 0.01 or 0.1
  15. G

    Help with CPC size

    It is ok, i forgot to square root the value of S
  16. G

    Help with CPC size

    Previous posts must be right, I must be using the wrong value for (t) I read this chart as saying I should use the value 0.01 Other posts say I should use 0.1 I don't see why The current is well over 200A, at which point the breaker would trip in 0.01s ???????????????
  17. G

    Help with CPC size

    I agree the final S value does not seam right, because 6mm cable has a 2.5mm CPC. You should be able to use a smaller CSA conductor than what is recommended, or at least the same. I can't see where I went wrong tho :(
  18. G

    Help with CPC size

    Thank you, don't know how that happened, think it happened when I converted from doc to pdf format, thank you
  19. G

    Help with CPC size

    Think I have corrected the errors
  20. G

    Help with CPC size

    Thank you, I think I have corrected the errors, apart from final S value, it comes out the same every time?

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc

YOUR Unread Posts

This website was designed, optimised and is hosted by untold.media Operating under the name Untold Media since 2001.
Back
Top