Electrical Question

Discussion in 'Anything DIY Related' started by Warr7207, 19 May 2009.

  1. Warr7207

    Warr7207

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    With the amount of electrical equipment we have on our tanks, will we ever overload a circuit ?

    I know a normal house circuit has 15A of current, but I have noticed on my DB that most of the floor level plugs are all connected to one breaker. Does this mean that all the appliances over and above my tank are on one circuit ?

    Am I correct in assuming that a standard house circuit can supply around 3000 watts of power ?

    Is it easy enough for an electrician to give a plug a separate circuit ?
     
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  3. martinhal

    martinhal

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    Tagging along. I was thinking about this last night
     
  4. trad

    trad Fish, thats the word!

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    I did some work as an electrician for my dads business while i was in varsity but havent done it for a long time. The circuit will not trip unless the amperage reaches 20A combinded. So if your heater comes on every 20min and your power keeps tripping then you've reached a max combided amps. I dont think there is a wattage limit?? If you think about a kitchen on one circuit could run the microwave 1200W kettle 800w and dishwasher 1000W and your fridge would still need to be connected.

    Higher wattage usually means lower amperage so the amount of power running through the line should not change or dim. It would be extremely difficult to overloan a circuit on watts.
     
  5. ben lloyd

    ben lloyd

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    HI Warr
    What i did on my db box (distribution box) was to run separate power supply to my tank with it's own db.(tap in from top of your main breaker)
    What you can also do is change the kv rating of your main breaker from 2.5 to 5 that will help if your breaker trips from time to time. The 5kv takes longer to trip so if you have short overload spikes it will not trip.
     
    Last edited by a moderator: 19 May 2009
  6. lIghty

    lIghty

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    Not at all difficult if he is qualified, and if the conduit has space.

    Incorrect, higher wattage means an increase in current (amps).
     
  7. brettb2020

    brettb2020

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    i agree with lighty. The equation is power = voltage x current. So the power directly proportional to the current.

    So a plug is 220v at 16A max

    So 220v X 16A = 3520w thats the max safe power a plug can handle.

    But say 3 plugs have been wired to the
    Db to a 30A breaker then that means only 10A can be used per plug.

    But yes its not to difficult to add a plug to its own circuit.
    Posted via Mobile Device
     
  8. Warr7207

    Warr7207 Thread Starter

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    Thanks, guys, I get my local sparkie out and seperate my new tank's power.

    Would it be cheaper to buy a DB myself or get a sparkie to supply and install ?
     
  9. lIghty

    lIghty

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    better of letting him do it all. 2 ways in which you could set this up.

    1. Running seperate breaker to your tank plug point and using the existing earth leakage switch.

    or

    2. doing the above but also a seperate earth leakage switch, this way if something in the house trips the electricity, your tank would still have power, as it has it own trip switch.
     
  10. RiaanP

    RiaanP Moderator

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    Builders warehouse got this plastic DB box, complete with earth leakage and a few trip switches. with see thru cover. Complete about R750
    I will do that on my future tank. I think Pete got this already on his setup. Just run a proper wire from your house DB to the tank DB
     
  11. martinhal

    martinhal

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    Ok let me get this right.
    The max feed from a breaker is volt X watts so in your example 3520w can be run off that circuit ?

    I would suppose if one added up all the wattage of items on a circuit and devided that by 220 one could determine the min rating of the breaker needed.
     
  12. Reef Maniac

    Reef Maniac MASA Contributor

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    Good topic :)

    It's not quite that simple... The circuit breaker is rated at the maximum amperage which the wires in the circuit can handle safely. Normal house plug wiring is done with 2.5mm² copper wire, and depending on the length of the conductors (wire), the type of conduit it is running in, and the maximum environmental temperature, this size wire can usually handle 15 Amperes. The next size wire is a 4mm² and this can safely handle 20 Amperes (or perhaps a bit more, it's been a while since I've read the SANS code...).

    You should thus not just "upgrade" a circuit breaker unless the house wiring is of sufficient capacity, else you stand the real risk of causing a fire.

    Again, it would firstly depend on the size of the wiring, but if the wires were of sufficient capacity one could either run 10A per plug simultaniously on all three plugs, or 15A from two plugs, if the third plug was not being used.

    I think you guys are not looking at the same thing here (you are both right...). A SINGLE 15A circuit in a house can supply about 3kW (230V x 15A = 3450W), the TOTAL power available to a "normal" house with a single phase 60A mains supply would be around 14kW (230V x 60A = 13800W).

    Hennie
     
  13. lIghty

    lIghty

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    Maybe I misunderstood, thought he was talking about the "total" house rating, thanks for the clearity!
     
  14. Alan

    Alan Admin MASA Contributor

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    Mmmm, okay first off Hennie is right in that the CB rating is to protect the cable so it wont over heat and cause a fire. 2.5mm cable is rated at 27odd amps. Plug circuits are normally rated at 20amps wired in 2.5mm cable. If you draw more than 20amps on the entire circuit fed by that CB it will trip, so yes it is possible to overload the circuit with your system depending on how big it is.
    Guys one word of advice if you want electrics done like putting in a separate feed or separate DB for your tank please get a Sparkie to do it and get a Certificate of Compliance when completed. If something goes wrong and you have a fire or electrocution you are going to need that certificate.
     
  15. Warr7207

    Warr7207 Thread Starter

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    Now that is a great idea :)
     
  16. lIghty

    lIghty

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    but like Alan says, get a qualified sparky to do it!
     
  17. Warr7207

    Warr7207 Thread Starter

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    I saw an interesting thing yesterday. A mate had connected his generator's AC output directly to one of his house's plug and this entire circuit/plugs were all able to work.

    He switched off the main electrical feed to the house, so as not to cause damage when the electricity came back on.

    What problems are there with this "Jippo" ?
     
  18. RiaanP

    RiaanP Moderator

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    Yes does work, My dads place are like that, but it got a protector added to prevent damage when the power does come on. Done by Sparky, so it is legal. Can run lights and TV DSTV kettle and a few other things.
     
  19. lIghty

    lIghty

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    Beside being ilegal and extremely dangerous!
     
  20. Alan

    Alan Admin MASA Contributor

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    The cable that connects the gennie to an installation like this is known as a suicide cable, with good reason. There are a couple of big problems here, you dont have any protection on the circuit when connected like that and if you forget to turn off the main switch when the power resumes it will turn the gennie into a fair size bomb.
     
  21. Reef Maniac

    Reef Maniac MASA Contributor

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    Alan, I don't have the SANS code with me, but don't the "environment temperature" requirement cause a de-rating of about 50% for wires running above the ceiling (as I'm presuming most wires do...). When I re-wired my house some time ago this requirement resulted in me having to use 4mm conducters for the plug circuits, as the combination of length, running in a conduit AND being above the ceiling resulted in the 2.5mm wires being just below the 15A capacity.

    Hennie
     
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