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volt drop calculation

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  • 30-03-2015 6:08pm
    #1
    086lavey
    Registered Users Posts: 76 ✭✭


    what calculation method are people using , wiring heaters in a chruch with long runs ,
    cable type PVC/PVC ,6sq,3 core,
    ran in plastic trunkig
    3kw load @ each heater .
    longest point is 95 mtr ,

    have tried 2 different calculations , with different results ,


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    #2
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    086lavey wrote: »
    what calculation method are people using , wiring heaters in a chruch with long runs ,
    cable type PVC/PVC ,6sq,3 core,
    ran in plastic trunkig
    3kw load @ each heater .
    longest point is 95 mtr ,

    have tried 2 different calculations , with different results ,

    Were the results slightly different, or one was double the other?


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    #3
    086lavey
    Registered Users Posts: 76 ✭✭086lavey


    Bruthal wrote: »
    Were the results slightly different, or one was double the other?
    They where slightly , not a lot in it , just wanted to see some one else method !!


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    #4
    TheChizler
    Registered Users Posts: 9,455 ✭✭✭TheChizler


    086lavey wrote: »
    They where slightly , not a lot in it , just wanted to see some one else method !!
    How have you tried it?


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    #5
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    086lavey wrote: »
    They where slightly , not a lot in it , just wanted to see some one else method !!

    The cable will have mv/amp/meter volt drop according to the cable size.

    So you multiply the mv X amps X length in meters to get the voltage drop.


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    #6
    Risteard81
    Registered Users Posts: 2,567 ✭✭✭Risteard81


    Bruthal wrote: »
    The cable will have mv/amp/meter volt drop according to the cable size.

    So you multiply the mv X amps X length in meters to get the voltage drop.

    But not forgetting submains etc.


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    #7
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Risteard81 wrote: »
    But not forgetting submains etc.

    The longer the run, the more losses that are read by the meter too, as a matter of interest. Although overall the heater will be operating at lower power, so costing less. But more of the metered usage is losses. More useless info there.


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    #8
    TheChizler
    Registered Users Posts: 9,455 ✭✭✭TheChizler


    Bruthal wrote: »
    The longer the run, the more losses that are read by the meter too, as a matter of interest. Although overall the heater will be operating at lower power, so costing less. But more of the metered usage is losses. More useless info there.
    Handy thing about space heaters and power loss to cable runs is it's overall 100% efficient!


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    #9
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    TheChizler wrote: »
    Handy thing about space heaters and power loss to cable runs is it's overall 100% efficient!

    Not really. You are paying the cost of inefficiency in the unit price of electricity.

    As for the Watt losses in the cable, it is probably heating things other than room space.

    Besides that anyway, my point was that the closer a meter is to the load, the lower it will read.


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    #10
    TheChizler
    Registered Users Posts: 9,455 ✭✭✭TheChizler


    Bruthal wrote: »
    Not really. You are paying the cost of inefficiency in the unit price of electricity
    Well that was kind of my point in a backwards way, that you're not saving money overall.


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    #11
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    TheChizler wrote: »
    Well that was kind of my point in a backwards way, that you're not saving money overall.

    I thought your point was that electric heating is 100% efficient.

    My point was simply a technical one. Nothing to do with saving money. A 3kw heater at the end of a long cable will be cheaper to run than at the db. But it wont be 3kw then. So my point had nothing to do with money saving.


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    #12
    TheChizler
    Registered Users Posts: 9,455 ✭✭✭TheChizler


    Bruthal wrote: »
    I thought your point was that electric heating is 100% efficient.
    Well, apart from the minuscule %age that gets radiated as light and magnetic losses (and most likely subsequently converted to heat) it is.

    The implication is that the energy that doesn't make it all the way to the heater is being radiated from the wires instead, and overall you're not making any cost saving.


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    #13
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    TheChizler wrote: »
    Well, apart from the minuscule %age that gets radiated as light and magnetic losses (and most likely subsequently converted to heat) it is.

    Yes but electricity you use does not originate at your meter. It is produced in generation stations, mostly by burning fuel.

    The unit cost of electricity mentioned earlier is the cost of generation and dustribution.

    From a lump of peat to the electric heater is far from 100% efficient, unless the last fraction of 1% of the process (Electrical conversion to heat) is the only one accounted for. Which is the case with anyone believing electric heating is 100% efficient. However, the unit cost of electricity is for the entire process.
    The implication is that the energy that doesn't make it all the way to the heater is being radiated from the wires instead, and overall you're not making any cost saving

    So you think a 3kw heater on the end of 200 meters of 2.5 will still dissipate 3kw overall including cable losses?

    You still missed my point which was about a meters location on a circuit reading differently in different positions. It was absolutely nothing to do with costs or savings (apart from mentioning it as a matter of interest), but a technical point that they read lower as they get closer to the load.


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    #14
    TheChizler
    Registered Users Posts: 9,455 ✭✭✭TheChizler


    Bruthal wrote: »
    Yes but electricity you use does not originate at your meter. It is produced in generation stations, mostly by burning fuel.
    Well obviously I wasn't including this, I'm talking about the scientific definition of efficiency; which is the ratio of useful energy output to input of a system.
    So you think a 3kw heater on the end of 200 meters of 2.5 will still dissipate 3kw overall including cable losses?
    Well no, it'll be overall 8% less power hungry so I should have probably said 'significantly' somewhere, but the end effect is the heater will probably be kept on longer to compensate for less heat output so there won't necessarily be any savings.

    Anyway, this has gone far off topic!


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    #15
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    TheChizler wrote: »
    Well obviously I wasn't including this, I'm talking about the scientific definition of efficiency; which is the ratio of useful energy output to input of a system.
    When paying for it, we could just say that the 100% effecient electric heating is expensive to run, or we could say that you are paying for 3kwh of heating because it takes 7 or 8kwh of fuel to generate that 3kwh of heat. In my mind, electric heating includes more than the heater. Others just see the heater in the house. Neither is right or wrong possibly.
    Well no, it'll be overall 8% less power hungry so I should have probably said 'significantly' somewhere, but the end effect is the heater will probably be kept on longer to compensate for less heat output so there won't necessarily be any savings.

    True, but we were not talking about trying to make savings.


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    #16
    Calahonda52
    Registered Users Posts: 12,471 ✭✭✭✭Calahonda52


    Just to add that for the EU Energy Efficiency Directive and related stuff such as Carbon Emissions, AFAIK SEAI says 1kWh at the end consumer needs 2.5 kWh at the gen station
    The IEA says 3.
    http://www.iea.org/statistics/resources/questionnaires/faq/#two
    but that includes a portion for nuke

    “I can’t pay my staff or mortgage with instagram likes”.



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