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18th Edition amendment one. Volt drop measurement, who is spreading the rumour we need new testers?

Sparkingchip
Who is the test equipment manufacturer and/ or importer spreading the rumour that we will need new volt drop testers?


Out of interest I have tried an internet search for volt drop testers than can be used to test UK fixed installations and drew a blank with only testers suitable for use in the USA at lower voltages coming up in the search results along with results for auto electrics.


Andy
  • 0
    Bobdenton summed it up in the first paragraph of his post over eleven years ago:


    ”It seems to me that verification of the VD is intended to be done before the load is connected, otherwise all you would need to do to satisfy 525 is measure the voltage across the load. It's either sufficient for the load or it isn't.”


    That is it in a nutshell, measure the voltage across the connected load and it is either sufficient or it isn’t.


    Andy
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    That makes sense, measure the Voltage across the supplied load or connect a temporary load bank of known Wattage to confirm acceptable Volt-drop.......or calculate Voltage drop from the tables in B.S. 7671.


    Z.
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    I too am not sure when you need it, except perhaps if there is already a problem - quite often in an existing circuit, neither load nor cable length is known,and an unknown fraction of the total drop is outside the building anyway.. For socket circuits the kettle or fan heater test seems as good as any, as it mimics real life. I guess with industrial motor inrush and so on, it gets more involved, but is then probably beyond the normal multitester anyway.


    You could do L-N loop PSSC tests at a more than just the origin I suppose. Again I'd think it is a bit OTT in most cases - if the lights dim there there is a problem, probably not otherwise.
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    In a domestic electrical installation I doubt we are going to be worrying about inductive loads, so loading the circuit with pure resistive loads like a kettle seems the way to go for a radial socket circuit that doesn't have permanently connected appliances. For circuits that do have permanently connected appliances turning them on and checking they have sufficient voltage at the load terminals seems the obvious thing to do.

    Anything else is just going off into the realms of fantasy for most simple installations.


    Andy
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    The “Martindale calculation” for want of something better to call it, bases the volt drop on the circuit’s overcurrent device rating, which is specified in the setup for the test. 


    Regards,


    Alan.
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    What are you verifying the volt-drop against?


    The requirement to verify volt drop is "where required" at the moment in 643.11, but more to the point, there is some fluidity in the actual volt-drop requirements, so 525.202 states Appendix 4 Section 6.4 is a "deemed to be OK" range, but 525.1 and 525.203 permit product standards to be used for fixed current-using equipment (might permit a wider utilization voltage range) and 525.201 implies manufacturer's instructions where the product standard doesn't have a utilization voltage.


    Additionally, there is actually no requirement in Section 525 of BS 7671 to guarantee a particular voltage drop for current using equipment that's not fixed (read carefully, 525.202 refers only to 525.1 and 525.201, both of which are for fixed current-using equipment).


  • 0

    Sparkingchip:

    Bobdenton summed it up in the first paragraph of his post over eleven years ago:


    ”It seems to me that verification of the VD is intended to be done before the load is connected, otherwise all you would need to do to satisfy 525 is measure the voltage across the load. It's either sufficient for the load or it isn't.”


    That is it in a nutshell, measure the voltage across the connected load and it is either sufficient or it isn’t.


    Andy 




    Right-oh! When did any of you last encounter voltage drop as a problem please?

  • 0
    One of my customers bought a secondhand commercial pressure washer that is fitted with a 13 amp moulded plug, however when they used it it knocked the fluorescent lights out, the lights then restarted once the washer was running.

    The lights were replaced by the guys who fitted the solar panels on the roof, they installed new LED battens on a new circuit running off the storage batteries they installed alongside the PV inverter, nothing knocks the lights out now.

    The last distribution circuit I added to that installation was 120 metres of 25mm two core SWA, generally I don’t have to worry about volt drop, but that doesn’t mean don’t have to take it into consideration.



    Picking up on what Graham said above, ultimately we don’t really have any control over what portable or moveable appliances someone may decide to connect to a socket circuit and cannot plan for unexpected usage.
  • 0
    There is another aspect to this and that is people thinking they can improve electrical test certificates by adding more boxes to tick and enter test results into.


    For EICRs I am using printed NCR handwritten report forms, at the bottom of the schedule of inspections there is a schedule of tests with boxes to tick including a box to tick for voltage drop verified, that is not on the IET model it is an item added by those who supply these particular pads of reports.


    Maybe I should just get some different forms to use that don’t have this box to tick and any potential issues regarding ticking this box will just disappear.


    Andy
  • 0

    Chris Pearson:




    Sparkingchip:

    Bobdenton summed it up in the first paragraph of his post over eleven years ago:


    ”It seems to me that verification of the VD is intended to be done before the load is connected, otherwise all you would need to do to satisfy 525 is measure the voltage across the load. It's either sufficient for the load or it isn't.”


    That is it in a nutshell, measure the voltage across the connected load and it is either sufficient or it isn’t.


    Andy 




    Right-oh! When did any of you last encounter voltage drop as a problem please?


     




    I rarely encounter a volt drop problem and if I do it is usually because a installation is not being used as intended, such as a farm building being used as an industrial unit with a distribution circuit that was intended for a grain dryer or a few lights and sockets now being used for welders and other fabrication tools and equipment.

    But what happens in reality is that fuses and trips open due to overload before the voltage drop is noticed to be an issue, when you’re on the phone trying to get a DNO fuse replaced on a pole voltage drop is not a real concern.


    I do however have pads of EICR forms with a box to tick to say I have verified the voltage drops within the installation when I tested it.


    In a small domestic installation you aren’t going to concern yourself about voltage drop, in a larger installation if a fixed appliance has sufficient voltage at its terminals when the appliance is under load are you really then going to start taking reference readings at the intake to work out the percentage drop in the circuit? Anyway as the voltage is possibly constantly changing due to loads altering and clouds in the sky affecting the output of the PV array on the roof how accurate can a figure derived from two two test results not taken simultaneously? How repeatable are loop test results?


    The whole process of determining voltage drop by testing is very iffy, if this and if that, unless the tester applies a fixed load or simulates to make a virtually instant determination of what the voltage drop would be.


    A simple little tick box on a certificate or report can really open you up to being quizzed as to what you did before you ticked it.


    Andy 



     

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