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R.C.D. Immobilising Electrical Appliances.

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They should be banned. Any electrical appliance that immobilises an installation R.C.D. should not be made. The deficiency should be engineered out of the design of the appliance. Imagine a loved one being electrocuted in the garden because the house R.C.D. was blinded and became inoperable by the vari-speed motor washing machine.

Imagine adding an accessory to your car and then finding that the brakes don't work. It is the same situation.

 

BAN 'EM.

 

Z.

Chairman, Safe Solid Earthing Association, Milton Keynes. Head Office,  over horse meat shop in the Balls Pond Road.

 

 

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  • 0

    Q. What exactly is 6mA when pulsating D.C. is involved? What does it refer to? How is it measured?

    Actually this a a good question, traditional RCDs are based on a transformer, where it is the rate of change of current that sets the voltage seen on the secondary (and primary, but we normally ignore the one turn voltage drop)

    The old sweats used to refer to continuous current or interrupted direct current, and that is very descriptive. Modern parlance is to use “DC” for both ( arguably a backward step, but then other things are in the right direction - try and use jars as the unit for for capacitance or any pre-metric magnetic units for a day…)

    For the RCD what matters is the peak-to-peak amplitude (p-p) of the pulsed DC (or the p-p of hte ripple on the back of a constant value) and its duty-cycle or mark-to-space ratio, but what most  meters will show is the mean.

    In terms of blinding currents the smooth DC part is the offset from a zero-centred waveform - a shift of the baseline if you will by adding a constant to it.

    For testing A RCDs an unsmoothed but rectified waveform is assumed, as if a single diode is in the fault path - this is credible, as many common items based on  SCR/triacs such as lamp dimmers can create this sort of waveform. A fault from the load side of a lamp dimmer to earth is credible, though such things normally blow dead short or dead open after a few cycles of more than the rated current.

    A smoothed DC fault requires deliberate effort to arrange, and neither a supply or load side fault on a VSD will do it.

    Mike.

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  • 0

    Q. What exactly is 6mA when pulsating D.C. is involved? What does it refer to? How is it measured?

    Actually this a a good question, traditional RCDs are based on a transformer, where it is the rate of change of current that sets the voltage seen on the secondary (and primary, but we normally ignore the one turn voltage drop)

    The old sweats used to refer to continuous current or interrupted direct current, and that is very descriptive. Modern parlance is to use “DC” for both ( arguably a backward step, but then other things are in the right direction - try and use jars as the unit for for capacitance or any pre-metric magnetic units for a day…)

    For the RCD what matters is the peak-to-peak amplitude (p-p) of the pulsed DC (or the p-p of hte ripple on the back of a constant value) and its duty-cycle or mark-to-space ratio, but what most  meters will show is the mean.

    In terms of blinding currents the smooth DC part is the offset from a zero-centred waveform - a shift of the baseline if you will by adding a constant to it.

    For testing A RCDs an unsmoothed but rectified waveform is assumed, as if a single diode is in the fault path - this is credible, as many common items based on  SCR/triacs such as lamp dimmers can create this sort of waveform. A fault from the load side of a lamp dimmer to earth is credible, though such things normally blow dead short or dead open after a few cycles of more than the rated current.

    A smoothed DC fault requires deliberate effort to arrange, and neither a supply or load side fault on a VSD will do it.

    Mike.

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