Can I really be confident in the use of a Type A R.C.D. that will tolerate up to only 6mA D.C. current and still operate?
I have a box of old Pifco torch bulbs as used in battery motorists' lanterns. They are filament bulbs rated at 6.2V 0.5 Amp. Their current draw is 500mA. And that for a not very bright torch bulb. That current is supplied via dry cells.
So, the Type A R.C.D.s can only work reliably with a D.C. current of up to 6mA. That is a piddly low current.
Comments please.
Z.
That is quite a nice illustration, thank you for finding it.
The implication is that the figure shows a case where “IRdc > 6mA”
Is sort of true, but actually a considerable understatement. As drawn, the example really shows the case when IRdc >> 6mA, indeed IRdc is still > 2.8* 30mA.
The degree of blinding, i.e. the extra current needed to force a trip, will be comparable to the DC bias, not many times it.
This is quite unfortunate, as I suspect many of the target audience will misunderstand it and over estimate the effect. This is especially likely given the way magnetic theory seems to be taught to electricians (or not - given the erroneous way some text books showing arrows for the directions of magnetic fields and eddy currents, it is sad but not so surprising that the general awareness often equates with the precision of an exercise in pin the tail on the donkey)
The degree you move over to the left or right on a BH curve is ‘H’ and is always proportional to the current. The amount of B you get for your H varies once you get outside the linear bit..
Mike
PS for anyone whose maths is a bit rusty.
>> is vastly greater than, whereas
> is just ‘anything greater than’
That is quite a nice illustration, thank you for finding it.
The implication is that the figure shows a case where “IRdc > 6mA”
Is sort of true, but actually a considerable understatement. As drawn, the example really shows the case when IRdc >> 6mA, indeed IRdc is still > 2.8* 30mA.
The degree of blinding, i.e. the extra current needed to force a trip, will be comparable to the DC bias, not many times it.
This is quite unfortunate, as I suspect many of the target audience will misunderstand it and over estimate the effect. This is especially likely given the way magnetic theory seems to be taught to electricians (or not - given the erroneous way some text books showing arrows for the directions of magnetic fields and eddy currents, it is sad but not so surprising that the general awareness often equates with the precision of an exercise in pin the tail on the donkey)
The degree you move over to the left or right on a BH curve is ‘H’ and is always proportional to the current. The amount of B you get for your H varies once you get outside the linear bit..
Mike
PS for anyone whose maths is a bit rusty.
>> is vastly greater than, whereas
> is just ‘anything greater than’
