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Type A R.C.D. 6mA tolerant.

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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.

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    davezawadi (David Stone): 
    Now we get to the slightly more tricky point, say the appliance has electronics incorporated that uses a rectified supply, does this present a danger. It seems that manufacturers are suggesting (via their instructions) that it does, and want “fancy” types of RCD protection. Now the question, what is the actual risk from a DC fault, remembering the additional protection clause? The appliance has a normal CPC and Earthing, so how does this fault occur in a dangerous way? The RCD protection of final circuits in BS7671 never says that these are a primary protection method against Earth faults (except for TT) so why do we need additional protection that works for DC (or some version of not pure AC)?

    This is more or less what I was asking. I don't see how direct contact could arise in a boiler - it's not like the frayed flex on Mrs P's steam iron. So it could only be indirect contact. Even if somebody put a 13 A fuse in the line, a 10 ohms fault will blow it reasonably promptly. In that case, I envisage some electronics which amount to say a 9 ohms resistance and allow 1 ohm for the fixed wiring, but wouldn't that give a touch voltage of only 23 V?

    Physics always did make my head ache, but I am struggling to see the danger.

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    davezawadi (David Stone): 
    Now we get to the slightly more tricky point, say the appliance has electronics incorporated that uses a rectified supply, does this present a danger. It seems that manufacturers are suggesting (via their instructions) that it does, and want “fancy” types of RCD protection. Now the question, what is the actual risk from a DC fault, remembering the additional protection clause? The appliance has a normal CPC and Earthing, so how does this fault occur in a dangerous way? The RCD protection of final circuits in BS7671 never says that these are a primary protection method against Earth faults (except for TT) so why do we need additional protection that works for DC (or some version of not pure AC)?

    This is more or less what I was asking. I don't see how direct contact could arise in a boiler - it's not like the frayed flex on Mrs P's steam iron. So it could only be indirect contact. Even if somebody put a 13 A fuse in the line, a 10 ohms fault will blow it reasonably promptly. In that case, I envisage some electronics which amount to say a 9 ohms resistance and allow 1 ohm for the fixed wiring, but wouldn't that give a touch voltage of only 23 V?

    Physics always did make my head ache, but I am struggling to see the danger.

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