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High voltage supply current limit to not be hazardous live (IEC 61010-1)

I'm working on a high voltage supply (150V) based on a current mode boost converter, the supply only needs to output <1mA at peak load. I want the output of the supply to conform to IEC61010-1 to not be considered hazardous live as I don't want to need to build in any safeguards.

I believe to achieve this, the capacitance on the supply output needs to be under 300nF (Figure 3, 6.3.1.c.1), and the current must be limited to 2mA (6.3.1.b.1) under normal conditions. Under single fault conditions these limits rise.

The current must be kept under 2mA through a 2k resistor to ground, according to Figure A.2, which I believe comes from IEC 60990.

For the current to only be 2mA through a 2k resistor, the voltage of the supply would be pulled down to 4V. This is well under the 60V limit for DC voltages. Does this mean that the 2mA limit no longer applies here? Or because the inital voltage was over 60V, which would lead to a breakdown and allow current to start flowing, the maximum current allowed is 2mA irrespective of the final voltage?

Secondly, the capacitors on the output of the supply will discharge through the 2k resistor leading to an initial spike of current as they are pulled down to 4V. I can't see any way to avoid this, or any limitations placed on this within the standard. Is it only the steady state voltage/current that matters after the 2k probe is applied?

Thanks!

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  • Then if the 150V never reaches the terminals, then ignore what I said earlier, a simple diode clamp on the wires to the accessible terminals to keep the voltage between any pair and any one and ground below 60V or whatever you decide.

    Inaccessible terminals can have any voltage on them you like.

    I would agree with that, but

    There will be an RS232 serial port on the side.

    RS232 ports often don't meet IP2X, either on the equipment, or at the remote end of the cable.

    Also, what if the connected equipment at the other end assumes the RS232 circuits are supplied by SELV or PELV (or ES1 limits to BS EN 62368-1, although note that these do not fully align with SELV and PELV touch voltage and touch current limits)?

  • In terms of sealing against pollution levels, I will ensure all connectors, cabling, and the enclosure are compliant.

    Does it matter if the connecting device is qualified against BS EN 62368-1 or BS EN 60950? If my device is a measurement device to be used in a laboratory, and the PC it's connected to is within that environment also, is it really a requirement for the measurement device to have outputs qualified to BS EN 62368-1? Achieving ES1 compliance is much more involved and would require an actual (basic/supplementary/reinforced) isolation barrier.

    I noticed the other day that according to BS EN 62368-1, the limitations for capacitance at 150V for a node to be ES1 is 41nF, or 300nF for ES2, compared to just 300nF for compliance against BS EN 61010-1. I suppose they are giving extra margin to laboratory equipment operated by more competent users in a more controlled environment?

  • I noticed the other day that according to BS EN 62368-1, the limitations for capacitance at 150V for a node to be ES1 is 41nF, or 300nF for ES2, compared to just 300nF for compliance against BS EN 61010-1. I suppose they are giving extra margin to laboratory equipment operated by more competent users in a more controlled environment?

    There are probably a lot of other differences, including perhaps alignment regarding SELV/PELV, and perhaps one or two other alignment issues of BS EN IEC 62368 series with BS EN 61140.

    Does it matter if the connecting device is qualified against BS EN 62368-1 or BS EN 60950?

    No, but it might matter if connecting your device defeats ES1 or SELV/PELV provisions in the connecting device, particularly if it might lead to someone getting hurt, or perhaps a fire.

    This makes the situation not easy to risk assess from a manufacturer's perspective. I agree it's not 100 % clear either.

  • I noticed the other day that according to BS EN 62368-1, the limitations for capacitance at 150V for a node to be ES1 is 41nF, or 300nF for ES2, compared to just 300nF for compliance against BS EN 61010-1. I suppose they are giving extra margin to laboratory equipment operated by more competent users in a more controlled environment?

    This is a question of energy delivered to the body`and the likely effect of a 'jump' of different magnitudes in  different situations, such as dry skin point contacts in a place where a flinch is unlikely to lead to any more than minor injury. or a large are contact, or up a ladder where a small finch could lead to a fatal fall.

    in terms of electrocution the body can survive several joules in a very short delivery, when the same energy over the period of a heartbeat coud be fatal. specs for fences and tasers reflect this.

    oh, and then different committees make different assumptions

    mike

Reply
  • I noticed the other day that according to BS EN 62368-1, the limitations for capacitance at 150V for a node to be ES1 is 41nF, or 300nF for ES2, compared to just 300nF for compliance against BS EN 61010-1. I suppose they are giving extra margin to laboratory equipment operated by more competent users in a more controlled environment?

    This is a question of energy delivered to the body`and the likely effect of a 'jump' of different magnitudes in  different situations, such as dry skin point contacts in a place where a flinch is unlikely to lead to any more than minor injury. or a large are contact, or up a ladder where a small finch could lead to a fatal fall.

    in terms of electrocution the body can survive several joules in a very short delivery, when the same energy over the period of a heartbeat coud be fatal. specs for fences and tasers reflect this.

    oh, and then different committees make different assumptions

    mike

Children
  • in terms of electrocution the body can survive several joules in a very short delivery, when the same energy over the period of a heartbeat coud be fatal. specs for fences and tasers reflect this.

    However, this changes dependent on contact area and whether the subject is wet/immersed. There may be no safe level of voltage for an immersed subject.

    It's also worth pointing out that, whilst BS EN IEC 62368-series covers off touch voltage and touch current reasonably well for normal conditions (give or take the fact that the limits are not valid for wet condition areas such as bathrooms), products to the standard may have the following considerations/limitations:

    (a) The resulting products are not always equivalent to SELV/PELV in terms of "leakage"

    (b) In single-fault conditions, voltages (and currents) may exceed SELV/PELV voltages, especially where the nominal voltage is less than the dry condition limits of 120 V DC / 50 V AC.