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

Question

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!

mapj1 · Accepted Answer

I believe to achieve this, the capacitance on the supply output needs to be under 300nF (Figure 3, 6.3.1.c.1), 
 Agree. This allows a short duration higher current at contact, as the body takes time to realize it is being shocked. In effect this is a transient energy limit. Only valid if the caps are not refilled fast enough to violate the current limit condition. 
 
 and the current must be limited to 2mA (6.3.1.b.1) under normal conditions. Under single fault conditions these limits rise . 
 agree This is to do with muscle lock and startle responses. 
 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? 
 No, you are not looking at this bit the right way ;-) 
 potential victims of electrocution may be assumed to have any resistance higher than 2k - that lower value is a large area wet skin contact. 
 Now if for example you had a 150V supply with 73k in series internally, the limits are met, but note that the highest dissipating shock victim is not 2K but 73k also. 
 Clearly for the low resistance victim, the not quite short circuit 2mA limit dominates, and the voltage falls to a few volts, yes, BUT now let us assume the same victim makes a more casual contact, and his or her resistance is a few tens of k, even so we do not want the voltage to rise to a level that will charge those caps to a dangerous level... 
 Think of the 2k test as you would a short circuit test.of the internal current limit, without the zap of screwdriver on capacitor terminals, but a shock victim of any impedance must always be limited to 2mA or less with the caveat that if you can be sure the open circuit voltage is always safely below 60V then that current limit requirement does not apply. 
 It may be this is not the best way to clarify, I already know what it means - feel free to say so if it makes no sense ! 
 
 The usual way to meet this sort of thing for e.g. an insulation tester, is with a proper current limiter circuit in the output to fold back the volts as the 2mA is approached. The most serious single fault is the failure of that current limit. 
 Mike.

Simon Barker · Answer

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. 
 
 You've already mentioned the limitation - limit the output capacitance to no more than 300nF. The smaller the capacitance, the less of a jolt that a person will get if they stick their fingers into the output of the power supply.

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

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