EVSE DC earth leakage limits with slowly increasing current

Question

Hi, I am testing a product that has been certified to meet TUV IEC 62955. 
 I have tested the DC earth leakage and found that if the earth leakage rate of change is kept over 10uA per second the product will trip correctly (under 6mA). 
 If the rate of change is less than this the product will not trip until currents of 15mA (or greater) are reached. 
 Is this product safe to be installed? 
 
 Thanks, 
 Nick

mapj1 · Accepted Answer

Interesting find - I suspect it passes the standard test, because the test method does not consider a fault may sneak up slowly. (and 10uA/second, suggests ramping up to the 6mA in an 10 minutes or more ) 
 However, it does suggest that a level of DC may be not be detected that has the potential to blind upstream RCD protection, if that upstream RCD is particularly vulnerable. 
 In practice a fault that comes on that slowly and smoothly is very unlikely (real faults tend to come on with all sorts of current steps discontinuities as things break down) and the risks from using the device will be small. 
 But it suggests the DC sensing method has some baseline drift compensation that is struggling, and is in effect the DC fault detection is very slowly AC coupled. I presume this is the result on a sample of one, and it would be interesting to know if that means others from the same design will have faster or slower rates of base-line drift, as if some are much faster then it could result in faults being missed. 
 I think the answer to the exam question is 'probably, but not too sure' 
 Mike.

Nicholas Shattock · Answer

There are other issues that cause it not to trip - I think as long as there is less than 6mA of change within 30 seconds the product will not trip (it doesn't' need to be a gradual ramp). I am worried that this will cause upstream RCD binding and I was hoping that there would be something in the regs that cover this situation. I've not yet carried out a long term test and my fear is that over the course of a couple of hours this current could continue to increase to even higher levels. IEC 62955 does not have any long term or absolute test thresholds (only step changes and ramp from <2A to 6A in <30s

EVSE DC earth leakage limits with slowly increasing current

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