Creepage and Clearance for high voltage low energy circuits

D

Deepa S

Hi All,

Can anyone please point me to the section in IEC 60601-1, that exempts high voltage low energy circuits from dielectric and creepage and clearance requirement? The circuit of interest is used to ignite ( trigger) a lamp just once with a 20KV 10uSec pulse with energy ~50uJ. If we consider this momentary high voltage into our isolation scheme, the creepage & clearance requirement would be ridiculous. Any help would be appreciated.

Thanks in advance,
Deepa
 
D

Dimitri2

A cheap advice can be to use decent insulation materials beside air gaps.
 

Peter Selvey

Leader
Super Moderator
This is clearly a case where "alternate solutions", risk management and the voluntary nature of standard are meant to kick in.

Creepage distances in IEC 60601-1 assume long term stress at the same continuous voltage, day in, day out, every minute, every second for years on end. A pulsed circuit, used only in treatment (i.e. a few microseconds, a few times a day) clearly does not require these distances.

Clearances similarly have some assumptions that don't fit the situation.

That said, most designs still have several options available which can gain compliance without any twisting of the standard. Shorting from the HV circuit to the secondary circuit is usually not an issue; the voltage usually collapses (a test might be needed to confirm, especially if large energy pulses are involved).

From the HV circuit to earth is similarly no problem (a test is usually a waste of time, but some labs might insist).

From bare parts of the HV circuit to the test finger over non-earthed, non-secondary parts, it is usually not difficult to have large distances (e.g. 50mm or more). If it is difficult to get the required distance, then you might need to go to IEC 60664-1 to determine the correct distance.

Keep in mind, 20kV is still a large voltage. There are variables such as temperature, pressure, humidity, small production variations which you are unlikely to simulate, so a good margin above the theoretical breakdown point is reasonable. Don't design around just what happens to be OK for your in-house bench test on one or two samples at 23C, 60% RH and 760mmHg. Do the research, know what the breakdown point is, then add a solid margin.
 
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