In this document it says "According to IEC 60601-1, the leakage current limits are provided in Table 1."

If the leakage current is due to Y capacitor, the load R and the the parasitic capacitance of the PSU transformer will form an RC divider.

But then the leakage current depends on the load. If the load is big the stray voltage will be big and the leakage current will be small. If the load is small(low impedance setting), then the voltage will be small but the current will be higher comparing to high load impedance.

For which load the leakage current is measured and presented in datasheets?

  • \$\begingroup\$ The 'load' in this case is the patient, with said equipment being connected to patient. To avoid this issue many hospitals now use battery powered equipment. \$\endgroup\$ – user105652 Mar 6 '18 at 21:15

The leakage currents referred to are those that flow from either of the DC output terminals to earth. The load between the two DC output wires is irrelevant.

See my answer here for details about an SMPS's transformer's inter-winding leakage capacitance and how this manifests itself in unwanted output noise AND how the output noise is removed by a Y capacitor BUT this then produces a common-mode AC power voltage (of low energy) on both output terminals.

  • \$\begingroup\$ Lets say we want to measure the leakage current ourselves. If the power supply is powered by AC plug; and lets say it is not loaded. And imagine now I short one of the DC power terminal of this power supply to earth by a wire. Now can we say this current is around the leakage current in the data sheet? When you say "DC output terminals to earth. ", do you mean when DC output is shorted to earth? \$\endgroup\$ – floppy380 Mar 7 '18 at 12:07
  • \$\begingroup\$ Yes you can - this is the leakage (AC) current and won't change with a DC load on the output unless that DC load is complex and has impedances to earth that might shunt away current from your measurement. \$\endgroup\$ – Andy aka Mar 7 '18 at 12:10

Leakage is specified with Line/Neutral short and measure current between that and ground. Factory tests set for 200uA limit for consumer products, less for medical. Some standards accept 250uA per unit and 500uA per system. They also allow 1.4*V for DC tests and additional 10% for reducing test time from 60 s to hold for 1 s with slow DC ramp.

It does not get affected by load Z but E field stress on primary is affected by secondary floating connected to earth ground. If there is breakdown, it will leak in Hipot with catastrophic failure unless current limited in tester. ( my fix)

  • \$\begingroup\$ If I short line and neutral I will trip the fuse what do you mean? \$\endgroup\$ – floppy380 Mar 6 '18 at 19:59
  • \$\begingroup\$ No it is a common mode HIPOT leakage test, no power. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Mar 6 '18 at 20:00
  • \$\begingroup\$ If the power supply is powered by AC plug. And lets say it is not loaded. And imagine now I short one of the DC power terminal to earth by a wire. Now can we say this current is around the leakage current in the data sheet? \$\endgroup\$ – floppy380 Mar 6 '18 at 20:04
  • \$\begingroup\$ The isolation transformer has a capacitance. When the HIPOT charges up line and neutral the voltage drop is across the smallest capacitance or biggest gap. Grounding secondary bypasses the isolation transformer but probably will never happen for medical apps, but I discovered some suppliers fail Hipot when this setup is used. ( process failure) So earth gnd on secondary is not specified. ( user option) \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Mar 6 '18 at 20:06
  • \$\begingroup\$ I tried many powers supplies to get rid of the stray voltages even medical approved ones no luck. Is there in the market a power supply which doesn't cause stray leakage just behave almost like a battery. please see my prev question: electronics.stackexchange.com/questions/360066/… i have random common mode due to such leakage; and people also want me to solve this electrick shock issue due to stray. I tell them harmless but they don't want to experience this \$\endgroup\$ – floppy380 Mar 6 '18 at 20:11

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