Power Supply Leakage Current Testing to IEC60990

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A buyer lately requested me why we specify leakage present on a Class II power provide, when a Class II power provide has no floor terminal.  A very good query, however first some background.

As a part of the testing for IEC60950, power provide producers measure leakage present to the IEC60990 normal.

To be extra correct, the phrases "Contact Current" and "Protecting Conductor Current" substitute the time period "Leakage Current".

Protecting Conductor Current (PCC)

Is the present that flows by the protecting conductor; generally referred to as the bottom connection.

As a note, the stand up to voltage and insulation resistance checks measure the present flowing by the insulation of the unit beneath take a look at.

 Contact Current (TC)
Is the present that flows when a human physique touches the tools, simulated by a physique impedance network.

The switches are used to simulate a line, impartial or floor fault, referred to as a single fault situation (S.F.C.).  Normally there's a polarity reversal change to reverse the road and impartial connections to the power provide.

So again to the unique buyer query, if a Class II power provide is used, there will probably be present that flows by a human physique upon touching conductive components in a system (like a USB port or a conductive product case).  That measured present is often listed on the power provide datasheet.

Right here is an excerpt from a CB report exhibiting the take a look at, enter voltage, frequency and the measured touch present.  Word half the checks performed had been with the simulated human physique touching the “output connector” or pins of the power provide. 

Enclosure leakage present (regular situations, regular polarity) 264 V~ 63 Hz 5,3 µA
Enclosure leakage present (regular situations, reverse polarity) 264 V~ 63 Hz 4,1 µA
Enclosure leakage present measured on output connector (regular situations, regular polarity) 264 V~ 63 Hz 89,0 µA
Enclosure leakage present measured on output connector (regular situations, reverse polarity) 264 V~ 63 Hz 87,0 µA
Enclosure leakage present (single fault situations, impartial open, regular polarity) 264 V~ 63 Hz 4,1 µA
Enclosure leakage present (single fault situations, impartial open, reverse polarity) 264 V~ 63 Hz 6,0 µA
Enclosure leakage present measured on output connector (single fault situations, impartial open, regular polarity) 264 V~ 63 Hz 3,0 µA
Enclosure leakage present measured on output connector (single fault situations, impartial open, reverse polarity) 264 V~ 63 Hz 129,0 µA

The ammeter used is a specialised meter; don't use an everyday hand-held multi-meter!

For extra particulars, together with the boundaries of the measured currents, please seek the advice of an expert security engineer.

Get the product brochure from TDK-Lambda Americas for product descriptions.