Session 2 “Plug Discharge” Test CTL WORKSHOP 2008 Session 2 “Plug Discharge” Test

Definition of “Plug Discharge” Slight misnomer – but “best fit” for the same test in several standards Voltage decay over time? Standards targeted: IEC 61010 IEC 60065 IEC 60335 IEC 60950

IEC 61010: 6.1.2 If any of the parts receive a charge from an internal capacitor, they shall not be hazardous live 10s after interruption of the supply. 6.3.1a The voltage levels are 33V rms 46.7V peak or 70V dc (in normal conditions)

IEC 60065: 9.1.6 Apparatus intended to be connected to the mains by a mains plug shall be so designed that there is no risk of an electric shock from stored charge on the capacitors when touching the pins or contacts on the plug after its withdrawal from the socket outlet… 2 seconds after the withdrawal of the mains plug, the pins or contacts of the plug shall not be hazardous live 9.1.1 A part is not hazardous live if the open circuit voltage does not exceed 35V (peak) ac or 60V dc The test MAY repeated up to 10 times to determine the most unfavorable situation.

IEC 60950: 1 2.1.1.7 Equipment shall be so designed that, at an external point of disconnection of an ac mains supply…the risk of electric shock from stored charge on capacitors connected in the equipment is reduced. (The circuit has a means of discharge) resulting in a time constant not exceeding 1s for pluggable type equipment… Note: during an interval for one time constant, the voltage will have decayed to 37% of its original value. The relative time constant is the product of the effective capacitance…. And the effective discharge resistance…. If it is difficult to determine (these) values, a measurement of voltage decay at the point of external disconnection can be used.

IEC 60335-1 :22.5 Appliances intended to be connected to supply mains by means of a plug shall be constructed so that in normal use there is no risk of electric shock from charged capacitors when the pins of the plug are touched. … One second after disconnection, the voltage between the pins of the plug is measured with an instrument that does not appreciably affect the value to be measured. The voltage shall not exceed 34V. The test is performed 10 times.

So… The overall purpose of the cited clauses in the standard are to ensure that residual energy in the item under test is not such that it may cause an electric shock when the item is unplugged. A common method for this determination is to measure the voltage over time after disconnection to prove/disprove compliance. Some standards allow a calculation in lieu of measurement if the required information is available or determinable. Laboratories should have capability to make the measurements.

Whole Group Activity: Use the summarised information provided (plus experience…) to populate the table. standard voltage limit time elapsed to measure special instructions/notes 61010   60065 60950 60335

time elapsed to measure special instructions/notes standard voltage limit time elapsed to measure special instructions/notes 61010 70 V 5s    60065  60V  2s The test may be repeated 10x. Test by measurement or calculation  60950 37%, 120V if we start with 230V  1s  Voltage decay measurement can be done instead of calculation  60335 34 V  1s 10x 

Discussion questions for group What voltage comprises “hazardous live” Under what circumstances would “discharge” after disconnection of the circuit not be dc volts? Each standard has a different idea of “hazardous live” There may be situations, particularly when there are additional internal components that could generate it, that ac voltage could be discharged after disconnection. However, the CTL assembled workshop group could not identify any specific situation where this occurs.

05e27.. Focus on measurement of voltage decay Accuracy of measurement Generic instructions to cover 4 standards (apply 230V ac, measure the voltage at 1, 2, 5 and 10 seconds) Option to measure 10 times or use automated equipment Opportunity to indicate whether each of the test conditions on the sample “passed” or “failed” according to the standards in question. (Do not answer if your lab is not in scope for the test)

Assessment of Participants: Statistical comparison of actual voltage readings at each time interval Determination whether participants correctly graded the sample according to the results they submitted (irrespective of the statistical value of their result) Participants divided into groups to ensure the capability wrt scope is determined fairly. (If lab equipment is geared to test at a particular time/condition, the results should be fairly compared with other labs testing to the same standard)

The samples Each sample contained 2 test conditions (A and B) Each test condition was a separate circuit including resistors and capacitors Because of likely homogeneity issues, program design meant that each sample was tested by 6 or 7 labs (one after the other) Participants were therefore compared only with a small group (And the program takes a long time to complete!)

Assigned Code Number TestA overall Vmax TestB overall Vmax probe impedance date tested 05e27 1 second 2 seconds 5 seconds 10 seconds Mohm   A-6-2 21.5 9.3 10.5 9.2 3.9 0.9 10 1/06/2007 A-6-3 116 37.5 219 147 46.9 3.1 1 2007.09.27 A-6-6 120 44 235 176 72 16 99 5/07/2007 A-6-4 122 48 6 224 160 56 12 100 29/11/2007 A-6-1 216 144 50 10th march ,2008 A-6-5 90 30 170 20 18/01/2008

Table 3: Participant Nominated Pass or Fail of Sample   Test A pass/fail IEC 60335-1 IEC 60950-1 IEC 61010 IEC 60065 code pass fail A-6-2 1 A-6-3 A-6-6 A-6-4 A-6-1 A-6-5 Test B pass/fail

Group activity Study the raw data provided and determine which laboratories are not in agreement with the other participants Provide possible reasons this has occurred Check the participants’ decisions about passing/failing of samples. Do you agree?

Outcomes from group activities Issues were identified with the results from participants whose results fell out of the statistical range. Participants were using input impedance that may not have been suitable for the testing (100M Ohm probe is recommended) Some results did not make sense (eg high result from a user of a low value probe) One participant’s results indicated an incorrect evaluation whether the sample passed/failed the standard

Required elements of this test Flow chart the test procedure and identify the inputs that could contribute to incorrect results All aspects of the test are important. Participants are reminded not to only focus on the measurement, but all stages of the test.