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

2. 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

3. 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)

4. 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.

5. IEC 60950:
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.

6. IEC :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.

7. 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.

8. 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

10. 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 

11. 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.

12. 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)

13. 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)

14. 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!)

27. 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
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

28. Table 3: Participant Nominated Pass or Fail of Sample
Test A pass/fail
IEC
IEC
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

29. 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?

31. 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

32. 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.