High voltage and errors are not words you want to see in the same sentence. When an error gets reported in a high voltage test, does that mean the cable is useless? Do you know what to do when an error is reported?
High voltage tests check for unintended connections by testing the insulation. If the cable passes, you can be confident the cable is safe and functional. If the cable does not pass, the tester will report one of three errors.
- Had leakage
- Dielectric Failure
Note: If you are using a CH2 tester, high voltage errors will be reported under different names (DW Arc Error, DW Current High Error, IR Has Leakage Error, etc). Although there is a larger variety of errors reported for the CH2, the errors are similar as those listed above. See the easy-wire software manual for more information.
The high voltage test checks for isolation between unintended connections, making sure the current is not escaping through weak points. For example, if the insulation is insufficient or the current is flowing through left over flux residue, the tester will report either an overcurrent error, a leakage error, or a dielectric failure error.
Note: The tester will not report problems with intended connections such as Open errors. A low voltage test is required for this type of information. All Cirris testers will perform a low voltage test before a high voltage test.
Here is what causes the tester to report each high voltage error:
This error occurs because current is leaking through the insulation. The tester expects to measure a certain amount of current. If a larger amount of the current is able to flow through the wire than the tester expects, the tester assumes the current is escaping and reports an overcurrent error.
Often this error is attributed to capacitance. With wires acting as conductors and insulation acting as a barrier, cables can build up high amounts of capacitance. The tester cannot tell the difference between insufficient insulation and unaccounted capacitance. Both causes will result in an overcurrent failure.
If you know the wire is highly capacitive you can set the tester to prepare for the error. See your tester’s user manual for instructions on how to change the high voltage settings for a highly capacitive net.
This error occurs because too much current leaks between unconnected points. It is natural for some current to leak through insulation or through contaminants such as flux residue. A Had Leakage error occurs because more current leaks from the wire than is acceptable.
You can determine an unacceptable leakage value by using Ohm’s Law.
I = V / R
If the cable specs call for 100 MΩ of insulation resistance at 1000 VDC, you can use Ohm’s Law to determine how much current can leak before the cable is unusable.
I = 1000V / 100 MΩ In this case, no more than 10 µA can escape the insulation. If more current than 10 µA leaks from the cable, the tester reports a Had Leakage error.
Damage to wires may lead to dielectric failure.
A Dielectric Failure means voltage has arced from one of the wires. This normally occurs between two exposed pieces of metal, but it is possible for voltage to arc through weak points in the insulation. If a weakness is found in the cable’s insulation and voltage arcs between wires, the test will immediately abort and report a Dielectric Failure.
In some cases, the weak insulation can self-heal. Similarly, dielectric failures caused by small solder slivers can vaporize during the high voltage test. In each of these cases, the consecutive high voltage tests will pass. This is why it is important to perform multiple high voltage tests when a failure occurs.
High voltage testing can help identify problems by detecting potential connections. These errors can alert you to defects in insulation. Once you know about these errors, you can repair them and make sure they do not occur again.
If you’d like to learn more about high voltage testing and errors, Cirris offers training courses that explain this and other topics in depth. Fill out the Training Interest Form to get started.