High Voltage Testing of Cables with Components


To "hipot test" a cable assembly means to apply a HIgh POTential between each wire and all other wires (and shields) to assure that they are properly insulated, (or isolated) from each other.

discharge1-322.jpgFor cables that contain only wires (and/or un-terminated points), this is a fairly simple task. But, if your cables have embedded components (resistors, diodes, capacitors, coils, IC's etc.) you run the risk of damaging these components by high voltage testing.

There are two elements of a high voltage test (For the purposes of this document "hipot" refers to both);
A DWV (dielectric withstand voltage) test commonly done with AC voltage.
A IR (insulation resistance) test always done with DC voltage.


Why you can safely test assemblies with components on Cirris Hipot testers without damaging the components:components-350.jpg

  • Cirris testers do a low-voltage continuity scan first, before doing the high voltage test.
  • Cirris testers can selectively apply voltage on multiple test points at a time.

Since we know the exact wiring pattern of the cable BEFORE WE DO THE HIPOT TEST (we just tested for continuity) we can now intelligently apply high voltage so that we;

  • Test each NET against every other NET that should be isolated from each other.
  • Combine NETS that are "linked together" with components so that we don't allow a voltage drop across, or current through, the components.

What is a 'NET'?net-graphic2.jpg

A 'NET'is:

  • Two points connected by a wire.
  • A group of points connected by wires.
  • A non connected (NC) point or points.


NC points, while not included in the NET List, are treated as separate nets for the hipot test since they must be checked for isolation from all other points/nets.


Sample Wire List

Let's look at a simple cable assembly as an example. The wirelist for this type of cable would look like this:7net-wirelist.jpg

NET
1 J1-001 J1-004 J2-001
2 J1-002 J1-003
3 J1-005 J2-002
4 J1-006 J2-003 J2-005

COMPONENTS
1 Capacitor J1-005 J1-006
2 Resistor J1-007 J2-007

REMEMBER: The NC points (J2-004 and J2-006), while not included in the NET List, are treated as separate nets for the hipot test since they must be checked for isolation from all other points/nets.


How a Cirris Tester would HIPOT this Cablegrp-nets

Complete continuity scan of all connections, including components.

NOTE: If the continuity test FAILS, the test is finished, as there is no need to hipot a BAD CABLE.


Step by Step High Voltage Test Sequence:

  1. Net 1 (GREEN - J1-001 J1-004 J2-001) is charged to high voltage while all other nets are tied together and held at 0 Volts.
  2. Net 2 (BLUE - J1-002 J1-003) is charged while all others are held at 0 Volts.
  3. Net 3 (PURPLE - (J1-005 J2-002) and Net 4 (J1-006 J2-003 J2-005) are tied together with a component, so ALL POINTS of BOTH NETS are charged to high voltage simultaneously while all other nets are held at 0 Volts. NOTE: Although the component is at a high potential, with respect to the other nets, both sides of the component are at the same voltage so there is NO VOLTAGE DROP across, OR CURRENT FLOW through the component.
  4. Net 5 (LIGHT BLUE - J1-007 J2-007) is a component, so again, both points are charged simultaneously. As before there is NO VOLTAGE DROP or CURRENT FLOW across the component, therefore there is no chance of damaging it.
  5. Net 6 (BLACK - J2-004) is a Single Point, but is charged to high voltage while other nets are tied together and held at 0 Volts.
  6. Net 7 (BLACK - J2-006) is also a Single Point, but (like the others) is charged to high voltage while other nets are tied together and held at 0 Volts.

 

Many hipot cable testers, because of their test point architecture, can only apply voltage to ONE POINT AT A TIME as follows:

  1. One point (the first point of a net) and all points lowersingle-point-test.jpg
  2. One point and all other points (only works for single point nets)
  3. One point (the last point of a net) and all points higher

Also, point-order is always defined as raw system point number, so there may be no correlation to the order of points in the way the tester is wired to the fixture.

Since they can't apply voltage to multiple points at a time you can see that, with this type of test, the capacitor linking nets 3 and 4 would be damaged when high voltage was applied to only point J1-005 (the head point of net 3) or point J2-002 (the end point). Also the resistor in net 5 could be damaged, depending on the amount of capacitive coupling between it and the other wires in the cable, when high voltage is applied to only one side of the net.



High Voltage Testing Precautions:

verity-test2.jpg

 

Although Cirris hipot testers can SELF-LEARN the components in your cable, you must VERIFY that the test program is correct BEFORE performing hipot tests in order to assure that no damage occurs to components in your cables. Here is the process we recommend:

LEARN:
Cirris hipot testers can self-learn an assembly, including most, but not necessarily ALL, components. It is your responsibility to make sure that all components are correctly listed in the test program.

VERIFY and EDIT if necessary:
Again, be sure to verify that the test program is correct, and includes all components. If the self-learn feature of the tester missed a component, or if you have a component that isn't identified correctly, you must MANUALLY add it to the test program to assure that it won't be damaged during the hipot test. If you have non-standard components you can add a LINK command in the test program to protect them from voltage.
(see LINK description below)

TEST:
Once you've verified that your test program properly lists all connections, and components, you can safely hipot test it without the risk of damaging any components.

 


The LINK Commandcomponents-learn2.jpg

When "component learning" is set up properly, Cirris testers automatically LEARN most common components (resistors, diodes and capacitors) and automatically link them together during the hipot test, as described above. You can also add a LINK command to link together any points or groups of points that you DON'T WANT TO HAVE HIGH VOLTAGE APPLIED BETWEEN.

To do this you simply add a LINK command in the COMPONENTS section of the test program (you only need to LINK one point in each net for this to work properly).

EXAMPLE: You don't want high voltage applied betwen nets 3, 4 and 5 of the following test program.

NET
1 J1-001 J2-001
2 J1-002 J2-002
3 J1-003 J1-004 J2-004
4 J1-005 J2-005
5 J1-007 J1-008 J1-009 J1-010 J2-007 J2-008 J2-009 J2-010
6 J1-011 J2-011
7 J1-012 J2-012

Edit the program, adding LINK commands in the COMPONENTS section like this:

NET
1 J1-001 J2-001
2 J1-002 J2-002
3 J1-003 J1-004 J2-004
4 J1-005 J2-005
5 J1-007 J1-008 J1-009 J1-010 J2-007 J2-008 J2-009 J2-010
6 J1-011 J2-011
7 J1-012 J2-012

COMPONENTS
1 LINK J1-003 J1-005
2 LINK J1-005 J1-007


Note that we LINKED the first point in Net 3 with the first point in Net 4, and the first point in Net 4 with the first point in Net 5.

EXAMPLE:

You don't want high voltage applied between nets 3, 4 and 5 of the following test program:

We could also have done it this way:

COMPONENTS
1 LINK J1-003 J1-005
2 LINK J1-003 J1-007

Linking the first point in Net 3 with the first point in Net 4, and the first point in Net 3 with the first point in Net 5. The effect is the same.