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Frequently Asked Questions

Connector Kits - General
5. Q: If a megger reading on one of our circuits goes down, does this mean that water is leaking into our circuit?
A: If all sections of your circuit are still working, probably not. Consider:
When a circuit is meggered, one is checking the electrical resistance between the conductor and ground.
If there was an actual path for water to ground, then the megger reading would be zero.
So lower megger readings actually mean that the electrical leakage to ground has increased. This electrical leakage may be through the rubber insulation of the cable, connectors, or transformers (no insulation is perfect), or along the interfaces between rubber surfaces. One example of the latter would be if a plug and receptacle were not fully mated, so the seal is shorter than usual. Another example would be if a connector housing is bent to the point where the seal at the cable entrance is shortened. In both cases the shorter the seal length, the higher the electrical leakage. Or perhaps the insulation materials are aging and no longer have the dielectric strength of new materials. Or the cable has been mechanically damaged and the insulation thickness is less than specified. Or…?
Another common reason is that water surrounds the circuit components such as after a rain. This is not because water leaks into the circuit, but rather that there is now a much better ground connection, so electrical leakage increases. Keep in mind that dry earth and air are very good insulators.
We have sometimes amused ourselves (don’t ask) by putting connectors on a piece of cable under water so that the connectors are full of water. When these connectors are joined (again under water), and are hipot checked at 15 kV, they have a high resistance, although generally a little less than the FAA requirement. If left overnight they easily pass the FAA requirement. This confirms that the FAA interfaces do not allow water to pass through them, and also that water inside a connector is not fatal (although to be avoided from the perspective of corrosion, etc.).