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What is Contact Resistance?

2025-09-02

When two conductors touch, you’d expect electricity to flow freely — but in reality, it doesn’t.
On a microscopic level, metal surfaces are rough, so current only passes through a few tiny spots. This creates contact resistance.

Why it matters:
Too much contact resistance in switches, breakers, or busbar joints can cause:

Overheating
Power losses
Damaged contacts
Equipment failure

What causes it?

Constriction effect – Current squeezed through tiny contact spots
Surface films – Oxides, moisture, or dirt blocking current
Material factors – Some metals (like silver, gold) resist oxidation better than copper

How do we test it?

The standard way is the DC voltage drop method:

Apply high current (100A–600A)
Measure the tiny voltage drop
Use Ohm’s law $R = U / I$ to calculate resistance

In short:
Contact resistance may be small, but it can cause big problems. That’s why regular testing is essential to keep electrical equipment safe and reliable.

Do you monitor contact resistance in your projects?

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What is Contact Resistance?

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High Voltage Test Equipment

High Voltage Resonant Test System

Transformer Testing Equipment

Electrical Power Calibrator

Transformer Oil Testing Equipment

Underground Cable Fault Distance Locator