Continuity testing, insulation resistance testing, and contact/micro-ohm resistance testing all involve a multimeter-like instrument and a resistance-style reading — which is exactly why they get confused. But they test completely different things, at completely different voltages, for completely different failure modes. Using the wrong one gives you a meaningless answer, or worse, a false pass. This guide is a quick decision map between the three.
The Three Tests at a Glance
| Test | Question it answers | Typical test voltage | Instrument |
|---|---|---|---|
| Continuity | Is this conductor unbroken, or is that switch/fuse/connection actually making contact? | < 9 V (multimeter continuity mode) | Multimeter |
| Insulation resistance (IR) | Is the insulation between this conductor and earth (or another conductor) still good, or is it degrading? | 500 V – 5000 V DC | Megohmmeter (megger) |
| Contact / micro-ohm resistance | Is this joint, contact, or winding carrying current with abnormally high resistance — indicating wear, looseness, or damage? | Low voltage, higher current (1 A+) | Micro-ohm meter (DLRO) |
Continuity — "Is There a Path?"
Continuity testing asks a yes/no question at very low voltage: does current have a complete path through this conductor, fuse, switch, or connection? It's a fast, low-voltage check — most multimeters beep instantly when resistance is low enough to indicate a solid connection. It cannot tell you anything about insulation quality or how much current a joint can safely carry — it only confirms the circuit isn't open.
Insulation Resistance — "Is the Barrier Still Good?"
Insulation resistance testing asks the opposite kind of question: is the material that's supposed to block current flow (between a live conductor and earth, or between two separate conductors) still doing its job? A megger applies a high DC voltage — much higher than a multimeter — because insulation that looks fine at low voltage can still leak dangerously at operating voltage. A good IR reading is a high resistance (megaohms to gigaohms); a low reading means the insulation is compromised.
Contact / Micro-Ohm Resistance — "Is This Joint Healthy?"
Contact and micro-ohm resistance testing sits at the opposite end of the resistance scale from insulation testing — it measures very low resistance (micro-ohms to milliohms) in things that are supposed to conduct extremely well: breaker contacts, busbar joints, winding conductors, bolted cable lugs. A standard multimeter can't resolve values this small (its own test leads have more resistance than the joint being measured); a dedicated micro-ohm meter using a 4-terminal Kelvin connection is required. A rising reading over time — even one that's still "low" — signals a developing problem before it becomes a hot joint or a failed connection.
A quick way to remember the direction
Quick Decision Guide
- Checking if a fuse, switch, or cable is broken? → Continuity test with a multimeter.
- Checking if a motor, cable, or transformer is safe to re-energise, or tracking insulation ageing over time? → Insulation resistance test with a megger. See our full megger guide.
- Checking a circuit breaker contact, busbar joint, or winding resistance for wear or looseness? → Contact/micro-ohm resistance test with a micro-ohm meter. See our micro-ohm meter guide.
CIE manufactures instruments across all three categories — digital multimeters for continuity, insulation testers for IR testing, and the MR-253A for micro-ohm measurement. Contact us if you're not sure which test your situation calls for.