When testing any electrical circuit, continuity is one of the most basic safety checks. It ensures every conductor, connection, and protective path is intact before any live power ever touches the system. But doing this test correctly isn’t just about connecting a meter and waiting for a beep.
It’s about following BS 7671 and, just as important, making sure your testing equipment and probes are GS38 compliant for safety.
This guide takes you through continuity testing step by step, explaining the standards, safe probe selection, and professional testing methods used on UK domestic and commercial sites.
What Continuity Testing Proves: And Why It Matters?
Continuity testing proves a circuit’s conductors (line, neutral, CPCs, or bonding) form a complete, unbroken path. Without this, protective devices like RCDs and MCBs can’t work as designed during a fault.
The test checks:
- All protective conductors are connected to earth.
- Bonding conductors are linked across metallic systems (gas, water, structure).
- Switches, fuses, and joints have low resistance continuity.
In practical terms, continuity testing is your proof of mechanical and electrical integrity before you energise.
Even one open joint or high-resistance connection can compromise safety or cause nuisance tripping when the circuit is live.
GS38 Explained: Why It’s Not Optional?
GS38 refers to the Health and Safety Executive’s Guidance Note GS38, which covers the minimum safety requirements for test leads and probes used on electrical systems.
In short, GS38 compliance means:
- Probe tips are partially shrouded, with no more than 4mm of exposed metal.
- Leads are fully insulated, double-layered, and marked with voltage ratings (usually 1000V CAT III).
- Fused leads are used where live circuits are being tested to limit fault energy.
Continuity testing is done on isolated (dead) circuits, but GS38 still applies. Accidents happen when isolation isn’t verified correctly or tools degrade over time. Using compliant probes isn’t overkill, it’s the minimum professional standard.
Essential Tools And Preparation
Before you start testing, preparation is key to accuracy and safety. Get your tools and make sure they’re in good working order.
You’ll need:
- A multifunction installation tester (MFT) or low resistance ohmmeter.
- GS38 compliant probes and leads (check shroud length and insulation).
- Lockout/tagout kit for isolating circuits.
- Calibration certificate (your test instrument must be within date).
Then check:
- The supply is safely isolated at the consumer unit or distribution board.
- The circuit is dead, using a proving unit and a voltage tester.
- Conductors are identified and labelled, especially when multiple circuits share containment.
Preparation avoids false readings and rework later, especially in rewires or multi-phase systems.
Step-By-Step: Continuity Testing Of CPCs
The most common continuity check is for the CPC. The aim is to ensure every socket, fitting, or accessory has a continuous earth back to the main earth terminal (MET).
Here’s the professional way:
1. Test Main Protective Bonds First
Before testing individual CPCs, test the main protective bonding conductors to services (water, gas, steelwork). This sets a baseline that the overall earthing system is good.
2. Link Line And CPC At The Board
With the circuit isolated, link the line conductor (L) to the CPC at the circuit’s origin. This creates a loop path for measurement from any accessory point.
3. Measure Resistance At The Farthest Point
Go to the farthest socket or light point and measure between the line and CPC terminals.
A low reading (usually under 1 ohm) means continuity.
If readings are different at different points, recheck joints or connections, a loose terminal or junction box can introduce resistance.
4. Compare and Record
Compare readings to expected values using conductor lengths and cross-sectional areas (from Table 9A of IET On-Site Guide). Record results clearly on your test record.
Continuity Testing Of Ring Final Circuits
Ring circuits require an extra layer of verification to confirm not only that the circuit is complete but also that there are no breaks or crossed conductors.
Here’s how:
- Disconnect both ends of the ring at the consumer unit (L1, N1, CPC1, and L2, N2, CPC2).
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Measure each conductor’s end-to-end resistance separately.
- Line (R₁)
- Neutral (Rₙ)
- CPC (R₂)
- Cross-connect the line and neutral at one end, then test between the line and neutral at multiple sockets. The readings should be within 0.05 Ω, no breaks or crossed pairs.
- Repeat for line and CPC to get R₁ + R₂ values for each socket.
Same readings = ring is complete and balanced. Big differences = loose terminal or wrong spur.
Testing Switches, Fuses, And Fixed Equipment
Continuity testing doesn’t stop at wiring. You’ll also check:
- Switches that contact open and close correctly.
- Fuses and MCBs that their internal paths that are continuous when in the ON position.
- Lighting points continuity between switched live, neutral, and CPC.
For switches, measure continuity with the switch ON; open circuit when OFF. For fixed equipment (like immersion heaters or extract fans), isolate and disconnect one leg to prevent backfeeds during testing.
Common Mistakes And How To Avoid Them
Even experienced electricians make mistakes during continuity testing, often due to workflow pressure or assumptions.
Watch out for:
- Not verifying isolation properly. Always use a proving unit, not the test meter itself.
- Testing through shared neutrals or borrowed feeds. This gives false continuity results.
- Not recording results systematically. Every circuit should have an auditable trail.
- Not doing a visual inspection. Damaged insulation or terminations are often visible before testing.
Professional testing means patience and process. The speed comes naturally once the method is second nature.
Evidence, Documentation, And Traceability
Under BS 7671, Part 6, test results must be documented as evidence of verification. For continuity tests, record:
- The measured resistance (in ohms).
- The test instrument used and calibration details.
- The name or initials of the tester and the date of verification.
Results are then appended to the Electrical Installation Certificate (EIC) or Minor Works Certificate.
Digital test logs from tools like Megger or Fluke Connect can simplify this, especially when auditing is required.
Bottom Line
Continuity testing proves the unseen that every joint, conductor, and CPC beneath plaster or trunking is doing its job.
When done right, it proves not just compliance with BS 7671 but craftsmanship and duty of care.
Whether you’re certifying a domestic ring, inspecting a 3-phase panel, or handing over a commercial fit-out, treat continuity testing as your signature on the system, a guarantee that it’s electrically sound.
