2.2 Test Equipment Safety & HSE Guidance Note GS38

2.2 Test Equipment Safety & HSE Guidance Note GS38

HSE Guidance: Health and Safety Executive (HSE) Guidance Note GS38 (Electrical test equipment for use on low voltage electrical systems, 4th edition) provides technical guidance for compliance with Regulations 4(4), 6 and 7 of the Electricity at Work Regulations 1989 (EAWR). Regulation 4(4) concerns equipment provided to protect people working on or near electrical equipment. Regulation 6 addresses adverse or hazardous environments; Regulation 7 concerns insulation, protection and placing of conductors. GS38 defines the constructional and operational safety benchmarks for test probes, leads, and voltage indicators used by electricians and inspectors.

A significant proportion of electrical flashover and burn accidents in low-voltage distribution assemblies occur not through direct contact with energized busbars, but when uninsulated or inappropriately specified test probes inadvertently bridge the gap between adjacent phase conductors or between a phase terminal and an earthed metallic enclosure. Guidance Note GS38 establishes practical design and operational standards to eliminate these catastrophic short circuits and flashovers.

---

GS38 Test Probe and Lead Constructional Specifications

To eliminate flashover, accidental phase-to-phase short circuits, and electric shock, GS38 sets precise mechanical and electrical standards for test leads and probes across all testing tasks:

1. Probe Tip Geometry and Dimensions

• Exposed Metal Tip: Must not exceed 4 mm in length.
• Recommended Shorter Tips: In confined distribution switchgear, compact control panels, and terminal enclosures where terminals are in close proximity, a maximum exposed tip length of 2 mm or retractable spring-loaded screened probes is strongly recommended.
• Retractable Spring-Loaded Sheaths: Modern compliant probes often feature spring-loaded insulating sheaths that cover the metal tip and only retract under positive pressure when inserted into deep terminal cavities. This ensures that the exposed conductive surface remains shielded during general manipulation.

2. Finger Barriers / Guards

• Probes and clips should have finger barriers or be shaped to prevent inadvertent hand contact with the live conductors under test.
• The barrier physically prevents the operative's fingers from slipping forward onto bare metallic tips or energized terminals during test application or awkward reach.

3. Lead Construction and Insulation Integrity

• Test leads must possess adequate mechanical strength, high flexibility, and sufficient insulation rated for the system voltage to resist mechanical abrasion, splitting, and snagging.
• Contrasting Double-Layer Insulation: Many modern high-specification silicone leads incorporate an inner layer of a contrasting colour (such as white, bright yellow, or orange) underneath an outer black or red jacket. Any cut, nick, abrasion, or heat damage immediately reveals the contrasting sub-layer, warning the user to withdraw the lead from service immediately. While this contrasting dual-layer design is an advantageous feature of modern quality leads, it is not a universal GS38 statutory or guidance mandate for all leads. All leads, regardless of construction, must undergo regular visual inspection before each use and be condemned if the insulation is compromised.

4. Fused Test Leads & Instrument-Specific Protection

GS38 distinguishes instrument and lead protection rather than imposing one fuse arrangement on every tester:

• Multimeters: Suitable HBC-fused leads are recommended for voltage work, usually with a fuse rating not exceeding 500 mA. GS38 paragraph 22 also addresses instruments with suitable internal protection and requires a risk assessment to establish whether fused leads are necessary. Follow the instrument's instructions and use the correct fuse type, current and voltage rating; glass fuses are unsuitable.
• Loop and RCD testers: A 10 A fuse is typical, or protection may use a current-limiting resistor and fuse. Use the specified lead set for the test current. Do not assume every RCD test draws amperes or that a 500 mA fuse must rupture instantly; this depends on current and duration.
• Two-pole voltage detectors: Compliant BS EN 61243-3 detectors with protective impedance/internal current limitation do not need additional HBC fuses or limiting resistors fitted externally. This does not make the detector incapable of failure.

---

Choosing Equipment for Proving Dead

GS38 recommends a suitable proprietary test lamp or two-pole voltage detector for establishing presence or absence of voltage, rather than a multimeter. Use equipment suitable for the system voltage and measurement category, and prove it before and after use.

Why Multimeters Are a Poor Choice for This Task

Multimeters are useful measuring instruments, but their selectable functions and input sockets introduce avoidable errors during safe isolation:

1. Wrong function or range: A setting unsuitable for the voltage can give a misleading indication or damage the instrument. A resistance setting is not a voltage test.
2. Wrong input socket: A current input can create a low-impedance path across the supply. Incorrect connections can cause excessive current, arcing, burns and shock. Do not treat a resistance input as identical to the current-shunt input.
3. Instrument or lead failure: A faulty detector, damaged lead or failed indication can conceal danger. No instrument should be trusted without the required proving checks.

Wrong setting or input -> misleading result, damage or dangerous current
Faulty detector/lead   -> possible failure to indicate live conductors
Suitable detector     -> prove, test every required conductor, re-prove

Preserve the Correct Blown-Fuse Distinction

A blown multimeter current fuse does not universally force the voltage function to display zero. Input circuits differ, and voltage and fused current paths may be separate. Follow the individual instrument's instructions; neither an intact fuse nor a plausible display proves that the circuit is dead.

Proving the Voltage Detector

Use a compatible proving unit where possible, or a safely accessible known live source of similar voltage with suitable precautions. Follow the detector's instructions and confirm the expected indication before and immediately after testing the circuit. If it fails either prove, stop, obtain serviceable equipment and repeat the proving-dead procedure. A two-pole detector is not fail-proof.

GS38 permits compliant two-pole designs with internal protective impedance and current limitation without extra external probe fuses. It does not require every detector to have a particular display, audible alarm or vibration feature.

Overvoltage Measurement Categories (BS EN 61010)

Electrical test equipment must withstand not only steady-state operational voltages, but also transient high-energy voltage spikes (surges) caused by atmospheric lightning strikes, utility network switching, and heavy inductive load disconnections. HSE GS38 describes three measurement categories for this work. The category identifies the measurement environment; check the voltage rating separately.

For every test, match both the category and voltage rating to the measurement location and possible voltage. Use CAT IV equipment at the utility origin and suitable CAT III equipment for distribution-level measurements. A CAT III 600 V rating does not become CAT IV merely because another voltage rating has a similar impulse test. GS38 does not impose one universal 600 V minimum at every origin. Check the ratings and instructions of the instrument and every lead, probe and accessory.