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Test instruments and GS 38 for the examWhich instrument doesn't need GS 38 leads?
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GS 38 is Guidance Sheet 38 from the HSE. It covers the leads and probes you hold, not the tester itself. It's non-statutory guidance, not law. But if someone gets hurt, the first question will be why you weren't following GS 38.
A common mix-up is "BS 61010 and BS 6157". The standards are BS EN 61010 (safety of the instrument) and BS EN 61557 (performance, i.e. how well it does each test). They're easy to mix up. Details are at the start of GN3 section 4.
Which of these does not need GS 38 test leads to be used safely?
- aAn insulation resistance tester
- bA low-resistance ohmmeter
- cA phase rotation tester
- dAn approved voltage indicator
- Insulation resistance: the tester generates 500 V at probe tips millimetres from your fingers.
- Phase rotation: only works on a live supply, with 400 V between phases.
- Approved voltage indicator: you're measuring live supply voltage.
- Low-resistance ohmmeter (continuity): only a few volts (about 5 V). It can't harm you, so the answer is b.
GN3 says to pay particular attention to safety with tests using instruments that can generate more than 50 V (like insulation resistance) or that use the supply voltage. Read "safety aspects" there as GS 38, but don't write it in.
GN3 · safety with tests over 50 V or using supply voltage GN3 · Section 4 · instrument standards
Worth knowing: a low-resistance ohmmeter's open-circuit voltage is between 4 V and 24 V under BS EN 61557-4, so "about 5 V" is typical.
What's the minimum short-circuit test current GN3 gives for a low-resistance ohmmeter?
- a50 mA
- b100 mA
- c150 mA
- d200 mA
Answer d: not less than 200 mA. Questions about the meter itself (ranges, settings, test currents) come from section 4. Section 2 is about how to do the tests. Don't read it as "no more than": it's a minimum.
GN3 · 4.3 low-resistance ohmmeters · ≥ 200 mA · p.135
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