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Earth leakage clamp meter

Updated: October 2026

A 30 mA RCD that trips at night is often blamed on earth leakage, and the number people quote is 9 mA. An earth leakage clamp meter is the sensitive tool for that current. A 400 A load clamp showing 0.0 A has not measured it. This page follows the 9 mA figure and the jaw position, and it explains why the meters in the [current clamp comparison](/hub/pliers/current-clamp) are the wrong certificate. The Products Compared editorial team used the IET’s May 2021 Wiring Matters article, HSE GS38, and these amazon.co.uk listings. There was no laboratory test. Updated 16 October 2026. A qualifying purchase can earn a commission at no extra cost to you.

A 30 mA RCD that trips at night is often blamed on earth leakage, and the number people quote is 9 mA. An earth leakage clamp meter is the sensitive tool for that current.

Our top picks

Kethvoz Kethvoz KE-7200APP clamp meter

Best overall

Kethvoz Kethvoz KE-7200APP clamp meter
6.8/10about £42.99
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BSIDE BSIDE ACM91 clamp meter

Alternative

BSIDE BSIDE ACM91 clamp meter
5.5/10about £49.99
View offer
BSIDE BSIDE UX1 clamp meter

Alternative

BSIDE BSIDE UX1 clamp meter
5.0/10about £49.99
View offer
On this page
  1. 1.What 9 mA means
  2. 2.Where the jaw goes
  3. 3.Why a normal clamp meter is the wrong tool
  4. 4.When you stop

What 9 mA means

BS 7671 regulation 531.3.2, as the IET explains it, caps accumulated protective-conductor current at 30 per cent of the rated residual operating current. On a 30 mA device that is 9 mA. Protective-conductor current is what flows in the earth conductor in normal use, from filters and damp equipment, rather than a fault that should trip at once. The same IET note says an RCD may still operate above 50 per cent of its rating, so 9 mA is a design ceiling for standing current. It is not a promise that the device will hold above half its rating. Regulation 543.7 treats protective-conductor current above 3.5 mA as high. The IET also points to leakage clamps as the sensitive tool below about 5 mA. Clamping one live core and reading the load tells you nothing about that standing current.

Where the jaw goes

Residual current is what remains when the live currents should have cancelled. On a single-phase circuit, put the jaw around live and neutral together and leave the protective conductor outside. The display is the difference, which is current returning by some other path. You can instead clamp the protective conductor alone. Clamping only the live core measures load, which can look fine while the imbalance is elsewhere. That single-core method is the right one for how many amps a heater is drawing, and it is on the how to use a clamp meter page. Pulling meter tails, or opening a live consumer unit, is live work. Regulation 14 allows that only when it is unreasonable for the conductors to be dead, reasonable to work live, and suitable precautions are in place. A householder with a tripping RCD and no proved-dead board should stop.
Kethvoz Kethvoz KE-7200APP clamp meter

Testsieger

Kethvoz Kethvoz KE-7200APP clamp meter
6.8/10about £42.99
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Why a normal clamp meter is the wrong tool

The KC604 is 400 A AC/DC, the Crenova goes to 600 A, and the Fluke 302+ is 400 A AC. None of those ranges resolves 9 mA, and 0.0 A is the last digit, not a leakage measurement. The Kethvoz states a range from 10 mA, already coarser than 9 mA as a digit you would trust, and a UK reviewer saw about 1 A with no current. Only the BSIDE UX1 and ACM91 advertise about 1 mA, and the stored UK reviews dispute that figure. Megger’s DCM300E, not in this basket, is specified at 0.01 mA. No price for it is recorded here. If you actually needed load current in a DC cable, that is the AC or DC clamp meter page.

When you stop

Stop if the trip comes with heat, a burning smell, or a shock. Stop if the figure is going on a BS 7671 certificate, a condition report, or an insurance form. A standing-current survey at a consumer unit is an electrician’s measurement, with a leakage clamp of known resolution. Buying the UX1 because the title says 1 mA does not make that a weekend job. If the question was whether the circuit is over 9 mA of protective-conductor current, none of the twelve listings is the tool to quote. Resolution sits early in the clamp meter buying guide. Until a meter shows a stable milliamp on a current you already know, a zero on a 400 A range means the range is too coarse.

Common questions

What earth leakage is too much for a 30 mA RCD?
The IET, on BS 7671 regulation 531.3.2, caps accumulated protective-conductor current at 30 per cent of the rated residual current. For a 30 mA device that is 9 mA. The device may still operate above half its rating, so 9 mA is not a guarantee it will hold. Above 3.5 mA, regulation 543.7 treats the current as high. A meter that cannot show those milliamps cannot make the call.
How do you clamp for leakage rather than load?
Put the jaw around live and neutral together and leave the earth conductor outside. The meter reads the difference. You can instead clamp the protective conductor alone. Clamping only the live core reads load, which can look normal while leakage is on another path. The conductors need to be already accessible and insulated. Do not pull meter tails to make the group.
Can I use a 400 A clamp meter for this?
A 400 A or 600 A load clamp does not resolve 9 mA. A display of 0.0 A is the end of its resolution, not a leakage result. The KC604, the Crenova and the Fluke 302+ are load meters here. The Kethvoz starts at a stated 10 mA and, in one UK review, sat about 1 A high with no current. Use a leakage clamp that shows milliamps, and confirm it holds zero.
Is a 1 mA clamp the same as a leakage clamp?
A 1 mA claim is not a leakage clamp by itself. The UX1 and ACM91 make that claim in this set. One UX1 review says it does not measure 1 mA. The ACM91 reviews describe drift after zeroing and a reading that changes if you move the meter. The Megger DCM300E is specified at 0.01 mA and is not in this comparison. No price for that Megger is stated here.
Should a householder measure this at the consumer unit?
Grouping live and neutral at a board means working where conductors may be live. That is live work unless the board is proved dead, and regulation 14 sets the conditions. A tenant should not open a landlord’s board to chase a trip. Heat, a smell, or a shock means stop and call an electrician. One core of an unplugged appliance lead is a load check, not this test.

Related pages

Best clamp meter UK

Current clamp

AC DC clamp meter: Hall jaw or current transformer

Clamp meter buying guide: jaw, CAT rating, True RMS

How to use a clamp meter: one insulated core, then zero

Sources

Public UK sources from the research digest, last checked on 16 October 2026. Shelf prices and star lines are the amazon.co.uk figures in the display file.

  1. HSE: GS38, electrical test equipment for use on low voltage electrical systems (retrieved 16 October 2026)
  2. Electricity at Work Regulations 1989 (retrieved 16 October 2026)
  3. IET Wiring Matters, May 2021: earth leakage (retrieved 16 October 2026)
  4. Martindale: choosing a clamp meter (retrieved 16 October 2026)
  5. Fluke: how to measure current (retrieved 16 October 2026)
  6. Fluke 302+ datasheet (retrieved 16 October 2026)
  7. GOV.UK: Electrical Equipment (Safety) Regulations 2016 (retrieved 16 October 2026)
  8. Elec-Mate: UK clamp meter guide (retrieved 16 October 2026)