“No Load” / “Appliance Off” Warnings During PAT Testing

Many PAT testers run a quick pre-check before the insulation test. If the appliance appears to be switched off (or the tester can’t “see” a load through the plug), the instrument may show a warning such as No Load, oFF or L–N resistance too high. These messages usually mean the same thing: the test voltage may not be reaching the parts of the appliance you’re trying to test. If the appliance is off, faults downstream of the switch (for example in a heating element or internal wiring) may be missed, and the insulation result can be misleading.

Different manufacturers use different wording. For example, Seaward Primetest instruments may show “Lo Load”, the Kewtech KT71 may show “oFF”, and some Metrel testers display a message such as “L–N resistance too high”. The important point is the same: check the appliance is switched on and set to a mode that energises the internal circuit being tested.

It isn’t always as simple as flicking a switch. Here are common reasons you may see a “no load” warning even when nothing is actually wrong:

• Thermostats / temperature controls: adjust the setting so the appliance actually switches on.
• Multi-function appliances: select a setting that energises the circuit being tested (e.g. each hob element separately).
• Momentary switches: items like drills or some toasters may need the trigger/lever held during the test.
• Electronic / soft-power devices: some equipment can’t be switched on until it is powered, so consider adding a leakage test where appropriate.
• Low-load items: phone chargers and some switch-mode power supplies can trigger warnings because they draw very little current when not charging.
• Blown fuse: a warning can indicate the fuse has failed, a functional check can help confirm this.

Some modern appliances use electronic controls or soft-power circuits that cannot be switched on in the conventional sense until they receive power. Examples include digital microwaves, some LCD/LED appliances, and equipment with standby logic. In these cases, an insulation warning may occur simply because the internal electronics have not yet powered up when the insulation test begins. For such equipment, a leakage current test can provide additional information about insulation integrity where an insulation test alone is inconclusive. See our article on leakage current and leakage testing for further guidance.

Related: see our guide to common PAT testing mistakes for other easy-to-miss issues that can produce misleading “pass” results.