Why is the double limit allowed in clause 16.2?

The statement of standard as below:
The values specified above are doubled if all controls have an off position in all poles. They are also doubled if:
– the appliance has no control other than a thermal cut-out; or
– all thermostats, temperature limiters and energy regulators do not have an off position; or
– the appliance has radio interference filters. In this case, the leakage current with the filter disconnected shall not exceed the limits specified.

1) “All controls have an off position in all poles”
If the user control(s) physically disconnect every live conductor (i.e. a true all-pole switch with adequate contact opening), the appliance can be fully isolated from the supply when switched off. That significantly reduces the chance that a user will encounter dangerous live voltage during normal handling/maintenance, so the committee permits a more relaxed leakage current limit during the leakage test. (The notion that the switch actually isolates the poles is important — contact gap requirements are referenced in guidance.)

2) “Appliance has no control other than a thermal cut-out” — and “thermostats, limiters, regulators do not have an off position”
These describe appliances that are effectively permanently connected (no user accessible disconnect) or that are controlled only by automatic protective devices (thermal cut-outs). For many of these types (stationary heating, embedded heaters, etc.) the expected leakage paths and the way the product is installed/user-interacted with differ from a portable appliance. The standard therefore allows a larger numerical leakage limit under those specific circumstances — but it still expects protection by earth/installation rules and still limits the maximum leakage. In other words: the allowed higher leakage recognises the real design/usage context, not that leakage is desirable.

3) “The appliance has radio interference filters”
EMI (RFI) filters commonly include Y-capacitors (line to chassis/earth) and common-mode paths that inevitably produce additional measurable leakage current to accessible conductive parts or earth. Rather than forbid filters (which would make compliance with EMC difficult), the standard allows higher leakage limits when filters are fitted — but it includes a safety check: with the filter disconnected the leakage must still be within the normal (non-doubled) limits. That requirement ensures the filter (not some fault in the appliance) is causing the extra leakage and that the appliance itself is safe without the filter.

The allowance is conditional, not unconditional. For example, if the EMI filter is the reason for higher leakage, the device without the filter must meet the normal limits (so the filter is the identified cause).
Measure leakage both with and without the EMI filter (or with the filter disconnected at test points) and record both values. If the device only passes when the filter is fitted, document the filter components and show the disconnect test that proves the appliance alone is within normal limits.

If you rely on an all-pole off switch to claim the doubled allowance, make sure the switch truly isolates every live conductor and meets the contact-gap/contact-opening requirements referenced in guidance (the standard and guidance notes discuss 3 mm openings / disconnection in each pole as an example).

Bottom line: The doubling is a practical allowance, not a weakening of safety: it recognises certain unavoidable or installation-dependent leakage sources (permanent connection, EMI filters, full-pole isolation capability) while requiring checks so that the extra leakage is understood, attributable, and bounded. In short: the standard balances practical design realities (EMI filters, permanently connected heaters, multi-pole isolating switches) with safety verification (tests with filters disconnected, proper isolation, national caps).