PRCD-S — portable residual current protection for hand tools on construction sites

The [guide on §704 — temporary installations on construction and demolition sites](/guides/nen-1010/704-bouwplaatsen) covers the fixed, installation-embedded 30 mA residual current protection required on a construction site for socket-outlet and hand-tool circuits up to and including 32 A. This article covers an additional, portable layer of protection that is often applied alongside — or instead of — that fixed circuit protection: the PRCD-S (Portable Residual Current Device - Safety).

What is a PRCD-S?

A PRCD-S is a portable residual current protection device connected as a kind of in-line adaptor or extension lead between a fixed socket outlet and the eventual hand tool. The device is standardised via DIN VDE 0661 and is distinguished, unlike a simple RCD-protected socket strip, by a mandatory pre-energisation self-test: only after the user presses the test button and the device internally verifies that the earth connection, the polarity of the connection and the residual-current function itself are all in order does it actually pass power through to the connected tool. If any of these checks fails (for example a missing earth connection at the socket outlet the PRCD-S is plugged into), the power remains off.

Why this is more than "an extension lead with an RCD"

The crucial difference from an ordinary extension strip with a built-in RCD lies in that pre-energisation self-test:

An ordinary RCD-protected socket strip simply passes power through as soon as it is plugged into a socket outlet, and only intervenes afterwards, in the event of an actual residual current.
A PRCD-S refuses in advance to pass power through if the earth connection of the socket outlet itself is already faulty — a situation that occurs more often on a temporary construction-site installation, with regularly swapped distribution boards and cable connections, than in a fixed installation.

This makes the PRCD-S suitable as a personal, additional layer of protection for the user of the tool itself, on top of — not instead of — the fixed 30 mA circuit protection already imposed on the installation itself by §704.

Variants: 30 mA and 10 mA, type A and type B

PRCD-S devices are available with different tripping currents and types:

30 mA is the usual variant for general hand tools, matching the 30 mA threshold that also applies elsewhere in NEN 1010 for personal protection (see the RCD guide §531).
10 mA variants exist for tools or environments with an elevated risk, where a lower tripping threshold gives an extra margin.
Just as with a fixed RCD (see the RCD type guide), there is a distinction between type A (suitable for alternating current and pulsating DC components) and type B (additionally suitable for pure DC residual currents) — relevant as soon as the connected tool itself contains rectifying electronics, for example a battery-tool charger or a tool with electronic speed control.

Practical relevance

When assembling a construction-site kit, it is important to establish which layers of protection are actually present: the fixed 30 mA circuit protection of §704 at the source, and — where used — a PRCD-S close to the tool itself, with the correct tripping current and the correct type (A or B) for the connected tool. A PRCD-S must, like fixed residual-current equipment, be periodically tested (see the guide on hand-tool inspection for the general test sequence for portable equipment) — the pre-energisation self-test of the device itself does not replace a periodic inspection of the device as a whole.

Common mistakes

Regarding a PRCD-S as a replacement for the fixed 30 mA circuit protection of §704, instead of as an additional, portable layer on top of it.
Ignoring a PRCD-S when the pre-energisation self-test refuses to pass power through, and instead looking for a different socket outlet without investigating the underlying cause (for example a missing earth connection) — the refusal is precisely a warning signal, not a fault to be worked around.
Using a type A PRCD-S with a tool that has a rectifying circuit that can cause a smooth DC residual current, while a type B is needed for that — see the RCD type guide for the background to this distinction.
Not periodically testing the PRCD-S itself, assuming the built-in self-test function makes a full periodic inspection unnecessary.