What a portable RCD is for
A portable RCD is a plug-in device that provides residual current protection between an outlet and whatever you connect to it. It exists to solve one problem: you do not control the supply.
If you are a contractor working in somebody else's building, you have no way of knowing what is behind the socket you have just plugged into. It might be a modern board with a Type A RCD on every circuit. It might be a 1970s installation with no RCD anywhere, which nobody has looked at since. Nothing on the wall tells you which.
The portable RCD makes that question irrelevant. You bring your own protection.
That is a genuinely good piece of thinking, and it is why these devices are mandatory in practice on most construction sites and standard issue for any trade working in other people's buildings.
PRCD and PSOA are not the same thing
This distinction used to be sloppy in practice and is now formally settled, which matters if your safety documentation uses the terms loosely.
The Electricity (Safety) Amendment Regulations 2025 cite AS/NZS 3012:2019 including Amendment 1 for construction and demolition sites, with New Zealand modifications. One of those modifications amends clause 1.4.17 to state:
"A PSOA is not considered to be a portable residual current device. All RCDs are to be either Type A in accordance with IEC 61009-1 or IEC 61008-1, or Type F or Type B in accordance with IEC 62423."
A portable socket outlet assembly (PSOA) is, at its simplest, a lead with outlets on the end. It gets power to where you need it. It may or may not contain RCD protection.
A portable RCD (PRCD) is a protective device. Its purpose is protection, not distribution.
The practical consequences:
- Do not assume a PSOA protects anything. Look at the device. If it does not say it contains an RCD and have a test button, it does not.
- Update your documentation if it uses the terms interchangeably. A site safety plan that says "PSOAs provide RCD protection" is now saying something the cited standard contradicts.
- Check the type. All RCDs on site are to be Type A, or Type F or B. See RCD types and what changes in November 2026.
There is also relief for existing gear, and it is not widely known. The same citation inserts: "Nothing in this standard requires the upgrading of an existing RCD in a transportable structure or transportable installation merely because it does not provide protection against pulsating DC current."
When you need one
The general test: would you bet someone's life on the protection behind that outlet? If you cannot answer confidently, use a portable RCD.
Concretely:
- Working in someone else's building where you cannot verify the installation
- Outdoors and in damp conditions — WorkSafe's own stated example of where RCD protection is required regardless of whether equipment is tested and tagged
- Construction and demolition sites, where all supply must be RCD-protected
- Older buildings where the fixed installation predates general RCD protection
- Temporary and event power, markets, marquees, outdoor functions
- Hire equipment going out to users and conditions you cannot supervise
- Wash-down and wet process areas where the fixed protection is unknown or in doubt
A portable RCD is not a substitute for proper fixed protection in your own building. It is the answer where fixed protection is absent, unverifiable, or where the equipment has left the building.
The testing nobody does
Here is the uncomfortable part, and the reason this page exists.
Portable RCDs are, on most sites, the least tested electrical devices present — while also being the ones deployed in the highest-risk conditions and taking the most physical abuse.
Think about the life of one. It lives in the back of a van. It gets dropped, driven over, rained on, left in the sun, coiled tightly, and dragged across concrete. It is then relied upon as the sole protection for a person using a grinder in a wet yard.
And nobody owns it. It is not on the building's register, because it is not the building's. It is not on the equipment register, because it is "just a lead". The person using it assumes someone checked it.
What it actually needs:
Push-button test before each use, and daily on construction sites. Seconds. This is the highest-value habit available on any site, and it is free.
Measured trip-time testing periodically, on the same cycle as the equipment in that environment — three-monthly on construction sites. The button proves the mechanism moves; it measures nothing. See push-button vs trip-time testing.
Inspection and testing as portable equipment, like any other item — cord, plug, casing, and the standard electrical tests. A portable RCD is an appliance as well as a protective device and needs both.
A place on a register, with an item ID, so that "when was this last tested" has an answer.
A portable RCD that has been dropped hard should be tested before it goes back into use, not at the next scheduled round. These are mechanical devices and impact is exactly the thing that damages them invisibly.
Choosing one
Four things to check, in order of how often they are got wrong.
Rated residual current. For protection against electric shock, an RCD should have a rated residual current no greater than 30 mA under the Electricity (Safety) Regulations 2010. Where children may be exposed to direct contact, the figure is 10 mA.
Type. Type A, or Type F or B. Plain Type AC is being designed out, and on a site feeding equipment with electronics in it, a Type AC device may not respond to the fault at all.
Ingress protection appropriate to the environment. A device rated for indoor use, on a wet site, is a fault waiting to happen — and its own failure mode is a leakage path.
Mechanical robustness. These devices live hard lives. The cheap ones fail early, and they fail as protective devices, which is not the place to economise.
Where they end up failing
Four patterns worth knowing, because each one has a simple prevention.
Nobody owns them. They belong to no register and no person. Prevention: put them on the equipment register with an item ID, like any other asset.
They are confused with PSOAs. Someone assumes the lead with four outlets is protecting them. Prevention: label them clearly and differently, and check the device rather than the assumption.
They get used as extension leads. Devices deployed for convenience of reach rather than protection, and left permanently plugged in behind a bench where the button is never pressed. Prevention: if you need reach, use a lead; if you need protection, use a PRCD and put it where the button can be reached.
They fail silently after damage. A dropped device that still passes power. Prevention: test after impact, and teach people that a portable RCD that has taken a knock goes in the box for testing rather than back in the van.
Related: when are RCDs required in New Zealand and test and tag on construction sites.