I'm living in France and encountered this 4 pole (3 phase) GFCI in my apartment:

The old GFCI

My understanding is that this thing protects against a difference, between the neutral (return) and the hot (phase), that is greater than 300mA. I hear that 300mA is too high to protect a human so I wanted to swap this out for the French norm which is 30mA. It looks like the brown wire entering into the 3rd top terminal is the phase wire coming into the house and the grey wires are just setting up two more parallel circuits. The blue wire, into the 4th top terminal is the neutral wire.

To minimize work I wanted to just swap everything in place so I bought this thing:

enter image description here

I hooked it up and everything works, but the TEST button does not have any effect! I'm assuming the new breaker is working and it is my understanding of the thing that is broken. Looking closer at the schematics, they are not identical. The old one seems to have the T connected to the N and L1 terminals, while the new one seems to have the T connected to the 3 and 6 terminals:

enter image description here

Could someone please help me understand the differences? Is the new breaker inappropriate for my setup?

  • I am not sure why you would purchase a 3 phase GFCI when only a single phase is being protected. The L terminals are for line voltage , the T terminals are for the load normally. The original unit is looking for an imbalance between all 3 phases and neutral, the new one looks like it may be for phase imbalance or phase to neutral. I am not sure if this will work in single phase mode because the imbalance is being created from 3-5 and you have 1-3-5 jumped together if wired like the original.
    – Ed Beal
    Mar 24, 2020 at 14:13
  • @EdBeal The idea was to change as little as possible. I thought I could just swap things out without understanding too much about the setup. Is it true that only "a single phase is being protected" in the old setup though? I was under the impression that a load imbalance between any of the "hot" lines and the neutral line would trip the switch. Mar 24, 2020 at 14:23
  • I see jumpers (or what I think are jumpers) on the old one and your comment that there was only 1 hot. All 3 phases would have to come in to the device for 3 phase to be protected. As I mentioned I don’t think this model will work with single phase or 1 hot. I believe you would need 2 phases on terminals 3-5 coming in and 4-6 going out.
    – Ed Beal
    Mar 24, 2020 at 14:35
  • @EdBeal It would work - all 3 phase GFCI do also work with only 1 or 2 phases. It is just Kirchhoff's law of summing up the current. No problem if 1 or 2 phases are permanent on zero Ampere. That would also happen in a 3 phase GFCI with all devices on 1 or 2 phases switched off.
    – xeeka
    Mar 24, 2020 at 14:46
  • @xeeka it’s not an issue of parallel paths but where the test gets its power from, if there is no differential to power the device or create an imbalance the test button won’t work and that is the issue the op is asking for help with. the test button doesn’t work. Only a single phase and the others with jumpers I don’t see from the simple print how it could work with a single phase.
    – Ed Beal
    Mar 24, 2020 at 15:11

2 Answers 2


I see what's going on here.

You have a 3-phase RCD, but your supply is only single-phase.

Let's look closer at that picture.

enter image description here

The top is the line side. The orange wire is the real incoming hot. The grey jumpers take the hot wire over to the other 2 phases.

What this brightened picture shows clearly is that the load side of the breaker is wired as 3 phases. The apartment wiring takes 3 conductors, one off each phase, to be distributed to various apartment loads. So the apartment is "3-phase-ready" even if the service is not (yet) 3 phases.

This is a danger area. Each phase could pull 40A before any breakers would trip. I doubt that gray jumper is rated for 80A. I also doubt the orange wire is rated for 120A. Maybe it is downline of other breakers.

Your new RCD won't trip because there's no voltage difference

And therefore no current flow. All phase (LINE and LOAD) conductors, all 6 of them, are at the same voltage potential. As such, there is no current movement through the TEST circuit.

So the upshot is, this device's Test functionality will not work here. If your house is grounded, you can use external GFCI testers.

30ma isn't that great for human protection anyway

It's certainly better than nothing at all, but 30ma can be lethal for humans, and will definitely stun. That is the motivating factor behind 5 ma protection on US devices; stunned people drown or fall, so a stun is the same as a kill. Generally Europe does RCD for parallel arc fault detection.

  • "This is a danger area." Normally it is no danger zone, because even old codes in Europe meant to have - from the provider to the house circuits: main breaker/fuse --> counter --> GFCI(s) --> circuit breakers --> room outlets/apartment/heating/light circuits. In this case, there must be (most likely outside of the pictured panel) a circuit breaker or fuse with 40A per phase for that apartment.
    – xeeka
    Mar 25, 2020 at 9:45
  • "30ma isn't that great for human protection anyway". According IEC time-current GFCI areas, both 5mA and 30mA are in the same AC-2 area, if the shut off time is 300msec or less. In practise, a GFCI 30mA needs less then 80msec to disconnect. Do you have any statistics or sources that shows the real world differences of human protection in regions with 5mA vs. 30mA thresholds? Only few countries seem to have this low 5mA threshold, most countries have 30mA for non-wet rooms.
    – xeeka
    Mar 25, 2020 at 10:29
  • If @xeeka is right about switching the wires between the 5,6 terminals and the N terminals, then I could restore functionality of my test button. That would complete my understanding of this setup. Mar 26, 2020 at 15:11
  • @Harper has described the setup accurately, although I'm not sure (and don't know how to test) if my apartment is receiving 3 phases or a single phase. Thanks for helping me understand the factors at play in this setup! Mar 26, 2020 at 15:15
  • "This is a danger area". There is a 45A breaker at the entry of the house, so the maximum any "jumper" wire would see is 45A. Not sure how much the wire can actually take. Mar 27, 2020 at 15:25

Assuming there is no problem with the GFCI itself: Most likely, the test circuit is connected to the same phase at both ends, i.e. 4=6.

Depending on the size of the apartment and on the heating sytem (water, room), there could be only 2 different phases (or even only 1 phase) arriving at the GFCI - instead of 3.

The old test circuit produced an imbalance between a phase and Neutral, the new test circuit between two phases.

Since the old GFCI's test circuit used to work, most likely there is only 1 or 2 different phases.

Edit: The lower side (2, 4, 6, N) goes to the circuit breakers, the upper terminals are the feed-in.

Since many apartments and houses do have 3 phases - especially with electric water heaters -, the 4-pole GFCIs with 40A, 63A or more are much more common, available and sometimes even less expensive.

In that case here, a 4-pole GFCI could have been used in a system with only 1 or 2 phases, i.e. a 2 or 3 pole GFCI would have been enough.

Also some pictures of the rest of the panel/circuit breakers would help.

It could be tested via measuring the voltages between the lower poles 2-4, 2-6, 4-6 and - for redundancy - all poles against N, i.e. 2-N, 4-N, 6-N.

It is assumed that N is really N and that the yellow-green Earth is only connected to N upstream of the GFCI.

This could be tested by measuring the resistance between N and Earth downstream of the GFCI, if the GFCI is open.

For safety, power must be switched off for that last resistance measurement.

Safety procedures:

  1. Switching off power/main switch.

  2. Securing against accidental switching on (other persons, work in empty apartment continued at another day/by another person, small children etc.)

  3. Testing, if all power is switched off at the working area.

  • Those grey wires are bridges. I think there are just 3 parallel circuits. I'm pretty sure there is just 1 phase here. I have a gas "on-demand" water heater and no serious electrical appliances in a small, very old, apartment. I think I know now that a 2 pole GFCI would have been sufficient, but there would have to be 3 wires attached to the same outgoing terminal. Mar 24, 2020 at 16:34

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