AC/AC adapter 77DA-10-09-MI & broken neutral wire

Hi guys, my 77DA-10-09-MI power adaptor is used with my EmonTX to compare voltage for the system. My house power system is a 3 phase (4 wires plus ground) 127V/220V (Brazil). Everything was fine for more than two years until yesterday after a problem realized in the power system. I measured the voltage of my house power system and saw that neutral wire was showing 127V to ground wires. After investigation I discovered that the AC/AC adapter was the responsible for injecting 127V into neutral. Has everyone here had such an issue before? It seems it short circuited the primary, right?

Thanks for the support as always!

I think that is not possible - a fuse would have blown or a circuit breaker would have tripped had this been the case.

I think you have a much more serious problem. I think your neutral connection has broken somewhere between your electricity supplier’s neutral and the place where you have connected the a.c. adapter. This represents a dangerous condition. If you are confident working on mains electrical wiring, check all the sockets and wiring back to your distribution panel, and check the integrity of the neutral connection there also. If you are not totally confident that you can do this safely, you should call a competent electrician to do the work.

Hi @Robert.Wall thanks for the quick reply. I was the adapter indeed. As soon as I disconnected it the neutral came back to zero again. Then I tested the adapter that was connected to the neutral and it was showing 127V to the ground (!!!). I took out of the system and everything is fine again.



From what you have written, and if I understand you correctly, the wiring in your house is dangerous.

Of course you will read zero volts between ground and an isolated piece of wire. Plug in a lamp where you had connected the a.c. adapter, and you will again read 127 V between neutral and ground. Plug the same lamp in somewhere else, on a different circuit, and it will work - this will show the lamp is not a short circuit.

Please read carefully what I wrote above and consider the consequences. If you have a broken neutral, you will plug in an appliance and if you are lucky, it won’t work. If you are unlucky, you will have a high resistance joint in the neutral wire which will get hot and start a fire, and your house will burn down.

Please, for the safety of yourself and your family, have all your wiring checked.

By way of explanation, I’ve done a couple of diagrams.

First, what I think your supply and house wiring might be like. I’ve only drawn the one circuit that’s supplying the a.c. adapter, and I’ve drawn the a.c. adapter as a lamp (because if you test with an ordinary tungsten filament lamp, you’ll see exactly the same as you did with the a.c. adapter).

Now, break the neutral wire to the socket outlet.

If you measure between GND & N, you will measure the full line voltage - 127 V for you, 240 V for me, between neutral and GND, because the neutral is connected to Line via the lamp (AKA the a.c. adapter), which has a very much lower impedance than your meter.

If you unplug the lamp, the wire between the socket outlet and the break is not connected to anything, so you will measure zero volts (or a very low voltage) between it and GND. You’ll also measure zero volts between it and Line (F on the outlet), which will make you think the outlet is dead - it isn’t.