Bizarre problem with 3 phase WYE system

I have a weird problem with the electricity in my house. The house has a three phase municipal supply 400/230V WYE electrical system. The house is old and already I have had problems with water causing short circuits. Before anyone crucifies me, I am going to leave this house in a month or two and leave all the problems to the owner to fix before he rents it out again. But it is unlikely he will fix the current problem so I have to repair it myself to enjoy the luxury of electricity for the last days I will be living here. I am quite capable, but I just need a memory jog. The house is so badly wired that I have been unable to determine how they distributed the loads.

So, during the present rainy season, all of a sudden on two phases I get 270 volts, the third phase is 230V (Phase to neutral). If I plug in a high load appliance such as a kettle on any phase, the other phases go ballistic, i.e. they either drop to below 200V or climb to 280V.

A while back I was a facilty supervisor and one problem we encontered was a failed neutral line on a WYE system. This puts 400V across all three phases (P-N). So I'm wondering if water has somehow gotten into the cables and caused this? It's obviously not a complete neutral disconnect otherwise I would measure 400V P-N on all of them.

• hmm, do you know a person with access to a vde tester? sounds something is totally fu...ed up. If you are lucky, just a fuse/FI is damaged in your cabinet. Outside stuff like lamps are also possible sources of such errors. Is this error bound to one location, a room, or all over the house? Commented Sep 8, 2020 at 21:44
• Sounds to me like an open circuit neutral. If there are loads from all 3 phases to neutral that would explain why you measure "off" voltages, not 400V or the correct 230V from a rock solid neutral. How close you get to 230V depends on how well balanced the loads are : a kettle on one phase unbalances them.
– user16324
Commented Sep 8, 2020 at 22:46
• More likely a fully open neutral, with random loads providing an unstable "virtual neutral".
– user16324
Commented Sep 8, 2020 at 22:52
• The symptoms are typical of bad neutral connection somewhere , it might even be fully open, and relying on a neutral-earth connection in the meter box, this can potentially make all the plumbing on the house a "bit tingly to touch" or worse. You need to pull the "pole fuse" to fix it otherwise you could end up with 230v across the neutral connector as you fiddle with it.
– BobT
Commented Sep 16, 2020 at 10:02
• @raffles If you had a 5HP 3phase 230v star wound transformer, you could connect that up and get much a much better neutral. Here in Australia we have "multiply earthed neutrals" or MEN , although that may not help that much, a typical local earth resistance of 1ohm would see 20v of variation with 20A of load.
– BobT
Commented Sep 17, 2020 at 8:24