Identifying a neutral supply problem?

[MickSmith5824]

Had a call today. Property has 400v 3 phase DB....it used to be old commercial unit but changed to residential. He's been in process of moving in but within day or two appliances starting to burn out. He's father had reported testing some sockets and voltages varied at times when other appliances were turned on on same circuit and he also reported 330v on one socket. DNO has been out but just live tested on incoming side of main switch as had been unable to find where to isolate our DB from. Customer has since found another DB in an area of this commercial unit that isolates his DB. I am due to go there tomorrow. My question is what is the quickest and most of obvious tests/readings that point to a dodgey neutral. ZS will only give me Line to earth, would a L-N loop reading potentially point to it or PSSC. My thinking is there is potential he has two crossed phases supplying a single circuit...but this would result in around 400v on sockets and wouldn't of fluctuated as much as he has said it did and also surely these problems would of been noticed by previous tenants and rectified

 

[MickSmith5824]

No, he is saying that if it is energised you can measure the voltage drop across the various possible points of failure in the neutral. However as the DB is isolated it would not be sensible to energise it until the fault is found and rectified.

Testing between phases and neutral is unlikely to find a fault in the neutral. Testing the resistance of the parts which could have failed will likely find the fault.

Thanks again Dave

 

[dmxtothemax]

You may have a high leg delta ?

 

[davesparks]

You may have a high leg delta ?

In London? That's pretty unlikely!