How does Neutral to Earth Voltage affect electronic systems and power supplies

[hareeshravi]

How does NEV affect electronic systems ?
Systems are working fine even if I interchange Phase and neutral.
After goggling, I am in impression that susceptibility to NEV is mainly due to electronic design issues (like PWM feedback of SMPS referenced to chassis) and designs after yr 2000 are almost immune to NEV.
So it means we should not worry of NEV (Electrical engineers should, as it indicates weak neutral integrity)
Can anyone explain the effect at circuits level?

Similarly I could not find any authenticated info / standard on NEV limit.
People use 0.1, 1%, 10V, e.t.c., but did not get on what technical criteria are they selected.
Please share our thoughts.

 

[chuckey]

Years ago I saw some one blow up two switch mode PSUs , on investigation, it turned out that the whole rack had L and N transposed. The input to the SMPSUs were symmetrical except for in the live feed where there was a small resistor (can't remember its value - 22 Ohms?). One can only hypothesize, that this resistor limited the current through stray capacitance to earth when it was in the live side, but when the L and N were interchanged, the current was too much for the switching transistor.
Frank

 

[schmitt trigger]

I have also seen equipment failure where the L and N were transposed. In this instance it was a CPU and a printer. By themselves they worked fine, but when the printer cable was hooked to the CPU, both units blew. Total and complete damage.

I suppose it depends on how specifically the power supply is designed.