True or False.....

[mechelec]

Three phase with lost neutral will give up to line voltage on one phase and down to zero on another. With single phase ie disconnected neutral at origin you will still get damage to electronic equipment especially with florescents trying to strike as the back EMF will try to find a way through the filter circuits in electronic devices back to earth.

 

[nickblake]

ive had this happen lost neutral in a hotel , blew every HF ballast and emergency light in the building cost a fortune to replace and two weeks after the same thing again but this time blew up 2 single phase pumps which cost a fortune to get rewound , cant remember what supply it was but i think it was tncs , as i was getting reports of people getting shocks off the metal work in the building

 

[Griffin]

mmmm...Interesting

My TV also has blown up.......

and I'm in Devon!!!..

G

 

[Scud]

Seemples. Imagine a number of houses connected to three phase supply cable. Each house is in rotation connected to one phase and neutral. Each house's supply flows in through the phase conductor and out through the neutral conductor. If at some point the neutral conductor is broken, the return voltage from one house can travel via the neutral conductor to the next house. That voltage meets another phase at the customer's equipment. Smell of burning. TVs, microwaves etc. damaged. Word goes around, and before you know it, half a dozen 32" CRT TVs have turned into a hundred 50" plasmas. QED. If it's a PME supply, and if the neutrals have been earthed at every joint as required, damage is much less likely. Similarly, if the supply cable is a ring, damage is avoided. It's where neither of these conditions is satisfied that the trouble starts.

 

[Scud]

mmmm...Interesting

My TV also has blown up.......

and I'm in Devon!!!..

G

Unless your house is connected to Lenny's supply cable, I fear you're on a loser there. Down to Curry's for you.

 

[RexT]

Hi guys,

I think you were lucky that the DNO people were truthful. Have you any experiences when things have blown up without a reason given?

Rex

 

[Andyfm]

Had a problem back in the winter when overnight during some windy weather not long after I`d finished some refurbishment work there, the 3 phase overhead supply into a local village hall somehow blew the circuit boards on three newly installed aircon units but caused no other damage, we reckoned at the time it was down to again a lost neutral or a momentary short L- N on the overheads causing 415v L- N.
I spoke to a mate of mine at EDF who agreed, but their official line was - No reported faults - not our problem . The Hall committee thought it was my work at fault and I had to check and test all the connections on the mains etc in the presence of a committee member, before they would believe me , and in the end they put in a claim on their insurance.

 

[xraytek]

If it's a PME supply, and if the neutrals have been earthed at every joint as required, damage is much less likely. Similarly, if the supply cable is a ring, damage is avoided. It's where neither of these conditions is satisfied that the trouble starts.

I dont know how supply transformers are configured, but if there is a commoned neutral rail with earth spike connected to the rail, and then a link to the star point of the transformer then I would imagine PME homes would still be effected.

The current of one phase winding would pass through all the home equipment of one phase, come back to the transformer neutral bar, through the neutral cable of homes on another phase, though all the equipment of homes on the other phase, then back through another transformer winding.
The voltage at the homes will depend on the amount of equipment connected on each phase at the time.

If you are lucky you are on the phase with the most equipment connected

 

[Guest123]

I think blown appliances would be the least of my worries with a lost supplier neutral on a TN-C-S supply......

 

[Scud]

I dont know how supply transformers are configured, but if there is a commoned neutral rail with earth spike connected to the rail, and then a link to the star point of the transformer then I would imagine PME homes would still be effected.

The current of one phase winding would pass through all the home equipment of one phase, come back to the transformer neutral bar, through the neutral cable of homes on another phase, though all the equipment of homes on the other phase, then back through another transformer winding.
The voltage at the homes will depend on the amount of equipment connected on each phase at the time.

If you are lucky you are on the phase with the most equipment connected

Close, but not quite. The multiple earthing of the neutral cable gives an alternative path back to star point, thus hopefully avoiding equipment damage.