True or False.....

[Guest123]

So, got a call this morning from local authority saying that a number of houses on a site we had worked on had "lost" power. Ok says I, I'll shoot straight over, no worries.


Turns up to about 17 ressies all standing on their doorsteps with pitchforks and torches in hand, waiting for me as it turns out.

What's up says I......come and smell my telly says one of them!!!!

To cut a long story short, it turns out that no less than 18 television sets had totally burned out....due to a SUPPLIERS problem, felt the relief I did.

So I'm chatting to the DNO guys assuming there was a surge of some kind on that particular line. no no says the chap.....we lost a neutral.

Lost a neutral......are you sure??? definately he says.

Now it may be me but would a loss of suppliers neutral really cause 18 T.V's to flombay themselves.....opinions please gents.

 

[acvc]

Earthing system PME?

 

[Guest123]

No Sir, TN-S.

Should have stated that really as it is the basis of my Q.

 

[pennywise]

It's an insurance job a well organized one, they all want new 50in plasmas by kick off tomorrow.

 

[davelerave]

could be overvoltage or undervoltage - DSO lost the 'star'(neutral) point on the 3-phase trafo

 

[pmac10]

from the mouth of a linesman i know from NIE, reverse polarity will take out every TV on a street.

 

[8145keith]

Hi there,

Just TVs out sounds like lightning to me.
regards kj

 

[xraytek]

Hi,
Definately true as we lost the main neutral at work and it resulted in every piece of equipment one of the phases smoking.

The way I visualise it is to imagine equal single phase loads on a 3 phase board.
If the neutral to the board was lost then equipment will still operate due to a return path through another load on a different phase as they are joined by the neutral rail.
The equal loads will mean that the voltage across each load will remain the same.
If the loads were not equal then you will get voltage rise on one load and voltage drop on the other.

If you had 2 resistors of equal value in series across a 24 v supply you will measure 12v across each resistor.
If the resistor values were different then the voltage across each resistor will also be different.

 

[Des 56]

Clutching at straws here perhaps but, maybe someone from the suppliers cross conneted an outgoing phase with a neutral on an item of switchgear or a cable joint that resulted in a 2 phase supply instead of phase- neutral

Why only televisions though ?

I thought BT were the biggest culprits for frying electronic equipment, with lightning strikes on their phone lines, when questiioned they say " Not us GuV"

 

[UNG]

It may have taken out the TV's but other appliances could have been damaged but have not failed yet.

About 10 years ago got called to an intruder alarm fault in a hospital it was quite a big system with multiple power supplies most had failed as the sub station earthing / neutral had failed and the resulting floating neutral caused one phase to have 300+ volts on it

 

[SirKit Breaker]

There is a post somewhere in the Chit Chat off topic section and fairly recent regarding something similar.
Some halfwit pikey broke into a substation and nicked the neutral link to weigh in for scrap, fried god knows how many consumer units. Have a look in there it make scary if not interesting reading.

Cheers........Howard

 

[davelerave]

ya -if you disconnect the neutral on a 3-phase board feeding SP loads

you're left with an unbalanced star connected 3-phase load

voltages will vary up/down from the nominal 230V

 

[GT1]

There was one in Cumbria a few months ago wasn't there. Put down to a "power surge". ?

 

[Guest123]

Done a bit of digging on this today, to try and find out exactly what went on.

Having spoken to a couple of guys from the DNO who were honest and weren't lying to try and save face, turns out that the connection at the star point of the trafo was lost, sending upto 400V AC down the "floating" neutral conductor. Basically a massive over-voltage situation causing thousands of pounds worth of damage to T.V's, heating boilers, showers, pir lights etc etc.


I suggested this situation to the chaps form the DNO who were on site yesterday and they swore blind it wasn't the case.....lying toerags!!! It seems they have now admitted liability and are going to pay up for all the repairs.

 

[davelerave]

ya that's it

 

[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.