Raised voltage mains power incident.

[Ian Worthington]

Parents-in-law house suffered a power "incident" the other day that damaged computers, TV, radios, and electric showers. Cabling was blackened as was the fuse box.

The power supply company say it was an internal fault and certainly no other houses appear affected. The only clue I have is that light bulbs brightened before they burnt out, suggesting an over-voltage condition.

This took place in Colombia, not the UK, and the house didn't have anything more sophisticated in the way of protection than a fuse box.

110V, almost certainly single phase.

I can't think of anything that could have raised the voltage on the live conductor. Could it be that their electric distrubution system mainatins neutral substantially above earth such that a short of neutral to earth would raise the voltage applied across appliances?

Any informed speculation welcome.

ian ...

[Dave Liquorice]

Are you sure? I'm under the impression that supplies across the pond are

110v bi-phase. So things that things that need real amounts of power can sit across the phases and live off 220v.

[Ian Worthington]

No, I'm not! I know they do that in the US so its very possible that its the case in Colombia too, but as far as I know there's no 220V service in their house -- certainly no appliances that use it.

If there was, can that fail in such a way as to present a much higher voltage across the appliances?

i

[The Wanderer]

I'm assuming you mean central America. The nominal voltage there is

110/220v. The 220v supply is for equipment with higher loads, like cookers.

I had a quick look on line for details about the supply industry in Colombia, there were *lots* of references to the business aspects, but I drew a blank on tech aspects. I'm guessing the lv distribution system is split phase, 110-0-110, with the centre point being connected to earth (call it neutral for the sake of convenience). I somehow don't think it would be 0-110-220, but you never know!

What I suspect happened, somewhere between your in-laws house and the transformer there was a break in the neutral. That caused the voltages across the outers to differ wildly depending on the loads connected.

What you need to ask your in-laws, do they have only a 110v supply or do they have 110/220. If they have 110/220, there's always a possibility that the problem could have occured on their wiring. If they are positive they only have 110v, the laws of physics dictate that the problem could *not* have occured within their property. It would have to be a problem on the system supplying them. Proving liability with the supply co is altogether another matter.

[Andrew Gabriel]

Yes, and it's not at all uncommon with the 120-0-120V supplies. Loss of the neutral connection means the 0V drifts in reverse proportion to the load on each side. If the loads on the two sides were nowhere near ballanced at the time, then one side (with the lighter load) will have had a significantly higher voltage than the 120V it's designed for (and the other side will have an equal drop).

[John Stumbles]

But it's probably common enough that there are lawyers and electrical engineers with experience of fighting such cases and that possibly, approached by such professionals, the leccy co may cough up.

[The Natural Philosopher]

Many things. lighning strike, disconneting an indctive load. Losing a phase on a three phase.

Could it be that their electric distrubution system

[terry]

Since the voltage is mentioned as 110 volts suspect it is similar to here in Canada (as in much of the Americas) where we have 115-0-115 volts 'single phase'.

That means that there is 230 volts (the two ends of a centre tapped distribution transformer winding) i.e. between the two outer wires, as someone has already described.

So if that middle wire. The one that is called 'neutral' and nominally at zero volts becomes open , either outside or within the house due a fault such as corroded or loose connection it is possible that 115 +

115 =3D 230 volts could be impressed through various devices across a 115 volt device.

With twice the intended voltage there is twice the required current and that means four times the amount of power being dissipated in any device or equipement that might be switched on at that time! Have seen that blow smithereens out of TV set.

Whether there IS a bad neutral connection outside or inside will have to determined; but it could happen again?

Dont know about Colombia but electric utilitiy crews in most countries pride themselves on a high standard of customer service. Here in this part of Canada they are are excellent, providing repairs 24 hours a day during the worst of weather. And usually willing to come and test the outside connections to a residence, sometimes giving a bit of advice about testing into the house circuit breaker panel or CU.

We take out hats off the the outside line crews of the Newfoundland Light and Power Company and Newfoundland Hydro.

[Ian Worthington]

Hi Andy.

Thanks for this, and to all who responded.

Fault was confirmed as a disconnected neutral, but apparently inside the house, so no claim against Codensa. Caused by ingress of rain I'm told.

Two questions:

1. If the neutral gets disconnected, what's the return path for the current?

1. Luckily my teenage sister-in-law had taken it upon herself to disconnected the most expensive of the white goods (fridges and washing machines cost a small fortune out there) and forget to plug them back in before this fault occurred, so saving them. But, given my father-in-law's apparently not to be trusted with mains wiring, what type of safety equipment should I insist is fitted to protect people and property before I put my hand in my pocket to replace the other damaged equipment?

ian ...

Andrew Gabriel wrote:

[Andrew Gabriel]

Through the appliances on the other leg.

Safety equipment is heavily dependant on local customs, what's available, and local regulations. I think you need to ask this in a Canadian or North American forum. That type of fault is so rare in the UK that over-voltage trips are never used in domestic situations. However, that type of fault is very much more common on North American 120-0-120V (Edison) type supplies, and there may be equipment and/or procedures which are used to minimise the incidence or impact of it.

[The Wanderer]

Hmm, but the OP had already said that he thought it was a 110 volt supply, not a 110/220 volt supply. That being the case, there is no return path and the problem could not have occured in the property, and Codensa are spinning the FiL a line. Hence my question/comment to the OP that he needs to establish if it is 110v 2 wire or 110/220v 3 wire.

I agree, it is rare, but I've come across a couple of instances of a floating star point.

[Ian Worthington]

This would surely suggest that the house *must* have both legs of the

120V supply available contrary to what I've been told?

Local customs in this area of town mainly consist of throwing a coat hanger over the cables in the street to steal some power whilst trying to not let it get too close to the petrol-powered cooking stove, (for example,

et al (taken about a mile from my parents in law's house)) so that's probably not a good starting point.... :)

I'm trying to suggest to the wife we need to talk to an electrician who knows what they're doing, and she's wondering just how to do this without upsetting her father... I'm in the dog house at the moment for plain speaking. Family politics, don't ya just luv it?

i

[Ian Worthington]

Hi Andy.

I've had it confirmed that the cable from the street carries only one live plus neutral and earth.

Any ideas?

[Andrew Gabriel]

In which case the raised voltage was fed to you by the power company, and I would regard that as their fault. I presume the other leg feeds someone else, in which case the disconnected neutral must have been at the supply transformer. A disconnected neutral inside your house cannot do this.

[meow2222]

It doesnt seem to me that the symptoms you describe line up well with a 110->220v overvoltage fault. Such fault would cause connected appliances to draw excess current, and the fusebox would clear this in the normal way. You'd have dead appliances and popped fuses, but nothing else. The currents involved would not usually be high enough to blacken fusebox & wiring.

Charring of cable requires either huge current (dead short on premises, PSCC flows, CU fails to clear fault due to inadequate breaking capacity) or huge voltage (lightning strike or high voltage flashover on power company's side)

The next question is where is the cable blackened. This will tell you if the charring occurred only in the CU (1), or only along one attached cable (2), or through out the whole installation (3).

1 means charring temps only occurred in the CU, which rules out lightning 2 means the fault occurred downstream on one cable, so a dead short. 3 means extreme voltage at the feeder, ie lightning, or I guess less likely a flashover at the pole pig.

Once you've established here what the fault was, then getting the cause confirmed in writing by a qualified spark would give you evidence to argue with. If its excess voltage, they would also need to confirm that it could not have been caused by anything on the premises.

Re safety equipment, I dont think there is any for any of the possible scenarios, including lost neutral.

NT