Gas explosions due to cut neutral

[bernardgreen]

The Real Rescues TV program ( episode 21 (?) on BBC 1 11th April 2013 featured a couple of terrraced houses blown apart by gas explosions seconds after fire brigade crews came out of the houses having extinguished kitchen fires in two houses.

The cause given by the officer in charges was that metal theft had removed "one of the electicity supply cables leaving the buildings live" and went on to say that as a result large currents had gone to ground via the gas pipes. The anaconda pipes to the gas meters had melted releasing gas.

I assume the metal thiefs had taken out the "safe" neutral supplying the terrace and neutral currents had gone via the bonding to to the gas meter and into the ground via metallic gas supply lines.

 

[plugwash]

Sadly I doubt it will make the cheapskate DNOs fix their practices.

 

[bernardgreen]

Apparently all six houses had had small fires in the kitchens as a result of the metal theft.


there is a link to the event

http://www.bbc.co.uk/news/uk-14335929

 

[ricicle]

I thought this one was down to the theft of the N/E link at the sub ?

 

[Graham3232]

Were the houses not supplied by overhead lines and timber poles on a PME network and the earth/neutral had been stolen and the link connecting the neutral to earth down the poles (if there was one), leaving the neutral current to pass through the gas pipe?

Most gas supplies are being replaced with plastic supplies now anyway so this isn't always an issue. I guess the lead water pipes had been replaced with plastic as they are usually better conductors, hence they used to be used as the main earthing.

I guess a situation where TT has been upgraded to TNCS without proper earthing at the poles?!?

 

[westie101]

There have been a few incidents (but not as severe) of this type. It is often caused by the theft of the neutral and earth connections and cables in substations.
It equally affects TNS and TNCS networks.

 

[gaspro1981]

Foooook a dooook that must of been **** ya pants time

 

[ban-all-sheds]

Old news.

 

[bernardgreen]

It is "old" news but recently back in the news and might be relevant in some ongoing discussions. Thanks for locating the earlier postings.

 

[josh451]

Anyone else think that when the bit when the door moves is really really creepy

 

[viewer]

Now I've watched again it does look like it is being deliberately closed! Actually, to add to the weirdness, the curtains move before the door closes.
This is what really happened:-
Aliens look out of window to see if anybody watching, slam front door to keep people out then leave in rocket ship through bedroom window.

 

[ericmark]

How many off the multiple earths need removing to cause this? Clearly the voltage can jump up and down with load once the centre tap to earth and neutral is removed but to melt the incoming gas pipe would mean also the multiple earths are also missing. Down to DNO I would think. I saw first hand where road works severed the neutral/earth and it melted a radio hams earth wire to his shack. Clearly although TN-C-S it was not PME and this is where the problem lies.

 

[viewer]

Help. Trying to get my head around this. Please see if my assumptions are correct.

The metal gas pipes in each house acted as neutral with the current flowing to earth.

A RCD would make no difference because the current through it would balance.

The current in the neutral would be the demand in the house which would be quite small once the houses had been evacuated.

The resistance of the gas pipe would cause it to heat, but the voltage across it would be low and the total cross section of metal would be high.

To melt a pipe would take an enormous amount of energy.

I've missed something important, but what?

 

[bernardgreen]

The current through gas pipes would be the entire neutral current for that branch of the local distribution system.

The first calls to fire brigade were for six small fires in the kitchens of six houses. I suspect this was bonding cables overheating even though they were probably sharing the neutral current.

The officer in charge did mention that the flexible metal pipe to the meter had melted.

If some houses on that branch of the network had night storage heaters and the network was not well balanced ( shared among the phases ) then the neutral current could be very high. It was obviously high enough to create 6 small fires although it is not clear if they all started at the same time. A weak bond may have burnt out first and then the next weakest went in flames.

It might also be that the cut network neutral was the neutral for other houses that shared the same metallic section of the gas supply main. The neutral current for those houses would go into the gas main and then come out of the gas pipes at the houses affected by fire to reach the neutral still connect to them.

 

[viewer]

Thanks, much appreciated.