Gas from DIY cable in duct

[bernardgreen]

Twin and earth through an under ground duct to a garden shed, no RCD protection.

Cable insulation is not good and duct flooded. Electrolysis of the water has created hydrogen and oxygen which came out of the duct into the shed.

Gas from the duct collected in a polythene bag over several hours did burn extremely rapidly when ignited confirming the gases were from the electrolysis of water.

Only small volumes of gas being produced and a well ventilated shed meant the hazard of explosion was virtually nil.

Cable disconnected and IR tests showed failure of insulation. Cable resisted all attempts to drag it out of the duct. Markings on cable show the cable at one end is not the same as the cable at the other end. There has to be a joint of some type in the duct.

A previous owner of the property was an avid DIYer.

EDIT my error, should be in electrics UK

 

[FDJ]

Hydrogen and oxygen mixture burns explosively. Its absolutely unmistakable.
Are you positive that this is not a "natural gas" leak?

Frank

 

[bernardgreen]

It was definately gases from electrolysis. Production of gas stopped when the cable was isolated.

Being a small bag and then time allowing the gases to separate and stratify the burn would have been less rapid than had they been well mixed. Freshly produced and still mixed they are very explosive, I know having had a gassing car battery blow two cells apart when I removed the charger lead from the terminal without turning the charger of first.

It reminded me of this event where gas had leaked into telephone cable ducts.

http://tlhs.org.uk/takeley_telephone_exchange_explo.htm

 

[Chri5]

Cat / cable tracer. A external BT one with tone on wire might be ok because I doubt the duct is 750mm down.

Also look for any dog leg or massive change in route along duct.

 

[bernardgreen]

hi Chris

It is not my project. I guess the existing duct will be abandoned and a new one laid during landscaping of the garden.

 

[markocosic]

Terminal blocks and water - great mix!


You've got to try hard to make the shed explode. Add some soap and crank up the current. (voltage is irrelevant) The bubbles hold the hydrogen/oxygen in close proximity in a perfectly explosive mix, whereas if you bag it the hydrogen escapes through the bag quickly leaving excess oxygen behind.


We caused something of a kapoof when somebody decided to use the grinder near this little setup:

(alternator rectifier diodes and twin 30A blade fuses in the tupperware box; fan heater was for cooling the old buzzbox not rated for continuous duty)


Cleans stuff up nicely though!

 

[dhutch]

We caused something of a kapoof when somebody decided to use the grinder near this little setup:

(alternator rectifier diodes and twin 30A blade fuses in the tupperware box; fan heater was for cooling the old buzzbox not rated for continuous duty)


Cleans stuff up nicely though!

I like that a lot.