Flooded Electrical Circuits Kept Working!

[Johnsey]

At an office building, a single phase cable joint box below the raised access floor and serving underfloor bus bars become flooded with water.
The circuits are protected by 32A mcb (no RCD protection).
Whilst the joint box was fully flooded with water, the mcb's did not trip.
I am guessing that the fault current was below that needed to operate the mcb, bit I am surprised and would have expected the mcb to trip pretty quickly once the flood had occured.
Does anyone have any similar experiences?

 

[sedgy34]

At an office building, a single phase cable joint box below the raised access floor and serving underfloor bus bars become flooded with water.
The circuits are protected by 32A mcb (no RCD protection).
Whilst the joint box was fully flooded with water, the mcb's did not trip.
I am guessing that the fault current was below that needed to operate the mcb, bit I am surprised and would have expected the mcb to trip pretty quickly once the flood had occured.
Does anyone have any similar experiences?

the joint box must be ip rated then, did the busbars get water in them?

 

[johnboy6083]

you will findthat if the flood is fresh water from say a broken pipe, then it will have a very high impedance value, where as dirty water from a river flooding will have a very low impedance. Ive actually meggered cables that had joints immersed and had a dead short, and they were immersed in very sloppy mud.

Pure deionized water is used to clean the EHV overhead lines, as it is an insulator, its the minerals contained within water that will allow it to conduct electricity

 

[Johnsey]

the joint box must be ip rated then, did the bus bars get water in them?

I'm not sure if the bus bars were flooded. I am told that the joint box was fully submerged and full of water - no IP rating - and that the water in the box had been warmed by the current.
I'm just surprised that the mcb's (probably 6 circuits passing through the joint box) didn't trip.

thanks for your thoughts.

 

[malcolmsanford]

Johnsey I have been in basement of an london Hotel where the main panels where and the 8" mains ruptured and this basement was under about 4 feet of water, and the electrics played on, but I didn't fancy going into that water with all that about to isolate panels

I have to admit this was the days of cartridge fuses, and a few MCBs had replaced them. Remember a MCB will only trip on over current or fault, well there is no over current, and unless the water shorts across the conductors, and as John said that could be unlikely then why would it trip.

It's like I've seen in a fire, the RCD still was closed, and everyone expecting it to trip, well if there isn't an in balance occurring before the cable burns through, why would it trip.

 

[Johnsey]

Johnsey I have been in basement of an london Hotel where the main panels where and the 8" mains ruptured and this basement was under about 4 feet of water, and the electrics played on, but I didn't fancy going into that water with all that about to isolate panels

I have to admit this was the days of cartridge fuses, and a few MCBs had replaced them. Remember a MCB will only trip on over current or fault, well there is no over current, and unless the water shorts across the conductors, and as John said that could be unlikely then why would it trip.

It's like I've seen in a fire, the RCD still was closed, and everyone expecting it to trip, well if there isn't an in balance occurring before the cable burns through, why would it trip.

Thanks for that, its somehow comforting!

Unless you've seen submerged circuits working it just doesn't seem possible. But as you say, if there is no over current then why would the device trip?

Thanks all.

 

[ackbarthestar]

Its an interesting fact that industrial water heaters use electrodes to heat the water, quickly, I dare say. You even get 3-ph electrode boilers. The outer casing is bonded to neutral/earth.

It would make an interesting experiment to have measured the rfc current with a clamp meter after removing the other loads on the circuit.

 

[Knobhead]

Like Malcolm I’ve switch rooms flooded and still live. It was getting a bit steamy in there.

 

[Engineer54]

As already mentioned, it's totally down to the dissolved contaminants in the water whether it's going to be conductive enough to trip a breaker or not.

I've actually had a play at washing live pylon 33KV insulators with a pukka tanker truck mounted high pressure hose cannon!! It goes against everything we have been told and trained, so a little deserting when you first aim it up at the insulators and pull the lever!! lol!! Again as already stated, the water used was deionized/distilled water, (And thoroughly tested before hand i might add lol!!).

 

[Knobhead]

Some people have all the fun.
View attachment 12171

 

[spark 68]

Hi E54,

Did you see that documentry (USA) where they were hosing the live Trans Am pylons down from a helicopter ?, they clipped the helicopter to one of the lines, scary stuff!, they were at half a million Volts due to the distances involved, which is far higher than anything in the UK.

 

[Engineer54]

Hi E54,

Did you see that documentary (USA) where they were hosing the live Trans Am pylons down from a helicopter ?, they clipped the helicopter to one of the lines, scary stuff!, they were at half a million Volts due to the distances involved, which is far higher than anything in the UK.

I've seen a few such video's on those American Super High Voltage pylon and transmission lines and on there maintenance. You wouldn't catch me doing anything like that ...lol!!

The cleaning truck i used, had 2 X 50cm connected earthing spikes which are pushed into the ground. They are attached/welded to the hydraulic stabiliser feet/arms!! (one spike diagonally apposed on each side) I would imagine those things would be totally useless in the environment we were working in (Sahara Dessert) lol!!!

 

[mogga]

in the good old street lighting days we use to get numerous callouts re "Bollard on fire" it wasnt on fire but steam coming from it due to some little darlings smashing it to bits and allowing water in the water could be used to make tea some of the overhead choke boxes were good when the chokes started going GOD they stunk to high heaven
Best one for smell was bollard in the middle of high st split when it had been hit,vandalised water in it bubbling away boiling the antsnest who sought refuge in the nice warm bollard previous to water penetration WHAT a SMELL that one was

 

[ackbarthestar]

As already mentioned, it's totally down to the dissolved contaminants in the water whether it's going to be conductive enough to trip a breaker or not.

I've actually had a play at washing live pylon 33KV insulators with a pukka tanker truck mounted high pressure hose cannon!! It goes against everything we have been told and trained, so a little deserting when you first aim it up at the insulators and pull the lever!! lol!! Again as already stated, the water used was deionized/distilled water, (And thoroughly tested before hand i might add lol!!).

A demonstration by a colleague who showed that firing a high pressure (jet) hose of water at 33kV lines will definitely electrocute you. But if you turn your jet hose to sprinkler setting the current drops off to zero.

Guess who uses this method?

 

[Guest111]

A demonstration by a colleague who showed that firing a high pressure (jet) hose of water at 33kV lines will definitely electrocute you. But if you turn your jet hose to sprinkler setting the current drops off to zero.

Guess who uses this method?

yes saw that when I was with fire service,the trick was called pulsing,short sharp bursts of water so it doesnt give the juice a path to earth down the water,sooner the lads on the hoses than me though I was on incident support the lads put it out and we dealt with the aftermath.True heroes every one.