Overcurrent in circuits

[dtec dave]

Evening all...just a quick question. A customer was using a wallpaper stripper on a ring circuit, smoke started coming out of the back of the socket before the 32amp breaker tripped, what I don't understand is why the 13amp fuse in the plug didn't break? Could someone tell me why? Thanks

 

[amlu]

faulty socket or dodgy connection at the back of the socket, wires got heated, insulation melted and current sufficient to trip 32A went in.

 

[alanl]

Loose connection either in the plug, or at the socket outlet.

Possibly a too-small conductor for the steamer, though unlikely.

 

[dtec dave]

Cheers..but wondering why the 13amp fuse in the plug didn't blow?

 

[Des 56]

Steam cools,water acumalates behind socket,tracking between L+N or E ( no rcd) breaker current exceeded and out it goes
Plug top fuse intact because there is no excess current after the socket terminals

 

[Tiny Spark]

Fuses dont operate as fast as MCB's.
Now I dont have a BGB to see how fast a 32A MCB operates and at what current but Apparently a 13A Fuse is required to operate at 1.9 times rated current (24.7A) within 30 minutes.
So if its operating at say 40A it may take 15mins to blow where a MCB will probably operate faster.

Did you find what caused the fault?

 

[Darkwood]

Ive see temperatures in switch gear weld the terminals and cables yet the heat damaged HRC fuses don't operate..... the current needed to operate the fuse-wire needs to get it white hot, so in principle heat generated by a loose connection may not get anywhere near the same temp that is needed to melt the fuse wire.... when you've seen fuses glowing red without operating its an headscratcher the first time ....same principle applies with plug-top fuses.

 

[dtec dave]

Not sure what caused the fault, going to put it down to either water getting into the back of the socket or a fault in the wall paper stripper, tested the circuit and found nothing wrong.

 

[Tiny Spark]

Ive failed a few wallpaper strippers in the past while PAT testing.
Some of them are very poorly made!

But yeah steaming the socket wont help either!!

 

[snowhead]

what I don't understand is why the 13amp fuse in the plug didn't break? Could someone tell me why? Thanks

The fault was upstream of (closer to the C.U) the 13amp fuse.

 

[plugsandsparks]

If its any consolation, i went to a tripped 32A socket MCB which was caused by a coiled up extension reel feeding a 2KW heater. THE 10AMP fuse on the reel plug head was still going strong.......

 

[ipf]

Cheers..but wondering why the 13amp fuse in the plug didn't blow?

Where the smoke signals came from should give you a clue. :indian_chief:

 

[Tiny Spark]

If its any consolation, i went to a tripped 32A socket MCB which was caused by a coiled up extension reel feeding a 2KW heater. THE 10AMP fuse on the reel plug head was still going strong.......

Pffttt thats nothing!
We had a fire alarm go off caused by 2x 3kw heaters plugged into a 25m rolled up lead.

It was a pile of PVC mush and coper when i got to it LOL

 

[SPARTYKUS]

Pffttt thats nothing!
We had a fire alarm go off caused by 2x 3kw heaters plugged into a 25m rolled up lead.

It was a pile of PVC mush and coper when i got to it LOL

Wasn't a hairdressers by any chance was it

 

[Tiny Spark]

Nah.
Even worse...
It was a poxy 6ft x 10ft office!!!

The scary thing is the guy working in there didnt see or smell the smoke/fumes!

 

[Knobhead]

Sawn off 6" nails tend to hold longer than the MCB.

Sockets seem to get a bit upset with gross overloads.

 

[plugsandsparks]

Pffttt thats nothing!
We had a fire alarm go off caused by 2x 3kw heaters plugged into a 25m rolled up lead.

It was a pile of PVC mush and coper when i got to it LOL

Yep ditto, i felt compelled to break open the reel to have a look see, i was impressed with the damage. The inner turns were all stuck together in a melted mass.

 

[Guest111]

I remember a few years back and one of the in ln laws wanted to borrow my welder,I asked him if he wanted the extension lead as well,because I had a nice heavy one for the welder.No he already had a nice new lead,anyway he brought the welder back later very annoyed as it had "broken" his new lead! He had bought one of those 50 foot roll ones from one of the sheds,pulled off about 20' and started to weld,his welding on the metal wasn't that good but he'd made a lovely job of "welding"the cable to the reel.obviously he didn't see the bit about unwind fully before use.

 

[gazj82]

Also don't forget a fault will usually take the weakest part of the circuit out. i.e if your ring main is already running at 25A with 7A to spare. 7<13 so you will probably take the MCB first. Well so I have always been led to belive.