Electrical Surges

Buy a knackered 50" TV quick! :P

Originally Posted by ophic

I wouldn't whinge about that. Those fuses stopped the devices from being knackered.

Personal pet hate of mine is that everything seems to come with fuses of a much greater rating than required. Electronic items with 5A when they should have 1A. Everything else just seems to get 13A and they don't use anywhere near that amount of current.

The new standards for fusing items given to manufaturers by the 'Government' changed recently. There's just going to be 2 fusing levels, below 700W will have a 3 amp fuse and everything above will come with a 13. I examined a brand new 710W drill last week and it had a 13amp fuse in line with that even though the cable would melt before it blew.

Originally Posted by arenalife

I examined a brand new 710W drill last week and it had a 13amp fuse in line with that even though the cable would melt before it blew.

The cable would be fine, the current carrying capacity of most cables can sustain quite high currents before melting out, well long enough for the motor to burn out before the cable melted.

But still 710w @ 230v would draw a current of 3.08 amps, take in to account a P.F of 0.75 the current would not exceed 4.1 amps, so one would think a 5 amp fuse should be suitable?

Anyway still an intresting one, as if there was a power surge on the mains surely the distribution board circuit breakers would trip?!

If its a Transformer/Switch gear fault then it sounds like an imbalance over the three phases causing the neutral to become live and thus frazzling the electrical equipment up the tradesmens entrance of the electrical installation!!!

Anyway still an intresting one, as if there was a power surge on the mains surely the distribution board circuit breakers would trip?!

not quite, the RCD measures earth and neutral current, a sudden change TO earth causes it to trip out.. hence why it did not trip until the excessive voltage had caused equipment to fail and thus induce an earth fault.

EDF are looking into the Liability of this now.. failing them ill be onto my house insurers.

True true, but then it depends if they have RCD's, if not than a MCB or fuse wouldnt!

Either that or Harmonics, but I dont claim to know that much about harmonics far as im concerned electricity is white mans witch craft!

I have MCB's on a rcd board... and that's all i know...

bottom line is about 3k's worth of kit is fooked..

[Ruffy]

Originally Posted by 454697819

not quite, the RCD measures earth and neutral current, a sudden change TO earth causes it to trip out.. hence why it did not trip until the excessive voltage had caused equipment to fail and thus induce an earth fault.

Strictly speaking, an RCD measures the difference between phase (live) and neutral current. Any significant difference in that current balance causes it to trip. There's no actual connection to, or monitoring of, earth current.

Your problem sounds like it was a voltage issue. An internal winding fault, for example, on the distribution transformer could cause the whole mains voltage to jump up dramatically, basically frazzling things that don't have sufficient insulation for the higher voltage.

(Others' recommendations to use surge protected sockets, especially on electronic items, is probably sensible. I use 'em myself. Flicker is a growing problem in electricity supply. Sorry this advice comes too late for you this time.)

[Ruffy]

Originally Posted by alexh

But still 710w @ 230v would draw a current of 3.08 amps, take in to account a P.F of 0.75 the current would not exceed 4.1 amps, so one would think a 5 amp fuse should be suitable?

For continuous current, yes. However, short term start up currents can be much higher and many fuses can't cope with that.

Overcurrent protection devices, i.e. MCBs and fuses actually have current/time characteristics, not absolute current limits, so selecting the correct device can be more complicated than it first appears.

Originally Posted by Ruffy

For continuous current, yes. However, short term start up currents can be much higher and many fuses can't cope with that.

Overcurrent protection devices, i.e. MCBs and fuses actually have current/time characteristics, not absolute current limits, so selecting the correct device can be more complicated than it first appears.

Yep true true, But like you said they have the ability to cope with start up currents.

The logic fits with say a 3 phase 6kW pump but its a drill, It'll be fine!!!

It still sounds like a major imbalance over the phases causes the neutral to become live, I've never heard of an over voltage in the domestic world, could you imagine the implications of a high line pressure? It would never happen otherwise EDF would be in court over corporate manslaughter as people would get frazzled (not just xbox's!).

Im going back to sleep!

If a transformer faults then your knackered but it shouldn't really with all the thermography and testing done on them at all.

If you've got a surge then an RCD should save everything but a breaker you got no chance by the time one trips even more so if you got a 32A breaker for a ring main and only a few little 100w items plugged in .

And the fuse thing is a joke because for example a 5ft single flourescent fitting is 58w which comes down to 0.25A which with a 3A fuse is no protection.

This pushes why people should have 16A breakers on their ring mains and a seperate circuit for anything big such as a washing machine etc . .

EDF will compensate you so don't worry. This is one of them once in a lifetime things as i doubt you will be the only one who got goosed equipment from a transformer.