3 phase blunder

[studips]

place i used to work at had a handyman......

need i say more..........

oh, all right then.......

i had a lovely 3 phase supply down in my pump house, but only one of the phases was in use, well, the handyman needed a 240volt supply to his new workshop, so joined onto my board. fair enough.

he came and saw me later that day having blown up a 240volt drill, a power plane and various other sacrificial power tools to ask my opinion.

although i know bugger all about electrics, i was able to inform him that the live neutral and earth he had picked up were (from memory, it was 5 or 6 years ago now) two of my phases from the pump house.......... i think he picked up the red and blue - he might even have mistaken the yellow for an earth come to think of it.............. or the black neutral? anyway. he was quality entertainment (and also the sites health and safety bod).

no wonder he was going through tools so quickly............

 

[wotan]

Proves the old adage....a little knowledge is a dangerous thing..

Wotan

 

[roberta1000]

Not so uncommon as you'd think (or hope!!).

Many years ago when I worked at a semiconductor factory in Glenrothes one of the company electricians managed to wire some single-phase computer-controlled (ie expensive) equipment across a pair of phases. Considerable damage (and a quick walk to the dole office) unsurprisingly!

 

[Nige F]

You think that`s bad I know of a caravan site where the Electricity Board themselves cocked up the phases on a Transformer renewal Blew half the homes on the place ....Luckily didn`t kill a resident ...IF they had - I know who would have blown the whistle on the clowns For weeks after, their vans were scurrying round with new appliances for the residents....I hope loads pulled a fast one and got new for old but working stuff. NOT the first time I`ve seen their antics either. The other one - again a tranny changeover - they had half the street out for days because they thought they could manhandle a tranny into place - a crane and some tracking over a grassed area was too easy

 

[Nitronick]

I recall working in a garage once and the boss (dodgy bloke to say the least) picked up some strip lights and I said I'll fit them for him.

Now hanging them in place as a doddle but the problem come was wiring them up. For some reason there seemed to be more wires then I expected. I now know it was a 3 phase fuse board. Every time I flicked the power on it popped a fuse. Thinking I had wired it wrong I played around with a few wires and amazingly all but one started working so I removed that one and put a new one up, thinking it must of been sort circuited or some thing. Feeling chuffed with my self sat down with a cup off tea to admire the newly illuminated work area.

Now this was in the summer and a few weeks latter we had a spot of rain. Hmm what is that tingling sensation I keep getting when I touch the 4 poster ramp made of metal? Myeah cant be anything serious, bit of static. A day latter it poured with rain and the boss's dog, big German Shepard, came running in total soaked and ran across the ramp letting out an allmighty yelp. Thinking she had hurt her self off I went to the ramp and let out an equaly all mighty yelp. That little tingle was a bit more now.

Got the test light screw driver thing out and touched the ramp and what do you know? Yep it lit up! Seeing as the last electrical work was done by me the boss pulled the fuse to the lights and hey presto the ramp was no longer live.

Still at least the tight git finaly got a sparks in to do the lights correctly to find that I had wired an earth into the neutral side of the lights or something daft like that. I recall the sparks saying "FFS dont let him servoce my van whenit comes in"

Thankfully I am a lot better Mechanic then I am Electrician

 

[Boilerman2]

I had a call -out to a boiler in essex last year, turns out that the Electricity Provider--somthing like EFD? had to do some work on the overheads that fed the area so arranged for a generator to be brought in to supply power, sadly they managed to connect it to the grid accros two phases i.e 415v, blew up our customers boiler, the fridge, microwave computer server and CPU's kettle etc etc whoopsy

 

[ericmark]

For me is started with a radio call with friend saying his wires were melting in spite of switching off the mains supply.

I got there to find the 4mm earth cable between the house and the shed had now melted completely. Taking front off consumer unit and testing the supply the voltage was changing all the time between near 0 and 400v.

I phoned the DNO and said I thought they may have lost their protective multiple earthing to which I was told it was impossible as there are multiple earths not just one.

Minutes latter the power went dead and walking around the streets we found the DNO people working down a hole where some road workers had hit the cable.

The shed was used as a radio shack and the guy had sunk four rods one at each corner of garden and linked them with copper tape to produce an earth for his radio. Then a 16mm cable connected this to an earth bar in the shed which had loads of wing nuts to connect radio earths to. When the electrician had wired the shed he had earthed this bar to the supply earth and because I guess he had plastic cases on the consumer units he had not used the SWA for earth but run a separate 4mm earth cable below it.

After we were told it would never happen again and more earth rods were going to be used by the DNO but we didn't take a chance and connected up the shed with TT supply. That would also stop RF from getting into the mains as easy.

He was only guy in street not to lose a single item as a result of it though. Lucky he was home at the time and able to turn off isolator before earth wire melted. It is about the only TT supply I have know with a ELI good enough not to need a RCD.

 

[plugwash]

Well that earth cable shouldn't have been as small as 4mm. The connection between his radio earth and mains earth was effectively main bonding and should have been treated as such.

What was the Ze of his radio earth?

 

[johnheritage]

You have to mighty darn brave or mighty stupid to start "having a go" with a three phase mains supply; the potential for problems is substantial.

I had the grid engineers around to see about fitting 3 phase to a normal domestic UK house. They wanted a separate box and a fire door between the two. And for them to be far enough apart that someone wouldn't try plugging one supply into the other.

Old floppy disc drive motors have even more phases to keep the disc turning smoothly. Check 'em out if you like phases.