Electric shock/static... in bed?!

[Lobster]

This is just too weird...

Had just climbed into bed with the missus last night, when she touched me on the arm and said 'Oh that's really odd, I'm getting a tingly feeling off you'.

Well I can recognise a green light when I see one on a Saturday night; but no - it wasn't that. It seems she was getting a very slight shock off me; but each time she touched me, it didn't discharge once and go away, like it does when you get out of a car on a dry day.

We were puzzling over this and she asks 'Is the electric blanket still on?' Don't be daft, I said, there's a dry blanket and sheet in between us and it, it couldn't possibly be that.

However, it turned out she was right (it's on a time-switch which cuts out at around the time we go to bed). To humour her, I leant out and switched it off, and apparently the tingling effect stopped immediately; and returned as soon as I switched the blanket on again.

Needless to say the blanket is now unplugged pending further investigation (it's certainly a pretty old one, but doesn't look in particularly bad shape and certainly works OK). However, can anyone offer a plausible explanation as to what on earth was going on?

Thanks David

[mark]

Do you still have those black nylon sheets?

mark

[Dave Liquorice]

Dump that blanket now, don't even think about trying to fix it. They don't last for ever. Just be thankful you have had a warning.

[Lobster]

Not disagreeing with that advice at all as it's the same conclusion we'd come to: but still can't figure out what mechanism could possibly be involved.

David

[Lobster]

Mm, nice.... no, just bog-standard polyester cotton mix ones. Sort of deep red / maroon in colour, if that helps...

David

[Owain]

Was Mrs Lobster a wee bit damp after her shower? ;-)

Fairly obviously the blanket is leaking voltage. If you imagine the blanket as a long continuous resistance from 240V at one end to 0V at t'other, if Mrs L is lying near one end at about say 50V and you are lying near the other end at say 200V then there is 150V between you and that would be enough to give a tingle from flesh to flesh, but not enough to leak to earth through bedding, mattress etc.

If on the other hand you at 200V reached out and touched something earthy then rather more current would flow and Bad Things would happen.

You could maybe cut the heating element out of the blanket, thread it through some heat-shrink tube and heatshrink it down, then wrap it round a barrel for fermenting home-brew, but I wouldn't recommend sleeping on it again.

Fire brigades or trading standards sometimes offer free blanket safety check.

[Lobster]

Partly because her towel rail isn't working yet, she was unshowered and bone dry (by the time things got a bit moist a little later the blanket was certainly switched off!)

The blanket actually has two separate elements, one either side (hers would have been switched off at the time). So are you saying that current is effectively leaking through the intervening blanket and sheet?!

Off shopping for a new blanket...

David

[gazz]

"Lobster" wrote

[Usenet Nutter]

And make sure when you throw the old one out that it is ripped up and unuseable in case anyone takes a shine to it ...

[Owain]

Even if her element was switched off, it's probably only a single-pole switch on the blanket controller so she could still have been connected to the N side

Owain

[ransley]

Insulation has worn off the wire, junk it, they do cause fires when they fail, my neighbor had a fire. Dont bother trying to fix it.

[Lobster]

It's in the wheelie bin. You know, what's particularly scary is that just before we went away on our summer holiday this year, I "borrowed" the plug-in timeswitch from said electric blanket to use it on a lamp, so the house wasn't in darkness every evening we were away.

I'm not saying who it was, but *somebody* plugged the blanket back in directly to the plug socket, with the result that when we got back from our hols we discovered that the bloody thing had been on, full whack, for 24/7 for a fortnight... I'm even more horrified now than I was back then!

David

[geoff]

In message , Lobster writes

So what do you need the electric blanket for

[geoff]

I dunno - some people pay good money for something like that

[Bruce]

I think the technical term is "moist". ;-)

[Andrew Gabriel]

Changing an electric blanket periodically is a good thing to do anyway.

I have a number of aluminium enclosures in the loft holding bits of electronics. They're all mains powered and earthed. A couple of times, I've brushed against one and instantly recognised that live buzzing feeling, and found it's enough to get a dim glow from a neon screwdriver. However, the boxes are all correctly earthed, so it must be me. Look around, and notice I'm kneeling on a row of T&E cables clipped along a plank. Lift myself clear of the cables, and no leakage. There's no fault in the cables, it's just that measurable current can leak and capacitively couple through normal insulation.

A 2kW heater somehow switched itself on when I was in the US for a month. It was on an X10 switch, and I could see from my X10 logging that there was no command sent to it, but it came on anyway somehow. Electricity bill was about £50 more than expected, so it must have cycled on its theromstat a bit, but there was no other heating on in the house (IIRC, it was autumn, but above frost stat setting). Changed the software which drives it to send a gratuitous X10 OFF command once every 24 hours when it's not meant to be on, so that if it happens again, it can't stay on longer than a day.

[Lobster]

Cause and effect - a warm bed definitely helps generate the green light as opposed to "'Kin 'ell, it's cold in here" and "Get your bloody cold feet off me" etc etc...

David

[Bruce]

Too much information. :-(

[Tim W]

If you don't mind the extra expense, you can get low voltage blankets.

[Tim W]

Bruce wibbled on Sunday 29 November 2009 15:47

Wine works too.

Failing that, there's rohypnol...