Shock from plug on hairdryer!

[Reg Hedge]

Hi.

Wife keeps getting a small belt (one only) if she touches the pins of the plug on her hairdryer after using it. I've experienced it too; it's basically nothing painful - a bit like a spark you might get off a wooly jumper as you take it off.

Apologies for being a bit thick, but would this indicate a fault with the appliance? Or the ring main? (or both? or neither?)

Obviously don't want to ignore it if it's a sign of something potentially dangerous.


Thanks in advance

 

[Taylortwocities]

There is usually what is called a capacitor connected across the motor in hairdryers. Its there to stop you geting interference on radios, TVs etc when it is running.
The capacitor charges up a small amount of electricity. If you leave the hairdryer plugged in (with the plug's switch OFF) for a few minutes then the capacitor should discharge.
Either that or keep your fingers away from the mains pins.

Its not a fault with the hairdryer - maybe the shock will recharge her batteries

 

[Space cat]

A capacitor would discharge through the motor as soon as you switched off. A capacitor on the mains side of the switch could hold a charge but that would be an unusual place to put one.

A more likely culprit is a static charge built up on the motor by the airflow. I used to get a similar shock from a vacuum cleaner plug if I pulled it out as soon as I'd stopped using it. When I investigated further, I found a very high value bleed resistor (I think it was 500 megohms) connected between neutral and the motor frame. (This was a Class II hoover.) It's purpose was to bleed off the static down the neutral wire but of course that couldn't happen if the plug was out.

 

[BS3036]

My razor does the same thing. Gives me a shock if I touch the plug pins immediately after unplugging it, even though it's been off all night. Even switched off, it needs to use the mains to charge the batteries, so I've assumed it's the X capacitor which gives the shock.

But for a vaccuum cleaner I would have to agree that you'd usually expect the switch to come first, before the X and or Y capacitors.

 

[briwire]

I had a hair dryer that used to do the same. If the capacitor is connected on the live side of the on/off switch, it would have nowhere to discharge, until someone touches it.

I used to get in the habit of holding the live and neutral pins of the plug against any handy metal after use. It would discharge on it's own after a few minutes.

There's nothing wrong with it.

 

[davelx]

I have food processors and liquidisers that do the same thing. As stated above, there is commonly a supressor connected directly across the incoming mains before the switch, so it cannot discharge through the motor when the switch is off.

I can get quite a decent crack/spark off of one of them by shorting the plug with a spoon!

 

[TicklyT]

I've had similar with a vacuum cleaner. That gave quite a healthy 'belt' off the plug pins when I flipped the switch without the thing been plugged in. The supressor was connected straight across the motor brushes, and should have discharged through the windings.

The trouble was one of the brushes had jammed in it's holder, so there was no discharge path for the supressor.

As already said, a supressor 'upstream' of the on/off switch could produce the same symptoms. Try turning the appliance power switch on after switching off the wall socket.