How much ac leakage across a transformer is normal?

[CoolJosh3k]

So I noticed when I hold onto the metal frame of my lamp, whilst I touch the side of my hairy arm against the metal base of my microphone, there is some electrical continuity.

I confirmed it to be my lamp with a multimeter between it's metal frame and my kitchen sink. It shows AC with around 400 to 600 micro amps.

Before I call my lamp faulty and bin it, how much ac should normally appear like this? Is this nothing to worry about at all?

Thanks for any help.

[Jeroen3]

For a real transformer that is too much.
For a switchmode supply that is normal.
Generally below 1 mA is allowed. See local regulations.

[CoolJosh3k]

Ah, thanks. Nothing to worry about then if I ever get tickled like that.

As a follow up question...
Why is it more strict for a normal (linear?) transformer?

[helius]

Switchmode PSUs contain EMI suppression capacitors that couple some of the input AC to the case. When the case is earthed, it travels to earth. When it isn't, you can sometimes feel the current passing through your body. 1 mA is approximately the threshold of sensation—20 mA and above could be dangerous. Some countries place the safety limit at around 400 uA, but the regulations for different types of equipment differ.

[CoolJosh3k]

Where would one find local regulations?
What is the proper way to read the current? I figure chassis to sink is not too typical.

[Gyro]

Where would one find local regulations?

That's where setting your country flag in your profile comes in really handy. 

If you're in a country that requires proper grounding of all plumbed fitting then chassis to sink, radiator etc is really quite appropriate.


P.S. If doing this sort of test, then it's a good idea to be cautious and insert some sort of safety series resistor in series with your meter, untill you've established that it is just leakage current and not a situation where the chassis really is Live. It might save you a meter fuse, nasty flash, or much worse (depending on the quality of the meter).

[Zero999]

Ah, thanks. Nothing to worry about then if I ever get tickled like that.

As a follow up question...
Why is it more strict for a normal (linear?) transformer?

It isn't more strict for a real transformer. It's just switched mode power supplies tend to be more leaky because of the Y capacitor.

[CoolJosh3k]

I have updated my profile.