Interestingly, they don't seem to be common in the US.

In the USA we have a similar device know as a GFCI , Ground Fault Circuit Interrupter ;  mandated by the National Electrical Code
You can buy  a portable  non  hardwired plugable unit and put it your gig bag.
http://www.ecmag.com/?fa=article&articleID=6133
 
(Message edited by sonicus on September 25, 2009)

I visited the web site of a major hardware store chain here in the US and could not find a portable non hardwired plugable unit; that's why I suggested that they don't seem to be common.  However, visiting just one site is not a thorough search, so it may indeed be the case that I am wrong in my assumption.

Try a search for inline GFCI and you should find sources.

That's it   Imiwa  you got it ______        'inline GFCI    
 
 Dave, I should have used the correct terminology in my post #405
 
I just check and they are in abundance under the search words that  
Imiwa suggested.
 
(Message edited by sonicus on September 25, 2009)

Thanks Loch; I did indeed!

Thanks Wolf; I just spent a half hour looking at these things and now know a lot more than I did.

Is it because in the USA you only get 55V out of each pin so less likley to get electrocuted??
As you know the live wire(brown coloured)on the cable in the UK has a lovely defibrillating 240V at 50Hz emitting from it!!!

In the USA  110  VOLTS  AC 60HZ   ;    Black=HOT
                                                         White= NEUTRAL
                                                         GREEN= GROUND

In the USA 110 volts  15 or 20 amps  AC 6Ohz  HURTS!!!!!
 
REMEMBER If your source of power can yield a HIGH AMPERE use it is really bad .      I used to get ZAPPED from  high voltage 'FLY BACK transformers when working working on live CRT displays @ 30 ,000 volts but at low amps . Once I really got A really BAD ZAP from a NEON SIGN transformer at 20,000 volts and that completely knocked the wind out of my sails , I felt my eye balls  projecting forward. That was at more amps then the fly back transformer incidents. What more can I say but I was lucky that i did not fry my self during one of my tinkering experiments 30 years ago.! All of these high voltages that I was working with were all at milliamps  . I would would venture to speculate that if the  amperage ratings were higher on those devices that I would not be writing this now .  
 
(Message edited by sonicus on September 27, 2009)