[UK-CONTEST] Safe working with HT

[Steve Knowles]

I could not agree more.

As a young man, an unspecified but long time ago, I got across (hand to 
hand) the undischarged capacitor bank of just a 750V PSU.  Even though the 
supply was switched off I was rendered unconscious and blasted across the 
room by the muscular reaction.  My parents heard the crash, investigated and 
called the ambulance and I was hospitalised for two days.  But it was some 
weeks before my nervous system returned to normal and the burns took even 
longer than that to heal properly.  Now I always keep one hand in my pocket 
when working on high-voltage equipment.

Ironically, DC is reckoned to be comparatively safe, even at high voltages, 
because it clamps the heart still and, assuming that insufficient energy is 
delivered to damage the heart muscle, it will restart of its own accord when 
the PD is removed.  AC, on the other hand, can cause ventricular 
fibrillation which is fatal within minutes unless treated with specialist 
equipment.  The best plan, of course, is not to get a shock in the first 
place!

Steve
G3UFY


----- Original Message ----- 
From: "Ken Eastty" <ken.g3lvp at btinternet.com>
To: <uk-contest at contesting.com>
Sent: Thursday, March 18, 2010 10:51 PM
Subject: Re: [UK-CONTEST] Safe working with HT


>> Be very careful, unplug it at the mains and wait till
>> the Hi voltage has dropped to zero on the meter and even then beware as
>> the screen supply might still be dangerous.  If you don't find anything
>> obvious I wouldn't take it any further than this unless you are
>> comfortable working on equipment with high voltages - there's an awful
>> lot of exposed Hi voltage and mains connections inside this amp.
>>
>> 73 John G3UUT
>>
>
> I agree with that but as well as unplugging HT supplies from the mains I
> always use a big  screwdriver (with an insulated handle) to short HT
> leads directly to ground even after allowing time for the C's to
> discharge. If you make a habit of doing this as well as disconnecting
> from the mains it reduces the chances of having an accident but if you
> do get it wrong you'll get one hell of a bang! Also avoid working on HT
> when your tired or distracted.
> The big HF transmitters that I worked on many years ago were all fitted
> with an "Earthing Stick" which we hung on the anode connections before
> venturing any further inside the TX, there was no second chance with
> 10kV supplies!
>
> Be safe,
>
> 73...
>
> Ken
>
> G3LVP
>
>
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