Steve Smith wrote:
> ICD2's go bang when you get this wrong.
>
> Using an isolated 130v dc with a pair of class y caps (4n7) to earth the
> stored energy in these burst the icd when it was plugged in the wrong order
> the power supply was fully floating. 
>
> The 0v (-ve supply) or the shell of the comms port is connected to earth. In
> my apps it's the battery -ve and is now a copper link around the icd... the
> usb is not isolated from the application.....
>
> Rgds steve 
>
>
>
> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
> Alan B. Pearce
> Sent: 08 June 2007 08:47
> To: Microcontroller discussion list - Public.
> Subject: Re: [PIC] ICD 2 Advisory (Grounding Question)
>
>   
>> I don't understand the need to have the system interface
>> floating when programming a non-isolated AC-powered target
>> device. I assume by "non-isolated," they mean the target
>> device's ground is an earth ground
>>     
>
> By 'non-isolated' I think they mean there is no transformer in the mains 
> supply to the target device, when running off mains power. Personally I 
> would be very worried about doing this as it means all the test equipment is
>
> connected to mains potential, and hence potentially (no pun intended) 
> lethal.
>
> On the other hand they may be talking about the earth, as it could be 
> possible to have an earth loop through the ICD and test equipment back to 
> the mains earth, as well as the earth direct from the target to mains earth.
>
> This could induce significant fault currents around the loop, and may be the
>
> cause of ICD buffers being destroyed (as has been reported here at various 
> times). 
>
>   
You are right. It happens often.

--Bob
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