[mythtv-users] PVR-150 Tuner Quality Issues

[Brian Wood]

On Apr 17, 2006, at 7:16 AM, Steven Adeff wrote:

>
> unless there's a short in your computer your case will never have
> enough voltage to kill someone sitting on it, your powersupply would
> shut off before that happened.


> As well, a single phase AC power system
> does not have a neutral, just two prong power and a possible ground.

Let's not get into a discussion of AC power systems, but here in the  
US a "single-phase", 117 volt outlet normally has three conductors -  
a "hot", a "neutral" and a "ground". A 220-volt outlet has hot-hot- 
ground. The hot and neutral are "polarized" such that the neutral  
slot is a bit larger then the hot one (a polarized plug). Older  
outlets had both slots the same size, so a newer polarized plug will  
not fit into the outlet.

Attempting to defeat the polarized feature, by filing the neutral  
prong or other methods, can result in a chassis being "hot" if a non- 
transformer "hot-chassis" power supply is used, one where the chassis  
is directly connected to one side of the AC line. Some AC/DC type  
radios and TVs used this type of power supply, and I wouldn't put it  
past some cheap (Chinese?) PSUs to do so as well, depending on the  
third-wire ground to trip out the supply if the polarity is wrong.

That is what I was referring to as a possible safety hazard, somebody  
clipping a third-wire ground in an attempt to "float" the chassis,  
and also having a polarity reversal, could in fact be killed if the  
circumstances were right (wrong?). Since I had mentioned the  
possibility of floating grounds I felt bound to put a warning in my  
post.

I most of Europe, with 220-volt systems, there is in fact no neutral.  
That was one of the attractions when the system was re-built after  
WWII, cheaper cost because no neutral conductor was required.