Ungrounded power cord: Will I die?

.

Just curious about your thoughts,... if the PS uses an IE transformer with an electrostatic shield that is connected to the metal chassis, enclosure, of the PS and the equipment ground contact of the IEC connector. If the ground is floating will that have any effect on the EMI/RFI rejection performance of the PS?

What is an IE transformer?

If the shield is tied to the neutral and the neutral line is tied back to earth ground I'm not sure if the lack of the 3rd line makes a difference, but I don't think all countries use polarized plugs with the neutral tied to earth. Interesting question but I'm not familiar enough with power around the world to answer it.

.

Herman,

Sorry bout that.... I meant EI....

If the shield is tied to the neutral and the neutral line is tied back to earth ground I'm not sure if the lack of the 3rd line makes a difference, but I don't think all countries use polarized plugs with the neutral tied to earth.

And that is why the shield shall never be tied to the neutral conductor. Reversed AC polarity would make the shield and the chassis hot.

The neutral is a current carrying conductor and should never be used as an equipment grounding conductor.

Per NEC code The Neutral conductor shall be connected to earth ground at service entrance and at no point there after.

Interesting question but I'm not familiar enough with power around the world to answer it.

How about just here in the US?
If the shield was connected to the chassis and the ground contact of the IEC and the equipment ground was floating would the PS enclosure act like an antenna?

Also what are the chances the B- of the DC output of the PS is connected to the chassis as well?

.

I understand where you are coming from but don't know enough about the power grid and design to say one way or the other.

I do know that a switching supply that doesn't use a transformer could get hooked up so the hot side of the AC line was connected to the output so I have to believe that type would never be used in a device sold to the public.

The more conventional way is to take the incoming line voltage to drive a circuit which jacks up the frequency much higher so you can then use a much smaller transformer that isolates the line from the load. There is no metal chassis so nothing to isolate.

I don't know enough about how these switching supplies generate RF and interact with the incoming line and how they radiate to comment further.

However, I am interested so if you come up with any more info please share.

.

Total number of people killed from home stereo, TV etc. is about 3 per year.

www.cpsc.gov/library/shock95.pdf

Chance of 1 in 100 million is not big but remember that ones who died had most likely something wrong with the wiring or grounding. What percentage of people have wrong grounding? Most of people buy equipment and don't modify it or use cheater plugs. Let say that one percent has wrong wiring or no grounding. Now your chances of fatal accident got 100 times higher - 1 in a million. Take into account that it is amount per year and we like to be alive for, let say, next 50 years - now your chance is 1 in 20 thousand. It might be still small but you would be ecstatic to play lottery at such odds. Don't play lottery with your life.

I have another problem with this attitude toward safety. I might be ignoring safety here and there, but would never ever tell anybody that it is OK to do so. That would be irresponsible and stupid of me. Would you recommend to your friends modifications to their car braking system claiming that only one car in so many millions have accident from malfunctioning of the brakes? No because it would place them in danger.

As for floating shields - they should be grounded. Non magnetic shield protects from electromagnetic pickup by means of skin effect. It means that current is induced, since non magnetic shield cannot stop it, but travels on the outside - shield because of skin effect. Equivalent field in the center of conductor is zero. Shield has to be grounded for this to work. At lower frequencies skin effect stops working but cable is too short to become effective antenna (below 1/10 of the wavelength).

Switching power supplies generate noise but it is noise at high frequency easier to filter out than 120Hz. For that reason Jeff Rowland uses switching supply in Capri preamp where efficiency is irrelevant. His newest class AB power amp model 625 has 1MHz switcher. It is difficult to say what a switcher is because every linear power supply is switching power supply operating at 120Hz where width of the current spikes is load depended. Properly executed SMPS switches at zero voltage/zero current and can be very quiet but they got bad rap from poorly designed cheap computer supplies. Don't forget that linear supplies are unregulated while SMPS are line and load regulated.
http://jeffrowlandgroup.com/kb/questions.php?questionid=145

.

Let's put this in perspective.............

You are more likely to be struck by lightning than to be killed by a stereo, radio, or television.

I don't think I'll worry about floating my preamp

.