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I am running an amp without PT just to hear how the sound is like. It is risky, so I do not suggest any one else to do it. I used lots of precaution and have been playing with electricity for a long long time since the radio was still tubes.
Anyway, when I connect the amp to the cable tv decoder, the main fuse jump. Eventually I found out that the natural AC line that is connected to my amp chassis caused the fuse to jump when it is in contact to ground.
Can any one explain how the protection circuit work? as measured by my meter, the potential different between the ground and neutral is about 1 volt only.
Anyway, since the short circuit occurred when I connect my media player HDMI to the LED monitor where there were HDMI from the cable TV, my media player can't turned on now...
Follow Ups:
You report that your meter measures only one volt between neutral and ground. When set to DC Volt DMM do not sense AC.
Have you tried AC Volt setting?
Sometimes it happens that supposed neutral wire is really hot just because of human errors in AC line cabling inside the apartment.
Best Regards
Luca
ecc230
If your power source uses a GFI (ground fault interrupter), there may be an explaination. GFIs work by monitoring the difference in current between the 'hot' and 'neutral' wires. They should always be equal an opposite, so that the difference is zero. Should the differance exceed a few mA, it means that some current is bypassing the neural wire; that is, current is flowing from 'hot' to ground. When that happens, the GRFI will 'trip'. By connecting 'neutral' and 'ground' together, you have created a condition where the ground and neutral wires share the load current. This is a very bad idea; the ground wire should never carry current. No equipment should ever tie the 'neutral' wire to chassis ground.
wlee,
The neutral conductor is a "grounded" conductor when properly applied. You may have a neutral conductor where the continuity to the grounding buss is interrupted. Usually, you see this in old installations. I've been "Bit" a few times by house wiring with current carrying Neutrals. Go through all of points of use in the circuit in question and ensure that the neutral flows back to your ground buss with no exceptions. This note assumes that you haven't done something stupid with your "please shock the piss out of me" amp ;> )
Stay Safe please
Stuben
Tks, I was thinking of connecting the neutral to the group except my cable has only 1 side grounded. In any case, my apartment is less then 5 years old, and there is no spark when I short the neutral to ground, except to flip the main fused. I suspect the safety condition is being controlled by micro processor in the fuse box... In any case my media player is no working as well as the HDMI input that the media player plunged into. I will chk with the building manager later..
A ground-fault interruptor will open the line if the same amount of current passing down the hot phase does not appear on the neutral.
So, that's probably what's happening. Somewhere, something is using
the earth ground as neutral in your chassis - so the GFI sees a current imbalance and promptly disconnects both phases to the load. The GF breaker is sensitive down to the single digit milliamp range too, so you might not even be able to "see sparks" by shorting neutral to ground.
So where is you neutral to ground phase leak? Just because a DVM shows
infinite ohms between neutral and earth doesnt mean you're out of the woods. :) A capacitor will gladly shuttle 60Hz AC while "blocking" a DC path. It's probably capacitatively coupled...
-- Jim
hi Jim,
If I connect 0.22 uf between the ground and neutral, it would not prevent ground-fault interruptor as it monitor the different in current between the hot and neautral right?
May be I need to cap couple the cable TV input cable instead!
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