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In Reply to: Hummm - Any isolation solution for LRV connections? posted by juanstein on December 8, 2004 at 15:57:46:
(1) does your receiver uses a 3-wire plug (unlikely)?
(1a: if yes) check the earth connection (likely broken somewhere, given the symptoms) and fix it.(1b: if no) there is an electrical insulation problem between main and the internal boards. It is a fault, which can give a failure someday by a "better" leak path, and may be dangerous to whom would touch ANY piece of connected equipment in case there is no earth connected equipment in your system.
So: get rid of it or have it fixed. Using transformers would work, but it is just like taking analgesics for any pain without doing anything about the cause of the pain.---------------
For technies and electronerds, here is the rationale behind my advice:
(case 1a):
Y-rated capacitors pairs for common mode EMI noise shorting is likely to be used.
They are set between each power wireon one side and the protective earth wire.
Without a solid earth connection, this third wire would settle at about an half of the power mains, that is 60V or 120V depending on the side of the Pond you operate. Happily, the standards set the max value of Y-rated capacitors in such a way that the current though them at the line frequency and admissible peak main voltage, is under 1mA (regular equipment) or 50µA (medical). You can feel 1mA, and get sparks from such a current, but cannot be hurt by it, according to the standards corps.
So, in this case, the advice is obvious.(case 2a)
There is no Y-rated caps between mains and earth, because it is useless, and better, forbidden. EMI protection is only done in differential mode (X-rated capacitor between the 2 main wires), with maybe a common mode inductance to make the common mode noise source imedance higher;and also maybe an Y-rated capacitor (among possible other components, but it's OT) between the chassis and the board ground.
Anyway, for the equipement to be legally sold, the insulation between the mains and the ground shall be EXCELLENT, that is >10GOhms at DC, no breakout at 3750V DC for one minute between both mains wires, connected together, and the chassis, and so on. That's the EU standard, but the US requirement should not be that very different. Anyway, with such an insulation, you just plain cannot get any spark or feel the chassis hot. And don't tell me that, though capacitive coupling, you could get them from the mains at 50/60Hz: you would, but with a capacitive coupling of about 1nF (calculation easy !), which means more than 2 square meters of parallel surfaces at 8mm apart (8mm is the standard-required spacing between main connected parts and chassis-connected parts). Little bit large for a poor receiver ;-) So, the leak comes from an insulation fault (likely initiated by a nearby lighning-induced transient if you get no transient protection on your main supply: it's the most common cause). Just has to be fixed before getting worse, if it does.
An subsidiary advice is (1) to use some Class A 5mA circuit breaker . Read the link about it (an example). I would even say use one in your audio power distribution panel, one in your kitchen, one in the bathroom. I don't know whether it's mandatory in the US, here it is.
(2) use a primary lightning protection at the head of your mains (rail mounted on the panel -ask an electrician-), and a secondary protection near your sensitive equipement (for example a protected distribution panel for computer equipment, in any good shop), provided they are not closer than 5m.
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Follow Ups
- Re: Hummm - Any isolation solution for LRV connections? - Jacques 09:34:37 12/10/04 (1)
- Thanks! - juanstein 11:08:27 12/11/04 (0)
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