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Old 28th January 2013, 07:43 PM   #33791
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When I teach firearms handling I begin and often repeat Colonel Jeff Cooper's four rules of firearm safety. They're chosen in such a way that if you violate only one and are lucky, nobody gets hurt. If you violate two at the same time, you're a serious risk and need some time for reflection. It's done this way because *everybody* will, at some time, violate one of the rules. We're all human. Electrical safety needs to be treated similarly - if one thing breaks still nobody gets hurt.

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Old 28th January 2013, 07:57 PM   #33792
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> Never seen that.

Right on.........
I'd like to see a comparison of death by electrocution
(2 wire mains vs 3 wire mains)
I'd bet the laws are more brought on by wire sales lobbys
than true safety concerns.
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Old 28th January 2013, 08:12 PM   #33793
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US practice is different from EU practice for AC power. In some countried the power is not connected to ground on either terminal. Others, one end or even a center tap. This can lead to a lot of confusion. I had to deal with these issues with Surge suppressors for EU countries. Each EC country has its own rules, despite harmonization. Similar issues exist around the world. The only countries that duplicate US practice are Canada and Taiwan. The rest of the world is different in significant ways. And with power you can never assume anything.

The actual connection reality needs to be understood or there will be a lot of confusion in understanding the issues and context.
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Old 28th January 2013, 08:16 PM   #33794
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Quote:
Originally Posted by hitsware View Post
I'd bet the laws are more brought on by wire sales lobbys
than true safety concerns.
Each time i was powered off by my GFI (washing machine, toaster or coffee machine), means 1 time a year, i thank the ground wire.
Writing this, i realize it is mostly due to liquids inside electric devices. Or singers tuning their electric lamps from their baths (Claude Francois) :-)

Oh, by the way, US is known as one of the country witch use the most electrical power by citizen: How can they manage such power with 110V only ?
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Last edited by Esperado; 28th January 2013 at 08:20 PM.
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Old 28th January 2013, 08:29 PM   #33795
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Another thing to consider- many products, especially newer ones, will have an AC line filter that will swamp and leakage from the transformer to the chassis. On those products the chassis will be at 1/2 the line voltage is the ground is disconnected (depending on the "match" of the caps). There are UL rules on leakage that limit the size of the caps.

GFCI's can be a good idea but using one for a whole house runs the risk of shutting the house down (darkness) in the middle of the night. I think local GFCI's make more sense.

Grounding is a safety issue, not a noise thing. Depending on a ground from the power network will not help reduce noise. Its not unusual to see 2-3V of noise between ground and neutral in the US and the two wires are large gauge and tied together not too far away (100') from the outlet.

Most of the rules exist because someone wound up dead or a large fire happened. They are not means for greedy companies to sell stuff (we Americans are just too cynical).
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Old 28th January 2013, 08:35 PM   #33796
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Quote:
Originally Posted by Esperado View Post
Each time i was powered off by my GFI (washing machine, toaster or coffee machine), means 1 time a year, i thank the ground wire.
Writing this, i realize it is mostly due to liquids inside electric devices. Or singers tuning their electric lamps from their baths (Claude Francois) :-)

Oh, by the way, US is known as one of the country witch use the most electrical power by citizen: How can they manage such power with 110V only ?
GFCI's work by sensing imbalance in the current going into the load. No ground connection is necessary for them to work.

The US has a huge power infrastructure to support our growing (excessive?) need for power. We pay for it. Some times excessively, remember Enron? California is still paying for that adventure.
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Old 28th January 2013, 08:38 PM   #33797
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I still try to understand the negative consequences of such an inversion, while it it just the primary of the transformer's device, supposed to be isolated from the equipment ground. If the leakage is reduced, the danger too ?
There is no harm if just swapping at the transformer's primary attachment/leads. The leakage comes from EI windings' C to its own core and grounded/mounted directly to chassis... and from transformers field coupling into chassis. Swapping wires causes the C to transformer core to change (often lowered)... depends on winding construction and symmetry. Toroids limit both leakage means as they are easily insulated from the chassis they are mounted to and have low radiated fields. -RNM
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Old 28th January 2013, 08:45 PM   #33798
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Quote:
Originally Posted by Esperado View Post
Each time i was powered off by my GFI (washing machine, toaster or coffee machine), means 1 time a year, i thank the ground wire.
Writing this, i realize it is mostly due to liquids inside electric devices. Or singers tuning their electric lamps from their baths (Claude Francois) :-)

Oh, by the way, US is known as one of the country witch use the most electrical power by citizen: How can they manage such power with 110V only ?
We have an 11kV step down about 30' from the main box. Virtually all homes get 220 in two phases and all very large appliances run directly on it.
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Old 28th January 2013, 09:30 PM   #33799
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GFCI's work by sensing imbalance in the current going into the load. No ground connection is necessary for them to work.
When there is a liquid, by example, making contact between one AC wire and the metallic enclosure of an electric device, connected to a ground wire, the current will flow immediately to the earth and the differential will see the > 30mA imbalance and cut the two ACs. And with a very good efficiency, because the ground wire is low impedance. no need for you to touch anything.

If no ground wire, it is your body that will create the imbalance, while the current flows across the metallic enclosure then your body then the earth of your floor. And you do not like-it.

Thanks Scott and Demian for your explanations.
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Last edited by Esperado; 28th January 2013 at 09:34 PM.
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Old 28th January 2013, 09:48 PM   #33800
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C core are better, because there is no (or very little) capacitance between primary and secondary, so no HF injection from the AC, if the core is not conductive (ceramic), and the HF will be send to the ground of the core are conductive and screwed to the enclosure.
I wonder why they are so rare and expensive.
Toroidal could be very good against HF injection if a shield is between primary and secondary, and primary wound first, but it is not often the case. They present a big contact surface between primary and secondary coils,
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