#302985 - 11/10/2007 21:28
Re: What good is a polarized AC plug?
[Re: AndrewT]
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carpal tunnel
Registered: 24/12/2001
Posts: 5528
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Quote:
Ah, right. He was talking about the figure of 8 "radio cassette" leads. No matter what mains connector you fit at the plug end, they are reversible at the appliance end.
Those devices are double insulated so you should never able to touch anything which is live.
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#302986 - 11/10/2007 21:38
Re: What good is a polarized AC plug?
[Re: tman]
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carpal tunnel
Registered: 20/12/1999
Posts: 31597
Loc: Seattle, WA
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Okay, that all makes perfect sense. Thanks, everyone!
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#302987 - 12/10/2007 00:01
Re: What good is a polarized AC plug?
[Re: tfabris]
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addict
Registered: 02/04/2002
Posts: 691
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We purchased a building about a year ago, which has a 120/220 single phase circuit, plus an additional 480v 3 phase delta circuit. After gutting all the unneeded stuff an rewiring everything to get a 480v 3 phase Y circuit, we noticed the old delta circuit had a hot ground to our water pipes. So you could literally stick the voltmeter into the ground and the other to any copper pipe in the building, and get a 120v circuit. Needless to say, we called and had the delta disabled that day 
_________________________
Oliver
mk1 30gb: 129 | mk2a 30gb: 040104126
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#302988 - 12/10/2007 07:45
Re: What good is a polarized AC plug?
[Re: mlord]
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addict
Registered: 11/01/2002
Posts: 612
Loc: Reading, UK
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#302989 - 12/10/2007 07:53
Re: What good is a polarized AC plug?
[Re: mlord]
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carpal tunnel
Registered: 18/01/2000
Posts: 5683
Loc: London, UK
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Quote:
it ensures that the outside screw conductor of a standard light bulb socket will not be connected to the hot voltage wire.
Ah, see, there's another cultural difference. In the UK, our light fittings/ceiling roses/etc. tend to be bayonet-fit, which means they have both conductors on pins inside the fitting.
Even the screw fit ones tend to have a plastic shell on the outside, so you have to put your finger in the fitting.
_________________________
-- roger
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#302990 - 12/10/2007 08:25
Re: What good is a polarized AC plug?
[Re: LittleBlueThing]
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carpal tunnel
Registered: 24/12/2001
Posts: 5528
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Quote:
I must admit we have a lot more respect for the mains over here in the UK - I don't know anyone who would *dream* of doing what Tony did to a plug. Maybe the added lethality/pain of the 240V instils more caution?
You'd have to be really determined to do that to a UK mains caltrop (Natural state of a UK mains plug in the dark and when you're barefoot is to be upside down. Closely followed by a 1x1 Lego brick for pain)
Not sure why but people just don't mess around with the mains like that in the UK. You wire the plug/socket exactly how they tell you to.
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#302991 - 12/10/2007 10:04
Re: What good is a polarized AC plug?
[Re: Roger]
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carpal tunnel
Registered: 29/08/2000
Posts: 14493
Loc: Canada
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Quote:
Even the screw fit ones tend to have a plastic shell on the outside, so you have to put your finger in the fitting.
It's rather easy to brush against the outside conductor of a partially unscrewed bulb (not the socket, but the bulb itself) while the bulb is still in contact with the ground lead of the socket. Thus the concern.
Cheers
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#302992 - 12/10/2007 10:12
Re: What good is a polarized AC plug?
[Re: LittleBlueThing]
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carpal tunnel
Registered: 29/08/2000
Posts: 14493
Loc: Canada
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Quote:
Quote:
With a newer home, probably nothing will happen.. can you guess why?
And for a really new home (with an RCD) all your lights and computers will go off and you'll have to reset your clocks and....
... Residual Current Devices ...
Exactly. Except that over here, all that's likely to happen is that the outside outlet gets switched off by the device while the rest of the house keeps on ticking.
Most homes here have per-circuit devices (or even just per-outlet) that are required by code in certain rooms (eg. bathroom) and on outside (the building) circuits.
The industry and codebooks call them Ground Fault Circuit Interrupters, but yes they are just a form of Residual Current Device and they work exactly as described by David: they detect differences in downstream current flow between the hot and neutral wires, and trip (open the circuit) when there's a significant (micro amperes) difference.
The cool thing is that no earth ground is actually required, so these devices can be used even in really old homes that don't have the third (earth) wire present at all.
Cheers
-ml
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#302993 - 12/10/2007 10:51
Re: What good is a polarized AC plug?
[Re: mlord]
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carpal tunnel
Registered: 25/12/2000
Posts: 16706
Loc: Raleigh, NC US
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Most homes here have per-circuit devices (or even just per-outlet) that are required by code in certain rooms (eg. bathroom) and on outside (the building) circuits.
Actually, a GFCI outlet will also protect any "downstream" outlet, too. Can be a pain when something trips and you have to wander all over the house trying to find which GFCI needs resetting. Less of a pain than getting electrocuted, though.
_________________________
Bitt Faulk
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#302994 - 12/10/2007 11:54
Re: What good is a polarized AC plug?
[Re: wfaulk]
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carpal tunnel
Registered: 12/11/2001
Posts: 7738
Loc: Toronto, CANADA
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Quote:
Actually, a GFCI outlet will also protect any "downstream" outlet, too. Can be a pain when something trips and you have to wander all over the house trying to find which GFCI needs resetting. Less of a pain than getting electrocuted, though.
Local code dictates what you can downstream from any single GFCI and how everything should be wired together. As an example, Ontario's electrical code has changed in the past few years with respect to kitchen and bathroom wiring, so even a relatively new home of 5 years old doesn't meet current wiring regulations. I'm sure code around the US has likewise changed in the past 5 or 6 years.
This home was built in 1999 and has only two GFCI outlets. One protects all the bathrooms and one protects all the exterior outlets, so it's easy to reset them if the need comes up. New regulations now require one in the kitchen and AFCI outlets are now required for bedrooms. I won't be upgrading the outlets before I sell the house (something I'm starting to try next week).
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(Canada is a strange place...)
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