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Old 3rd February 2011, 10:48 AM   #11
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Quote:
Originally Posted by AndrewT View Post
Does that equate to polarised plugs and sockets?
One cannot insert the plug top the "wrong" way around.
They are polarized - a 2 prong, double insulated unit will only plug in one way.
Some older equipment still has the non-polarized version of 2 equal width prongs. I can't recall when they changed it, but I do know it was in my lifetime.

3-way-split-receptacle-diagram-left.jpg
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Old 3rd February 2011, 11:01 AM   #12
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MJ: agreed that its not a large transfo but what you need is not necessarily what you want.

AndrewT: The outlet does have a + and - side doesn't it? The white wire to ground shows 0V and the black wire to G shows 110V
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Old 3rd February 2011, 11:04 AM   #13
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MJL: I've also seen a 2 prong outlet. Some older installations had this and this is why I replaced my whole house wiring and outlets. This is why I asked the original question: does it matter if the 3 resistors are tapped to plus or minus?

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Old 3rd February 2011, 11:08 AM   #14
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Why not just read my reply?
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Old 3rd February 2011, 11:16 AM   #15
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MJL: I did read your reply. The resistors should go on the hot wire. But what if there are the 2 prong outlets? Can't be sure unless you test them and then, everytime I change the amp from one outlet to the other, I would need to test to make sure of the correct polarity.
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Old 3rd February 2011, 11:30 AM   #16
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This is getting old already.
You said you have experience and rewired your house - did you install new, polarized receptacles?
What type of power cord are you using? It should be 3 conductor: hot, neutral and ground. This will only go in ONE WAY. If you are using a 2 prong plug (you certainly shouldn't be) then this should be polarized too - one prong is wider!!!! Neutral is wider!
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Old 3rd February 2011, 11:44 AM   #17
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MJL: Yes my house is polarized correctly. Just want to make sure, for instance, I was to rent a chalet up north and the outlets are not polarized. I agree that this is getting old
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Old 3rd February 2011, 12:12 PM   #18
AndrewT is offline AndrewT  Scotland
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Both the Neutral and the Live must be considered as dangerous.
The Live and Neutral inside the amplifier must both be protected from inadvertent interference to the same insulation/isolation standard.
In the UK, we are required to use 2pole mains switches to ensure that both Live and Neutral are switched OFF together. Just to avoid the risk that some eejit has wired up the house wiring incorrectly or another eejit has wired up a rewire-able plug top the wrong way.
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Old 3rd February 2011, 12:16 PM   #19
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I rented a USA house once where the few 3 prong outlets and big blade small blade outlets installed were backwards, with the big blade hot and the small one neutral. This mattered as I was trying to fix a 1975 television, as the entire chassis was hot. Many times 3 prong outlets are installed because that is all they sell, but the walls contain 2 wires. Two prong houses wired should not be "grounded" internally, but let the electric company do it outside at the pole. The big blade is neutral, white, and closer to earth potential than the black. Amateur wired houses from the thirties to fifties often have the black wire as the lower potential side and the lamp base ring, as black is used in automotive electricity (which came to the country first) as the frame or return side. This is incorrect.
Most audio equipment does not tie the chassis to the neutral side, and is "double insulated". Other designs with an exposed metal chassis tie it to the rounded safety ground pin. I find the fear of mains voltage a bit strange, as most of us have rewired lamp switches or appliance cords long before we ever touched a piece of audio gear. Rule 1 is, don't touch the metal with the cord plugged in. Audio devices contain energy storing capacitors, so that brings up rule 2, which is don't touch any metal until you prove it is less than 25 VDC to the chassis or safety ground. And rule zero is "don't work alone".
Three prong outlets and 3 wire Romex were available when My father & I wired a room in 1962, but none of my Dynakit equipment (ST120 designed 1966) nor my Hammond organs (design 1968) had 3 prong plugs. The chassis in this equipment is not tied to either blade of the power plug. However, certain replacement capacitors might have grounded cases, and may inadvertantly tie one side of the DC power to a power blade. This has to be thought out carefully. TV's always had a grounded chassis, and my mother's 1954 philco TV would bite due to the cardboard insulation between the chassis and the steel enclosure, if the humidity was high and the non-polarized plug was in "backward."
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Old 3rd February 2011, 12:23 PM   #20
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Quote:
Originally Posted by indianajo View Post
And rule zero is "don't work alone".
I'd never get a damn thing done, if I lived by this rule.
Fact is, any of our homemade audio equipment should be grounded to safety earth. If the receptacle is wired incorrectly, you should have allowed for that possibility in the build (as Andrew says, double pole switch, insulate both hot and neutral).
Does it make a difference for normal operation if your soft start is on the hot or neutral? No, strictly speaking it does not.
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