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Original Message

RE: Why would reversing AC leads reduce hum in a component?

Posted by jea48 on February 11, 2017 at 18:20:16:
Ryelands said:
I never suggested such kit came with a 3-wire cord or a "3 wire grounding type plug" (whatever that is).

Really?

Ryelands said:
Can't off-hand comment on old kit or US rules. IIRC, UK regulations have stipulated 3-pin plugs for pretty much everything other than lighting circuits since the 1930s except for what we now call 'double insulated' devices. (What domestic users did was of course a different matter.)

A 3 wire type grounding plug is a plug that has 2 line prongs and a safety equipment ground prong/pin. In the case of a standard NEMA 5-15P 120V 15 amp plug a straight blade for the HOT, a straight blade for the neutral, and a round pin for the safety equipment ground. A wider neutral blade is not needed on a 3 wire plug because the ground prong/pin keys the plug so it will only plug into the mating receptacle in one direction.

Ryelands said:
I wonder if you know what "double insulated" means.

As matter of fact I do. And I also know double insulated power wiring for audio as well as video equipment did not exist in the 1970s, let alone earlier.

Ryelands said:
In fairness, your confusion may have arisen because appliances sold in the UK with two-wire cords do nowadays come with a three-pin plug though the "earth" pin is unconnected and typically plastic. There are valid reasons for that but they are not relevant here; I'd hate to add to your muddle.

LOL, fairness?

I would imagine the dummy ground pin is there so the plug can only be plugged in only in one direction. It's used to maintain plug to receptacle polarity orientation.

In the USA we don't waste the extra money on dummy ground pins. UL, NEMA, NEC, dictates 2 wire plugs must be polarized. They will only plug into a mating polarized receptacle in one direction. The neutral blade is slightly wider than the hot blade. In the USA it is against electrical safety standards as well as codes to install a 3 wire grounding type plug on a 2 wire cord. It's an electrical safety thing.

//

jea48 deleted from post prior to Ryelands response:
The rest of your post was not worth the effect to respond.

Ryelands said:
If, as I assume, you meant "effort", I know how you feel.

No, I doubt if you do.

Hind sites 20/20. I should have left it in the original message.

Best regards.