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Proper grounding for 100V adapter
Old 25th December 2019
Gear Head

Proper grounding for 100V adapter

I live in the land of 120V, but have about 10 rack synths/effects that I picked up in Japan. I have a 1500w adapter that feeds all of it. This adapter, pictured below, looks like it has some provisions for grounding the Japanese plugs, but I'm a little unclear on how to use it. The little metal tab can be swung to touch one of the prongs, but that seems a little extreme. Is that really what you do?

Some of the gear is clearly marked as needing a ground, and I'd like to avoid damaging components. (my impression is that the grounding is more about not shocking the user)

I also have a 3-to-2 prong adapter that has a little grounding fork coming out of it, but again, not sure what you are supposed to do with it.

Google isn't being very helpful about it, so I'm hoping some of you might be able. Sorry if it's a little off-topic.
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Proper grounding for 100V adapter-20191224_185303.jpg   Proper grounding for 100V adapter-20191224_185424.jpg  
Old 25th December 2019
Gear Head

I remembered having an outlet tester, so was able to test it out. It seems the pigtail fork needs to touch the metal tab on the adapter. Not sure how that would help 2 prong devices up the chain, but I guess it will do.
Old 25th December 2019
Lives for gear

Two blade plugs are not grounded. If they're polarized (one blade is larger than the other, so they only fit in the socket one way), the wider blade is the neutral and should be at ground potential, but the neutral and ground lines should not be directly tied together in general. If the converter uses an isolated transformer then tying the output neutral to the input neutral, or to ground, would be okay; neutral probably would be the right way to do that. If the converter uses an autotransformer, which I suspect it does, then its output neutral should already be tied to the input neutral directly and so you don't need to do anything more.

The three prong to two prong plus wire adapter is intended for use with wall outlets that lack a grounding prong but are grounded anyhow; the wire is attached under the screw holding the outlet cover plate in place, and connects to ground.

Grounding is primarily for safety. It provides a low-impedance path for any fault current to get back to the source, thus preventing you (a higher impedance) from forming the return path in a fault condition, and getting a shock or worse. It also in the case of a hard short would cause the breaker to trip or the fuse to blow, shutting off the current.
Old 25th December 2019
Gear Head

Wow. Thank you for the explanation.

I have a 3 prong power strip plugged into the 3-to-2, which is then plugged into the adapter. My outlet tester in the power strip shows "faulty ground" unless the fork us touching the metal tab on the adapter. Some of the gear uses a 3 prong IEC connector, so I'm guessing that keeping the power strip grounded is a good idea.

Interesting to know about the fork going under the panel-screw. I grew up over there and never learned about it, even though those adapters are a pretty common sight.
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