grounding

[Allan Adler]

I have a device that comes with an AC adaptor, with the following description
(whatever it all means):
AC ADAPTOR
CORD CONNECTED CLASS 2 POWER UNITS
MODEL: TEAD-57-122000U
INPUT: 120VAC 60Hz 36W
OUTPUT: 12VDC 2A
UL LISTED 4G38 E159614(T)

Then some diagram and MADE IN CHINA.

To me, it looks like a perfectly ordinary 2-prong adaptor. The instructions
for the device that uses it (a shop machine with motors that run off the
adaptor) say that it is important to ground it and that one needs to purchase
a 3-prong adaptor and shows pictures of how it fits into a 3-prong wall socket.

I've done that in the past when I've connected stuff directly to wall sockets.
There is usually a screw or something that one can use to connect a lead
coming out of the 3-prong adaptor. However, at the moment, I want to
plug it into a power strip and there is nothing to connect the lead
wire to. So I'm not sure what to do.

Normally I wouldn't worry about it. I would just plug the 2 prong adaptor
into the power strip and forget about the third hold. But I'm trying to
do this as carefully as possible, including confronting possibly unnecessary
details that might turn out to matter. So, with apologies in advance for
what is undoubtedly the dumbest question of the new year so far, can someone
please explain how to make sure the thing is properly grounded under these
circumstances?
--
Ignorantly,
Allan Adler <ara@zurich.csail.mit.edu>
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.

 

[Allan Adler]

Let me try to state the problem again a little more simply. I have an
AC adaptor from 120VAC to 12VDC. It has two prongs. The manual says
it has to be properly grounded using a 2-prong to 3-prong adaptor.

I don't think that makes any sense. I just don't see what anything one
does with a 2-prong to 3-prong adaptor has to do with the electrical state
of the AC adaptor or the devices that it powers.

Here is exactly what the manual says: "GROUND THIS PRODUCT: The 12 Volt
Transformer for this product is equipped with a 2-prong Plug and requires
the use of a grounded, 3-Prong Adapter Plug (not included). To comply with
the National Electric Code, and to provide additional protection from the
risk of electrical shock, this product should not only be connected to a
120 Volt, 3-hole electrical outlet that is protected by a Ground Fault
Circuit Interrupter (GFCI). (See Figure A.)".

Figure A shows the 2-prong plug being plugged into a typical 3-prong
adaptor plug which is in turn being plugged into a 120 volt, grounded
electrical outlet.

What does one need the 3-prong adaptor for? A 2-prong plug will plug
into a 3-prong hole and the 3-prong adaptor seems to have nothing to
do with what is happening electrically with the transformer?

If they had sent me a device with a 3-prong plug and I only had a 2-prong
hole in the wall socket, then some kind of adaptor that let me plug a
3-prong plug into the wall socket and included a way to ground it might
make sense.
--
Ignorantly,
Allan Adler <ara@zurich.csail.mit.edu>
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.