DIYbanter - View Single Post - 2-prong outlet, 3-prong power strip

bud--

On 2/10/2021 2:53 PM, wrote:
On Wed, 10 Feb 2021 05:09:35 -0800 (PST), trader_4
wrote:

On Wednesday, February 10, 2021 at 1:58:09 AM UTC-5, Jim Joyce wrote:

Since someone started this thread up again, might as well point out
that if you were to plug a 3 prong surge protector into a two prong ungrounded
receptacle using an adapter, there are a few issues.

First, it's an old system and it's unlikely that a ground is present at the
receptacle box. An adapter is really supposed to be used by using the
wire to ground to the box via the cover screw. But very few are used
that way and even then unless the box is grounded, which is unlikely,
it's useless. So if you did that, the computer and anything else plugged
into the strip would not be grounded.

Next is the issue of what happens to the surge protection. Without
a ground, that path for the surge to dissipate is gone. You would
still have clamping though that would limit the voltages between
the conductors and between the conductors and the strip and
PC ground. So you'd have some protection, but not the best.
A GFCI would provide safety protection from faults that could
be dangerous without a ground, but it won't change the surge protection
issue as there still is no ground.

The only way to be sure about the ground is by using a bug eye tester

Those tester will probably show if the ground is good. But the tester
uses a very small current for the test, and will indicate good if there
is a high resistance in the ground path, like 100 ohms. A ground path
with 100 ohms resistance is useless. A more reliable test would be
connecting a 200W light bulb from hot to ground. I have a tester that
tests with a relatively high current pulses. I think from a previous
thread you have a similar tester.

The testers will also not catch problems that should be very rare, like
if some idiot connects the ground contact to the neutral and an idiot
has reversed hot and neutral. A non-contact voltage tester can be used
to determine if hot is actually hot and neutral and ground are not.

IMHO it is useful to know the limitations of test equipment.

with the adapter bonded to the screw or by visual inspection.
Grounding the boxes predates the universal use of 5-15 receptacles by
at least a decade tho.
My old house was built in 1954 and it had grounded boxes with 1-15
receptacles. That was using the paper covered Romex and the 16ga
grounding conductor. That smaller conductor is probably sufficient for
grounding purposes but in 68 they made it full size for 14ga-10ga
cables.
I am not sure exactly when grounding the boxes showed up in the NEC
but it had to be early 50s, late 40s.
YMMV depending on when your AHJ adopted the code.