Note that if you can't put in a grounded outlet, a gfci outlet is an acceptable alternative for safety. I've done that at several places in my old house. When installing without a ground, there's a sticker that should be applied essentially saying "yes, we know there's no ground, don't panic if the tester tells you so but also don't expect to use anything plugged in here as a ground."
It is not controlled by a switch and I didn’t break any tabs.
What could make this happen?
- Debris inside the socket of the ground conductor
- A defectively manufactured outlet
Is it safe to use the outlet or just the bottom of the duplex?
Safety is a relative thing.
If you use the ungrounded top outlet it will be as safe as older houses that were built before grounding was a thing, and were considered safe in their time. It will also make no difference for two prong appliances.
If you crazyglue an outlet protector over the top outlet to prevent use of the top outlet, then it will be as safe as not using it.
But maybe the DC converter will short to hot and electrify the phone someone is holding up to their head.
I say take it back to the store and report the fault and get an exchange.
You got a product that is less than it should be. Safety or not, you'd return a plasma tv if it had lines down it or only received even channels. Return this outlet too.
Do outlets with USB ports show open grounds?
Only busted ones.
would putting a GFI outlet in that box assure it is grounded?
Nope. GFCIs do not create ground.
Changing the part out (with a gfci, or with any other outlet) would most likely solve the problem though. And in a kid's room, I think a GFCI is worth more than USB outlets if its a kid you want to keep.
Perhaps consider installing one GFCI in the "first" outlet box in that room, or in what ever the next closest junction before the circuit enters that room. Then USB outlets inside the room. In 60 seconds of Googling, I could not find an outlet that had GFCI and USB in one. You could also use a GFCI breaker but those are a pain in the neck.
something I may be missing
The receipt for that usb outlet, and its original packaging? With that, you should be all set. Let the clerk know it is dangerously faulty so they think longer before re-shelving it. If you get another of the same model and it has another fault, then you should tell us what model it is so it can be avoided. Good on you for testing the outlets after installing. I haven't done that on nema 5's in a while....
Best Answer
Stop. Stop worrying about the silly message from a $3 tester.
We call them "Magic 8-ball" testers
Because like the magic 8-ball, whatever answer is stated on the legend is an amusement at best.
The style of these testers is to have 3 lights and a litle "legend" that tries to interpret the lights. Worse, newer testers embed a little computer that changes what the 3 lights mean! On the originals, the lights are semi-useful if you understand what they are indicating and how to interpret half-lit lights. (And your tester is built well enough you don't see bleed-through between lights). The legends were always useless. one is in my toolbox for the lamps.
I don't know if your tester is an "at least the lamps are ok" ones or not. Assuming that it is, and you are getting two yellows and one yellow extinguishes with a big load attached.... But the load works.
It might be exactly what it says on the tin, a weak neutral-ground bond, but with these, it usually isn't.
Start upstream
It sounds like the 5 receptacles are hooked together properly, so I would look upstream (toward supply). Either a sixth outlet* you don't know about, or the panel itself.
To start, run this test on another circuit and see if it also does it. That would make it a full-panel problem and we can just go there.
Then shut off this circuit breaker and scour the house for any outlets* that went dead. Obviously those would be on the same circuit, and their box is worth looking inside for anything out of order.
Next go to the panel and scour the safety Equipment Grounding Conductor system in your panel for anything amiss. Making sure all the grounds are on the ground bar.
If the panel is a main panel: it's the first panel past the meter, neutrals and grounds are spammed onto the same bar. Inelegant but legal because of the next step.
Next, we need to go to the main panel/breaker and look at the Equipotential Bonding System. This is simpler than it sounds: it's a fat wire between neutral and ground bars in the main panel only. This can't be too beefy. Sometimes this is a magic green screw in the neutral bus that screw into panel chassis. I have seen those fail. I prefer a beefy #4 bare wire from neutral bus to ground bus or chassis. When I say One Place I mean the one main panel. Redundancy inside that panel is permitted.
Neutral and ground must not be bonded anywhere else.
Lastly we can declare the grounds "golden" once we look at the Grounding Electrode System - but that isn't involved in this problem.
If you have an older subpanel that only has a 3-wire connection (hot-hot-neutral) then you may see grounds on the neutral bar in that subpanel. That is obsolete and a bit dangerous. You are allowed to retrofit just a ground wire back to the main panel, and separate neutral and ground in that subpanel, as is normal for new work.
Back to the branch circuit
If you found any grounding system defects, that should lick it. If not, we have to go back to the branch and check it through-and-through for defects. I assume you've a) already been doing that, and b) doing it correctly, so at this point the most likely failure point is b). Re-educate on how to do this stuff, and take another look.
* an "outlet" means any point-of-use for electrical power, not just receptacles.