The receptacle that the disposal is plugged into is fed from the Load side of the GFCI receptacle, thereby providing ground fault protection to the receptacle. There is a ground fault somewhere between the GFCI and the disposal, which is causing the GFCI to do it's job and trip.
You'll have to locate the fault, and fix it. If you don't have (or know how to use) a multimeter, you'll want to contact an Electrician. If you have a multimeter and know how to use it, you can narrow down where the fault is by checking continuity between hot and ground.
Start by turning off the breaker, and insuring power is off in the area you'll be working. Unplug the disposal and do a continuity test between the hot blade (smaller blade) on the plug, and the ground pin (long roundish pin). If the test shows there is not fault in the disposal, move up the circuit to the next device (receptacle) and test again (don't plug the disposal back in). If you still haven't found the fault, continue working your way up the circuit (the switch next) until you reach the GFCI. If you still haven't found the fault, try replacing the GFCI receptacle (making sure to hook it back up the same way).
If you still cannot resolve the issue, it's probably best to call in an Electrician (since they'll have cooler gadgets to troubleshoot the circuit). I would focus most of my attention on the disposal and the switch, since those tend to be the usual culprits.
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
The outlet contacts may be too dirty to carry a heavy load. Or they may be loose. Or the wires to the outlet may be loose either at the outlet or the in the breaker/fuse panel. I would recommend not using this outlet for anything until the point of cause is determined and corrected.