electrical
I have identified three receptacles in my garage coming from the same circuit breaker. All three boxes have two romex cables entering the boxes. There appear to be no other devices on this breaker.
Why would the last outlet receptacle on this circuit have two cables entering its box if it is the end of the run?
You might be able to get away with mounting an extension to the existing box, then using a box cover with conduit knockout and a cable clamp you could run your cable out the front of the box instead of through the side knockouts.
From your coments it sounds like you wired things correctly , Not sure ablut "voltage drop" meter I always check the ground to neutral vlotage if it is above ~2V most switching supplys will have problems but not usually fry, however if you have 2 seperate circuits could you have ended up with 220 there, I would double check especially your grounds as it sounded like they may be twisted together and not wirenutted, I would also verify white to silver, black to copper and solid grounds, let us know what you find.
Best Answer
Then it's not the last outlet.
An outlet is any point of use, i.e. an overhead light or hardwired exhaust fan. A receptacle is the fancy name for the familiar socket. A receptacle is one type of outlet.
And it's not n cables entering the box. It's 1 cable entering the box and n-1 cables exiting the box to go to downline load(s). n can be 3 or more, by the way.
Every load must attach at a junction box or fixture that must be accessible without disassembling the house in any way (other than the fixture itself, obviously). So there should never be a need to unscrew wood panels, bust up and re-mud drywall, etc. Between accessible points there can only be wires.
So if you take covers off things, and remove lamps etc., you should be able to find it. There are electronic tools which can aid in the search greatly.