I have a detached garage that the former owner built and wired. He ran 12 gauge (it might be 10) romex 2 conductor + ground through a pvp pipe underground (about 60 feet) to the garage. At the source it's double lugged to a 220 60 amp breaker (servicing the dryer) with the bare ground wire acting as neutral, at the garage it's split (using wire nuts) into two 120 circuits in a junction box at the garage.
I since added a panel at the garage end, back feeding the input line to a 30 amp double pole breaker then distributed to four 120 v garage circuits (2 for outlets and 2 for lights) via 15 amp breakers.
The service (source) end junction box I'm talking about only handles 220. There are six 60 amp breakers in this box, servicing the dryer, a/c, heater, stove, water heater, and the house panel.
In the house the neutral and ground are connected via a metal bar.
When adding the junction box in the garage, as I untangled the 'rats nest' that was his original connections, I saw that he had twisted together all the ground wires from the receptacles and lights but they did not actually connect to anything except each other.
Wanting the ground plug to be connected to a ground, I did some research and found that normally a 4th ground wire would be run from the service panel to the remote building, but I had only three wires, two hot and one neutral. Research revealed that if the remote building had no other metallic connection to the main site, that is no phone, water, cable, nothing, then it was acceptable to drive a ground rod at the remote building and to bind the netural and the ground (assuming local code required ground and netural bond).
My detached garage meets this requirement, so I dorve an 8 foot ground rod and attached it with heavy gauge copper wire to the netural of the incoming feed at the panel in the garage.
Now when I put a 12 amp load on the garage circuit (a window a/c unit + lights) I measure 3 amps at the ground rod.
So 3 amps of the 12 amps (25%) is returning to ground through the ground rod instead of the neutral wire.
My question is this:
Why am I seeing current at the ground rod?
How concerned should I be?
Keep in mind this circuit operation for 15 years with no problems before I installed the panel or the ground rod.
Is the reason because the neutral wire is not of sufficient gauge to carry the current back the 60 feet to the main panel and back to the neutral coming from the electric company?
This made me think further about the ground rod of the house. Forget the garage, in a normal home wiring setup when electric code mandates the ground and neutral be bond at the service panel, I would expect to see current flowing through the ground rod as well. My reasoning is that the current has to return through the neutral (assuming no fault in the circuit) and when it arrives at the service panel it has a choice of returning through the electric company neutral or the ground. Electricity will flow through the path of least resistance, and logically I think the ground rod would offer the least resistance - the wire length is shorter to the ground rod than to the transformer on the pole.
However when I measure the current on the house ground rod it is zero.
Why is this? How is it that all the house current will flow to the pole neutral and none to the ground?
Could someone please educate me on what I am missing here?
I know the ground rod is a safety backup for the electric company neutral, and ideally would not carry any current, but I don't understand why, when they are bound at the service panel, the ground rod would not have at least some current like I'm seeing in my garage setup.