Is a neutral back to main feed from satellite circuit box necessary if neutral is bonded to ground remotely?

Question

I have a shed about 300 feet from my house. There is a circuit breaker box with two 20 amp breakers. Each breaker feeds a single 20amp outlet. Each breaker is connected to a #6 stranded wire that go back to a 30 amp breaker in the main panel. There is not a neutral or ground going back to the main panel.

In the box in the shed, the outlet ground and neutral go back to a neutral bus that is bonded to the ground bus. A single #6 solid copper ground wire connects to two eight foot long ground rods (the rods are about 8 inches apart if that matters). This setup was installed by a previous owner and has worked for years to power a light and some tools, and sometimes a space heater. Recently, a friend said I had to run a #6 neutral wire back to the main panel, but could not tell me why it had to be done. I looked in the main panel, and all the neutrals and grounds go to the same buss. This new wire would be pretty expensive and I don't want to do add it if it is not necessary.

Answer 1

It sounds like any current taken by an appliance in the shed is traveling thru the live #6 wire and returns via the soil back to the main box at your home. This is unacceptable in the UK according to wiring regulations.

The reason it would be unsatisfactory is because earth (and earth wires) are reserved for enabling the detection of faults (should one occur). Imagine you have a hand operated drill that developed a live wire fault to the metal on the drill - you'd be electrocuted and there would be nothing to protect you - any current passing through you to earth is undetectable from actual appliance current.

Many, many places insist on RCDs (residual current devices) - these wire in series with live and neutral and any current that does not flow through both live and neutral, generates an imbalance current that can be detected and trip the supply. This usually means you will receive up to 30mA for a few tens of milli seconds maximum - short enough to prevent you frying.

Another problem of not having a neutral and relying on earth return thru soil is that if the soil dries you get no decent connectivity.

If you want to avoid this do some math on what #6 wire can safely withstand and rewire one of the two wires making it a neutral wire.

Answer 2

It really isn't clear from your question whether there is just one strand of AWG6 running between the house and the shed, or two (one for each breaker).

If there are indeed two, then you'd be much better off using one of them for neutral. The resistance of one 300' length of AWG6 is about 0.115 Ω, which is at least an order of magnitude smaller than the resistance of your ground connection. The increased voltage drop on the line connection would be more than made up for by the decreased voltage drop through the ground.

But regardless of whether the second strand already exists, the real issue is a legal one. (I'm assuming you're located in the USA.) Your present setup was legal (allowed by the National Electric Code) at one time, but it no longer is. If you ever want to sell the property, you'll have to bring it up to code (unless the inspector is simply "looking the other way"). So why not do it now, so that you can enjoy the benefits, too?