I have a 50 amp subpanel in my barn. It appears the grounds and neutrals are on the same bus. My understanding is this was acceptable on a 3-wire subpanel until around 2008, when code changed to require a 4-wire.
Question is, what's involved to repair/upgrade? Separating them, and running a separate ground all the way to the main/service panel? Can i leave it as is? Can i seperate and just install an additional ground at the barn? Original install was probably in the 1990s, before i owned the property.
I have 220v working fine in the barn already. Looking to add a new 220v compressor and want to make sure wiring is in good shape. I'm ok with having an electrician do the work, just hoping to get independent opinion on what's required.
Thank you for any ideas or info.
It should be wired exactly the same as a new service. You have 2 energized conductors and one Grounded Current Carrying Conductor (GCCC), commonly called the neutral conductor even though that is not always true, in the feed line from the Service Equipment's location.
In your feeder supplied panel at the barn you need to connect the 2 energized conductors to the main breaker. If the Building Disconnecting Means enclosure at the barn has no main breaker and contains more than 6 individual breakers you must install a 2 pole breaker with a tie down kit that prevents it from being removed from the busbars without tools. If it were removed while the feeder were energized the breaker's busbar grips would still be energized and exposed to accidental contact. That held in place breaker becomes the Barn's Building Disconnecting Means. The 2 energized conductors are terminated to that breakers terminals were loads are normally connected. That single breaker will cut off all electric power to the barn with a single throw of your hand.
The GCCC (Neutral) connects to the multi terminal busbar that was built into the panel at the factory. That is commonly called the Neutral busbar.
The "Neutral" busbar is bonded to the panel's cabinet in all cases were there is no Equipment Grounding Conductor run with the feeder conductors. Cabinet is the proper name for a panel board's enclosure in sizes of 400 amperes and less.
A grounding electrode array consisting of a minimum of one driven rod with a resistance to earth of 25 OHMS or less or 2 driven rods at least 6 feet apart is built. [Best practice is to separate the rods by twice the length of the longest rod. That would make the separation between 2 rods 8 foot in length 16 feet.] The US NEC only requires 6 feet of separation and no one can make you do more but 2 driven rods only 6 feet apart is some steel pretending to be grounding electrodes. Early on in my career I bought a used 4 pole, fall of potential, Grounding System Impedance Tester. I later bought a used clamp on ground impedance tester. I tested the grounding electrodes I installed as often as I was able sometimes staying an extra 1/2 hour on the site to do so. I only saw the 2 rods at 6 feet apart come under 25 Ohms a couple of times. They were usually above 50 Ohms and sometimes over 100 ohms. I never had a concrete encase electrode come in above 25 ohms. Genuine Ufer Grounds with all of the 1/2 inch steel rods in the footer and floor of a "slab on grade" bottom floor with no insulation nor vapor barrier under the concrete were often so low on the impedance meter that it was difficult to get any impedance reading at all. Sometimes I would put a 25 ohm resister in the current line of the fall of potential ground impedance tester just to be sure that the equipment was working before I was able to believe such low readings.
The other Grounding Electrode that performs rather well is a Ground Ring. That is 20 or more feet of bare #2AWG copper wire encircling the building at a minimum depth of 30 inches. The 20 foot minimum is to deal with pump houses, guard shacks, fueling sheds, and other small foot print buildings that would not achieve adequate performance if the loop were just long enough to tightly circle the building.
The National Institutes of Standards and Technology (NIST) has done extensive work on the effectiveness of various Grounding Electrodes. What they recommend for a fully effective grounding electrode system for a residential building is a 20 foot trench with a depth of 30 inches. 2 rod electrodes are driven through the bottom of the trench at each end and a bare number 2 copper conductor is connected to the furthest rod, the closest rod to the building, and on to the Building Disconnecting Means of the Feeder supplied structure were it is terminated on the neutral busbar. It is not a code requirement in any sense but it nearly always has a low impedance connection to the earth. It is also the easiest effective electrode to install.
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Tom Horne
