An electrician looks at a wire's color. Different colors mean different things. For example, in house wiring green is usually ground. In industrial and marine systems, however, colors get tricky. For example, a ship has both AC and DC circuits. In AC, black is "hot". In DC, black is ground. If a marine electrician sees a black wire, it may be either AC hot or DC ground. Tom Baker of The International Municipal Signal Association (IMSA) stated, in a IMSA Journal article of January / February of 2003, that in traffic signal systems, ground can be either white or grey for different systems. He wrote extensively about the problems of color coding, and how the National Electrical Code (NEC) addressed the problem.
An electrician examines the blueprints first, usually found in a central office. He examines the blueprints closely, looking for grounded or ungrounded wires drawn in. He takes note of the color codes drawn in, because of the aforementioned color code problems. Finally, he makes a copy of the blueprints to take along when he is physically looking for the wires at the jobsite. By taking along a copy of the blueprint, he does not have to run back to the office if he has a reference question. Seasoned electricians also carry a walkie-talkie to confer with the electrical engineer or other professionals.
An electrician runs circuit diagnostics to determine if a conductor is grounded or not. After physically finding the wire drawn in on the blueprints, he tests the wire for voltage. He uses a voltmeter to determine if any voltage is present. After testing, he walks along the wire, and traces it back to its source to determine if indeed they are attached to a ground lug or ungrounded. A ground lug is a terminal end, attached to a ground rod. The wire is attached to the ground lug by a bolt. In a large factory, wire runs may be thousands of feet long, so the process of circuit tracing may take considerable time.
Troubleshooting a wire is another aspect of an electrician's work. Theoretically, a grounded conductor should carry no current, except in a momentary short-circuit situation before the breakers trip. If a wire carries zero volts, this does not automatically mean it is grounded. The wire could be broken, and becomes unattached from the ground lug. The attachment bolt on the ground lug may come loose, and the wire falls off the lug. in effect, it is now an ungrounded non-current carrying conductor. This is a dangerous situation, since a short could "blow out" the equipment because a current surge is not diverted to ground. Another reason a wire has no voltage at the time of testing is because it's a control wire. Control wires carry momentary short pulses of electricity, such as to momentarily start and stop a conveyor belt's motor. The voltage pulse may only last a half a second or less. Again, the electrician has to physically trace the wire back to its source to determine if it's supposed to be attached to a ground lug, a computerized controller, or to some other power source.
Another glitch that occurs during the testing phase is the blueprint may specify a ground wire. However, when the electrician physically tests the specified wire, she may discover it has a voltage. This is caused by induced electricity. Faraday's Law states that a magnetic field induces a current in a wire. In a factory, large electrical fields induce a current into the ground wires, This is bad, since the induced current backfeeds into the equipment, causing erratic operation. A seasoned electrician never assumes that just because a wire is carrying a voltage, it is an ungrounded conductor.