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1) Yes, if the H20 heater tank is a gas type with black gas metal pipe supply and the plumbing supply pipes are metal (typically copper), all (3) three metal; pipes (hot, cold & gas) are required to be bonded together at the hot water heater with (1) one contiguous copper Grounding Electrode Conductor (GEC) using 3 separate ground clamps.
2) Yes, this is required in the National Electrical Code under Article 250.104 Bonding of Piping Systems and Exposed Structural Steel.
3) The GEC bonding jumper at the hot water heater is sized according to the main service amps. If the service to the home is 100 amps, then an 8 AWG Copper wire is used. If the service to the home is a 200 amp, then a 4 AWG Copper wire is used.
4) GES = Grounding Electrode System. The GES is the grounding system in a building for exterior ground rods, bonding at the hot water heater and bonding a ground at the cold metal pipe water supply to the street side of the water meter (if metal piping) and then jumpered back across the meter. The conductors that are connected to the ground rod, neutral bus bar, hot water heater metal piping and cold water city supply metal piping are all called Grounding Electrode Conductors.
5) The above grounding requirements have existed within the National Electrical Code for many years. Although keep in mind, that your local electrical codes can always over ride the NEC and the water heater bonding may not have been a local electrical code requirement in your municipality at the time of construction.
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