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Subject - Bonding Methods
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David Hyatt
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I would like to get some ideas on bonding metal in a residence? Not to be confused with grounding or the grounding electrode system. Just methods of personal saftey. Stuff that is not already grounded.
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Electricman
| I dont know if this answers your question but alot of the single family dwellings that I wire have an on site well so I run a bonding wire to the copper side of the well (incoming supply is almost always pvc) then I will jump a bonder between the hot and cold at the water heater and if there is an LP supply I will bond that from a cold water pipe to the gas line. Additional bonding that I run into alot is at whirlpool tubs where I'll run a bonder from the pump motor to the cold water pipe at the tub. The AHJ that I usually use insists that the gas bond NOT be run back to the service panel.
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wireman
| Pardon my ignorance, I'm still learning. Woludn't a whirlpool pump motor be grounded well enough through the electrical system? Is bonding to a waterpipe just a supplimental ground or is this something else that's required by code?
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David Hyatt
| I think on spas and swimming pool motors the equipment ground is isolated from the motor shell itself. So bonding the shell of the motor and other metal parts back to the grounding electrode system is a big saftey cocern. I used to drive a seperate ground rod at Jacuzzis until I learned this would cause a difference to potential to ground, so now everything goes back to electrode system.
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Electricman
| wireman, bonding and grounding are really two different things. Bonding is defined as, The permanent joining of mettalic parts to form an electrically conductive path that will ensure electrical continuity and the capacity to conduct safely any current likely to be imposed.NEC definition. In a real world senario (David will like this one ) lets say a 20amp 120volt live wire contacts a gas or water pipe that has not been bonded, the pipe will now be energized with 120volts, If there is an insulated joint you will have a poor path to ground. Lets assume a resistance in the pipe of 8ohms, do the math 120 divided by 8 you get 15 amps not enough to open the overcurrent device. If a person touches the pipe and his or her resistance is 12,000 ohms, 120 div by 12,000 equals 0.01 amp you get . With an effective bond the amperage (depending on the conductor size will exceed 30,000 amps enough to open the circuit.Bonding a water pipe is not a supplemental ground, thats what ground rods are for, most AHJs in my area insist upon 2 spaced 6 ft apart. Whirlpool,hydromassage tubs whatever you want to call them must have there motors bonded to the immediate water system ,680.74 NEC,the only way you do not have to bond the motor is when all plumbing is done in cvpvc.
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wireman
| Thank's for clairfying. It makes perfect sense to me now.
I love this website! Finally a place to go for real answers! WM
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