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Thursday, February 6, 2003
Question:
The 1999 NEC Sec 680-73 requires a No. 8 jumper to bond the hydro-massage tub metal motor casing to the tub's metal piping system. Can you explain why such a large jumper is required on a GFI protected 20-amp circuit?
Typically the motor is connected to the tub by plastic pipe. I have been requiring that the motor's metal casing be bonded to the grounding conductor that is run with the tub's 20 amp GFI circuit. Finally the dwelling's interior piping system is already bonded at the water heater.
Thank you for the daily education on electrical code.
Steve
A
Answer:
Thank you for your nice comment Steve. First of all there is a new Section 680.70 General in the 2002 Code. All of the original 1999 sections have been pushed forward one number. The 1999 Section 680-73 is now 680.74 in the 2002 NEC. The new section is titled General and says “Hydromassage bathtubs as defined in 680.2 shall comply with Part VII of this article. They shall not be required to comply with other parts of this article.”
The purpose of 680.74 is to eliminate voltage gradients in the hydro-massage tub area. The bonding together of all the metal piping systems and metal parts of electrical equipment and motors will eliminate any difference of potential between metal parts. The 8 AWG bonding conductor is required to have a strong, stable bonding connection, not to carry heavy currents.
Connecting the motor to the 12 AWG equipment-grounding conductor run with the circuit conductors is proper and this establishes a ground-fault return path from all the metal parts to the panel serving the hydro-massage tub.
It’s true the metal water piping may already be bonded at the water heater but the continuity of this metal piping is questionable and bonding to eliminate voltage gradients is the safe route to take.
v