bonding to a two wire system

Status
Not open for further replies.
R

robm

Member
We are in disagreement about whether a two wire, 120v system is to be bonded from the cold water to the neutral, and a newly driven ground rod. the concern is a parallel path for the neutral carrying the unbalanced load. A clear, thoughtful response would be greatly appreciated.
 
robm said:
We are in disagreement about whether a two wire, 120v system is to be bonded from the cold water to the neutral, and a newly driven ground rod. the concern is a parallel path for the neutral carrying the unbalanced load. A clear, thoughtful response would be greatly appreciated.
Click to expand...

If you only have two wires, how do you get an unbalance? Is this a 2-wire branch fed from a 120/240 3-wire service?
 
let me try to be clearer. An older home with a two wire, 120v, hot and a neutral, changed its plumbing sytem from galvanized to copper pipe. He was then instructed to drive a ground rod, attach a grounding electrode, and bond to the cold water and neutral bar. Is there a potential problem having the water piping bonded directly to the neutral?
 
An old home with a 120 volt service is the exact same as a modern home with a 120/240 service. You're just missing one hot leg. Treat it as a normal service. Bond the neutral bar at the panel, and run your GEC(s) to the panel as normal.

It's only once or twice a year that I still run into 120 volt services. I don't suspect that there are many left.
 
robm said:
. Is there a potential problem having the water piping bonded directly to the neutral?
Click to expand...

No, the NEC has required that for years assuming a metallic water supply and the NEC requires that electrode be backed up with another, typically a ground rod.

Yes, this creates parallel paths on the line side of the service disconnect.
 
Yes it should be bonded and ground rod.Its a service the same as any home.The only differance is you have no ground wire on the branch circuits.Most items today do not even have a ground.Its a start in the right direction so bond it and drive 2 rods as per code.
 
Robm, see 250.24(A)(1). It requires the grounding electrode system to be connected to the service neutral.

250.50 requires you to use all the electrodes you have access to.

250.53(D)(2) requires the supplementary grounding electrode (the ground rod) to supplement the water pipe.

250.56 requires that if that ground rod (all by itself, with nothing hooked up yet) measures over 25 ohms to earth when driven, it needs a second (final) ground rod.

Just throwing a couple code references up there to send you around the book a spell. :)
 
Status
Not open for further replies.
Top