Grounding cast iron water pipes

[bunuelbresson]

Do you usually ground Cast Iron water pipes? We have had a debate about this. My opinion is that as long as it's an electric conductor then you ground it. However I cannot find any conductivity table for cast iron.

 

[jumper]

If it qualifies as an electrode you would have to use it and size your GEC according to 250.66.
The conductivity of the pipe does not really matter as a water pipe electrode needs additional electrodes installed to augment it.

If it does not qualify as an electrode just bond it with a jumper sized to 250.102.

 

[iwire]

Do you usually ground Cast Iron water pipes? We have had a debate about this. My opinion is that as long as it's an electric conductor then you ground it. However I cannot find any conductivity table for cast iron.

Metal water piping systems are required to be bonded. The conductivity has nothing to do with it.

 

[tom baker]

Is the cast iron a driain-waste-vent as in sewer line? I suppose you can call it a water line, but typically we bond metal water supply lines. Galv and copper have good conductivity due to threaded or soldered joints. Cast iron uses leaded spigot joints, or in newer systems no hub couplings, which are a rubber band with a ss clamp over it.
IMO, the cast iron is not a continuous metal water system, and does not have to be bonded. There are some drain systems that are gavl with threaded Ts, Ys etc...

 

[infinity]

Cast iron sewer pipes do not require bonding. I've never seen cast iron water pipes although we still have plenty of old galvanized water pipes around here.

 

[kwired]

Cast iron sewer pipes do not require bonding. I've never seen cast iron water pipes although we still have plenty of old galvanized water pipes around here.

Aren't they at least "other metal piping"?

I have applied bonding jumpers from water pipe to drain pipes before in cases where there was a elevated grounded conductor voltage - likely just voltage drop but could have even come from POCO MGN. Water pipes were bonded to electrical system and operating at this same potential but because drain pipe in bathtub was not bonded it was at ground potential since it eventually ran into the ground, so users would experience a small voltage between supply piping and drain - the drain was continuous with water as well as the cast iron tub, so just being in the tub and touching the faucet gave you a tingle.

Bonding jumper between water supply and drain pipes eliminated the potential difference.

 

[infinity]

Aren't they at least "other metal piping"?

I have applied bonding jumpers from water pipe to drain pipes before in cases where there was a elevated grounded conductor voltage - likely just voltage drop but could have even come from POCO MGN. Water pipes were bonded to electrical system and operating at this same potential but because drain pipe in bathtub was not bonded it was at ground potential since it eventually ran into the ground, so users would experience a small voltage between supply piping and drain - the drain was continuous with water as well as the cast iron tub, so just being in the tub and touching the faucet gave you a tingle.

Bonding jumper between water supply and drain pipes eliminated the potential difference.

Not saying it's a bad idea but it's still not required even for a hydromassage tub.

 

[Tony S]

Depending on the manufacturer some ductile iron pipe has galvanic protection. Not sacrificial anodes but a surface coating of zinc that if the coating is damaged self heals by forming a zinc blister.
Bonding the pipe could impede this self healing process or cause problems with other galvanized pipe.

Epoxy coating is also used on some pipe. It will insulate the pipe so making a connection will damage the coating.

It’s Saturday afternoon here so I won’t get an answer from our technical department.

 

[kwired]

Depending on the manufacturer some ductile iron pipe has galvanic protection. Not sacrificial anodes but a surface coating of zinc that if the coating is damaged self heals by forming a zinc blister.
Bonding the pipe could impede this self healing process or cause problems with other galvanized pipe.

Epoxy coating is also used on some pipe. It will insulate the pipe so making a connection will damage the coating.

It’s Saturday afternoon here so I won’t get an answer from our technical department.

How would one prevent inadvertent bonding on such piping? If it attaches to a pump, a water heater, or other electric powered appliances it very well may be bonded through the appliance even if it isn't intended to be. It could also be secured to or just happen to be in contact with a bonded object.

 

[Tony S]

You can’t but I wouldn’t recommend deliberately damaging the coating to create a bond connection. Modern DI (ductile iron) pipes use a rubber sealing gasket so you would only bond 18Ft of pipe at best.

It took many years for the old GI (grey iron) pipes to rust, the bonding connection is likely to drop off first. These pipes used lead in various forms as the seal.

GI has a life span of 100+ years if undisturbed/undamaged.
DI is a bit of an unknown, it hasn’t been in general use for that long. With modern coatings, how long is a piece of string?