A few grounding and bonding questions

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JFletcher

Senior Member
Location
Williamsburg, VA
Looked at a home yesterday that needs some fairly straightforward work, tho two things came up I'm not entirely familiar with:

#1: There is no ground wire for the cable demarc, which is at the other end of the house (70') from the service and ground rods. Am I interpreting 830.100(A)(4)* exception and 830.100 (B)(3)(1)* correctly in that I can use an insulated ground wire of at least 14ga to bond to the bonded water pipe, which is within 20' of the cable demarc?

#2: There is a 3rd ground rod (first two being at the service) outside of the full bath (~35' away) that has a #6 solid bare copper wire going to a clamp on the hot water pipe to the tub valve. This rod and wire do not go to anything else, and I was told this was installed because a previous owner was getting shocked in the shower. The water pipe is bonded with solid #4 on the feed side of the water heater (cold water line) just a few feet from the panel. Is this okay as-is as a supplementary electrode, or does it have to be bonded to the other 2 rods? Could it be eliminated by supplying a bonding jumper from hot to cold water lines?

#3 There are 4 steel 4sq boxes in the attic which are not bonded, because the original cloth NM has no ground wire. This doesnt sound kosher to me tho I can't find a code reference atm. Is this okay, and, if not, would switching to plastic or fiberglass boxes make it code-compliant?

*2008 NEC code refs
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
Looked at a home yesterday that needs some fairly straightforward work, tho two things came up I'm not entirely familiar with:

#1: There is no ground wire for the cable demarc, which is at the other end of the house (70') from the service and ground rods. Am I interpreting 830.100(A)(4)* exception and 830.100 (B)(3)(1)* correctly in that I can use an insulated ground wire of at least 14ga to bond to the bonded water pipe, which is within 20' of the cable demarc?
I'd go to the service. Water pipes get cut out and replaced with plastic all the time.

#2: There is a 3rd ground rod (first two being at the service) outside of the full bath (~35' away) that has a #6 solid bare copper wire going to a clamp on the hot water pipe to the tub valve. This rod and wire do not go to anything else, and I was told this was installed because a previous owner was getting shocked in the shower. The water pipe is bonded with solid #4 on the feed side of the water heater (cold water line) just a few feet from the panel. Is this okay as-is as a supplementary electrode, or does it have to be bonded to the other 2 rods? Could it be eliminated by supplying a bonding jumper from hot to cold water lines?
If the water pipes are all metal it's already bonded, getting rid of it, jumpering the cold and hot shouldn't matter. More than that though, if it is in the budget I'd do some investigating to see if there is a shock hazard at the shower.

#3 There are 4 steel 4sq boxes in the attic which are not bonded, because the original cloth NM has no ground wire. This doesnt sound kosher to me tho I can't find a code reference atm. Is this okay, and, if not, would switching to plastic or fiberglass boxes make it code-compliant?

*2008 NEC code refs
Steel boxes was all that was ever used with old two wire romex. Personally, any thing added or changed I'd use plastic.
 

drcampbell

Senior Member
Location
The Motor City, Michigan USA
Occupation
Registered Professional Engineer
... If the water pipes are all metal it's already bonded, getting rid of it, jumpering the cold and hot shouldn't matter. ...

Water heaters are often installed with dielectric unions, insulating the hot & cold piping systems from each other. Bonding the hot & cold to each other won't address the root cause of the problem, but it couldn't hurt.

If they are metal pipes and they screw into the same mixing/diverting valve, they're already connected to each other. (but not necessarily to the tub)
 

JFletcher

Senior Member
Location
Williamsburg, VA
I'd go to the service. Water pipes get cut out and replaced with plastic all the time.

True, however going back to the service would mean a ground rod at the cable demarc and a #6 from there to the service; more time and expense. The copper pipes are all intact; there isnt a single piece of PEX in the house, tho it is 60+ years old, and likely just a matter of time...

If the water pipes are all metal it's already bonded, getting rid of it, jumpering the cold and hot shouldn't matter. More than that though, if it is in the budget I'd do some investigating to see if there is a shock hazard at the shower.

Agreed. I'm at a bit of a loss as to how a ground rod would fix a shower that is shocking.

Steel boxes was all that was ever used with old two wire romex. Personally, any thing added or changed I'd use plastic.

I dont know when they were put in, just that they arent original to the house. Like you say tho, every other box is steel, and none of them are bonded.
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Water heaters are often installed with dielectric unions, insulating the hot & cold piping systems from each other. Bonding the hot & cold to each other won't address the root cause of the problem, but it couldn't hurt.

If they are metal pipes and they screw into the same mixing/diverting valve, they're already connected to each other. (but not necessarily to the tub)

I hear it is common practice, but I don't think I have ever seen one.
 

kwired

Electron manager
Location
NE Nebraska
Cable - IMO is cable provider or satellite installer's problem, but it essentially needs to be bonded to the electrical system grounding if anything just to equalize voltage potential that could exist between the two systems.

Getting shocked in the tub? Most of what I have seen troubles with is old plumbing - especially if still using metallic drain piping. The water pipe is often bonded to the electrical system but the drain pipe is not. Voltage drop on the service neutral or even from POCO MGN will put all of your grounded conductors (and equipment grounding conductors) at a little voltage above earth, and if you have metal drain pipe that runs into the ground but is not also bonded to the other systems then you bring true earth potential to the tub drain and have a little voltage to the water pipe that is at service neutral potential. Bonding the metal drain pipe to the water pipes solves this problem.
 

kwired

Electron manager
Location
NE Nebraska
I googled them myself to be sure but I'm fairly certain I have not seen one installed. Then again, CRS is more apparent every day.
I think many misunderstand the real purpose for using them - dissimilar metals that will have galvanic action between them if in contact with one another.

Most the water heaters today come with a short "heat trap" nipple already installed - I think the majority of those are compatible with most any type of metal pipe or fitting you may connect to them, but I think some installers, in places where they have plumbing inspections, or when those plumbers come out to the sticks, they put on a dielectric union anyway because they have always done that. A union may be desirable anyway but may not necessarily need to be a dielectric type.
 
Looked at a home yesterday that needs some fairly straightforward work, tho two things came up I'm not entirely familiar with:

#1: There is no ground wire for the cable demarc, which is at the other end of the house (70') from the service and ground rods. Am I interpreting 830.100(A)(4)* exception and 830.100 (B)(3)(1)* correctly in that I can use an insulated ground wire of at least 14ga to bond to the bonded water pipe, which is within 20' of the cable demarc?

#2: There is a 3rd ground rod (first two being at the service) outside of the full bath (~35' away) that has a #6 solid bare copper wire going to a clamp on the hot water pipe to the tub valve. This rod and wire do not go to anything else, and I was told this was installed because a previous owner was getting shocked in the shower. The water pipe is bonded with solid #4 on the feed side of the water heater (cold water line) just a few feet from the panel. Is this okay as-is as a supplementary electrode, or does it have to be bonded to the other 2 rods? Could it be eliminated by supplying a bonding jumper from hot to cold water lines?

#3 There are 4 steel 4sq boxes in the attic which are not bonded, because the original cloth NM has no ground wire. This doesnt sound kosher to me tho I can't find a code reference atm. Is this okay, and, if not, would switching to plastic or fiberglass boxes make it code-compliant?

*2008 NEC code refs

#1. The cable company violated code. Get them out to fix this -- better to relocate the cable service entrance to near the POCO service and connect to the same ground electrode or panel. A 20ft long 14 ga GEC might have too high impedance to protect lightning current gets through the wall and to someone sits near the cable modem or rebooting the modem.

#2. The installed 3rd ground rod is not a code violation so why spend time and money to rid it?

#3 code violation. What if a hot wire touches the metal box and someone is up there leaning on a vent pipe (earthed or grounded) and touches the box?
 

kwired

Electron manager
Location
NE Nebraska
Most water heaters are ferrous metal and it needs to be isolated from copper pipes. If the pipes are metal then I don't see the need.
Copper is a metal, so are the dielectric unions, what is different is the dielectric unions are a metal that doesn't react with most other metals, not sure exactly what the typically are though.
 
Copper is a metal, so are the dielectric unions, what is different is the dielectric unions are a metal that doesn't react with most other metals, not sure exactly what the typically are though.

No. The dielectric union is not any special material; just a normal galvanized metal like galvanized water pipe, but the union's two halves are electrically isolated by using plastic washers inside. It is used not only at the heater tank, but also whenever connecting copper pipe to galvanized pipe during partial re-piping an old house. This is to prevent fast corrosion when two different metals (copper and iron) are connected. A little half of the metal union connected to copper pipe at the joint causes no concern since it's small mass compare to directly connected to 20ft of galvanized water pipe.
 

iwire

Moderator
Staff member
Location
Massachusetts
No. The dielectric union is not any special material; just a normal galvanized metal like galvanized water pipe, but the union's two halves are electrically isolated by using plastic washers inside. It is used not only at the heater tank, but also whenever connecting copper pipe to galvanized pipe during partial re-piping an old house. This is to prevent fast corrosion when two different metals (copper and iron) are connected. A little half of the metal union connected to copper pipe at the joint causes no concern since it's small mass compare to directly connected to 20ft of galvanized water pipe.

Maybe where you are Brain but not here.
 

kwired

Electron manager
Location
NE Nebraska
No. The dielectric union is not any special material; just a normal galvanized metal like galvanized water pipe, but the union's two halves are electrically isolated by using plastic washers inside. It is used not only at the heater tank, but also whenever connecting copper pipe to galvanized pipe during partial re-piping an old house. This is to prevent fast corrosion when two different metals (copper and iron) are connected. A little half of the metal union connected to copper pipe at the joint causes no concern since it's small mass compare to directly connected to 20ft of galvanized water pipe.

The insulator is there to keep current from flowing in the dis-similar metal joint. I still believe the union is a better alloy intended to increase the life of the connection and won't corrode as fast as a standard union would, that is just my suspicion I have no evidence to back it up with, feel free to present some - for or against what I said.

Galvanizing is primarily zinc. If you have zinc, copper and an electrolyte (water is an electrolyte, how good depends on pH level) all present you have a battery, this alone causes a current to flow and starts to corrode the dis-similar metal joint.
 
I have not found a fancy alloy union yet, but here is one generic unit. It has one brass and one iron ends. I will look at mine to make sure if it has both ends in iron or brass and iron.

water pipe dielectric union:
https://www.zoro.com/value-brand-dielectric-union-34-in-mip-x-solder-147825/i/G0968152/?gdffi=047ada998cf641fa93e55ae8579df863&gdfms=547E647B643F4C469298DC54249C6F43&gclid=Cj0KEQjwo_y4BRD0nMnfoqqnxtEBEiQAWdA128t0_MRrgRw6u2X2IlhHG1BCr4JP1o0decKH-GlKOQ4aAvf68P8HAQ&gclsrc=aw.ds


Body Material: Malleable Iron and Brass

Nothing special about its material. One side brass for copper pipe and other side malleable iron for metal pipe. It’s the plastic washer between that prevents or minimizes the corrosion. If the plastic washer

"The insulator is there to keep current from flowing in the dis-similar metal joint."

Why do we want to stop the current flow in the dis-similar metal joint if it is not for anti corrosion?
 

kwired

Electron manager
Location
NE Nebraska
I have not found a fancy alloy union yet, but here is one generic unit. It has one brass and one iron ends. I will look at mine to make sure if it has both ends in iron or brass and iron.

water pipe dielectric union:
https://www.zoro.com/value-brand-dielectric-union-34-in-mip-x-solder-147825/i/G0968152/?gdffi=047ada998cf641fa93e55ae8579df863&gdfms=547E647B643F4C469298DC54249C6F43&gclid=Cj0KEQjwo_y4BRD0nMnfoqqnxtEBEiQAWdA128t0_MRrgRw6u2X2IlhHG1BCr4JP1o0decKH-GlKOQ4aAvf68P8HAQ&gclsrc=aw.ds


Body Material: Malleable Iron and Brass

Nothing special about its material. One side brass for copper pipe and other side malleable iron for metal pipe. It’s the plastic washer between that prevents or minimizes the corrosion. If the plastic washer

"The insulator is there to keep current from flowing in the dis-similar metal joint."

Why do we want to stop the current flow in the dis-similar metal joint if it is not for anti corrosion?

There are dielectric unions that have same metal on both sides of the union, the purpose of those would definitely be to interrupt electrical continuity. I don't know plumbing codes, but interrupting continuity and separating dissimilar metals provides maximum protection from electrolysis degrading the dissimilar metal junction point.
 
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