Another grounding question...

Got a 1000 sq ft house that was built before grounding was std (1940s I'm guessing) and according to info I got (via grapevine) if you don't rewire the whole house then just add GFIC to all the outlets to be (relatively) "safe". This has been done.

But a few of the outlets (suspect these were added later but before i bought the house) are actually grounded; someone ran a separate ground wire under the house (on a crawl) and clamped it to the cold water pipe. As far as I knew that was good (can you tell I'm not a pro electrician?).

But last weekend I happened to be in the local technical bookstore with time to kill so I'm looking through the NEC book in the grounding section. I think i read that attaching ground wire to the water pipe is not enough; that you still need a ground rod in addition to the water pipe ground. Is that correct for my situation?

Thanks for your help!

The equipment grounding conductor is useless unless it is properly bonded at the service. Just connecting it to a water pipe and or a ground rod does absolutely nothing.

IN the old days, before plastic water piping, the ground was clamped to the water lines, and the external underground water supply pipe became the ground rod. Now, with plastic water pipes, dielectric unions, and other "breaks" there is no way to insure the integrity and/or continuity of the water lines, so a ground rod is essential. Many of our panel boxes are labled, "Nonmetallic water pipe" so that no one accidentally removes the connection to the ground rod.

Hi,

JW is right the ground wire connected from an outlet to the water pipe does absolutely nothing.

An electrical service to your house should be grounded to a metal water pipe leading out of the house and/or to ground rods. This is done mainly to give lightning someplace to go in the event of a lightning strike.

Electrical outlets have a ground pin. The job of the ground pin, when used with a grounded appliance, is to provide a low resistance path back to the electrical panel to (hopefully) trip the circuit breaker in the event of an electrical fault in an appliance that you are using and prevent you from being electrocuted. The ground pin of an outlet should be connected to (in most cases) the neutral bar in your electrical panel which is the exact same place your neutral wires from your outlets go.

Personally I'd pull out all of the supposed ground wire. Either completely rewire the outlets or don't bother to do it at all. If you feel that its already there and you want to use it you need to connect it to the neutral bar in your panel.

Also you don't need to replace EVERY outlet with a GFCI. Most times outlets are wired one after another on the same circuit. If you can locate the first outlet in the circuit you can just replace that one with a GFCI as those devices have both line and load connections and the remainder of the circuit can just be connected to the load terminals and it will be protected from the first GFCI.

-rick

Thanks to all who replied; very helpful info and also appreciate you reminding me of the obvious (doh!) point that the ground wire needs to be tied to neutral at the panel. Not sure if the ground wire runs back to the panel but will ck asap.

But it also sounds like i read the NEC passage correctly; can't depend on water pipe being a continuous ground rod; though in this case I think it would be since it's copper from under the house to the hook-up at the meter about 60 ft away. Yes? But again, to be safe (and up to code) would be best to add a ground rod too.

Also I did know about needing only one GFCI per circuit, so i got that going for me...

The eight grounding electrodes outlined in 250.52 if present on a site must be bonded together to make one grounding electrode system as outlined in 250.50.
The sole purpose of this grounding electrode system is outlined in 250.4(A)(1) and states the following reasons;
“shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.”
This is the reason for connecting our system to earth.

We are also required to bond the grounding electrode to the service enclosure, equipment grounding conductors, and neutral in the service disconnect. This bonding in the service equipment creates a path from the fault to the equipment grounding conductor back to that gray thing hanging on the pole outside our home or to the big green box sitting on the ground somewhere close by. Through this path high amounts of current is allowed to flow without much resistance which will cause the breaker to trip or the fuse to blow.

To figure the amount of current that flows in a circuit we simply divide the amount of resistance into the voltage applied. Using the requirement found in 250.56 of 25 ohms and the voltage found in our homes we can ascertain the amount of current that would flow should we take a conductor straight from the panel to a driven rod in our yard. 120/25=4.8 amps. This would not trip or blow a 15 amp overcurrent device.

By bonding to the neutral in the service equipment we create a low impedance (resistance) path for the fault current to travel on in order to open the overcurrent device.
Let’s use the following for the purpose of this illustration.
The resistance in this path includes
100’ - #2 AL OH Distribution .032
25’ - #4 AL Service Drop .013
25’ - #2 CU Service Entrance .005
100’ - #14 CU Branch Circuit .307
Resistance to the point of fault .357 ohms
This gets us from the transformer to the point of fault and then the same amount back to the transformer would equate to a total resistance of .714 ohms.
120/.714= 168 amps which would open the overcurrent device instantly.

As one can clearly see the connection to earth plays absolutely no role in the operation of the overcurrent device but the proper bonding at the service does.

Some devices want a real ground, and a GFCI without an incoming ground won't provide all of the protection you want. They still are good, though. Also note, the GFCI will usually come with some stickers to put on protected receptacles to indicate they are protected by a remote GFCI...use them!

Again thanks guys; especially jw for the in depth explanation.

This thread has quickly become a tutorial on the how and why on grounding in a residence!

You guys rock!