Ground rods

[Jim Elbrecht]

I'm digging the basement out in my 100yr old house & am at a point that there is no poured floor & think it would be wise to drive some ground rods for my electric service.

The current service is grounded to the city water pipe. [a 1"copper line]

I've been here 20 years and the service is probably 10 yrs older than that. There is no other ground inside or out.

The soil is wet clay - so I don't see any problem in driving a couple

8' rods.

My plan was to drive one directly under the breaker box alongside the footing - and the other 6' away. [would more distance make any difference?]

Questions- Copper is expensive, but we're only talking about

[RBM]

The rods should be a minimum of six feet apart. Acorn connectors work fine. I would leave the conductor connection above the concrete to be sure the connection is in good shape. The size of the conductor between the rods and to the service ground buss depends upon the size of the service, but #4 is suitable for any service up to 200 amp and doesn't need supplemental protection. Leave the existing water pipe ground in place as well

[John Grabowski]

6' apart is the code minimum standard, but 16' or more apart is optimum. It has something to do with the length of the rods.

[HeyBub]

Leave the connection to the pipes. The connection to the pipe is to ground the plumbing, not provide a ground for the electrical system.

[RBM]

This is incorrect. The existing water pipe ground is indeed part of the grounding electrode system, when attached to the first five feet of entrance pipe. You'll find it in NEC 250.50 Grounding Electrode System

[Nate Nagel]

True, but under current code it is not to be relied on as the primary ground, as it apparently is in the OP's house.

nate

RBM wrote:

[hallerb]

while your upgrading grounds add jumper around meter for safetys sake. frequently meters arent good grounds because of rubber washers, and the possiblity a meter might be removed at some point

[RBM]

That N8, is why I said "part" of the grounding electrode system. Supplemental rod(s) are also required

[Tom Horne]

I see that we have another devotee of w-Tom's religion of no watter pipe grounding electrode. For what it is worth I will just paste the applicable code section.

250.50 Grounding Electrode System. If available on the premises at each building or structure served, each item in 250.52(A)(1) through (A)(6) shall be bonded together to form the grounding electrode system. Where none of these electrodes are available, one or more of the electrodes specified in 250.52(A)(4) through (A)(7) shall be installed and used. 250.52 Grounding Electrodes. (A) Electrodes Permitted for Grounding. (1) Metal Underground Water Pipe. A metal underground water pipe in direct contact with the earth for 3.0 m (10 ft) or more (including any metal well casing effectively bonded to the pipe) and electrically continuous (or made electrically continuous by bonding around insulating joints or insulating pipe) to the points of connection of the grounding electrode conductor and the bonding conductors. Interior metal water piping located more than 1.52 m (5 ft) from the point of entrance to the building shall not be used as a part of the grounding electrode system or as a conductor to interconnect electrodes that are part of the grounding electrode system.

Please note the use of the term SHALL. If the "Metal Underground Water Pipe" is "available on the premises" it is one of the electrodes that "shall be bonded together to form the grounding electrode system."

-- Tom Horne

[Steve Barker LT]

Quite the opposite in my local town. They consider the water supply pipe to be a suitable ground as a standalone. (they also require that supply to be metal all the way to the meter)

s

[Steve Barker LT]

That depends on WHAT current code you are referring to. The 2006 IRC does in deed allow the metal underground supply pipe in contact with earth for at least 10 feet to be the sole grounding conductor.

s

[gfretwell]

[gfretwell]

BTW if you do want to take your vapor barrier all the way to the wall, lay it out on the floor part, roll it back around the edge and pour your trench up to the base of the floor dirt level, flip the vapor barrier over the wet concrete and pour the floor.

[bud--]

Apparently a religious cult.

---------------------- You said in a different thread (and different newsgroup) that a "concrete encased electrode" is not identical to a Ufer ground. What are the differences?

== bud--

[gfretwell]

A Yfer is a concrete encased electrode, named after George Ufer who developed the system in WWII to ground ammo dumps in the desert.

[gfretwell]

Sorry for the typo but I had to spell Ufer phonetically in case GW was reading this forum ;-)

[HeyBub]

It's interesting that you place reliance on NEC 250.50 which, to my certain knowledge, has never visited the houses in my neighborhood. All the houses here have PLASTIC pipes from the city system to the houses.

Reliance on such for grounding the electrical system is foolhardy at least and fatal at best.

The pipes IN the house, however, are metal and are connected to the electrical system. It is obvious, therefore, that the purpose in so doing is to ground the pipes, not provide a ground for the electrical system.

A good rule of thumb about NEC is the dictum: "Thou shalt not worship false gods!"

[RBM]

That's fine and well, but the OP's question was regarding a metal water pipe and you answer was completely wrong.

[pawlowsk002]

HB:

Sure it's visited. "If available". Not available, therefore you don't use it, but still must bond the pipes to grounding electrode like any other pipes. No false gods here.

G P

[pawlowsk002]

OP:

Don't forget the meter jumper.

G P