The reason is that teh NEC does not trust plumbers.
We don't a copper section of pipe that we are depending upon for our ground to be replaced with a non metallic type. The liklihood of this occuring is lessened by requiring the bond to be closer to the entrance of the building.
I gave "super" jumper cables to a couple of my plumber friends for Christmas. (Cheap guy that I am, 1 set was good for 2 plumbers). They often cut waterlines in older homes (with bonds that were installed before the 5' rule, [we used to bond them to the CW in the water heater closet] and old services were only bonded to cold water) in order to install T fittings or make repairs. When they're under a house (older homes are of a raised wood floor design, with no basement) drenched in water, I just feel better knowing that they won't become a statistic if the house has a bad neutral. The 5' rule increases their safety too...S
[This message has been edited by electure (edited 03-20-2004).]
Here is my understanding: Guys correct me if I am wrong. When the bond is within 5 feet (visible not under the house) This way the chance of the first 5 feet of the pipe being replaced by a plastic is very low AND If That Does Happen then the metal city supply will be long enough for it to have a low resistance or supplement the ground rod.
Hi Edward. I think that for the most part you are correct, but I think that if the copper is replaced with plastic between the earth and your wire's connection to the pipe, there is nothing that would give it the path to earth that is required.
OK.. But he NEC allows that CW bond to be beyond the 5' if they customer is not going to install a transformer and tie GEC to the CW. Case in point, just like an earlier post that bonded the CW within the hot water heater closet. You can still do that in a non-commercial, non-industrial application. I understand the concept of re-piping, I guess that having the first 5' covered is the intent of the code?
I think we are mixing two separate but related code requirements.
First is 250.52(A)(1)
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.
This is not bonding, this is grounding the service to the water main and this must be done within 5' of entrance of the water pipe.
But what if you have a plastic water main and metallic piping inside after the meter.
Now bonding is what we are doing and we follow 250.104(A)
250.104 Bonding of Piping Systems and Exposed Structural Steel. (A) Metal Water Piping. The metal water piping system shall be bonded as required in (1), (2), (3), or (4) of this section. The bonding jumper(s) shall be installed in accordance with 250.64(A), (B), and (E). The points of attachment of the bonding jumper(s) shall be accessible.
It happens that if we ground the service to a metal water main and jump the meter we have also bonded metal water pipes in the building, if jumpers are installed across insulating sections, like the plastic housing of a water filter or maybe the water heater.
Grounding a service to a metal water service must be done in the first five feet.
Bonding metal water pipes can be done anywhere.
Many times both code articles are complied with at the same time.
Clear as Mud?
Bob Badger Construction & Maintenance Electrician Massachusetts
Bob, this has been my take on this subject. In addition, you are correct, bonding and grounding are always confused. Here's another one, based on 250.104, why do electrical inspectors insist on grounding the neutral on a separately derived system to the CW, rather then building, even if building steel is available? Clearly this is a violation.