250.104 (a)

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stickboy1375

stickboy1375

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Litchfield, CT
Any ideas on why, when bonding a metal water piping system ( not being used as a grounding electrode) I must size the bonding jumper with 250.66, and not let the equipment grounding conductor from the equipment that might actually energize the piping to begin with?
 
Stick, This is from the handbook following 104(A). Maybe it will help.

Bonding the metal water piping system of a building or structure is not the same as using the metal water piping system as a grounding electrode. Bonding to the grounding electrode system places the bonded components at the same voltage level. For example, a current of 2000 amperes across 25 ft of 6 AWG copper conductor produces a voltage differential of approximately 26 volts. Sections 250.104(A)(1) and (A)(3) require the metal water piping system of a building or structure to be bonded to the service equipment or grounding electrode conductor or, where supplied by a feeder or branch circuit, to the building or structure disconnecting means or grounding electrode conductor.
 
RUWired said:
Stick, This is from the handbook following 104(A). Maybe it will help.

Bonding the metal water piping system of a building or structure is not the same as using the metal water piping system as a grounding electrode. Bonding to the grounding electrode system places the bonded components at the same voltage level. For example, a current of 2000 amperes across 25 ft of 6 AWG copper conductor produces a voltage differential of approximately 26 volts. Sections 250.104(A)(1) and (A)(3) require the metal water piping system of a building or structure to be bonded to the service equipment or grounding electrode conductor or, where supplied by a feeder or branch circuit, to the building or structure disconnecting means or grounding electrode conductor.
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So how come on gas or other piping systems I can just use the EGC with the branch circuit that may energize the piping? Whats the difference between one system and another?
 
Because in not my words.......

from the hand book;

Unlike the metal piping systems covered in 250.104(A), this requirement applies only to metal piping systems that are likely to become energized. What this means is that where metal piping systems and electrical circuits interface through mechanical and electrical connections within equipment, a failure of electrical insulation can result in the connected piping system(s) becoming energized. Gas appliances are a common example of metal gas piping and electrical circuits being connected to a common piece of equipment, and in this case the 250.104(B) requirements apply. The required bonding of these other piping systems can occur at the same locations specified in 250.104(A), or an additional provision within this paragraph permits the equipment grounding conductor of the circuit that is likely to energize the piping as the means for bonding the piping. Typically, the use of an additional bonding jumper is not necessary to comply with this requirement, because the equipment grounding connection to the non?current-carrying metal parts of the appliance also provides a bonding connection to the metal piping attached to the appliance. This is a bonding requirement, and the other piping is not being used as an electrode. Therefore, this requirement does not conflict with 250.52(B)(1), which prohibits the use of metal underground gas piping as a grounding electrode for electrical services or other sources of supply. To prevent the underground gas piping from inadvertently becoming a grounding electrode there must be electrical isolation between the portion that is required to be bonded from the underground segment of metal gas piping. This may be inherent at the interface between the gas supplier's equipment and the premises gas piping.
 
RUWired said:
Because in not my words.......
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This is all fine and dandy if you were comparing it to an electrode that was in the ground for 10 feet or more. Sticky is saying the copper water lines are isolated from the ground with plastic piping. The gas pipe is also isolated from the ground thru a dielectric fitting at the meter.
 
Let me start over, In my area where I work, there is no city water, and its plastic pipe out to the well, now lets say the house has 50' of copper water lines for the house, what is the real reasoning for bonding the water pipe with 250.66, when the power supplying the well also hits the pressure switch which bonds the copper pipe.

I guess I just dont understand what the bonding wire 250.66 accomplishes that my egc at the pressure switch does not? :-?
 
stickboy1375 said:
Any ideas on why, when bonding a metal water piping system ( not being used as a grounding electrode) I must size the bonding jumper with 250.66, and not let the equipment grounding conductor from the equipment that might actually energize the piping to begin with?
Click to expand...

If you relied on the ground wire that is likely to energize the metal piping, you might have a hard time clearing a fault from another circuit with a higher ampere rating.Like if you used the # 10 ground for the water heater to bond the water pipe and the sub panel feed hot leg wore through the water line,the 10 guage would not clear the fault.

Rick
 
Dennis Alwon said:
This is all fine and dandy if you were comparing it to an electrode that was in the ground for 10 feet or more. Sticky is saying the copper water lines are isolated from the ground with plastic piping. The gas pipe is also isolated from the ground thru a dielectric fitting at the meter.
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Are you sure about that di-electric fitting Dennis. I had a improperly wired stove a few weeks back that had the gas pipe on both sides of the meter hot.
 
iaov said:
Are you sure about that di-electric fitting Dennis. I had a improperly wired stove a few weeks back that had the gas pipe on both sides of the meter hot.
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Not all utilities have them but many do.
 
RUWired said:
If you relied on the ground wire that is likely to energize the metal piping, you might have a hard time clearing a fault from another circuit with a higher ampere rating.Like if you used the # 10 ground for the water heater to bond the water pipe and the sub panel feed hot leg wore through the water line,the 10 guage would not clear the fault.

Rick
Click to expand...

This is my exact point, why is OTHER piping systems allowed to be bonded through the equipment but not the water piping? What is so special about a water pipe in a house that needs 250.66 sizing?
 
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