When the instructions with the "Household Fire Alarm" panel tell the installer to ground the equipment by connecting ro a water pipe, is it acceptable to go to the nearest water pipe or would he need to go to within 5 feet of where the water pipe enters the building? Assume 10 feet of water pipe in contact with earth. Code reference please.
George this looks like an issue you should take up with U/L or the other listing agency. It is clear the writer of those instructions never saw plastic water pipe. As an inspector I would want to see it bonded to the EGC of the circuit feeding it. As an installer I would bond it to the PVC pipe with weedeater line and a tywrap for a clamp. (after I made the EGC connection in a proper manner) Inspectors need a laugh too.
I'm still waiting for input and I know you guy/girls have an opinion, after all this is a grounding issue. I wrote a violation and didn't quote a solid code reference (bad move) and now I need some input. My violation said "Ground alarm panel". The contractor ran a green #12 THHN to the nearest water pipe. I thought he should go to within 5' of where the water service entered the building but that wording has to do with the GEC.
George, what you describe is all to common, whether the appliance be a Ham radio, an antenna, a satellite dish, cable TV, or the phone box. As I understand it, this grounding is simply there for lightning protection, and not in any way associated with clearing a fault current.
I would think that, were faults an issue, the thing would have a three-prong plug.
Even so, I believe code requires all grounds to be bonded to each other, while being pretty vague as to what this might mean. I've certainly never seen one of these things capable of accepting the #8 wire we're required to use here (for bonding pipes to the ground system). As long as there is continuity between this wire, and the grounding system, I'd say he's met the requirement.
I can't provide a code reference, but as a physicist, I can say that whenever grounding critical electronic equipment, whether it be for an alarm system, a stereo system, or a computer network, there is always a choice of many metallic paths that eventually find a route to the earth. Many of these options may not be good ones for the following reasons.
The primary purpose of grounding in electronics is to avoid having the metal box containg the electronic circuits "float" and thus unable to provide shielding from EMF radiation which generates noise in these circuits.
Since the failure of an alarm control circuit often is more critical than a failure of a computer network circuit, choosing the best route to earth ground is important.
The only way to be confidant that the ground wire from the alarm panel connected to the water pipe stands the test of time, is to bring that ground wire (without splices) directly to within 5 feet of the water entrance, assuming that this same water pipe is buried in the soil outside the building. I personally have more confidence in the ground wire connecting the electrical panel to the copper rod which is driven into the soil, but I think the alarm manufacturer wants to minimize the cost of grounding by allowing a water pipe within the building to be substituted.
The alarm manufacturer is assuming that no segment of the chosen metal water pipe will ever be altered (by introduction of a threaded union with plumber's sealant) or replaced in part by a plastic pipe.
Almost as important, is the problem in electronics due to infamous "ground loops". This is a situation where multiple pieces of electronic equipment which are all interconnected to each other are also individually tied to the electrical ground of the building via different paths.
What happens is that even though each piece of equipment is grounded, the ground wire for each piece of electronic equipment can have a different distance (and possibly a different route) back to the main panel.
The difference in these ground paths causes a small (millivolts) amount of 60 hertz electrical voltage to be picked up within the ground wires which are acting as antennae. All the grounded electrical boxes are pulled to this same voltage(s).
Normally a few millivolts of voltage in ground wires wouldn't bother anybody. But for stereo equipment where the interconnections are often over unbalanced RCA cables and where the audible signals are measured in microvolts, we often hear the background hum in our loadspeakers. When this happens, it is necessary to ensure that only one piece of equipment (usually the receiver) is officially grounded and all the other equipment is "floating" by blocking the ground pin in the 3 pin plugs of all equipment except the audio receiver. Sometimes we even need to "float" the receiver to mimimize the hum.
For TTL and CMOS logic circuits such as used in computer networks or alarm control, the operating voltages are often between 2 and 5 volts DC, so if we have a ground loop generating a few millivolts in the alarm box, the control circuits have adequate immunity and the background hum will not interfere with the circuitry.
However, and this applies for all sensitive electronic equipment that is grounded, if there is a major electrostatic discharge within or nearby the building (lightning, high amperage short circuit, etc), the ground wires will pick up the pulse which in this case may be substantially higher than the few millivolts from ground loops, and there is a risk that our electronics will be fried. The use of varactors (as found in power bars) will provide the "surge protection".
But starting with a robust copper ground wire between the alarm equipment and the point where the water pipe enters the building and keeping this wire as thick as possible and its length as short as possible, will protect the alarm equipment in the best possible way.
As always, the ground connection to the water pipe has to be as professional as the ground connection at the alarm box, that is, solid connectors and no possiblity of corrosion ever reducing the electrical contact.
[This message has been edited by montreal (edited 03-21-2006).]
IMO, Fire alarm systems are required to be grounded even if there is no sticker in the panel alerting the installer to the requirement. 760.9
Again, IMO, this is not an equipment ground being used to facilitate the operation of an overcurrent device and all thats left for it to be is a grounding electrode conductor and it could connect to any point on the grounding electrode system or to any other grounding electrode conductor. If connected to a metal water line, then 250.52(A)(1) should apply. I think you're on the money for requiring the connection to be in the first 5 feet of pipe.
Few things are harder to put up with than the annoyance of a good example.
Tom is on the right track. A water pipe, more than 5' from the entrance is not a "ground" unless you can demonstrate "... industrial and commercial buildings or structures where conditions of maintenance and supervision ensure that only qualified persons service the installation..." applies.
Connection to the EGC in the circuit would be code conforming. 250.110 250.134 If this is supposed to be a clean ground for the electronics I still get back to the IG principles (insulated conductor, run with circuit conductors and isolated all the way back to the ground electrode connection. I see no way that a terminal, identified as a "ground" can be connected legally to a water pipe more than 5' from the entrance in a dwelling.
This is really a manufacturer's labelling problem. Just because a label says something stupid, does not negate your obligation to insure a code conforming installation.
[This message has been edited by gfretwell (edited 03-21-2006).]
I disagree. The ground that the manufacturer is requiring is not part of the Grounding Electrode System. I would think if the manufacturer ask that the equipment be grounded to a water pipe and they don't specifically say "within 5 ft. of the entrance to the building", then they are just looking for the metal case to be bonded. Doesn't 250.130 (c) (1) and (2) allow a non-grounding receptacle to be replaced or a branch circuit be extended and be grounded to "any accessible point on the Grounding Electrode System or any accessible point on the Grounding Electrode System. It doesn't seem to say within 5 ft. of the entry to the building...or am I reading this wrong?