bonding/grounding copper pipes

Discussion in 'Electrical Forum discussion & Blog' started by reed50, Nov 18, 2010.

  1. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    MOST of the "smart" people out there with numerous degrees have no common sense indeed. Some that do have no ambition to get dirty.

    Some of the HUGE paying jobs that these guys get with some institution or university have goals or results that are so obtuse and useless that it boggles the mind. Even the titles of their "work" are indecipherable. Our tax dollars at work again.

    I have contacted a few high voltage lines with an excavator, with no ill results except some wild sparks. The window sticker says to stay put and dont move if you cant get off the wire. If for another reason you must evacuate, they say that the longest jump you can manage out the cab is the poor second choice.
  2. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,566
    Location:
    North Carolina
    Nuke man

    You are almost correct and I think you know your mistake.
    There are basically four components to Ohm’ S Law; voltage the force of pressure, current the amount of electrons passing a point, resistance or the opposition to the flow of these electrons (current), and wattage or the amount of work being done, or W=IXE and E=IXR.

    Current or the movement of electrons is what is moving through any conductor be it a wire or a human. Voltage is the pressure that is pushing that current through a conductor be it a wire or a human. The amount of damage done in an electrical shock is the power or wattage produced.

    In order for this current to flow through this conductor be it wire or human three things are required. 1- a power source 2- a path 3- a load. The path can also be the load. We don’t want to be either.

    To the best of my knowledge the lowest voltage that has ever caused death was 50 volts. Using Ohm’s law at this voltage a person would have to have a body resistance of around 500 ohms. This would mean that the current has entered the blood steam or the person was coated with some sort of conductive something.
    The average male will have a body resistance of between 3 and 5 thousand ohms stand completely dry. This means that at 120 volts a current of 24 and 40 milliamps will travel through the body. This would be well above the let-go-threshold .

    As to bonding the short pieces of metal pipe in the dwelling and one becoming energized I will ask where this power source is going to come from? If there is no source of electricity then why bond?
    If you are going to bond one piece are you going to bond all of them or are we going to make the pieces of metal pipe electrically continuous?

    I would first find out where the source is coming from. If I cannot find a source then I am not going to bond.
  3. nukeman

    nukeman Nuclear Engineer

    Messages:
    711
    Location:
    VA
    The voltage difference across the body and the resistance of the body will determine the current. Power is power. It is part of Ohm's law and relates other parameters:

    W=I^2R, W=V^2/R, W=IxV, etc.

    In this case, we don't really care about the power. Primary concern is the current. Power is only useful in this case if you wanted to figure out how quickly you can raise the person's temperature. It is all related, though. If you want to say xx mA kills or does damage to a person, you have to make assumptions on the resistance of the person if you want to relate to power or to a voltage. You might also argue duration of the shock (energy=Watts x time). Bump 240V with the back of your hand and get a quick zap. Grab onto the same line and not let go is a whole other issue. The other sticky point is that it really only depends on voltage across your body if you are going to calculate power or current. For intance, you might get hit with a fairly high voltage, but there is a large voltage drop across the soles of your shoes. You wouldn't just use the "normal" body resistance or the full voltage to calculate the damage to the person's body as a lot of that energy is going into trying to melt the bottom of your shoes. :) You instead would look at the voltage difference between the tip of your fingers (or whatever) and the bottom of your foot. That is the real voltage (and related current/power) that your body is seeing.

    For bonding, I was taking the whole house to be copper, but plastic coming in. If you have access (like a basement), it is so easy to do, you might as well. For power source, you may or may not know where all your NM cable is in relation to your plumbing. They could touch at some point. You could have a rodent chew through the insulation or you could have a careless plumber. What I mean by the plumber part, I opened up a ceiling during some reno work and found that the plumber torched the hell out of the NM wire that was running near a coupler to feed the shower. The probablilty of the piping becoming energized is small, but if it is not difficult to bond, I would do it just for added protection. In my case, the cooked wire wasn't touching the plumbing (and the plumbing was bonded anyway), but you can see how it could have been energized if touchng and not bonded. If all of the plumbing was behind walls and could not easily be accessed or if it was bits and pieces of copper mixed with plastic, then I wouldn't bond it. My point is that you don't usually know who has done what in the house before you, so you often don't know what is going on behind those walls.

    My opinion is that if something can reasonably be done and can have some possible benefit, then I am going to do it and do it right. Some things that I did, but didn't have to:

    - WH wasn't grounded when we moved in. The sellers had a handyman run a separate ground (the wire was 10/2 w/o ground). Since I had everything open, I replaced this with 10/2 w/ ground
    - Replaced 3-wire to dryer with 4-wire.
    - Added ground rod in addition to the existing water system electrode.
    - Re-ran the bonding to the water system to within 5' of where it comes into the house instead of having it bonded somewhere in the middle

    These are just some examples of things that probably won't make a difference in any real way, but it was easy and cheap. Why not bring things up to code if you can?

    If you are paying a pro to come in and do it, then you might be better off just leaving things unless your inspector want it done due to the reno work that you are doing.
  4. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,566
    Location:
    North Carolina
    And this is the exact same thing I was saying to thatguy. Is thatguy really a woman??

    In order for someone to even be able to feel 3 volts AC the total of the series resistance of the human body his shoes and whatever he was standing on would have to be below 200 ohms. In order for it to kill the total resistance would need to be around 30 ohms.
    Now we both know this just aint gonna happen at no 3 volts AC
  5. nukeman

    nukeman Nuclear Engineer

    Messages:
    711
    Location:
    VA
    I agree with you. However, I think that thatguy is saying the same thing in a different way. He is saying that you can look at voltage. You can use the voltage and the person's resistance to figure current. As I mentioned before, it is difficult to really know what the real current could be because it depends on the resistance of the person (this can vary greatly from person-to-person and that doesn't even include other variables such as shoes/clothing). Because of this, it is often helpful to look at voltage to determine how dangerous a circuit might be to a person. We all know that you can grab onto 12v all day and it won't do a thing. If you are working on a 480v AC circuit, then you have to be very careful. There is some threshold voltage between what is safe and what is somewhat dangerous. This depends on the person. In terms of common voltages, one might say 110v+ you better play it safe. Under say 50v, you are likely safe. Between 50v and 110v, you are also probably safe, but probably should start thinking about what you are doing.

    Another factor is the frequency. Normally, one (in the US anyway) will only run across 60Hz power. However, higher frequencies behave differently (both in how the current flows and how it interacts with the person's heart/muscles/nervous system. In fact, most higher frequencies are safer than the 60Hz that is commonly used.

    Here's an example. In the picture that I posted with the guy in the cage, that spark is coming from a Tesla coil (I am a bit jealous that I don't have one that big. :( ). The way this works is it uses an inductor, a capacitor, and a spark gap on the primary side (along with a high voltage transformer). This primary side is connected to a coil with lots of windings. The primary side is adjusted and tuned to the secondary side. This magnifies the voltage a great deal. I built a small Tesla coil just out of HS. Mine uses a neon sign transformer (6kV) and a bunch of simple things. The output is something like 250kV (it can throw sparks a good 12" in air). In fact, I could add a sphere or a torus and get even bigger sparks. Although the voltage is high, the frequency is also high (~22kHz). I can take sparks to my wrist without any other protection and get nothing more than a tingle. The larger Tesla coils (like in the pic) will use a small Tesla coil like mine on the primary side. They then magnify this and can get several million volts or more.

    Fun stuff. :)

    http://en.wikipedia.org/wiki/Tesla_coil
  6. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,566
    Location:
    North Carolina
    But what he said is simply wrong.

    1. Originally Posted by Thatguy
    I would do this for a reasonable price. With wet skin you are very vulnerable to electrocution, but you have to check that grounding actually gives you 1 VAC or less. For some people some of the time 2 VAC would be above the let-go threshold.


    There is no such thing as a voltage let-go-threshold and it sure isn’t 2 volts. This is incorrect information plain and simple.
    The let-go-threshold is measured in current and in current alone. Voltage plays no role what so ever in the let-go-threshold.

    As an engineer you should know that voltage does not move nor flow. Electrons move or flow and it is the flow of electrons through the human body that is felt, hurts, and does damage. The movement of electrons is measured as current or amps. This is a law of physics that cannot be changed.

    Now we can play around with voltage all day long but the fact still remains the same, it is current that does damage not voltage. It is current that flows not voltage and it wouldn’t matter what the resistance was. It doesn’t matter if it is parallel or series. It is still the movement of electrons that is the flow of electrical energy not the pressure pushing this flow. Simple electrical theory taught in the first semester of class.
  7. nukeman

    nukeman Nuclear Engineer

    Messages:
    711
    Location:
    VA
    Okay. It looks like that post was deleted and I didn't see it. That is why we aren't making a connection.

    I understand 100% that current is what causes damage and the relationship between current, voltage etc. Yes, you can have a voltage and no current. This is why I said that when you are talking about voltage in the case, you have to talk about the voltage difference across the person and not a voltage referenced to something else. If there is a voltage difference, there will be a current (unless the resistance = infinity)...Ohm's Law.

    My point is that it is hard to identify a circuit that might harm you based on the current that could flow through your body. If the average person is working around a 220v circuit. Say they happen to know (or maybe they don't know) if they come into contact with that voltage, how much current will flow through their body and what the damage will be (tingle, knock you on your rear, death, etc.). Because of this, it is often helpful to say the average person = ***x Ohms and the amount of current to cause major damage = yy mA. With these, you can use Ohm's Law to multiply together to get a voltage that would cause this damage. It is not perfect since there are many factors, but could be a good measure of risk.

    It is just a way to measure risk (12v car battery vs. 700kV transmission line). The voltage drives the current. 12V across you is nothing. Try that with the 700kV transmission line and you'll ruin your day. :)

    Thatguy is also talking about probability. The idea is that you gather all of your cases (or as many as possible) of people who have got a shock of some kind. You might bin them into different categories (feel, hurt, death, etc.). If you can figure out how much current went through their body, you can seperate these people into "bins". For instance, you might find that 25% of the people sampled were in extreme pain with 65-75 mA. You might have another group that this current caused death. Anyway, you come up with a distribution. The current ranges that you normally see for feel, hurt, death, etc. are in the peak of this distribution. However, there will be people who fall outside of this range. As you go away from the peak, the probability of finding a person where that current does that damage drops off. It depends on the type of the distribution, but many extend to infinity (in both directions) with the probability dropping to zero. I think that Thatguy is talking about the very few people that are outside of the normal range. There might be a handful of people in the world that a current that would cuase a mild shock in "normal" people might cause death in their case. It also goes the other way and there can be a group of people that can take the current better than most people. However, most people (say 95%) will be in the "normal" range for current vs. damage.
  8. reed50

    reed50 New Member

    Messages:
    20
    Location:
    tennessee
    I appreciate everyone's responses. Just so I understand the reasons why some recommend bonding the pipes: it's because a stray wire may come in contact with the pipe. Does it have anything to do with the things that use water and electricity (water heater, dishwasher, washing machine). I guess what I'm trying to ask is it in case of someone not wiring one of these things correctly, or am I totally off base on understanding this? Once again, thank you to everyone for their patience (and my stupid questions).
  9. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,566
    Location:
    North Carolina
    We have been making a total connection. Just as you have explained in the post i have quoted you from you maintain throughout that post that the current that travels trhough the body not the voltage.

    Thatguy made the statement that 2 volts might be above the let-go-threshold and here he is completly wrong. Herein lies all this debate.
  10. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,566
    Location:
    North Carolina
    There is no code requirement to bond anything concerning these pipes. Your equipment such as those appliances you have listed here will have an equipment grounding conductor that bonds any metal pipes connect to them so nothing else is needed.
    Don't let anyone try to scare you into doing anything different either.
  11. reed50

    reed50 New Member

    Messages:
    20
    Location:
    tennessee
    I want to again thank everyone for their responses. On a side note, the electrician said the pipes need to be grounded because of this scenario: what if I was cooking, touched the stove and my ungrounded kitchen faucet at the same time, there was a chance of getting electrocuted. Needless to say, it did scare me.
  12. nukeman

    nukeman Nuclear Engineer

    Messages:
    711
    Location:
    VA
    That wouldn't/couldn't happen. Your stove is already (or should be) grounded, so you can't get the frame of the stove to be energized. In the other way, the only way that the faucet could become energized is what I mentioned before: some damaged wiring somehow makes contact with the metal piping. It is a long shot as the damage would have to be right where the wire crossed the pipe and the pipe would have to be touching the wire. Bonding the plumbing would prevent this, but I really wouldn't worry about it.

    In my case, I bonded, but for several reasons:

    1. metal pipe coming into the house and using it as a ground rod
    2. easy access during basement reno
    3. did the work myself, so the only cost was a bit of wire

    In your case, it looks like he is trying to make some money off of you.
  13. reed50

    reed50 New Member

    Messages:
    20
    Location:
    tennessee
    Again, thanks for the reply. The scenario the electrician gave me was in answer to my question of: "how do my copper pipes become energized". That's when he talked about the stove. And yes, this guy is licensed--I looked on the state's website.
Similar Threads: bonding/grounding copper
Forum Title Date
Electrical Forum discussion & Blog City Light leader fell for ‘Indian’ copper con Jun 24, 2014
Electrical Forum discussion & Blog using copper waterlines under slab for additional ground ? Mar 25, 2013
Electrical Forum discussion & Blog Joining allum nm to copper nm Jun 6, 2012
Electrical Forum discussion & Blog copper pipes under mobile home (doublewide) Dec 11, 2010
Electrical Forum discussion & Blog copper pipes grounded ? Jul 22, 2010

Share This Page