How to add ground wires?

Discussion in 'Electrical and Wiring' started by zannej, Sep 18, 2019.

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  1. Sep 18, 2019 #1

    zannej

    zannej

    zannej

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    I've found that while I have 3-prong outlets, I don't think there are ground wires. I also have a situation where I have a dryer with 3 prongs instead of 4. I would like to add a ground wire & am wondering if I can do this without having to run all new wire. So, a few questions:
    1. Does a ground wire have to be in a casing/shield or coating?
    2. Instead of running all new wiring, can I run a separate ground wire from the breaker the outlet is attached & back to the outlet?
    3. Or can a ground wire be run directly to a grounding rod instead of to the breaker?
    4. If it needs to be sheathed or coated, can automotive electrical coating be used? Or do the sell just single grounding wires in various gauges?
    5. Does the ground wire have to be the same gauge as the rest of the wire (say I have an 8 gauge for a dryer, would I need an 8 gauge ground)? If the dryer's plug could normally work with 10 gauge could I use that instead?
     
  2. Sep 18, 2019 #2

    Snoonyb

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  3. Sep 18, 2019 #3

    hornetd

    hornetd

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    1) no
    2) yes
    You can run an Equipment Grounding Conductor (EGC) separately to any of the points listed in section 250.130(c) of the National Electric Code (NEC)

    "VII. Methods of Equipment Grounding
    250.130 Equipment Grounding Conductor Connections.
    Equipment grounding conductor connections at the source of separately derived systems shall be made in accordance with 250.30(A)(1). Equipment grounding conductor connections at service equipment shall be made as indicated in 250.130(A) or (B). For replacement of non–grounding-type receptacles with grounding-type receptacles and for branch-circuit extensions only in existing installations that do not have an equipment grounding conductor in the branch circuit, connections shall be permitted as indicated in 250.130(C).

    (C) Nongrounding Receptacle Replacement or Branch Circuit Extensions. The equipment grounding conductor of a grounding-type receptacle or a branch-circuit extension shall be permitted to be connected to any of the following:
    (1) Any accessible point on the grounding electrode system as described in 250.50
    (2) Any accessible point on the grounding electrode conductor
    (3) The equipment grounding terminal bar within the enclosure where the branch circuit for the receptacle or branch circuit originates
    (4) An equipment grounding conductor that is part of another branch circuit that originates from the enclosure where the branch circuit for the receptacle or branch circuit originates
    (5) For grounded systems, the grounded service conductor within the service equipment enclosure"


    3) Unless that Ground Rod is part of the grounding electrode system ABSOLUTELY NOT! The National Electric Code (NEC) specifically forbids using a separate grounding electrode as a means of Grounding equipment. vis

    "250.54 Auxiliary Grounding Electrodes. One or more grounding electrodes shall be permitted to be connected to the equipment grounding conductors specified in 250.118 and shall not be required to comply with the electrode bonding requirements of 250.50 or 250.53(C) or the resistance requirements of 250.53(A)(2) Exception, but the earth shall not be used as an effective ground-fault current path as specified in 250.4(A)(5) and 250.4(B)(4)." emphasis mine.

    4) Green colored wire in gauges up to American Wire Gauge AWG 6 is available at electrical supply houses or at most of the big box home improvement stores.

    5) The size of the Equipment Grounding Conductor (EGC) has to comply with table 250.122 which is based on the size of the Over-Current Protective Device which protects the circuit and NOT by the size of the other conductors in the circuit. But it does not work out any differently than the same size until you are above a 30 ampere circuit. For 15, 20, and 30 ampere receptacles the answer is yes it must be the same size as the circuit conductors.

    I would think that the connection point named in 250.130(c)(4) may be the easiest to find near many of the outlets that you wish to ground.

    --
    Tom Horne
     
    Last edited: Sep 18, 2019
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  4. Sep 19, 2019 #4

    zannej

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    By part of the grounding electrode system, does that mean the one that the other wires all run to? Like, if I wanted to run to the grounding wires that the circuit box runs to?
    My brain is a bit fuzzy today. (I wrote but fuzzy at first). Tired.

    For a dryer, what about this adapter: https://www.amazon.com/dp/B07DLQDKLN/ ?
     
    Last edited: Sep 19, 2019
  5. Sep 19, 2019 #5

    zannej

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    Now that my brain is working a little better, another odd question: If I have 10/3 cable but want to upgrade to 10/4, can I take a 10 grounding wire that is sheathed & tape it to the existing 10/3 with electrical tape to run it from the box to the outlet? If I did so, would it be a good or bad idea to use conduit?

    Soonyb, don't GFCI outlets need to have grounding wires somewhere? My house is very old so the wiring is not great. I have 3-prong outlets but when I test them, it shows they are not grounded. I don't even know if my house has a grounding rod.
     
  6. Sep 19, 2019 #6

    hornetd

    hornetd

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    The Grounding Electrode System is all of the Grounding Electrodes that are used to ground the Service Equipment which is the first switch, breaker, or fuse pull out/s were the power to the premises wiring comes from the Electrical Utility's wiring. In most modern panels that would be the Main Breaker.

    Yes you can run the added Equipment Grounding Conductor (EGC) back to the panel which the circuit comes from. I know that the National Electric Code (NEC) language can be hard to understand for anyone who has not had to use it much but that was covered in my previous reply. viz

    (3) The equipment grounding terminal bar within the enclosure where the branch circuit for the receptacle or branch circuit originates.

    --
    Tom Horne
     
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  7. Sep 19, 2019 #7

    hornetd

    hornetd

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    Yes you can run it next to the existing cable but you cannot support the Equipment Grounding Conductor by just taping it to that cable. It has to be fastened in place within one foot of the box or enclosure which contains your dryer outlet and within one foot of the panel's enclosing cabinet. It also has to be fastened every 4&1/2 feet or less along it's entire length or run though board holes that are no father than 4&1/2 feet apart. It is important that the EGC enter each metal enclosure through the same connector that the cable does. Bringing the EGC in through a separate opening would raise the impedance of the GEC; that is it's total resistance; to a higher level thus impeding the flow of current during a fault and slowing the operation of the Over-Current Protective Device (OCPD). For that same reason you can not put the EGC in a separate Conduit unless you put the original cable in the same conduit or bond the conduit to the new EGC at both ends. Again in order to bring the EGC into the panel the circuit comes from and into the electrical box which contains the receptacle you would stop the run of conduit short of either enclosure and bond the EGC to the conduit at both ends and then run it into each metallic enclosure through the same entry as the original cable. Although that is certainly NEC compliant it seems to me to be a lot of extra work for no gain in performance. If you have enough access to the branch circuit cable to follow it back to the panel which it comes from;especially with conduit; then best practice would be to replace the cable and be done with that circuit for good and always. You could also run both the original cable and the new EGC in the new conduit but again that would be a lot more work with no increase in utility.

    If your house has only a connection to an underground metal water pipe or a metal well casing then that is the entire Grounding Electrode System. If your house were being built today it would have to have a minimum of two driven electrodes (Ground Rods) in addition to the metal water piping but that has not always been required. It depends on which addition of the locally adopted electrical code was in effect at the time the permit to build your home was drawn at the code enforcement office of your local government.

    The additional Grounding Electrodes are now required to guard against the house having no grounding electrode at all if the underground metal water piping were replaced with some sort of non conductive piping.

    --
    Tom Horne
     
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  8. Sep 20, 2019 #8

    zannej

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    Thank you very much, Tom. I tried to make sense of the language of the code & my eyes just kept crossing & mind drew a blank. I do better with pictures for some reason.

    So, if I can run a ground wire right next to a 10/3 & bind it to the 10/3 cable and put them in the same conduit would that work? For the dryer outlet I'm going to be removing my entire subfloor to replace it & the electrical box is in the room the floor will be pulled from. I had planned to sort of link it to the cable as if it were part of it-- sharing conduit and ports in outlet boxes. If any of the wires run under the floor, I will be able to access them to add the ground wire in. 10/4 wire is rather expensive, but you are right that it might just be easier to pull all the 10/3 and just replace it entirely. I'm switching my laundry room with a bathroom (and tearing down non-loadbearing walls). My outlets are currently on the south side of the wall between the two rooms. I'm going to be moving the machines north & turning them 90 degrees so their backs will be facing the east wall. I'm debating whether I should move the outlets closer & run them up through exterior boxes (on the inside of the house) so I won't have to put them in an exterior wall, or if I should just keep them in that same wall & flip them to the north side instead of south. I think the latter might be easier. I'll just be sure to keep them on the opposite side of the stud of the area with the plumbing. If my appliance cords are not long enough, I can get longer ones. I'm going to have to replace the 10/3P with a 10/4P anyway (I think that is the designation-- P= plug & R= receptacle?).

    I have a gray/silvery colored metal pipe in the ground at the back of my house where a bunch of wires run into it that I *think* is what serves as the grounding rod for the house. It probably wouldn't hurt to put in a real grounding rod (8ft copper stuck in the ground). Maybe my stuff will get fried less often during power surges. I'm also going to put in a whole house surge protector.

    Another question: I saw a video from Leviton on how to install outlets & it mentioned tamper resistant & tamper resistant with grounding.. I know there was a metal plate, but I didn't quite understand how the grounding worked or how to tell if something was self-grounded. I've been reading a book on wiring but I'm still trying to get the concepts to sink in. It's been a very very long time since I took electronics in high school & electronic engineering in college. (don't worry, I *will* bring in an electrician when the work begins bc I'm not risking screwing that up, but I want to know for my own edification & to know what supplies & such will be needed). I do think that I can safely turn an outlet box around in the wall though. Power to whole house will be shut off for that.

    One more question before I forget: If I have an outlet that is the end part of a run, can I add more wires to it to run to another box to put one more outlet in (so long as it doesn't exceed the load for the circuit it's on?). And is a "hidden junction box" one that can't be accessed, or one that just isn't evident. Because I want to move a wall switch from one wall to a perpendicular wall but I want to extend the run of the wires from the location of the current switch to reach a new GFCI outlet & switch near a vanity. Can I add a junction box where the switch was & put a wall plate over it? (I'll try to draw up some layout & diagrams of what I'm talking about later if need be). I can even see if I have photos.
     
  9. Sep 20, 2019 #9

    hornetd

    hornetd

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    If you are not going to relocate the receptacles you may want to take advantage of the code exception which allows then to remain in use as is. You then follow the instructions which came with your clothes dryer for installing the 3 wire cord. If it already has a 3 wire cord just leave it in place.

    Is there a single bare insulated or armored conductor that connects that conduit to the Service Equipment? If there is not then unless that conduit is connected to the Service Equipment enclosure with a bonding conduit connector it is not a Grounding Electrode. Do not attempt to use it as a Grounding Electrode unless you are sure that the underground portion is at least 20 feet in length and that it is NOT coated with a non-conductive mastic, tar, or other anti corrosion coating. The connection to the Grounding Electrode Conductor has to be made by a listed Grounding Clamp.

    A Self Grounding Receptacle would be marked on the box as Self Grounding. It would also have a brass colored contact spring on one of the mounting screw holes that assures continuous contact between the receptacles yoke and the mounting screw.
    [​IMG]

    Tamper proof receptacles have an internal shutter which will not allow anything to be inserted into the receptacle unless there is fairly equal pressure on both openings at the same time. That is to keep foreign objects from being inserted into the receptacle slots. Notice the letters TR molded into the face of the receptacle shown above.

    Yes you can extend an existing circuit from any electrical box, as long as the box has sufficient room for the additional wires, if it is on the correct type of circuit. You could not, for instance, extend a laundry circuit out of the Laundry. A laundry circuit is one that serves receptacles which are only in the Laundry and no other receptacles or other loads. A general purpose circuit which serves other rooms or loads, such as luminaires, can be extended beyond the room/s it already serves.

    The National Electric Code (NEC) used in the United States does not use the term “hidden box.” It classifies boxes as either readily accessible or accessible. A box with a surface mounted cover plate would be “readily accessible” and is always permitted. If the box were to be concealed by a readily removable cover it would be an accessible box.


    Tom Horne
     
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  10. Sep 21, 2019 #10

    zannej

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    Thank you again, Tom.
    My dryer has a 3-prong plug & the existing outlet is 3-prong but I wanted to update both to 4-prong to make it safer and in case we ever want to upgrade our appliances. I figure while I'm making changes I might as well do some safety improvements. I may have to move the outlet for the washing machine closer to the electrical box bc it has a 5' cord but the dryer plug can probably stay in that same wall. I saw a Leviton 4-prong receptacle for about $6 so I might get that. Some of the dryers won't work with 3-prong plugs (my friend just discovered this with his LG dryer he just got) so I want to have things up-to-date (plus, knowing my luck, something would go wrong with the 3-prong). My friend discovered that the dryer he just got was wired with a range plug instead of a dryer plug.

    Sounds like I can extend the wiring from the light switch to another switch & a vanity light since it's not part of the laundry.

    I saw that the self-grounding thing has a little copper plate, I'm just struggling to understand how it works & what the guy in the video meant about a grounded box vs an ungrounded box and something about a pigtail (can't remember if the pigtail was for grounded or ungrounded). I know what a pigtail is at least. I think I sort of understand but am not fully clear on it & I like to know how things work.

    I have no idea about whether there is a single conductor connecting to the conduit. I'll have to take a picture after the weeds get tamed enough to see it. The meter is mounted on a pole about 6ft from the house on the southeast side. From there wires run to a pipe in the roof and down to the box in the hallway with the exterior door. The pipe I saw in the ground with a bunch of wires is on the southwest side of the house. I don't think it is connected. I don't see any wires coming down from the power pole with the meter to the ground (but I can look again to see if there is one that I missed), but I don't think there is.
     
  11. Sep 21, 2019 #11

    bud16415

    bud16415

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    Tom @hornetd and others.


    How much safer do you think a 4 prong dryer is than a 3 prong given they are both wired correctly. I know it is not an exact question but would like to hear your opinion and others.
     
  12. Sep 21, 2019 #12

    hornetd

    hornetd

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    I seems that you have this one figured out.
    Yes you can.
    The copper plate has a spring that will maintain contact between the mounting screw and the yoke of the receptacle which is bonded to the Equipment Grounding Conductor contact which the round pin of a plug connects to. The threads of the mounting screw will maintain continuity between the mounting screw and the electrical box in which it is mounted. If the circuit supplying that box contains an Equipment Grounding Conductor that is properly terminated to the box the spring assures continuous continuity from the Round contact openings of the plug and the Equipment Grounding Conductor which is connected to the box. A box with an EGC is a grounded box.

    If there is no EGC run with the conductors of the circuit which supplies current to that box then the receptacle would still be ungrounded because there would be no low impedance pathway back to the center tap of the Transformer which is supplying current to that circuit. That would be an ungrounded box.

    The wire that you are looking for is called a Grounding Electrode Conductor (GEC). The GEC could be connected to the "neutral" of the Service Entry Conductors at any point between the splice that connects it to the Service Drop's neutral and the Bonded Neutral busbar in the Service Equipment's cabinet. So look at the Service Entry Conductor adjacent to the Utility's splice, the Meter Pan, and the panel that has your main breaker in it. With rare exception the GEC will be connected in one of those 3 places and will run to one or more of the Grounding Electrodes.

    --
    Tom Horne
     
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  13. Sep 22, 2019 #13

    hornetd

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    In the 3 wire arrangement the frame, and other non current carrying conductive parts, of the Clothes Dryer are bonded to the Neutral Conductor of the branch circuit which supplies the dryer. If the branch circuit and the connecting cord of the dryer are in good condition any fault which might energize the frame; thus exposing anyone who touches it to electric shock; will cause a large flow of current via the faulted energized conductor and the neutral. That flow would trip the Over-Current Protective Device (OCPD); a fuse or a circuit breaker in most cases; and cause the OCPD to open the circuit thus "clearing" the fault. [By definition a fault is "cleared" when the fault current is stopped not when the fault contact has been corrected.]

    If the Grounded Current Carrying Conductor, which most of us call the neutral, of the dryer's branch circuit develops a resistive connection for any reason any subsequent fault will energize the Dryer's conductive metallic surface. A resistive connection which could cause a dangerous touch potential on the dryer's surface would not always keep the dryer from functioning. Keep in mind that it takes a current of more than 30 amperes to open the OCPD but only 30 milliamperes to stop a human heart. If the occupant of the home begins to dress and discovers that they need an item of clothing from the dryer they will go to get it. Upon grabbing the Dryer's door handle, while standing on the conductive concrete or tile floor in their still bare feet, or with one hand on the skin of the adjacent properly grounded Clothes Washer, they receive a dangerous and possibly fatal shock.

    In the 4 wire arrangement, which is now required for all new installations, the Neutral is completely insulated from the non current carrying parts of the dryer. If the neutral conductor goes open the dryer's motor and controls cease to function and in all likelihood the occupant summons a repair person to fix the dryer. Opening the continuity of the insulated neutral cannot cause a dangerous touch voltage on the exposed metal surface of the dryer. It would take 2 additional failures to energize the dryer's outside surface. The Equipment Grounding Conductor would have to be open and one of the energized conductors would have to fault to the dryer's non current carrying conductive parts. Having all three of those failures occur at the same time and in the order necessary to remain undetected is very unlikely.

    I'm only one of the nations thousands of Firefighters and Emergency Medical Technicians and yet I attended 2 incidents of electric shock from the surface of a 3 wire dryer during 35 years of active service. That said I have also attended incidents arising from electric shock that were caused by the abuse of the equipment from which the current came which had been properly wired to Best Practice.

    --
    Tom Horne
     
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  14. Sep 23, 2019 #14

    zannej

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    Thank you very much, Tom! That all makes sense now. I was going to have my friend who was certified as an electrician look at the panel to see if he could find any indication that things are grounded but it seems he lost a lot of his knowledge in the wreck that gave him a traumatic brain injury. He didn't even recognize a 20amp outlet & I had to explain it to him & also tell him that the "weird" side "blade" on a 20amp extension cord was to make sure it was only plugged in to 20amp outlets. I also showed him this thread when he was trying to figure out what to do about his dryer not working with a 3-prong plug. He got an adapter that has a green wire that plugs in to the ground of an extension cord he has running to the laundry room from a 20-amp outlet for his washing machine. Not sure if that is sufficient, but it's a temporary fix. I'll show him your response about the dangers of the 3-prong plugs vs 4-prong. He's already been zapped hard & lost the feeling in his entire right arm & hand from it. For years he had no feeling in his feet & wasn't able to drive. (It happened bc he didn't check to see if the electrical was live when changing out a light fixture for his grandparents & ALL of the breakers were off but somehow the wire was hot). Once the weeds are cleared enough from the outside I will take pictures of the meter pole & I will see if I can get pictures of the wiring to the circuit box. He's actually run some of his own wiring successfully but he did consult the local electrician & had him inspect it to say whether or not it was good. The electrician will let other people do the work while he supervises or inspects & charge a lower fee.

    Even though the problems with 3-wire are rare, I'd rather be safe than sorry-- especially with the kind of luck I have. Not too long ago, my microwave's body & door became electrified with a low current & gave me a little zap. I had to unplug it & move it to a different outlet. I think I'm going to replace all of my receptacles with new ones bc most of them are well over 20 or 30 years old and have been through numerous power surges.

    Is Leviton a good brand for outlets? I've seen Leviton and Eaton & a bunch of off-brands. I'm debating whether or not to get this for the dryer outlet: https://www.amazon.com/Enerlites-Electrical-66300-W-Receptacle-Industrial/dp/B07BN773K4/ or this one https://www.amazon.com/gp/product/B000GAQG5C/
    or something else... I'm open to suggestions. I would like to have a white plastic wall plate but if there isn't one that fits I'll go with what is available. I've been having a hard time figuring out the diameter of the round part that the plate will have to go around on some of the receptacles. Some have it listed but others don't.

    Am I correct in assuming that plastic gang boxes are NOT grounded? Or does it have more to do with the wiring to the box?

    Again, I very much appreciate the information.
     
  15. Sep 24, 2019 #15

    hornetd

    hornetd

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    I'm concerned about your microwave problem. What more can you tell me about that receptacle outlet? Have you tried any three wire tester on the outlets in your home? What did it show on the microwave's previous receptacle outlet.

    Do you have access to a Wigginton type solenoid voltage tester like the one shown here?
    [​IMG]
    Solenoid voltage testers, unlike neon testers or multimeters, place a small load of about 7 milliamperes on the circuit under test. They are thus immune from false voltage readings caused by inductive pickup of a false voltage from adjacent conductors and will only show a voltage when there is actual energy on the conductor under test. By placing one lead to the round pin terminal and the other to the shorter straight terminal you will find if the ground connection is good enough to actually carry current. Then by testing the resistance between the longer straight slot and the round pin opening with a multimeter set to OHMS you can get an idea of whether the connection between the 2 points is several feet away in the panel were it belongs or bootlegged right in the box to give a false OK reading on a simple plug in tester. A measurable resistance suggest a proper Equipment Grounding Conductor path back to the Main Bonding Jumper in the Service Equipment enclosure and out on the Grounded Current Carrying Conductor to the long blade of the receptacle. An extremely low resistance suggest a bootlegged jumper in the box under test.

    Without some experience using a solenoid voltage tester even it cannot tell you if someone deliberately attached the Grounded Current Carrying Conductor to the Equipment Grounding Conductor terminal of your receptacles in order to deceive the simple 3 light tester. The only way to detect such shenanigans is to open up the cover plate and pull the receptacle out of the box and check for the presence of a jumper, as shown in the picture below, between the green colored terminal and a silver terminal or a splice of white wires OR to apply a multimeter to the outlet as outlined above.

    A circuit analyzer, shown below,
    [​IMG]
    would be easier to use but they are expensive costing more than 300 dollars when new. The photograph shows a bootleg ground jumper with a normal reading on the three light tester and the bootleg ground detected by the circuit analyzer. The circuit analyzer does the comparative measurement which I outlined above but it does it automatically. The three light tester detects a ground connection but the circuit analyzer tests the quality of that connection.

    You should not have gotten any shock off of the skin of the microwave unless it is internally faulted even on an ungrounded circuit. You can eliminate that possibility completely by measuring the resistance between each of the straight blades of it's plug and the EGC round pin. Any OHMS reading other than infinity, meaning no measurable connection, indicates an internal fault in the microwave.

    With a bootleg ground the microwave could be in perfect operating condition and by connecting the shell of the microwave to the Grounded Current Carrying Conductor could raise the voltage on the surface; which is called the touch potential; high enough to cause a shock sensation. The volts used in moving the current through the the Grounded Current Carrying Conductor back to the panel; commonly called the voltage drop; can be enough to cause a shock. The poorer the condition of the Grounded Current Carrying Conductor the greater the voltage drop will be.

    --
    Tom Horne
     
    Last edited: Sep 24, 2019
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  16. Sep 24, 2019 #16

    bud16415

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    Tom thanks for the explanation and I don’t want to take zannej’s thread too far off topic. The part I have trouble understanding is when you get back to the main panel the EGC and the neutral are connected to the same bar. Won’t that connection give the outside shell of the dryer the same potential as the neutral or as it would have had in the 3 wire setup?
     
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  17. Sep 25, 2019 #17

    zannej

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    Tom, to my knowledge the outlet was either installed in the late 1980s or was pre-existing before we moved in. House was built in the 30s or 40s but it's possible it was put in anytime between the 30s to 70s because there was some remodeling done over the years. It's in the area where the refrigerator used to be when we first moved in. There is some blue expander plugged in to the outlet to allow more things to be plugged in-- I think it's a total of either 6 or 9 but I'd have to go look again. It could be that piece is bad or it could be the outlet or both. The electrified microwave thing only happened once in all the time we've lived here & it was after a nasty thunderstorm.

    I have also noticed that sometimes I get a little zap & I see a small spark/light when I turn some of the lightswitches in the house. Not sure if that is static electricity or bc my hands were damp. I want to switch from toggle to rocker switches (because the rockers are easier to find & flip).

    I think I *might* have that meter in the first picture but I need to look for it. It looks similar to the one I made in Electronics class back in the early 90s. The teacher got us kits & we had to make the circuit boards & wire them up. I remember very little of that class unfortunately. Thank you for explaining how to use the meter, I never knew exactly how to use it (or at least, didn't remember).

    When I plug in the 3-prong testers it tends to light up with something not being right but I don't recall what problem it indicated-- either hot & neutral flipped or no ground. I need to find my tester and see. I need to figure out which breaker the microwave is on & see if it's 20amp or 15. It should be 20 for a microwave though. Would using a GFCI be a bad idea for a microwave?

    Bud, I'm curious about that as well so it's not off-topic. The more info the better.
     
  18. Sep 25, 2019 #18

    hornetd

    hornetd

    hornetd

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    In the path that the Equipment Grounding Conductor (EGC) takes between the shell of the drier and the center tap of the transformer you have the EGC itself, the Neutral conductor of the Service Entry Conductors, and the neutral conductor of the Service lateral or drop. Between the Neutral busbar and the center tap of the transformer the Neutral portion of the circuit is too large and has too low a voltage drop to cause any significant voltage drop at all. So that point were the EGC and the Grounded Current Carrying Conductor (neutral) come together is effectively 0 volts. Since the EGC is not carrying any current during normal operation; and when it is carrying fault current will do so for tenths of a second; it has essentially no voltage drop so the skin of the dryer is essentially at zero volts as well.

    With the 3 wire arrangement the skin of the dryer is bonded to the Neutral Conductor of the dryer branch circuit. As long as that circuit remains in good condition the current on the neutral conductor will not cause enough voltage drop to raise the voltage on the surface of the dryer to a dangerous level. The difference is that, in the three wire branch circuit, if the neutral goes open or develops high resistance the voltage drop and thus the touch potential of the dryer rises to a dangerous level.

    In the 4 wire branch circuit the skin of the dryer is not bonded to the neutral but only to the separate EGC. A high resistance on the 4 wire branch circuit's neutral conductor has no effect on the voltage on the skin of the dryer. The neutrals high resistance would cause erratic operation of the dryer since the dryer motor and controls are generally 120 volt loads which use the neutral as part of the pathway for their normal operating current. If the neutral goes open the dryer stops working and in either case a repair person will be called.

    --
    Tom Horne
     
  19. Sep 25, 2019 #19

    hornetd

    hornetd

    hornetd

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    The thunderstorm makes me suspect that you may have an intermittent failure of the service drop which occurs during high winds. After the high winds subside it may be taking hours or even days for the defect point to resume being adequately conductive. That would cause the perceptible touch potential to come and go.
    One issue at a time please.
    I would really like to see the results of the resistance test which I suggested on the circuit were the microwave was plugged in when you got the shock. Just check what the resistance is between the long slot of the receptacle and the round hole were the ground pin inserts using a multimeter set to the OMS position.

    A GFCI breaker would be a good idea on that circuit or any other were the existence or condition of the EGC is suspect. If there is no effective EGC in the circuit you would apply the stickers which come with GFCIs to each receptacle face plate on that circuit. That sticker reads "No Equipment Grounding Conductor."

    --
    Tom Horne
     
    zannej likes this.
  20. Sep 26, 2019 #20

    zannej

    zannej

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    I'll have my friend look at it on his next day off. He's more familiar with the meters & has better vision. I misplaced my reading glasses somewhere & I have a hard time reading things without them. I have to use large fonts on my computer to see. I have it bumped up to size 20 font.
     

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