That scenario is easily tested out as oppose to reading something in the internet that may or may not be questionable. It’s basically boils down to is it safe to touch neutral while the hot have load. You can run a hair drier while check the voltage between that neutral and ground. It will have some voltage, just not sure if it will kill you. Maybe it’s something for electroboom. Not home so can’t test.
multi-wire branch circuit (shared neutral) question
- Thread starter dcg9381
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That scenario is easily tested out as oppose to reading something in the internet that may or may not be questionable. It’s basically boils down to is it safe to touch neutral while the hot have load. You can run a hair drier while check the voltage between that neutral and ground. It will have some voltage, just not sure if it will kill you. Maybe it’s something for electroboom. Not home so can’t test.
A non contact tester is mostly a toy, use a proper tester.
wyliesdiesels
Well-known member
BINGO
people have heard the "least resistant path" BS, the "electricity goes to ground" BS and other BS false claims so many times that they start believing it.
If you believe that you cannot be shocked by a neutral, you are sadly, very much mistaken....
Firebrick43
Well-known member
Any wire that is not attached CORRECTLY to the neutral bar or ground bar is a HOT wire irregardless of the color of insulation. The is both in accordance to physics and the NEC.
Wylie
If you use ohms law and plug in the 1.5 ohms for copper wire and 1000 plus ohms for a human shape resistor there is still no shock. Go up in voltage then the math shows that a shock will start to occur.
And I don’t advocate stroking white color wires for fun, I have witnessed extremely dumb things done and always use a fluke tested against a live circuit before working on a circuit. Just last a couple of weeks ago I found a 3hp 480v 3 phase motor wire with wire nuts, one was pretty melted. Wire nuts on motor connections have been illegal (for good reason) for quite some time.
DCG
You got shocked because the box was not earthed correctly. Probably just grounded to the pipes and not with ground rods.
Current seems to be perceptible at .4ma, with the perception of shock at 1.1ma (roughly) - per what I read.
I'm in Texas. I'm always sweating when I work. Salt water substantially lowers the resistance (which I agree is normally 1000+ ohms). I've been shocked by car batteries... I assume everything in that box can shock me at all times, unless I've shut down the main. It's no fun to figure out that you're got a branch circuit "by hand".
wyliesdiesels
Well-known member
this statement right here shows you dont know what youre talking about
ground rods have NOTHING to do with the fault current pathway
ground rods are for shunting lightning, limiting potential to earth, and shunting high voltage current when primaries lines hit secondary lines
Earthed isnt even a term used here in the states. thats an australian term.
If a j box is bonded to pipes that are grounded/bonded to the panel enclosure, then the j box is grounded and the breaker would trip upon fault current energizing the box. But that has NOTHING to do with a neutral touching a grounded j box. remember, the neutral is at the same potential as any ground wire that is bonded to the neutral bar. So a neutral touching a j box wont cause a breaker to trip
these are basic fundamentals. you could use some studying to better understand them
sparky 1971
Well-known member
Anyone that relies on a non contact voltage tester deserves what they get. I am old school, but I always carry an Ideal Vol-Con wiggy type tester.
wyliesdiesels
Well-known member
i carry and use a non-contact tester but always use my T5 or Sq D wiggy to prove dead
TRWham
Well-known member
No difference in potential means no current regardless of how small the impedance or high the voltage. If there were no voltage, even if it's really small, on the neutral at the load, then no current could flow to the neutral bus. Further, just because a conductor is connected to ground by some path does not mean its potential is magically reduced to zero throughout its length. At the (bonded) bus we can assume the potential of the neutral and the ground is the same, but anywhere else, and a current carrying neutral will be at a higher potential.
alfredeneuman
Well-known member
Oh please point out where in the Code they are forbidden. (Hint: They're not)
grounded-b
Well-known member
Please explain where in the NEC it says wirenuts ( spring pressure wire connectors ) are "illegal" to wire a motor. I have wired plenty of smaller ( under 15 HP ) 480V 3 phase motors with wirenuts. And I didn't even tape them up !!
It may be common practice where you are , to use split bolts ( bugs ), varnished cambric and rubber tape, but it certainly isn't in the NEC.
Steve
sparky 1971
Well-known member
I use a nctv also, but I will be damned if I am going to trust it. I work a lot of 120 volt stuff hot just out of laziness, the non contact comes out after I break the joints open so I can verify which wire is "hot" then I can cap it with a wire nut.
wyliesdiesels
Well-known member
i missed this earlier
you are completely incorrect here. theyre not prohibited or as you put it, "illegal" on motor wiring. Illegal is not a term used by the NEC...
where do you get your horrible information?
Metal-Marc
Well-known member
It's the Interweb. Some people love to share their ignorance.
Taken verbatim from the Urban Legend Electrical Code.
Firebrick43
Well-known member
NFPA 79-2007, Clause 13.5.9.2 states, "Electrical connections at motor terminal boxes shall be made with an identified method of connection. Twist-on wire connections shall not be used for this purpose."
Ask any 3 phase motor manufacture, they will tell you the same thing.
Ask any 3 phase motor manufacture, they will tell you the same thing.
wyliesdiesels
Well-known member
that is a standard for industrial machinery built by manufacturers not individual standalone motors
that is also NOT the NEC which is NFPA 70
https://t3.lappcdn.com/fileadmin/DA...Servicecenter/Lapp_NFPA79-Whitepaper-2018.pdf
Firebrick43
Well-known member
I never said it was the NEC. You jumped to that conclusion. NEC/NFPA 70 covers building wiring and overload devices. Why would one quote the NEC for a motor of a machine? Once it enters the machines control panel or even peckerhead its under NFPA 79 as referenced by article 670 of the NEC/NFPA 70. There is no one exclusive standard, they work together, and reference each other.
NFPA 79 applies to industrial machinery(non hand portable) which would include wood working machinery, air compressors, material handling equipment (like car lifts), pumps, metal working machines, and et cetera.
Sounds like most of the equipment in my shop and most other shops, does it not?
I guess if you install a "stand alone motor" it would not apply to you. Do you regularly set induction motors that do not drive some kind of machinery, the kind that is commonly discussed here on the board? And since you want to be uber technical, what is a "stand alone motor" The only reference in the NEC I could find that included the phrase "stand alone" was in reference to systems where a generator of some type driving a load that was not connected to the grid.
The only motor that the output shaft wouldn't be attached to some kind of load I can think of is a rotary phase converter but I think it could be argued that it is still industrial.
As far as my use of the term "illegal" you would be correct. I am sorry for that. The NFPA 70, 79, and all the other codes are used as a professional standards. They are not the enforcement agency. The local governments are and would be in charge of prosecuting injury or death due to negligence for not following the "professional standards" set by code and or the venue for a civil lawsuit to for injuries or property damages.
As far as the ground rods and bonding conductors at the service panel, that should be bonded to all other grounds, is not just for as you quote
"ground rods are for shunting lightning, limiting potential to earth, and shunting high voltage current when primaries lines hit secondary lines"
It also "Bonds electrical equipment together to establish a low impedance path (effective ground-fault current path) from the fault location back to supply source to facilitate the operation of overcurrent devices."
Article 250 of the NEC requires the service entrance ground rod/rods(sized by the tables) and most explicably be bonded to all other ground pathways. If not bonded it can cause shocks, like you experienced. It was found that the old way of the only ground was to the pipes was not effective for a multitude of reasons including soil conditions. This is well document and searchable on google.
As for my use of the term Earth or earthed, sorry, its used across much of Europe as well as a general term for ground. And I spend my working days on German and Italian made equipment nowadays.
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Firebrick43
Well-known member
I had assumed that a big reason to have a tied breaker was incase there was a fault in the wiring. For example a bad/broken connection in the common neutral line. A neutral with high resistance might not be obvious if the L1 and L2 loads happen to be balanced. But if one leg is turned off for any reason then that poor neutral connection can mean significant voltage on at least part of the neutral wire.
I think what would be helpful here is a simple describing when having half the circuit energized could be a danger. I admit when I first thought about it I didn't see why the common tie would be needed until I thought of the example above. I'm not sure I can think of a case where an over current trip would result in dangerous voltage on the neutral if the wiring is solid.
I think what would be helpful here is a simple describing when having half the circuit energized could be a danger. I admit when I first thought about it I didn't see why the common tie would be needed until I thought of the example above. I'm not sure I can think of a case where an over current trip would result in dangerous voltage on the neutral if the wiring is solid.
Handle ties tell the electrician that it is a multi-wire circuit without removing the panel front, & disconnects all legs of the circuit. There are a lot of multi-wire circuits that were done before the requirement for handle ties for multi-wire circuits, so always have to be aware.
alfredeneuman
Well-known member
...and before the requirement the separate breakers of the MWBC could be anywhere in the panel and not necessarily next to each other
IMO, the biggest reason is the frequent use of MWBCs in Kitchens and workshops. In my case where there is more that one receptacle in a box, they are on different hots of the same MWBC. So, the tie assures that anyone opening one of them for work will kill both conductors. Otherwise a real surprise could be waiting when one sticks a screwdriver in there.r
Metal-Marc
Well-known member
...and before the requirement the separate breakers of the MWBC could be anywhere in the panel and not necessarily next to each other
That was back in the days when electicity was mild and didn't electrocute people. Those were the days.
Shouldn't be any surprise if you tested for power...
In your example, if you had two circuits with separate neutrals there would be no requirement for handle tied breakers even though both receptacles are in the same box.
wyliesdiesels
Well-known member
has nothing to do with that. has to do with servicing the circuit.
wyliesdiesels
Well-known member
If you think the ground rods and the earth provide a low impedance fault current pathway so that breakers can trip and open to clear the fault current, you are sadly mistaken. The earth is a poor conductor and if you rely on it for a low impedance fault current pathway, youre gonna have major problems. As i previously said, ground rods are NOT for establishing a low impedance fault current pathway. THAT is the job of the EQUIPMENT GROUNDING CONDUCTOR.
Terry D
Well-known member
They make a 2-pole AFCI breaker where you can share the neutral. What is going to be a thing of the past is tandem breakers
Sent from my SM-G960U using The Garage Journal mobile app
Firebrick43
Well-known member
I look at the grounding system as a system. I don’t understand how one looks at it as individual components?
I specifically mention bonded several times and even highlighted the word bonded. Does that not mean a copper conductor tying metal piping, panels, and other possibly energized equipment back to the service entrance panel? As far as the rods at the service entrance maybe it’s just experience in old farm houses but that used water pipes were many times were not well bonded and many were shocked. Using water pipes for the service entrance electrode is not accepted any more as an only means by 250.52.
And if we really wanted to be technical even bonding(ground fault pathway) doesn’t prevent shocks as stray current or current leakage can be present in low enough amps as to not Trip the breaker. Do they make GFCI MBs ?
wyliesdiesels
Well-known member
As someone who does grounding for microwave communication towers, I can and do look at components individually and understand their function. Their function on an electrical system is the same.
If youre getting shocked by a water pipe, it means the neutral on the service is bad and neutral return current was flowing on the water pipe. Water meter techs often get shocked when removing and replacing water meters that dont have bonding jumpers on them.
alfredeneuman
Well-known member
You do, of course, realize that prior to 1990 the only thing required for grounding was 10' of continuous buried metallic water pipe and the clamps could be anywhere on the pipe?
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Firebrick43
Well-known member
Yes that is one possible source, I have seen a hot wire have insulation broken down to, but not a dead short, leaking to a pipe. The neutral return is a very big problem in rural areas. Cows are much more sensitive to stray voltage and dairy farms try to alleviate it with equipotential planes(very controversial for even the professors)
As far as before 1990, yes, they saw the error in the code and changed it
They changed the code because of the use of plastic water lines over copper & galvanized.
If the code required use of metal / copper pipes, there was no reason to change it. Although we don't know the actual reason for the change, having been zapped (mildly) in a <1990s home with plumbing grouds (no PEX or plastic pipe) - this is one of those code changes that makes sense to me..
Terry D
Well-known member
Todays codes still only require 10 or more foot of buried underground metal water pipe to qualify as a grounding electrode. What has changed, and I'm not sure of which code, its been awhile ago, is the location of the connection of the GEC. It was allowed to be anywhere on the interior cold water line. They would usually connect it to the closest cold water line. Now since plastic and PEX water lines are get installed, The NEC has limited the connection to within 5 foot where the metal water line comes in the building, assuming they did not switch over to plastic within 5 foot. We like to get the connection right where it comes through the foundation.