Electricution on neutral of 3 wire run?

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  #1  
Old 02-06-07, 08:53 PM
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Electricution on neutral of 3 wire run?

I want to replace a receptacle in my new house which is 6 months old. I basically want to change the color. When the house was wired, I noticed that the electrician used 3 wire runs to do most of the wiring for 15 AMPS. I could tell simply by counting the number of electrical leads leaving the circuit panel versus the number of separate circuits I have.

Even if I shut the breaker off on the circuit with the receptacle, I suspect there is still the real possibility of getting a shock from the neutral since it shares the circuit that is shut off with a circuit that is still on.

I always check the hots and neutrals with a voltage detector to insure there is no reading, but I can imagine a situation in which something on the other circuit malfunctions while changing the receptacle.

From what I can tell, I have no way of knowing which two circuits are on the 3 wire run unless I am actually working on the receptacle where the 2 circuits split off. In my former home which was 3 years old, whenever the circuits split off, I would find one hot going into the receptacle with 2 neutrals on the other side (one going in and one going out to the next circuit). I saw 4 receptacles like this. I suspect that this is an OK way to wire a home on a 3 wire run (correct me if the builders electrician is wrong).

On that receptacle where the two circuits split off, my voltage detector can detect what I think is called an induction current which is about 9 to 18 volts on the hot line with no amperage as a result of the hot that is shut off getting an induction charge from the other hot that is wrapped around it. My electrician had told me I couldn't get electrocuted from that and I was shown that this induction charge can be momentarily discharged by touching the hot wire (which was shut off) to the ground wire, but as soon as they are released the charge builds back up.

In any case, what I am getting at is that I suspect I can find the two breakers sharing the neutral at the split off junction box from this reading of the induction charge, but I also noticed in my former home that none of the other receptacles have this induction charge so if I don't know where the split occurs, I can't tell which two circuits to shut off.

I am guessing that I need to shut off the master breaker to be safe. Am I paranoid or does this sound about right.
 
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  #2  
Old 02-06-07, 09:03 PM
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current can flow thru the neutral of a multi-wire circuit, no doubt. Either find the other breaker or turn off the main breaker.

..and anxiously await racrafts' lecture about knowing exactly what is on each circuit BEFORE doing any electrical work....
 
  #3  
Old 02-06-07, 09:37 PM
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1) What type of tester do you use?
2)Why do you feel the electrician is so inept?
3)Are these realy multi-wire ckts?
(yes neutrals can carry a deadly current, rarely in your case).
4)If the house is only six (6) months old, Why did you not specify the devices you wanted? Surley this was within your control.

If I were the contractor , At the FIRST sign of someone else rearranging or adjusting my work. Any and all warrenties would be null and void.

The job was signed off by the authorities.

By the way... There is no return fom Electricution! It's a one shot deal.
 
  #4  
Old 02-06-07, 09:38 PM
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What your discussing is called a multiwire circuit. these circuits require two single pole breakers positioned on opposite legs of the incoming service or one double pole breaker which does this automatically. I'm not going to go into all that stuff about charged inductive neutrals or hot wires. Maybe someone else will take the time to explain where your right and wrong on that belief.
You need to determine which double pole breaker or which two single pole breakers generate the multiwire circuit. The electrician probably made note of this on the panel index. If he did not the only sure way to tell which two breakers control a multiwire that has been split at a jb is to pull the panel cover and trace all 14 awg and 12 awg 3 wire cables (H-H-N-Grd) (black, red, white, and bare) and find which breakers the black and red land on. Turning these breakers off will de-energize the multiwire. Then you can update the index to reflect what is on that multiwire circuit.
Turning breakers off until you dont read phantom voltage on the shared neutral (if it is a shared neutral) is a good way to get that shock your worried
about. BTW if your using a digital meter those aren't good testers for house wiring. Use Analog, light, non-contact, or solenoid testers. Non-contact is for
testing if power is present in the box.

What makes you think your receptacle is on a multiwire? If your using a digital any neutral (white) shared or not will show voltage.

Roger
 

Last edited by Roger; 02-06-07 at 10:35 PM.
  #5  
Old 02-06-07, 09:44 PM
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it is pretty common for many electrician to wire multi circuit in both single and three phase verison

i will keep it simple here we will use the single phase verison here:

the multicircut it will have two hot and netual plus ground along the way

for the " homerun" they will run the wire[s] to the first junction box and they will split off to branch it out.

but to find the first box it can get little tricky here if you know two breaker handle this MWBC [ multiwire branch circuit ] then you able can track the wires in the basement to first floor and kinda rough guess it will land in there like a quick example :

living room lights and living room repetcale [ dupex outlet ] it will go the first one near electric breaker box and you may see 3 wires like red , black , white from there it will split one go for light and other one go to the repectailes
[ this is a example in real spot it willbe very simuair to this ]

the samething with few other room[s] as well

why allow the MWBC ?? the code do allow it but a catch that you have two breaker to work together in case you have do some service on the devices or what ever you get in there .

you may have to look at the breaker box and map it out when you get done mapping it out then look at the number[s] of cables going out of breaker box you will see how many MWBC there so keep in your mind with this


with the MWBC anytime you work on the switch or repecale or other device with this set up make sure you have complety two breaker off on this MWBC other wise the netural will keep it " alive " if you only turn off one breaker and the other breaker still on and it can catch you off guard with it

if you want to play really safe on this you can shut the main breaker off it will shut everthing off when you work on it

if need more question please do post it here

Merci , Marc
 
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Old 02-06-07, 09:55 PM
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22 years, I have never run a multi-wire homerun. Why would you?

That's just plain cheap. What do you realy save?

Quality, thats bottom line.
 
  #7  
Old 02-06-07, 10:01 PM
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Lee i dont do this often on resdentinal area but it is common in commercal with 3 phase system especally with lighting circuits if you know what i mean

but for commercal side it get spooky if you mention 277 / 480 volts i will tell ya it get ya hard i got shocked from this system a bit


Merci , Marc
 
  #8  
Old 02-06-07, 10:29 PM
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french277: Correct. In commercial work quite often.
My comment was for residential work.

I don't suggest that it is bad... Just, I feel it should not be the preferd method. Multi wire ckts are both SAFE and Legal (code compliant). If done correctly. I have found in the past, more of a headache than needed.
 
  #9  
Old 02-06-07, 10:33 PM
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very true Lee ;

i am not too crazy with MWBC but one way or other we have to deal with it but what i am worry about the DIY's most of them dont get the idea with the MWBC and side effect.

i know the code did allow the MWBC for so many years i dont know what year they start but i am sure it was way back like 20 or 30's maybe more earlier like Edison days

but i wish we set up some kind of photo array so the DIY's can understand the term and describtion so make it more easier to understand the sisuation

Merci , Marc
 
  #10  
Old 02-06-07, 10:42 PM
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Great idea. Unfortunatly, I don't have the (computer) skills to pull it off.

I personaly would not recomend DIYrs attack a multi ckt, unless confronted with it.

There are too many variables to start from scratch.
 
  #11  
Old 02-07-07, 12:43 AM
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1) What type of tester do you use?

I use two, I use a non-contact detector initially and waive it completely around the box to see if it beeps to detect free current. I then use a digital voltage detector. I also have a 120v/240v light contact detector, but I mainly have used the digital one.

2)Why do you feel the electrician is so inept?

I never said that the electrician was inept. But since you asked, I do start to wonder when the electricians over lamped my fixtures in both homes. In my current home, every 60 watt fixture has a 100 watt bulb in it. Also, the recessed lighting was mis-matched between the trim and the housing (2 different companies) which they will correct. The back stabs in both homes showed a lack of care in measuring the wiring lenght, it was not uncommon to see 1/3 an inch or more of exposed wiring.

As for the electrician that I mentioned who explained certain things to me, that was one who I hired who I feel was very competent.

Interestingly, 2 electricians that I have hired in the past have shocked themselves in my home. They like to do all their work with the breakers on. Go figure.

3)Are these realy multi-wire ckts?

(yes neutrals can carry a deadly current, rarely in your case).

Well, in my old home, I saw one hot in and two neutrals out. My electrician told me these were all 3 wire runs. I am not certain about my new house, but I suspect they are 3 wire runs as well.

4)If the house is only six (6) months old, Why did you not specify the devices you wanted? Surley this was within your control.

This was not in my control. Both homes were production homes and I have no say in the switches and outlets. I asked and was denied a number of upgrades in my new home. The builder wanted to keep the house as close to spec as possible.

Based on this, should I hire an electrician to map out the circuits for me for the occassional small jobs of replacing one receptacle, or should I just shut off the main power?

I am currently replacing my switches with dimmers. Since these are switches and dimmers, no neutrals are involved as they by-pass the switch and go straight to the fixtures. For these jobs, does it matter if the other circuit is on or off?

Thanks for your help.
 
  #12  
Old 02-07-07, 03:52 AM
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"22 years, I have never run a multi-wire homerun. Why would you?

That's just plain cheap. What do you realy save?

Quality, thats bottom line."

Lee, as much as I value your opinion, I have to strongly disagree here.
It is not as much about money as every opponent to multi-wire circuits always cites. That is the easy answer.

It is about lessening.
-There are less cables entering the panel.
-There are less neutrals and grounds in the panel (which we all know is a BIG issue these days).
-There is less voltage drop on long circuits.
-There are less cables in drill holes in framing, so in the long run there are less holes.


See, everything is not always about money. And multi-wire home runs in a residential setting are NO less quality than separate two-wire cables.

I will give you that multi-wire circuits done by DIYs should always use handle tied breakers. This is an issue I have changed my view on over the years.

Bottom line is if you don't know what you are doing, and don't have the proper test equipment to possibly save your life, DON'T MESS WITH IT! I think this is the number one key factor in all this.
When in ANY doubt, TURN OFF THE MAIN BREAKER, and STILL test everything!



And to the OP: If you were electrocuted, you'd be dead.
Electrocution mean to die by electric shock.
 
  #13  
Old 02-07-07, 04:17 AM
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We do not need to go on a tangent about multi-wire circuits. They have advantages and disadvantages. They are legal (if done properly) and are in existence.

As has been said, the only safe and proper way to determine which two hot wires go with the same neutral is to physically open the panel and examine the wiring. Assuming NM type cables, the red and black in the same cable use the white as the shared neutral. Any other methods are prone to possible errors.

shopgreatvalues, take the time to take the panel cover off and make these determinations. Don't just look for the circuits in question, but look for the entire panel. Then make detailed notes.

Finally, do not make changes to the panel unless you fully understand what you are doing. If not done properly, multi-wire circuits can be a fire hazard. Done properly they are safe.
 
  #14  
Old 02-07-07, 04:47 AM
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I think there is some mis-understanding. I have no intention of making changes to the panel, just changing a single receptacle to change a color.

In any case, I think I will hire an electrician for the day to change all receptacles to spec grade using back wiring that is secured by a clamp instead of back stabs and replace all switches with dimmers. As stated, my entire house is back stabbed with 49 cent receptacles that don't even have screw terminals (except for the 20 AMP ones of course).

I used this as a selling point and of course the buyer wanted assurance that all work was done by an electrician.

I called UL and asked about the back-stabs and was basically told that they meet minimum safety standards (emphasis on minimum), they are safe enough to be used in millions of homes with the current standards, but if I can, I should consider using spec grade because they have a number of benefits over the 49 cent ones.

I did this with my former house as well. What I did was shut off the main breaker and removed all switch plates and pull out all the receptacles and switches from the wall to save the electrician time and me money.
 
  #15  
Old 02-07-07, 05:11 AM
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Perhaps I am wrong, but this would not be a selling point to me. While I would certainly spec a new home to be wired using better quality devices and with the colors and styles I wanted, I would not pay more for a house if the seller promised to do this for me on an existing house.

Understand that you probably cannot "replace all switches with dimmers." Any switch that controls a receptacle cannot be a dimmer, for example.

Further, dimmers everywhere does not make sense, to me anyway. I use fluorescent light bulbs in many places which do not tolerate dimmers, and I see no purpose in dimmers for garage lights, for example. I also would not put dimmers on hallway or stairway lights.

I think posters were just expressing concern about the multi-wire circuits. Often we get people posting here who want to do all sorts of things, adding circuit here and there, etc. Many do not know what a multi-wire circuit is, let alone how to properly wire it. By cautioning you about your multi-wire circuits, we are also cautioning everyone else who reads this thread.

I'm still not sure how we went from your new house being wired with cheaper products to your selling the house, but no matter.
 
  #16  
Old 02-07-07, 05:40 AM
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The selling of the house I referred to was my former house. I am not selling my new house.

Also, I think on those 3 wire runs I had, the junction box receptacle had two hots and one neutral, not the other way around as it must have been at the beginning of the run, not the end (it was several years ago). I think the neutral was pony tailed at the junction box, otherwise there is the risk of a voltage surge on the other line should it ever detach from receptacle from what I understand.

I have dimmers for all areas except the following: the garage where I plan to install a lighted switch, the one switched receptacle in my house where dimmers are not allowed, all fan switches, ect. I don't use CFL's and my house is way over lit including the hallways and stairs even using reduced wattage bulbs.

At the very least, I will probably have an electrician map out the circuits for me so I know which ones are multi wire branch circuits and I can then shut off both circuits safely.

Question, why are digital volt meters bad? Someone suggested analog. Does this have to do with phantom voltage readings? I always use the digital meter in conjunction with a non-contact voltage wand.
 
  #17  
Old 02-07-07, 08:08 AM
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Digital voltmeters are subject to "phantom voltage" (google it), which can be very misleading. Use your digital voltmeter to figure out whether you have 0 volts, 120 volts, or 240 volts. If you get any reading other than these three, it's probably phantom.

For most applications in which you only want to know whether something is "hot" or not, simple neon testers and/or non-contact testers and/or plug-in outlet testers are so much cheaper, accurate and easy to use.
 
  #18  
Old 02-07-07, 10:10 AM
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Shouldn't all these multi-wire circuits be on double pole breakers for the very reason this thread was started? I have found two multi-wire circuits in my house, neither of which were on double pole breakers and I was more lucky than anything.
 
  #19  
Old 02-07-07, 10:40 AM
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Sure, it's a lot better if multiwire circuits have a common trip lever. But it's only required in certain situations.

There are two big rules to follow here: (1) don't touch the wiring in your home unless you understand how it works, and more importantly, (2) never touch anything without testing it first, no matter how many breakers you have turned off.
 
  #20  
Old 02-07-07, 05:23 PM
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hi Folks.

Shopgreatvalues: Your answers have cleared alot of questions, Thank you and be safe. The proximity tester is great for general evaluation,I would strongly recommend the 2-wire tester for assurance.

Speedy: Well taken points. Very logical, thanks for the other veiw.

Racraft: You tagged it! These multi-wire ckts can be a blessing or a curse!
To the DIYr, be carefull, Mark all ckts. When in doubt shut it ALL off.

Don't fear it, learn and respect it.
 
  #21  
Old 02-09-07, 08:29 PM
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The builders electrician came by my house today to replace the mis-matched trims and housing with my overhead lights. They used DMF trims on Juno housing. After talking with the electrician, I have decided to hire him next Wednesday to intall my dimmers and other devices. In addition, he will map out the circuit panel for me so that I will know which circuits share the multi wire runs.

He was fairly frank with me and appeared to be a nice guy, a seasonal electrician with 20 plus years experience. I told him my concerns about the work done on my house by their electricians such as overlamping and shoddy work on stripping the wires to long so that quite a bit of copper was exposed in certain switches.

From what he told me, the company he works for wires over 200 homes a month and they have good and bad electricians, but felt bad that the trim wasn't neater.

The company charges $90 an hour which I think is the going rate in my area.

He told me that they use multi-wire runs in all residential applications because it saves time and money. He told me that none of the bedroom circuits could be multi-wire because they are AFCI breakers which can not share a neutral, I did not know this.

On the down side, I can never add additional AFCI breakers in the future on any circuits that are multi-wired, something else I didn't know.

I guess when he maps out the circuit panel, I will have him inspect the wiring to be sure their other electrician did it right. If not, I believe the additional time to correct it will be free.

Is there anything else I should have this person do?
 
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Old 02-09-07, 08:36 PM
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"On the down side, I can never add additional AFCI breakers in the future on any circuits that are multi-wired, something else I didn't know."

Not entirely true.
There are two-pole AFCI breakers for this for some panel brands. I would bet VERY soon all manufacturers will be offering them as well.
 
  #23  
Old 02-09-07, 08:43 PM
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Your on a good track. You seem to have found an honest pro (there are alot of them out there).
You appear to be comfortable with this one, thats great. Ask and understand.
I can't confirm or deny the comments, somethings we must see to understand.So far, I don't feel any "BS" going by.
 
  #24  
Old 02-09-07, 08:50 PM
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I think the time and money saved is for the builders benefit, not the electrician. He told me his company charges $75 hour for the builder rate instead of $90, something he felt was not entirely fair, but that is what it is. So I am guessing the builder pays by the hour rather than by the job, so the benefits go to the builder.

He told me that most of the large builders in my area are super cost sensitive.
 
  #25  
Old 02-14-07, 06:04 PM
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Follow-up:

The electrician came out today to work on my house. It was a different person than what I was told due to a mix up as they both have the same first name. In any case, this one also had 20 years experience.

The work took 7.25 hours but I like the piece of mind knowing (or at least hoping) that everything I wanted was done correctly. In this case, I replaced 30 toggle switches with dimmers, 5 toggle switches with times, 7 toggles with rockers, 5 receptacles replaced (I wanted to mark my dedicated 20AMPS with T-bar outlets), installed a brand new overhead cam near the shower, map out all the multi-wire runs (there were 4 sets of them), correct the breaker size for the A/C (the builder used 50AMPS at the circuit panel and 60AMPS at the A/C itself as an outside on/off switch - the A/C recommended 60AMPS and the eletrician said the wire can support over 70AMPS so he replaced the 50AMP with a 60AMP in the garage).

At each switch, he used the terminal scews and ponied tailed all continuous hots going to other locations. He showed me his work and saw lots of neatly done twists in the wiring. Seeing the twists, I can not imagine them ever coming apart with or without a cap, although wire caps were used of course.

On the downside, when I moved into my new home 6 months ago, I hired an eletrician to do some work including an installation of 4 toggle dimmers which I have just replaced with flat dimmers. This electrician was highly rated by consumers in Checkbook. However, a pony tail he did failed which I noticed after he left (he did come back and correct it at no charge). On top of this, I saw when my current electrician pulled out the dimmers he installed, that he not only backstabbed all of them, but failed to ground 3 of them, he simply pushed the ground wire way in the back. Now I have to tell you that I can not do nearly the quality of what a good electrician can do, but this other guy really ticks me off for not grounding the dimmer. My current electrician believes dimmers are safer not being grounded, but grounds all of them and said the others should have been because the code requires it.

I guess the one thing I feel comfortable with is that if my house ever does burn down due to faulty electrical work, I should be covered by my homeowners insurance who would probably go after the electrical company for damages whereas if I did something wrong, I suppose I migh not only lose the house, but might not get paid to replace it.
 
  #26  
Old 02-14-07, 06:31 PM
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"I guess the one thing I feel comfortable with is that if my house ever does burn down due to faulty electrical work, I should be covered by my homeowners insurance who would probably go after the electrical company for damages whereas if I did something wrong, I suppose I migh not only lose the house, but might not get paid to replace it."


Just one footnote to your post. The statement above is a myth. As evil as some insurance companies are they DO pay in cases like you describe. If your house burns down because you did not know what you are doing they still pay.
The only time this is not true is if they find it was done intentionally. In this case though the insurance company is the least of your worries.
And yes, I have this on good authority. My information came from an insurance underwriter with 20 years experience.
 
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