Multi Wire Branch Circuit safety question

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  #1  
Old 10-21-14, 12:09 PM
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Multi Wire Branch Circuit safety question

My son just bought a house in Orlando, Florida built in 1987. I have been going through documenting and mapping out all the circuits (e.g. "Kitchen" written in the panel door is too sketchy for me).

At one point I took the circuit breaker panel cover off to confirm something. Glad I did. Some breakers had a red wire attached versis a black one. What??? OK, I confess that I had never heard of multi wire branch circuits before but I'm learning fast.

My concern is for safety. Isn't it true that if you are working on one circuit that you also need to knock off the circuit breaker that is sharing the neutral? I followed the black and red wires coming out of the romex and the breakers are NOT right next to each other (they are coupled 2&6; 16&28; 20&24;22&26).

I read where some places require a bar between two so both must be shut off, but that is certainly not the case here nor would it be possible with the distance between the breakers. I am thinking of color coding them so anyone (even fifty years from now) doesn't get a big surprise. Am I thinking properly about this? Thank you!
 
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Old 10-21-14, 12:15 PM
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I like your thought process. Had to do this at my old man's house after he and a neighbor (retired master electrician) added some circuits and replaced the panel - inspector said they had to be tied together. Luckily, his were all adjacent.
 
  #3  
Old 10-21-14, 12:51 PM
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Yes they should be tied together. It is now Code but wasn't in '87.

You can splice in the panel box (in most jurisdictions) so you could "fix" it.

What brand is the panel first or post a pic. The breaker labeling, and the leg the breaker is on, vary.
 
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Old 10-21-14, 02:29 PM
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The current code calls for both hots to be able to be turned off at the same time by using a two pole or two single poles with a handle tie. Previously the code only required this if both hots were on the same strap.

You do need to make sure the hots are on opposite legs of the panel so the neutral current does not add together.

Can you post a picture of the inside of the panel?
 
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Old 10-21-14, 03:01 PM
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The house is 20 miles from me, but I may be able to get a picture tomorrow night. I do believe that the hots are on opposite legs (as I understand it) as I was wanted to verify that point myself.
 
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Old 10-21-14, 03:12 PM
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The legs cascade ABABAB down each side of the panel top to bottom.
 
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Old 10-21-14, 06:22 PM
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I do believe that the hots are on opposite legs
In all four examples it appears the multi wire branch circuits have both circuits on the same leg, assuming the circuits are numbered properly.

(they are coupled 2&6; 16&28; 20&24;22&26).
 
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Old 10-21-14, 07:43 PM
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I thought the same thing CJ. I was wondering if tandems were involved.
 
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Old 10-22-14, 09:12 AM
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Double check using your voltmeter to be sure that you get (approx.) 240 volts when measuring between the two legs of each multiwire branch circuit.
 
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Old 10-22-14, 05:57 PM
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[ATTACH]40537First, thanks for all the responses. Now that I truly nderstand how the legs are staggered, then it does appear that they are all on the same leg after all. I was very careful in documenting where the black & red wire came out of whick romex and where it went down to a breaker.

The panel has a Square D logo on it. Below are two photos that I quickly took. I was not able to use a multiumeter this evening as all were waiting on me to leave for a birthday dinner. I was rushing to get just the photos, but I am quite certain now about them being on the same leg, so I am wondering how it ever passed inspection back in '87.
 
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Old 10-22-14, 06:19 PM
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If you have correctly identified the black and red from the same cable you need to measure voltage between them to make sure you get 240 and not 0. If you get zero volts you could overload the neutral.
 
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Old 10-23-14, 01:14 PM
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This forum is SO much appreciated. I could not wait to get out of work to stop at my son's house to take multimeter readings. Sure enough, the circuit groupings I had indicated are verified as being on the same leg as the readings were zero between them. Confirmed that every breaker read 120 just for peace of mind.

I believe with some creative movement of the wires that I can get the paired up multi wire circuits in adjacent, correct postions. Are handle ties sold individually so they can be added?

I started this whole thing in the name of safety. In case I am questioned as to why I am making an issue of something that has been this way for about 27 years, how do I best explain how this "same leg" situation be a problem and under what circumstances? Thank you again!
 
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Old 10-23-14, 01:25 PM
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Someone will answer the neutral question. Basically it's overloaded.

I just wanted to comment that is one of the neatest/cleanest panels I have ever seen!
That would be a joy to work on.
 
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Old 10-23-14, 02:21 PM
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Are handle ties sold individually so they can be added?
Yes, but probably in a bag of five or ten at BigBox. Hardware store might sell an individual one.
how do I best explain how this "same leg" situation be a problem
When the 240 is on opposite legs part of the return current is on the opposite 240 leg. The neutral caries only the difference between the current on the 240 legs.

If there is 20 amps on leg A and 0 on leg B the the neutral carries 20 amps. If there is 20 amps on leg A and 20 amps on leg B the neutral carries no amps. So you can see between those extremes the max current on the neutral can only be 20 amps without tripping the breaker.

However when both breakers are on one leg the neutral carries all the return current. So using the example above if both breaker carry 20 amps but are on the same leg all return current is on the neutral. Therefore the total load on the neutral is 40 amps but only 20 on the breakers so they won't trip.
 
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Old 10-23-14, 06:09 PM
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I had to download the picture and then enlarge it but it appears that maybe there are some cables entering the box without the benefit of a cable clamp; specifically the ones immediately to the right of the service entrance cable. If this is true then it is highly doubtful that the additional work was ever inspected because an "inspector" might miss the incorrectly wired MWBC but no way would he miss the elimination of cable clamps.
 
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Old 10-24-14, 12:33 AM
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Thanks for your efforts and bother in trying to have a closer look. For the record, those cables immediately to the right of the service entrance cable DO have clamps. The takeaway for me is that despite codes and inspections, errors can still occur since humans are involved. This forum is helping reverse the trend, however. For this I am grateful.
 
  #17  
Old 10-24-14, 04:00 AM
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Why on some two pole breakers do I see a black wire on each pole?

If multi wire circuit, shouldn't a three conductor cable have been used? One red and one black to each pole and then sharing the neutral. This is telling me that two 2 conductor cables were used each having its own neutral on a two pole breaker.
 
  #18  
Old 10-25-14, 02:46 PM
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It just seemed appropriate to provide an update. Today I was able to move wires around to get the multi-wire circuits on opposite legs and now all read 240 across them (handle ties were not immediately available locally so that will have to wait). I am very pleased about this and without the folks on this forum, I would not have even been clear about the existence of a problem. So, thank you!!

As to the previous comment, I observed that on the two pole breakers (left side of panel) that some of the wires were taped in black. I can't speak to the significance of that. My focus were circuits on the right side of the panel.
 
  #19  
Old 10-25-14, 05:44 PM
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The black tape could have been used on a white conductor to show it is a hot and not a neutral. No issues with doing this and it is required to mark the conductor as a hot.
 
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