why i HATE shared NEUTRALS!!

[brother]

There are so many different ways to get shocked this way, I'd say the most effective weapon against it is preparedness, rather than banning MWBC's starting today. Who would expect a neutral snagged from a different panel? That's a violation of code anyway: 300.3(B).

This is true, however the means of avoiding shared neutrals wouldve reduced risks. Read the other examples there. when going into old houses and some of the 'so called commercial remodles' :wink: I start using an amp probe on the neutral, just to see if its STILL carrying a load on it, and even then, just as good practice i still treat it as though its being used when re hooking it up :wink: :!: .

Some of these remodles are 'scary' :shock: (no updates on panels or anything) Yes, i will admit a LOT of these were NOT done by electricians. But like some of those articles said, there are ELECTRICIANS getting shocked on this.

Ok im done, I enjoyed debate and i KNOW i have NOT changed ANYONES mind about shared neutrals. Just wanted to show why i dont like them. When i build my new home, I will spend the EXTRA money to seperate neutrals on my new home :wink:

I think its cheap compared to potentially getting a $3000.00 plasma tv fried because a GOOD electrician had a BAD GOOF that particular day.

Because Im sure most you are are great electricians. and even GREAT ELECTRICIANS can have a BAD DAY. :wink:

 

[iwire]

Read the other examples there. when going into old houses and some of the 'so called commercial remodles' :wink: I start using an amp probe on the neutral, just to see if its STILL carrying a load on it, and even then, just as good practice i still treat it as though its being used when re hooking it up :wink: :!:

BINGO!

We have a winner. 8)

Your post above is in my opinion the true answer for the 'problem' treat every wire that you do not know the use of as a live wire.

Always!

Every example you gave was not the result of shared neutrals but unsafe work practices.

Lift the a neutral on a live two wire circuit and you can also receive a shock.

I, like Roger and Trevor will alays use as many MWBCs as I can. 8)

 

[Minuteman]

I, like Roger and Trevor will alays use as many MWBCs as I can. 8)

Me too!

 

[don_resqcapt19]

electrician received an electric shock Shocked from the neutral wire while terminating the wire on a relocated electrical panel. Voltage did not show during the zero-energy check because the neutral wire created a complete circuit through the neutral bus. The voltage potential to ground was identified only after the neutral wire was de-terminated.

The same thing will happen in any circuit, two wire or multiwire, if the source is still live.
Don

 

[Pierre C Belarge]

I think this thread shows in part an example of what is occurring in our great industry.

There is tremendous growth of electrical usuage/installation. There is a shortage of EDUCATED/EXPERIENCED electrical personnel (I used that phrase for good reason). We add all of this together with very tight budgets, and jobs moving faster, and it spells disaster. Some people get hurt/killed.


The wiring practice is not the problem, the personnel are the issue. We need better training, mandatory training and some accountability in this industry.

MWBC are similar to guns... the item is not the killer, the person behind it is!!!


It is a shame/sham that the code has to change because this country has not got off it's butt and started enforcing the electrical industry to have its work installed by licensed and permitted jobs, like doctors, attorneys and yes even the hair cutting industry!!!!!!!!!!!!!!!!!!!!!

 

[dnem]

I don't find that genuine reputable electricians screw up multis on common breakers. But I do find good electricians far too often follow a trained pattern of landing the black and red side by side. It's a pattern that works great for regular breakers but can be a disaster on minis.

One of the biggest potential dangers from electrical fire is the overloaded neutral. With no OC it sits there and burns.

David in a home panel with both legs of a MWBC on the same leg as you describe what is the actual chance of a neutral 'burning'?

Look at the 310.16 rating of 12 and 14 AWG.

Not that I am saying it is a good thing when a MWBC is landed improperly just that I do not think it is the disaster you make it sound like. :wink:

I opened a panel one time and wondered why they used brown wires for neutrals. When I examined more closely, they were white neutrals that had turned brown, dry, and cracked insulation. The insulation just flaked off to the touch. Since that time I've seen a number of panels with brown flaky neutrals.

Using the simplist example, on a house single split phase system. If you have a properly installed multi: When the black 12gauge phase wire is loaded to its maximum of 20amps and the red 12gauge phase wire is loaded to its maximum of 20amps, the neutral will have no current flow since there's no unbalanced current.

But if you don't have a properly installed multi and the black and red get landed on the same side of the single split phase: Then when the black 12gauge phase wire is loaded to its maximum of 20amps and the red 12gauge phase wire is loaded to its maximum of 20amps, the neutral will have 40amps of current flow. Table310.16 gives 30amps for 12gauge THHN, but since 240.4(D) cuts back the OC, I doubt there is a much of a fudge factor built in.

If the breakers are tolerating more than 20amps, which happens more often than many people imagine, you can get over 40 on the neutral. Now add higher ambient inside the panel and you have insulation that is getting hotter than it can handle without damage.

How many of you guys have seen brown crusty neutrals in a panel ?

David

 

[dlhoule]

Pierre said:

It is a shame/sham that the code has to change because this country has not got off it's butt and started enforcing the electrical industry to have its work installed by licensed and permitted jobs, like doctors, attorneys and yes even the hair cutting industry!!!!!!!!!!!!!!!!!!!!!

Ah, Pierre, in many parts of the country, we do have such laws. Unfortunately they are seldom enforced in any way shape or manner. We have laws for all kinds of things, most of which are not very well enforced.

 

[dnem]

On one job years ago, I was working on 277v lighting in an office drop ceiling. The orange and the yellow circuits were turned off so we could do some changes to the lighting layout on those circuits. I was up on a ladder with most of my body above the ceiling line. I saw what appeared to be a ceiling tie wire sticking out straight toward me in the dim lighting above the ceiling. I went to grab it to bend it to the side so I wouldn't have to worry about it getting me in the eye and it turned out to be a neutral. It was a shared neutral for 3 circuits including the brown circuit which was still on but the neutral home run was disconnected in one of the jboxes.

When my finger just barely touched the neutral, an upper front spot on my leg was apparently touching the ceiling grid. My arm contracted violently. My arm jerked back as hard as my muscles could generate the force and it propelled me off of the ladder and onto the ceiling grid.

Thankfully the grid held my weight and even more thankfully I didn't get my hand around the wire and clamp down and get hung up on it.

If someone was standing down below they might have seen the lights on the brown circuit blink on for an instant. They had power the whole time. They were just sitting there waiting for a return path to allow current flow so that they could light up. They found their return path thru me and I got "lit up" along with them.

I was very surprised at the extreme violence of my muscle response to the hit from the 277v.

A few years later, one electrician that I worked with for about 6 months was electrocuted on the very next job after he left the site we were together on. He got hung up on a 277v neutral. It fried him for a few minutes and then dropped him off his ladder. They're not sure if he was still alive when he hit the floor or died from the fall.

Open HR multi neutrals (or any neutral on any hot circuit) can kill just as easily as a phase wire. The problem with the multicircuit neutral is that the person working on the circuit can turn off the circuit their working on and still get blasted from the neutral.

Untrained people are risking their lives when they do electrical work and risking the lives of others by the installations that they leave behind.

David

 

[dnem]

Pierre said:

It is a shame/sham that the code has to change because this country has not got off it's butt and started enforcing the electrical industry to have its work installed by licensed and permitted jobs, like doctors, attorneys and yes even the hair cutting industry!!!!!!!!!!!!!!!!!!!!!

Ah, Pierre, in many parts of the country, we do have such laws. Unfortunately they are seldom enforced in any way shape or manner. We have laws for all kinds of things, most of which are not very well enforced.

In Ohio, there's no certification or licensing for electricians but there is for hair cutters.

The one yearly renewable certification we have for electrical workers (that are not independent contractors) is fire alarm and it's never never enforced or checked anywhere at any time.

David

 

[DGrant041]

Hey, guys. Thanks for your comments. They've been constructive without insulting and I appreciate your point-of view and experience.

The DOE link that iwire posted said this:

"Shared or common neutrals in electrical circuits can pose an
electrical safety hazard because they are not always identified
during zero-energy or safe-to-work checks. It is only after a
worker receives an electrical shock or after the neutral has been
lifted and checked with a meter that this potentially dangerous
condition is identified. The following recent events are examples
of this hazard."

My question to everyone is, "Do you make a habit of labeling circuits with shared neutrals?"

This is something I haven't seen mentioned on any of the other threads nor have I seen this labeled in the field. If not, the only other alternative to find out if a circuit is sharing a neutral with another(s) is to open the panelboard. Is that what you do when you change a lighting ballast?

Don, I have a feeling that it will not stand, there are to many instances, (such as in a hospital) where circuits can not or would not be practicle to be turned off or opened at the same time.

I couldn't agree more. Especially if the other three circuits were the rest of the lights in the corridor. OR lets say instead of frying someone's plasma TV, you cut off their plasma?

I understand that proposals for the 2008 code that will require handle ties on all MWBCs and also require group identification of the hots and grounded conductors at the panels have been approved.

Thanks for the info. This would ease my dislike for shared neutrals. I know this notion is unpopular around here. iwire has a habit of bringing up often times overlooked sections in the code that prove to be the basic foundation of what it is built-upon. One of my favorites is 90.1(B)

Adequacy This Code contains provisions that are considered necessary for safety. Compliance therewith and proper maintenance results in an installation that is essentially free from hazard but not necessarily efficient, convenient, or adequate for good service or future expansion of electrical use.

Thank to everyone who participates! Fire-away!

[/soapbox]

 

[roger]

David, you summed it up here,

Untrained people are risking their lives when they do electrical work and risking the lives of others by the installations that they leave behind.

Amen, "untrained" is the key word.

Roger

 

[roger]

Dale,

This is something I haven't seen mentioned on any of the other threads nor have I seen this labeled in the field. If not, the only other alternative to find out if a circuit is sharing a neutral with another(s) is to open the panelboard. Is that what you do when you change a lighting ballast

a clamp on ammeter will tell you if the neutral is carrying current without opening a panel.

We must also remember that after the junction point of a shared neutral, everything down stream is simply a two wire circuit.

Roger

 

[infinity]

We must also remember that after the junction point of a shared neutral, everything down stream is simply a two wire circuit.

Agreed. Changing the ballast would require de-energizing the circuit that the fixture is connected to. Not all of the circuits of the MWBC. In an office setting we have used individual wall switch lockout device to only affect one room when changing a ballast.

 

[dlhoule]

I like the fixtures with a plug in connection for the ballast. You unplug the plug, change the ballast, and plug it back in.

 

[DGrant041]

I understand that proposals for the 2008 code that will require handle ties on all MWBCs and also require group identification of the hots and grounded conductors at the panels have been approved.
Don

That would just plain suck. How on earth would I then be able to run ckts. 1, 4 and 42 with a single neutral if they did something crazy like require tiebars on the breakers? Some people just don't think before they throw out these dumb proposals. :roll:

Roger-

Assuming Paul is not kidding about this, how else would I know which circuits are sharing a neutral w/o opening the PB? Good point though, the neutral would still be carrying current--unless it was cancelled out by two other balanced phases.

BTW, nice conduit runs! I know those don't just happen, they show a lot of skill. And I can't believe you sold those pieces of painter's tape for a $1000. :lol: (just kiddin')

Thanks for responding. Do you label shared neutrals on the PB? Why or why not?

 

[dnem]

Dale, a clamp on ammeter will tell you if the neutral is carrying current without opening a panel.

We must also remember that after the junction point of a shared neutral, everything down stream is simply a two wire circuit.

Roger

Be very very careful with that type of thinking !

It's true when taking amperage measurements, but if you're talking about working on the circuit, if the neutral HR is disconnected, you can be working on a deenergized 2 wire circuit section of the multi and get blasted by the neutral. It doesn't matter where you are on the neutral, in any box any where in the whole multicircuit branches. If the HR is lost, then every single point that you can contact the neutral is the same point electrically.

You can be killed by the neutral on a deenergized 2 wire section of a multi.

David

 

[iwire]

Using the simplist example, on a house single split phase system. If you have a properly installed multi: When the black 12gauge phase wire is loaded to its maximum of 20amps and the red 12gauge phase wire is loaded to its maximum of 20amps, the neutral will have no current flow since there's no unbalanced current.

David I understand how a MWBC works.

My question was a real one.

What is the 310.16 ampacity of 14 and 12 AWG?

It is not the same as 240.4(D)

You mentioned that the neutral would 'burn' (your term) I doubt highly we would get anything remotely near burning.

I have seen brown crusty neutrals on two wire circuits.

As always we can not protect idiots from themselves.

 

[George Stolz]

Well, I will say this much. The discussion has prompted me to purchase a solenoid tester, and I've permanently added them to my bags. I never really thought about the one shock hazard I could encounter that my tick tracer isn't good enough for.

(Like I needed an excuse... )

You mentioned that the neutral would 'burn' (your term) I doubt highly we would get anything remotely near burning.

If two 20A breakers on the same phase were feeding the same neutral? What's to stop it?

Or am I missing something?

...if the neutral HR is disconnected, you can be working on a deenergized 2 wire circuit section of the multi and get blasted by the neutral.

But you're talking about two breaks in the system at once. Why would that occur? Someone would have to intentionally lift the neutral from energized circuits.

 

[roger]

Dale, thank you.

I guess I should have held out for more on the painters tape.

I agree that the panel cover would have to be removed to find the associated breakers (unless someone wanted to take the time with a circuit tracer)

I don't, and don't ask my employees to identify MWBC neutrals, but I agree it is a good idea.

David, as pointed out by George, you are looking at a multiple fault condition and the bottom line is, an open neutral is an open neutral regardless of how many ungrounded conductors it is common to, so I don't understand why you would think an MWBC is more dangerous than a two wire circuit with an open grounded conductor.

With that said, when trouble shooting or working on any circuit, caution must be used and the worst must be expected.

Roger

 

[Shockedby277v]

We use a sharpie and label box covers w/ panel , voltage , ckts/ shared neutrals and where ckts go. When their painted we label on the inside.