open neutral...big problem

[hurk27]

My home service is not a multi-wire branch circuit. It is a service feeder tapped off low side of 7.5kw can.

Its still a multi-wire circuit, whether it is a branch circuit, a feeder circuit, or a service circuit, its still multi-wire and if you loose the neutral it will cause the same sea-saw effect on the voltage.

 

[reddy kw]

I dunno 'bout that. A MWBC with reasonably balanced load running will have better voltage "control" as the voltage drop of the neutral will be canceled, thus halving the voltage drop each side's load experiences.

Regardless of the load type (early 1900s or early 2000s), the voltage control on the end of a MWBC is still good engineering to me. With respect to AFCIs, that may be changing. The new GE MOD 3 AFCI in the single pole 15 A and 20 A sizes can be used to protect a MWBC, as shown in a GE diagram that Dennis Alwon posted here. Note that the MWBC neutral is only connected to one of the single pole AFCIs.

GE is, evidently, accomplishing this, in part or whole, by dropping the GFCI-like component of their breaker circuitry.

GE has released very little information about this development, even though the breakers are already out in distribution. I've even seen them on the shelves of the local Big Orange store just last week.

I'd like to see those 120/240 volt 3-wire AFCI's on the shelves of my local distributors, but they haven't reached here yet. I also understand they'll be almost 5 times as expensive as a single-pole AFCI ($36 vs. ~$150).
I don't know about eliminating part of the circuitry. Will it meet code for a combination-type AFCI?
IMHO, AFCI breakers work well. I sleep better knowing my customers' wiring is protected by the highest level safety equipment available.

 

[roger]

IMHO, AFCI breakers work well.

Can you provide back up for that besides what the manufacturers tell us?

Roger

 

[Smart $]

I thought they already had "Ω" in it. Every slide was built from a bitmap..... there's no text other than what's along the top.

The lower characters are also "text"... but the "omega" character is of the GreekC true type font. If the viewing computer does not have the GreekC true type font installed on their system, PP probably substitutes with another font. The rest of the text is Times New Roman font, which does have the "omega" character... so I don't know why GreekC was used.

 

[e57]

My home service is not a multi-wire branch circuit. It is a service feeder tapped off low side of 7.5kw can.

Still a split phase multi-wire system - FWIW all the bashing or head in sand attitudes about MWBC's or the NEC dumbing down the trade install for non-believers to create some unfounded 'safety' by requiring handle ties, or simultaneous disconnect on MWBC's does NOTHING to eliminate the present dangers of the service, or panel that is fed the same way... A high/low voltage event can and will still happen

It's cheap and easy to run one 3-wire to get 2 circuits, but it's not sound engineering. Is it possible MWBC's are obsolete in 21st cen. residential wiring? Along with danger of open neutrals, they don't work with AFCI or GFCI breakers. When MWBC's were prevalent 100 years ago, there were no electronics. Houses had resistive loads, almost no leading/lagging loads. 3-wire MWBC's were NOT meant to be used for electronics or Sub-Zeros.
14/2/2 and 12/2/2 give us '2 for 1' cable pulls without any issues associated with "Edison Circuits" (as they used to be called). More expensive then 14/2 or 12/3? Yes, but far less expensive then having to buy your client a new frige and microwave.

Apart from demanding the inefficiency of a 120 system feeding a home - sans any other voltage - the fact will remain - a lost neutral can still happen... GFCI's and/or AFCI's will do nothing to safe equipment - before they too fail....

Running a Sub-zero, or some expensive AV gear will not be effected by a MWBC unless they were on the same one... Separation of equipment and appliances by type and use is an easy and sound method of reducing noticeable interference of voltage drop by other loads on lighting or electronics... Otherwise - putting a microwave or some other type of motor load and the most expensive refrigerator you can find on the same MWBC will cause no issue.... And since they are STILL on the same transformer - there is no way to completely separate these items - no matter where the connections are made - either in a J-box, or in the main or sub-panels....

FWIW - 100 years ago - it was rare use of a MWBC... The wider spread practice of MWBC's post dates NM cable... K&T of the 1900 ~ 1930's was typically 2 wire w/ fused neutrals. As was conduit installations in both residential and commercial of the same eras... Once fused neutrals became obsolete, and copper became really expensive during and right after WW2 - the 3-wire circuit became more popular...

 

[dbuckley]

Its still a multi-wire circuit, whether it is a branch circuit, a feeder circuit, or a service circuit, its still multi-wire and if you loose the neutral it will cause the same sea-saw effect on the voltage.

That's absolutely bang on the money.

Doesn't matter if its split phase domestic or three phase industrial, losing the neutral integrity is always bad (and usually expensive) news.

In the theatrical and presentation arts, we have a little saying:
Lose a live, lose the show
Lose the neutral, lose the rig <=== sound familiar?
Lose the ground, lose a life

 

[480sparky]

The lower characters are also "text"... but the "omega" character is of the GreekC true type font. If the viewing computer does not have the GreekC true type font installed on their system, PP probably substitutes with another font. The rest of the text is Times New Roman font, which does have the "omega" character... so I don't know why GreekC was used.

Because they look the same. I did this PPP about 3 or 4 years ago, so I don't exactly remember everything about it. It also took me a couple weeks of working on & off to compete it.

 

[mcclary's electrical]

My home service is not a multi-wire branch circuit. It is a service feeder tapped off low side of 7.5kw can.

2 hots, 1 neutral. What's that?

 

[480sparky]

2 hots, 1 neutral. What's that?

Strictly by the NEC, it's not a MWBC. B stands for Branch, and your service conductors are not a branch circuit.

But it still acts the same when the noodle is opened.

 

[al hildenbrand]

I'd like to see those 120/240 volt 3-wire AFCI's on the shelves of my local distributors, but they haven't reached here yet. I also understand they'll be almost 5 times as expensive as a single-pole AFCI ($36 vs. ~$150).

If any of the panels you work on are GE and have the full size space (1") available, then you'll be able to use the MOD 3 AFCI. It sells for ~$36.00.

I don't know about eliminating part of the circuitry. Will it meet code for a combination-type AFCI?

It is, in fact, the combination-type. Look on the breaker body near the handle and you should find small faint printing that includes "MOD 3". It's the first AFCI, to date, that will work on one leg of a MWBC.

 

[kwired]

...FWIW - 100 years ago - it was rare use of a MWBC... The wider spread practice of MWBC's post dates NM cable... K&T of the 1900 ~ 1930's was typically 2 wire w/ fused neutrals. As was conduit installations in both residential and commercial of the same eras... Once fused neutrals became obsolete, and copper became really expensive during and right after WW2 - the 3-wire circuit became more popular...

Many of those 100 year old wiring systems were not 120/240 but just 120 only so there would be no possibility of using a MWBC.

 

[jumper]

IMHO, AFCI breakers work well.

Can you provide back up for that besides what the manufacturers tell us?

Roger

Ya mean you don't trust all them there swell fellers at the big blue box or Joe Bubba at the supply house?:-?........grin

 

[Smart $]

Because they look the same. ...

I'll agree they are the same character... but I don't see them as looking the same.

...but hey, it's your puppy. You can have it look however you want

 

[reddy kw]

Strictly by the NEC, it's not a MWBC. B stands for Branch, and your service conductors are not a branch circuit.

But it still acts the same when the noodle is opened.

MWBC=multi-wire branch circuit.

In NYC, service is run underground. Wintertime means burn-outs from salty melt run-off into manholes under road.
I've been called to repair both 3-wire and 4-wire services where one leg was down-the neutral. When building had good ground, lights stayed on. This is when you tell the landlord it's necessary to pull in a new service.
If ground continuity is %100, neutral bonded to ground at SE, grounding electrode + cond. are working properly, ground will temporarily carry neutral in situation with burned-out neut. service conductor. Same doesn't apply to open branch neutral.
NYC's grid is oldest in USA (1882, Edison's 'First District', Pearl St. Station). 'Edison Circuits'= 3-wire 125/250 volt dc systems (usually in wooden wireway). Sometimes still found in operation in old buildings downtown and in Brooklyn. The 'advantage' of these circuits with resistive lighting loads and balanced inductive loads is lost when digital information systems are hooked up, with high constantly changing transients on the neutral.
I have 1911 Electical Engineer's Handbook that repeatedly refers to 'Edison Circuits'. The term could have other meanings elsewhere in the land.
As far as AFCI's I've put in a hundred or more, GE's are the best. I didn't know I could use the new 3rd-gen single-pole on one leg of MWBC. Since I run dedicated neutrals for all branches, I never tried.
I'm a worry-wart. Wood-frame one-family homes seem like matchbooks to me. When I read annual fire death stats in the NFPA Journal, and see how many could be prevented by better wiring, AFCI's, etc., like I said, I sleep better knowing I did what I could.

 

[LEO2854]

MWBC=multi-wire branch circuit.

In NYC, service is run underground. Wintertime means burn-outs from salty melt run-off into manholes under road.
I've been called to repair both 3-wire and 4-wire services where one leg was down-the neutral. When building had good ground, lights stayed on. This is when you tell the landlord it's necessary to pull in a new service.
If ground continuity is %100, neutral bonded to ground at SE, grounding electrode + cond. are working properly, ground will temporarily carry neutral in situation with burned-out neut. service conductor. Same doesn't apply to open branch neutral.
NYC's grid is oldest in USA (1882, Edison's 'First District', Pearl St. Station). 'Edison Circuits'= 3-wire 125/250 volt dc systems (usually in wooden wireway). Sometimes still found in operation in old buildings downtown and in Brooklyn. The 'advantage' of these circuits with resistive lighting loads and balanced inductive loads is lost when digital information systems are hooked up, with high constantly changing transients on the neutral.
I have 1911 Electical Engineer's Handbook that repeatedly refers to 'Edison Circuits'. The term could have other meanings elsewhere in the land.
As far as AFCI's I've put in a hundred or more, GE's are the best. I didn't know I could use the new 3rd-gen single-pole on one leg of MWBC. Since I run dedicated neutrals for all branches, I never tried.
I'm a worry-wart. Wood-frame one-family homes seem like matchbooks to me. When I read annual fire death stats in the NFPA Journal, and see how many could be prevented by better wiring, AFCI's, etc., like I said, I sleep better knowing I did what I could.

THEY HAVE TWO POLE AFCI's now so you can put a MWBC ON THEM

 

[reddy kw]

THEY HAVE TWO POLE AFCI's now so you can put a MWBC ON THEM

When my local supplier get them in and they come down in price, I would be in.
Except:
With the IT equipment my clients are using, with high transients on the neutrals, why do I want to undersize the branch neutral conductor by having it carry twice the load as the two 120 cicuits it serves? If it were balanced, okay. Two circuits, both with IT systems on a shared neutral, will not be balanced.

 

[reddy kw]

Ya mean you don't trust all them there swell fellers at the big blue box or Joe Bubba at the supply house?:-?........grin

'Tain't 'bout trustin' Bubba, Bubba. I jest does it like them fellers what rits up thet NEC say. They seem ta know what ta do. .

Besides, it really doesn't matter what I think. It's the Code and eventually enhanced levels of safety (I.E.: AFCI or GFCI breakers on all branch circuits) will be mandatory everywhere, in all 50 states.
Might as well get used to it and learn how to do it right because call-backs in the middle of the SUCK (and so do elecrical fires)!

 

[e57]

Well reddy kw, you seem to be a man who believes the hype... GFCIs wont do much in the way of protecting against fires. And I'm sure there are many who wont buy into most of the manufacturer provided evidence that AFCI's will either. (Huge debates about series vs parallel faults for years now...)

And while running only two wire branch circuits makes you feel better - they still will originate from a multi-wire system. And the neutral & hots of each are still connected to the same 'filthy' transient laden power everything else is on... That is if you believe in transients or harmonics being that big of an issue - since they will have very little effect on IT and audio equipment due to the power supplies and filtering in them.... In fact it is these items and florescent lighting that is creating them in the first place... And having a multi-wire circuit doesn't get rid of them... (While there is some debate on the possible triplen harmonics causing problems on WYE circuits, and over-sizing of neutrals. But they have little effect in a center-tapped single phase system that most dwellings are served by.)

Earth is a relatively poor conductor - no matter what type of soil it is. And if you completely loose a neutral on a service and it holds a voltage/current balance - most likely it is the underground water line that may be saving the day. In-fact (while plumbers would disagree) I think it should be mandated that bonding be across the water meter, and we should outright ban plastic underground piping to better serve as electrodes, and act as a back up neutral connection through the buildings adjacent to each structure.... :roll:

 

[reddy kw]

I meant to say "Call backs in the middle of the night suck".

"Well reddy kw, you seem to be a man who believes the hype... "-I also believe that we really did land on the moon, and that Elvis really did die in 1977.:grin:

"...GFCIs wont do much in the way of protecting against fires...."
-No, but they're good at preventing electrocution. I meant it as a general reference. Both are recent improvements in electrical safety.

"... And I'm sure there are many who wont buy into most of the manufacturer provided evidence that AFCI's will either. (Huge debates about series vs parallel faults for years now...)"
-I have to follow the NEC. That's my job. I do not think there's a conspiracy between electrical manufacturers and the NFPA, UL, and AIEA.

"And while running only two wire branch circuits makes you feel better - they still will originate from a multi-wire system."
-That's why we put branch circuit OPD's at the point of distribution.

"That is if you believe in transients or harmonics being that big of an issue..."
-I've been callled in to repair many aging electrical systems. It's always the neutrals that burns out first. Transients and harmonics are possible explanations.
Modern circuit loads are not constant, they're always in flux.

"...And having a multi-wire circuit doesn't get rid of them..."
-I never said MWBCs would get rid of them.

"...debate on the possible triplen harmonics causing problems on WYE circuits, and over-sizing of neutrals. But they have little effect in a center-tapped single phase systems.."
-I'm not an engineer, so I just play it safe and follow the NEC.

"... if you completely loose a neutral on a service ... it is the underground water line that may be saving the day..."
-That's why in NYC, only metal water pipe is used. No plastic pipes (or for that matter, Romex, Sched. 80 NMRC, non-metalic boxes or enclosures, or aluminum wire). It's all copper, steel and lead. The building's ground IS the underground metal water piping system.

"...bonding be across the water meter..."-It's been in the Electrical Code of the City of New York for many years.

"...act as a back up neutral connection..."
-That's what I said.

 

[LEO2854]

When my local supplier get them in and they come down in price, I would be in.
Except:
With the IT equipment my clients are using, with high transients on the neutrals, why do I want to undersize the branch neutral conductor by having it carry twice the load as the two 120 cicuits it serves? If it were balanced, okay. Two circuits, both with IT systems on a shared neutral, will not be balanced.

I woul say that the intent of the two pole AFCI Breakers are 240 volt loads like window A/C and Electric baseboard heat.
I don't think that running MWBC for 120 volt loads is a good idea but if you do
you need a two pole AFCI breakers