Can a multiwire branch circuit be considered an individual branch circuit?

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SPROCKET

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My dilema, on a recent project, 2 A.O smith boilers were installed. These require 120 volt circuits to power blower and control at each blower. after installation and start up began experiencing prover failures, boilers randomly lock out on comm fail and ignitors are burning up like candles. Manufacturer installation instructions require individual branch circuits. E.C. installed multi wire circuit two hots /one nuetral. one leg powers Fractional horsepower circ pump 120V and other supplies boiler control/fan. manufacturer is voiding warranty claiming improper installation, E.C claims circuits are considered individual per nec 210.4 The two circuits are on individual 20 amp single pole breakers and are not grouped in panel per 210.4d.no handle ties are used. E.C.also states they are installed per engineered drawings.(we all know these can contain mistakes) I feel they should install a seperate circuit (single hot nuetral and ground) to each boiler per Manufacturers instructions. and a sperate one for circ pump. Your opinions would be greatly appreciated
 

roger

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A MWBC is a single circuit, it can be be considered multiple circuits per 210.4 but the circuit is a single circuit.


Roger
 

hurk27

Senior Member
I don't see a problem with a multi-wire circuit if it is installed per code.

2008 would require common trip breaker, but since it's not connected to a device with a common strap, I don't think it would require even handle ties in any earlier code.

With that said, it is still required to have both ungrounded conductors on opposite phases, or the neutral will have the whole load on it from both circuits, and if it is on opposite phases, and the neutral has a bad connection or if the run is long then the start up current can cause over voltage of the other phase, so IMO I would have run separate neutrals with each circuit.

But to answer your OP, a multi-wire circuit can be multi circuit (210.4) or a single circuit (225.30), depends upon which part of the code you apply.
 
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Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
A manuafacturer request of individual branch circuit is not the same as a Dedicated circuit which is what the manufacture seems to want. This whole notion of dedicated or seperat may be open for interpetation.

what is the load on the other circuit?

Most electrical installations have shared nuetrals at some point. I think the manufacture has a problem with the unit and is claiming it the fault of the EC. How is it that the manufacture even knows that there is a shared nuetral.
 

SPROCKET

Member
Manufacturer has made multiple site visits to asses issues and observed installation. they claim that the boilers not having a seperate hot nuetral and ground to each unit is an improper installation per their inst instructions. They are hiding behind this for the failures of the units. They suspect circ pump starting is causing the comm fails and shut downs. However they have stated if this is corrected they will deal with any further failures during warranty period. There manuals does spec a dedicated circuit with 0 voltage nuetral to ground. I feel the E.C should have submitted RFI about installation requirements after seeing manufacturer specs to engineer.
 

e57

Senior Member
Manufacturer has made multiple site visits to asses issues and observed installation. they claim that the boilers not having a seperate hot nuetral and ground to each unit is an improper installation per their inst instructions. They are hiding behind this for the failures of the units.
Sure they are..... :rolleyes:
There manuals does spec a dedicated circuit with 0 voltage nuetral to ground.
So do they also require the units be installed within 20' of the main panel - where the main bonding jumper would be? As the would be hard pressed to get 0.00v more than spitting distance from it! - That said, if your EC takes a small 2 space panel, and puts it right next to the unit fed by the 3-wire that is there right now, then take two 2-wire circuits out of that - he'll fit the specification by all interpetations, AND still would not get 0 volts N-G. (No bonding is allowed after the main...) Yet all that has changed is location of the over-current protection...

Since you are not an EC - I guess we should say that the service, and all of the sub-panels are also multi-wire circuits from the source. Extending a multi-wire circuit changes nothing about the circuit configuration. No matter where you split it up - it will always share the neutral at some point. If the length of the circuit is long - this MWBC is actually saving in voltage drop splitting it close to the unit....
I feel the E.C should have submitted RFI about installation requirements after seeing manufacturer specs to engineer.
You choose your battles and allies.... What you have there is what I call a 'finger pointing party' - since you say the EC built what was on the "Engineered Drawings" then I think he should give you a CO for this extra work you want. Then you should both gang up on the Manufacturer. And if you have some type of "power quality problem" Gang up on the Engineer, but if he's your buddy or wont stand for it - gang up on the Utility.... ;)
 
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infinity

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New Jersey
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If the MWBC is properly installed I don't see how this can have any affect on the boilers' operation. IMO the manufacturer is way off base.
 

M. D.

Senior Member
........ if your EC takes a small 2 space panel, and puts it right next to the unit fed by the 3-wire that is there right now, then take two 2-wire circuits out of that - he'll fit the specification by all interpetations, AND still would not get 0 volts N-G. (No bonding is allowed after the main...) Yet all that has changed is location of the over-current protection...

I love this idea,.. I wonder if those instructions were part of the U.L listing?... o volts N-G ??? an out for almost all occasions

What is the name of this manufacturer that won't stand behind their product.?
 

nakulak

Senior Member
I think the manuf is full of bs, but it sounds like the best way to shut them up is install a new ckt to one of the units, then you can hold their feet to the fire. I'm not sure you can hold the EC liable, this is a very common installation and if in fact the shared neutral is the problem, then this manuf is going to have a lot of trouble if these are common units.
 

JohnJ0906

Senior Member
Location
Baltimore, MD
You are obviously fearfull and lack trust in the use of the edison circuit.
Nope, I use MWBCs wherever I can.

And/or lack the confidence that the licensed EC who performed the work could do it?
There is obviously a problem, with either the circuit, or the unit. I can't comment on the units themselves, I merely offer suggestions to double-check that the MWBC is connected correctly.
 

e57

Senior Member
Nope, I use MWBCs wherever I can.

There is obviously a problem, with either the circuit, or the unit. I can't comment on the units themselves, I merely offer suggestions to double-check that the MWBC is connected correctly.
Sounds like the veiled ramblings of a 2-wire circuit man in disguise.... :roll: :D
 
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