Neutrals

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epd807

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I posted a week or so ago about installing (2) 120 volt receptacles for separate cappucino makers. Could these circuits share a neutral if placed on a 2 pole breaker? The 2 pole breaker would insure simultaneous disconnection of both ungrounded conductors, in addition to putting the hots on different phases, so the current in the neutral would cancel. Will this comply with sec 210.4? Thanks for any insight!
 
Re: Neutrals

Originally posted by luke warmwater:
yes, it will comply, but it is Not Required.
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I should have asked if these are in a dwelling.

If they are then 210.4(B) would only Require the 2-pole if both ungrounded conductors are supplying a device or equipment on the same yoke.
 
Re: Neutrals

Originally posted by luke warmwater:
Originally posted by luke warmwater:
yes, it will comply, but it is Not Required.
Click to expand...
I should have asked if these are in a dwelling.

If they are then 210.4(B) would only Require the 2-pole if both ungrounded conductors are supplying a device or equipment on the same yoke.
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Luke - 210.7(C) has extended the 'same yoke' requirements to all structures (not just dwellings).
 
Re: Neutrals

Originally posted by dana1028:
[Luke - 210.7(C) has extended the 'same yoke' requirements to all structures (not just dwellings).
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Dana, this is not true of the "Multi-Wire Branch Circuit", which would be the topic here.

A set of conductors meeting the definition of "Multi-Wire Branch Circuit" would not be "Multiple Branch Circuits", but is in fact one circuit, so with this being the case, a "Multi-Wire Branch Circuit" in other than a dwelling would not need handle ties or a multi pole breaker.

Roger
 
Re: Neutrals

I agree with Roger as well. Multiple branch circuits would be two circuits and two nuetrals, where a multiwire branch circuit would be 2 or more phases and 1 nuetral. I'm not sure why you need a handle if there are two nuetrals and you don't need one if there is only one, but that is the way it is written. :)
 
Re: Neutrals

I appreciate all the responses, but I must admit I'm still a bit confused. If a 2 pole breaker is not required, then the two ungrounded conductors could be placed on the same phase, thus doubling the current in the shaired grounded couductor. What am I missing here?
 
Re: Neutrals

I would run a neutral for each circuit,if you would lose your neutral you have the possibility of 240v across your equipment.I have run into this on several service calls. Not fun to fix at a later time.
 
Re: Neutrals

Originally posted by epd807:
If a 2 pole breaker is not required, then the two ungrounded conductors could be placed on the same phase, thus doubling the current in the shaired grounded couductor. What am I missing here?
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And who would do this, a qualified electrician?

We can try, but in reality we can't guard against the unqualified destroying or jeopardizing there own well being if they tread where they shouldn't.


Criselect,
[QB]if you would lose your neutral you have the possibility of 240v across your equipment.[QB]
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if the supply voltage is 240v, you would have 240v dropped across all the equipment combined, but you could not have 240v dropped across any one load in this series circuit.

Roger
 
Re: Neutrals

ROGER: If both pieces of equipment are sharing one neutral and both are plugged in and on and I would disconnect the neutral from the panel you would have 240v at each appliance. Because they both have heating elements.
 
Re: Neutrals

Originally posted by criselect:
If both pieces of equipment are sharing one neutral and both are plugged in and on and I would disconnect the neutral from the panel you would have 240v at each appliance. Because they both have heating elements.
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If both heating elements are the same wattage the voltage at each element will still be 120 volts.

If the wattages are unequal the voltages will be unequal but neither element will receive 240 volts.
 
Re: Neutrals

criselect,

These sketches illustrate an example of the voltage division in a three-wire circuit with the neutral disconnected. Line voltage drop is not included in this example.

Ed

3wire3.gif
 
Re: Neutrals

criselect, now that you can see what I was saying per Ed's open neutral diagram, take the same diagram and make the resistors equal, now calculate the voltage drop across each resistor and you will see what Iwire is pointing out.

The "240 volts across all equipment" is a common misconception

Roger
 
Re: Neutrals

As per the diagram if everything is perfect then you will have 120 volts. (IF) I still say pull seperate neutrals.
 
Re: Neutrals

Originally posted by criselect:
As per the diagram if everything is perfect then you will have 120 volts. (IF) I still say pull separate neutrals.
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Chris I am going to guess you do not work large jobs.

Multiwire branch circuits are a good choice for a lot of reasons, not the least of which is cost savings to the customer.

The lost neutral can still happen in your feeders so the potential for over voltage is not eliminated by the use of two wire circuits.

Installed and maintained by qualified personal multiwire circuits work great.
 
Re: Neutrals

Ed, just so I am clear, in your example, if one of the coffee-makers was not turned on, and the other one was in use, wouldn't it get the full 240 Volts across it if the neutral was open? I know I'm reaching here :D
 
Re: Neutrals

Originally posted by wirenut1980:
Ed, just so I am clear, in your example, if one of the coffee-makers was not turned on, and the other one was in use, wouldn't it get the full 240 Volts across it if the neutral was open? I know I'm reaching here :D
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No, you would get 0. :D
 
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