Borrowed Neutral

[mull982]

It would still be a MWBC even though the current wouldn't cancel the same as it does in the single phase scenario.

Roger

In this same picture example lets say at first one of the 120V circuits was feeding a receptacle with its respective hot and neutral. Then we wanted to add a light from the other 120V leg and bugged onto the same existing neutral to now have 2 circuits as shown in the picture.

Would this be an example of a borrowed neutral?

 

[mivey]

In this same picture example lets say at first one of the 120V circuits was feeding a receptacle with its respective hot and neutral. Then we wanted to add a light from the other 120V leg and bugged onto the same existing neutral to now have 2 circuits as shown in the picture.

Would this be an example of a borrowed neutral?

Depends how the wires were run. If the wires were all run together like a MWBC, it would not be borrowed.

Supposed you had a 120 volt 2-wire circuit in one conduit, and a second 120 volt 2-wire circuit in a second conduit. If you ran a circuit from the ungrounded conductor in a second conduit, through the load, then through the grounded conductor from the first conduit, it would be a borrowed neutral.

 

[roger]

In this same picture example lets say at first one of the 120V circuits was feeding a receptacle with its respective hot and neutral. Then we wanted to add a light from the other 120V leg and bugged onto the same existing neutral to now have 2 circuits as shown in the picture.

As Mivey points out, if we were to pull the other ungrounded conductor in the same raceway we would simply create a MWBC.

Roger

 

[mivey]

Also, consider if both two wire circuits were in the same conduit. Let circuit #1 = grounded_1 and ungrounded_1. Let circuit #2 = grounded_2 and ungrounded_2.

If we paired grounded_1 and ungrounded_2 or paired grounded_2 and ungrounded_1, we would have a "borrowed" condition.

 

[mull982]

Also, consider if both two wire circuits were in the same conduit. Let circuit #1 = grounded_1 and ungrounded_1. Let circuit #2 = grounded_2 and ungrounded_2.

If we paired grounded_1 and ungrounded_2 or paired grounded_2 and ungrounded_1, we would have a "borrowed" condition.

I dont follow the reason behind your example

 

[mivey]

I dont follow the reason behind your example

The reason is because the grounded conductor you used was not intended to be used with the other ungrounded conductor. Let me give the example in a different way:

Let circuit #1 = grounded_1 and ungrounded_1 using 4/0 conductors. Let circuit #2 = grounded_2 and ungrounded_2 using #10 conductors.

If we paired the ungrounded 4/0 conductor with the grounded #10 it would be obvious that the #10 was the wrong/borrowed neutral.

 

[roger]

If we paired the ungrounded 4/0 conductor with the grounded #10 it would be obvious that the #10 was the wrong/borrowed neutral.

Not neccessarily, 4/0 may have been all we had on the truck when we pulled the new ungrounded conductor

Roger

 

[Jack Linville]

Definitions

Definitions

The difference may be that multiple phases/wires may share a common neutral but multiple CIRCUITS may not. There is a difference between a wire and a circuit.

 

[roger]

The difference may be that multiple phases/wires may share a common neutral but multiple CIRCUITS may not. There is a difference between a wire and a circuit.

As far as making a blanket statement, that is not true, see 225.7(B)

Roger

 

[Jack Linville]

A "blanket statement" would not have included the word "may". I was just trying to suggest a way to look at this and make it easier to approach as several seemed to really struggle with "borrowing" a neutral.

Thanks

 

[mull982]

So lets say in a conduit going out to a panel I had one ciruict with a hot and a neutral both #10 feeding a receptacle. Lets say I had another ciruict with a hot and a switch leg feeding a temperature switch (no neutral just a contact switch). Lets say the hot and switch leg feeding the temp switch were both #12.

Now it has been decided that we want to replace the mechanical temp switch with an electronic one so besides the hot and switch leg we have, we will not require a neutral. Is it legal to bug onto the neutral that is existing at the receptacle that I stated above?

 

[jumper]

So lets say in a conduit going out to a panel I had one ciruict with a hot and a neutral both #10 feeding a receptacle. Lets say I had another ciruict with a hot and a switch leg feeding a temperature switch (no neutral just a contact switch). Lets say the hot and switch leg feeding the temp switch were both #12.

Now it has been decided that we want to replace the mechanical temp switch with an electronic one so besides the hot and switch leg we have, we will not require a neutral. Is it legal to bug onto the neutral that is existing at the receptacle that I stated above?

I got lost at at that word, do need a grounded conductor or not?

If so, 300.3(B)
(B) Conductors of the Same Circuit. All conductors of
the same circuit and, where used, the grounded conductor
and all equipment grounding conductors and bonding conductors
shall be contained within the same raceway, auxiliary
gutter, cable tray, cablebus assembly, trench, cable, or
cord, unless otherwise permitted in accordance with
300.3(B)(1) through (B)(4).

 

[roger]

So lets say in a conduit going out to a panel I had one ciruict with a hot and a neutral both #10 feeding a receptacle. Lets say I had another ciruict with a hot and a switch leg feeding a temperature switch (no neutral just a contact switch). Lets say the hot and switch leg feeding the temp switch were both #12.

Now it has been decided that we want to replace the mechanical temp switch with an electronic one so besides the hot and switch leg we have, we will not require a neutral. Is it legal to bug onto the neutral that is existing at the receptacle that I stated above?

This takes us back to 300.3(B) so it would not be legal. Even though it would be minimal you would have net current flowing and possibly EMI problems due to the EMF

Roger

 

[Dennis Alwon]

You might be able to do that if the circuit conductors run with grounded conductor back to the panel. You would also have to make it a MWBC as you would need handle ties.

 

[LarryFine]

I got lost at at that word, do need a grounded conductor or not?

I'm 99 & 44/100% sure he meant now, not not.

 

[LarryFine]

So lets say in a conduit going out to a panel I had one ciruict with a hot and a neutral both #10 feeding a receptacle. Lets say I had another ciruict with a hot and a switch leg feeding a temperature switch (no neutral just a contact switch). Lets say the hot and switch leg feeding the temp switch were both #12.

Now it has been decided that we want to replace the mechanical temp switch with an electronic one so besides the hot and switch leg we have, we will not require a neutral. Is it legal to bug onto the neutral that is existing at the receptacle that I stated above?

Now, presuming I'm correct, the answer would be "Yes, as long as both circuits are in the same conduit and the two hots are not supplied from the same phase."

 

[mivey]

Not neccessarily, 4/0 may have been all we had on the truck when we pulled the new ungrounded conductor

Roger

Well, yeah, there's that. :grin: