Neutral Conductors in conduit

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Greg1707

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Alexandria, VA
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Business owner Electrical contractor
I am running 8 #12 THHN conductors in a conduit for branch circuits. How many ungrounded (neutral) conductors must I use? Sorry for this stupid question but I alway use cable and rarely use conduit.
 
How many phases in your system? I'm assuming you're asking about multiwire branch circuits and don't want an answer of 8 neutrals.
 
single phase

single phase

I would not consider this to be a multi wire branch cirucit. I am installing a new panel adjacent to the old panel. I am using the old panel as a J box. I will be running FMC between old panel and new. I have to make splices in the old panel. HOw many neutrals will I need to run? One neutral for each branch circuit conductor?
 
Greg1707 said:
I am running 8 #12 THHN conductors in a conduit for branch circuits. How many ungrounded (neutral) conductors must I use? Sorry for this stupid question but I alway use cable and rarely use conduit.
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I'm confused. "...ungrounded (neutral)...." Ungrounded are 'hots'.
 
That was my first assumption, but you know what they say about the word 'assume.'

My best advice is if you are simply extending the circuits from the old panel, which will become a j-box, to the new one, you simply need to count the wires you have in the old box.

I think you could technically convert a pair of 2-wire circuits to a multi-wire, but that would complicate things and may limit your choices of how to land the circuits in the new panel.

Butif you're new to the world of pipe, you also need to take into account your fill numbers as well as derating.
 
Greg1707 said:
I would not consider this to be a multi wire branch cirucit. I am installing a new panel adjacent to the old panel. I am using the old panel as a J box. I will be running FMC between old panel and new. I have to make splices in the old panel. HOw many neutrals will I need to run? One neutral for each branch circuit conductor?
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Assuming #12 is appropriately sized for all 8 circuits, you don't need to run 8 neutrals (assuming that's what you meant). But exactly how few you can get away with depends on several things:

Under what code edition is this installation? This will determine whether mwbc ocpds need abutted and with handle ties.

Is it a 1? or 3? system? For 1?, you must run at least one for each L1, L2 combination and leftovers. For 3?, you must run at least one for each L1, L2, L3 combination, each two-line combination, and any leftovers.

I think I got that right...?!!!
 
Greg1707 said:
I am running 8 #12 THHN conductors in a conduit for branch circuits. How many ungrounded (neutral) conductors must I use? Sorry for this stupid question but I alway use cable and rarely use conduit.
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Why do they ask silly questions and just bail out on us. How the heck are we supposed to help when they do a hit an run. How bad does he need the answer?

:-? :-? :-?

Sometimes I feel Like we are giving matches to a child. :)

Ungrounded neutral conductor? There is a difference right? :grin:

sorry, see signature. :cool:
 
480sparky said:
Let's not forget about the possibility of harmonics if it's 3?.....
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OK... nuances as such is why I put in the escape clause, "...you must run at least one..." :grin:

...and then again, I did not specify size either, which an upsized neutral could handle even extreme harmonics.
 
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If your running the conductors through a nipple, shorter then 24", cram as many in it, as you can.

The number of neutrals from the j-box to the new panel should be the same number of neutrals that you are connecting to in the existing panel, do not combine them.
 
With 8 ungrounded #12 conductors in a conduit with a neutral for each, that is 16 CCCs, for which they must be derated to 15 Amps. If they must have circuit protection at 20 Amps, then the conductors must be #10.

If the system is installed as MWBCs then the the neutral (grounded) conductors are not CCCs, they are derated to 70% for 8 CCCs in the conduit, and the #12s can be used to the normal 20 Amp limit.
 
Bob,
With 8 ungrounded #12 conductors in a conduit with a neutral for each, that is 16 CCCs, for which they must be derated to 15 Amps.
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The nipple in question will likely be less than 24" in length eliminating the need for derating.
 
Smart $ said:
OK... nuances as such is why I put in the escape clause, "...you must run at least one..." :grin:

...and then again, I did not specify size either, which an upsized neutral could handle even extreme harmonics.
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Technically speaking, this is all that is required, as long as it is properly sized.
Most people in our industry have a hard time wrapping the mind around this concept. But if ampacity adjustment is an issue, the can reduce the number of current carrying conductor under certain circumstances.
 
Neutral conductors

Neutral conductors

I am sorry for bailing out on everyone but I had to go to bed last night.

Okay, here is the situation again. I have an old Federal Pacific panel smack behind the fridge. I cannot replace the panel in this location because the fridge blocks access to the panel. I am installing the new panel on the adjacent wall. The old panel has some romex circuits but mostly circuits run in conduit. There are several neutral conductors entering from the conduit. Some are #12 and some are #15.
The neutrals are connected to the neutral bar. The grounds are connected to a separate ground bar. This correct because the service panel is outside with a main disconnect.

I have removed the feeder conductors and connected them to the new panel. I am now running romex for each circuit from the new panel back to the old panel where I will splice the ungrounded (hot) conductors. No problem.

Now, can I attached all of the new romex neutrals entering from the new panel to the neutral bar where all of the neutral conductors from the old panel are attached in the old panel? Essentially, can I connect all of the neutrals together in the old panel?

I hope so because there is no way for me to sort out which neutral conductors entering from the conduit should be paired together with the appropriate ungrounded conductor.

I hope this makes sense.
 
Greg1707 said:
....Essentially, can I connect all of the neutrals together in the old panel?
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No. They must be kept seperate in extending them to the new panel.

Is there a reason why you cannot find out which neutral goes with which hot? If it's NM, it's easy.
 
kingpb said:
If your running the conductors through a nipple, shorter then 24", cram as many in it, as you can.
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You can only cram until you get to 60% fill as Don pointed out.
 
Greg1707 said:
I have removed the feeder conductors and connected them to the new panel. I am now running romex for each circuit from the new panel back to the old panel where I will splice the ungrounded (hot) conductors. No problem.

Now, can I attached all of the new romex neutrals entering from the new panel to the neutral bar where all of the neutral conductors from the old panel are attached in the old panel? Essentially, can I connect all of the neutrals together in the old panel?

I hope so because there is no way for me to sort out which neutral conductors entering from the conduit should be paired together with the appropriate ungrounded conductor.
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You should be able to sort the neutrals out. You can disconnect the neutrals from the bus, and energize each hot conductor and see which neutral becomes hot through the existing loads.

After that, combine pairs of hots (either already paired as shared-neutral multi-wire branch circuits (MWBC's), and/or pair the 2-wire circuits) and run four 3-wire MWBC's between the panels.

That will give you eight CCC's in the interconnecting nipple or raceway.
 
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