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Jadnashua

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Lots of fill tables on the web....here's one: http://www.westernextralite.com/resources.asp?key=47

It can be a major pain pulling the wires. They do sell special lubricant, and don't expect to go around corners, at least sharp ones with fittings without an intermediate pull fitting.

One thing that can minimize the wires required is to run a two pole circuit breaker for two circuits using a common neutral...saves one wire (since the two poles are on opposite legs, the current in the neutral can never be greater than having one side fully loaded, and will be zero if the loads are balanced). This saves one neutral wire for each two circuits, but means that if one trips, it trips both because of the connecting bar on the breaker.
 
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Speedy Petey

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Any more than 3 current-carrying conductors and you have to start de-rating.
While this is true, due to the ampacity nature of #14, 12 & 10, you do not have to worry about derating #12THHN until you get to nine current carrying conductors (CCC).
 

Speedy Petey

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OK, first off, when pulling wires in conduit multi-wire branch circuits (MWBC, or shared neutral) are your friend. This is due to the fact that neutrals ARE CCC's, so they count towards conduit fill with regard to derating. Neutrals of a MWBC only carry the imbalance of the load of the two hots, and conductors only carrying an imbalance do not count towards derating.
For example;
Two circuits with individual neutrals:
2- hots, 2- neutrals = 4 CCC
Four circuits
, using MWBC:
4- hots, 2- neutrals = 4 CCC

Again, you can run up to 8 CCC in any conduit before you need to be concerned with derating. So if I were you I'd run three sets of MWBC for a total of six new circuits, and only 6 CCC.
If you did the same with individual neutrals you'd have 12 CCC.
 

hj

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quote; It looks like the number is 16.

If that is in a 3/4" conduit, you would need a tractor to pull it IF you could get them into the conduit in the first place, (you might need a conduit with a bigger i.d. than the o.d.).
 

Reach4

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Note with shared neutral, current codes require you to drive the red and black with a 2-pole breaker rather than two single pole breakers. The reason is to protect the electrician if the neutral fails. In that case, turning off a single pole breaker could provide power via things plugged into the other leg. Not a big deal. It just means that when you turn off the breaker for one leg, the breaker for the other leg goes off also.
 

hj

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IT has almost NOTHING to do with the "neutral failing". If only one leg "trips" the other one will still be live. If it is a 'shared" outlet, the technician could receive a shock from the live side while working on it.
 

Reach4

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IT has almost NOTHING to do with the "neutral failing". If only one leg "trips" the other one will still be live. If it is a 'shared" outlet, the technician could receive a shock from the live side while working on it.
Wouldn't that be the case even if a separate neutral were run for each hot?

I read that killing both legs keeps the neutral from having a voltage due to current thru the neutral. I think that voltage would only be a few volts. If the neutral were actually faulty, there could be much more voltage passed through items that are plugged into the non-interrupted circuit.

I see that as an alternative to a 2 pole breaker, 1 single pole breakers can be used with a handle tie. While this causes both circuits to go dead when one is switched off by the handle, an overcurrent on one does not automatically kill power to the other.

I even found a reference that one of the motivations for the rule is to make sure that the two hots sharing a neutral are from different legs of the breaker box. Using adjacent positions for breakers or using a 2-pole breaker insures this.

Here is some early discussion:
https://terrylove.com/forums/index.php?threads/shared-neutral.24216/
 

DonL

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quote; It looks like the number is 16.

If that is in a 3/4" conduit, you would need a tractor to pull it IF you could get them into the conduit in the first place, (you might need a conduit with a bigger i.d. than the o.d.).


Yes, Tie wrap the wire to the outside of the conduit.

It may take a bit of KY Jelly to get it in.
 

Speedy Petey

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I'll run 2 blacks, 2 reds and 2 blues (?).... One of each color on the red phase bus... and one of each color on the black phase bus.

Each set of colors will share one nuetral white wire.
Hold on!
What you describe suggests 3-phase? Is this in a home? Commercial building condo? What?
 

Jadnashua

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Normally, in typical residential service, you'd only use black for your hot...red is sometimes used as well, but has the implication that it is a switched hot. IF you're dealing with three-phase power, it's a different story. IN a MWBC, you'd use the black and red for your CCCs.
 
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ActionDave

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Hold on!
What you describe suggests 3-phase? Is this in a home? Commercial building condo? What?
Black Red, Blue Black, Red Blue works on single phase. Would be just as good to use the two blacks for circuits one and two, two reds for circuits three and four, two blues.......
 

hj

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If the circuit has a dedicated neutral it is carrying the same amperage as the hot leg., but since it is at "ground potential" the same as you you do not receive a shock from touching it. A common neutral between two legs only carries the difference between the loads, while a common neutral between two circuits on the same leg will be carrying the TOTAL of both circuits and could be overloaded without a circuit breaker to protect the wire.
 

Speedy Petey

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Black Red, Blue Black, Red Blue works on single phase. Would be just as good to use the two blacks for circuits one and two, two reds for circuits three and four, two blues.......
I guess I misunderstood what he said. Looking back on it I see I did.
I just don't see the point of black, red & blue. Unless of course he has a bunch of it laying around.
 

ActionDave

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I guess I misunderstood what he said. Looking back on it I see I did.
I just don't see the point of black, red & blue. Unless of course he has a bunch of it laying around.
I do something similar on service upgrades a lot because it makes it easy to keep track of circuits and because I usually have several short spools left floating around waiting for a higher purpose. Couple or three EMT's piped into the crawl and/or attic, spider out with NM from there.
 
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