multiple current carrying conductors in a single racway (loading the boat)

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follybeacher

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USA
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Estimator
My question is a high level estimating question, not a granular engineering question. I understand how to calculate available fill per Ch. 9 perform adjustment factors per 310.15(B)(2)(a). When required to perform these calcs, I do so. That's not the question...

The question is what rules can an estimator most always apply to reduce cost in regards to 'loading the boat'? I build receptacle assemblies with an average conduit length to reach a 4sq box. Then I group 3 together and sending them to the respective panel. My rule (which I'm trying to expand on) is always using 3 ckts per homerun.

Can I apply other rules without having to perform engineering calcs? Time is short these days and I want to be as competitive as code compliantly possible.

I made a quick sketch to show you what's in a typical assembly and the 4sq/homerun I'm wheeling off. (This sketch is drawn as if they're dedicated ckts :roll:)

sketch.jpg
 
jumper

jumper

Senior Member
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3 Hr 2 Min from Winged Horses
I do not do estimating, but I have a question.

With the common disconnecting means rule (handle ties or multi pole breakers) for MWBCs how are you incorporating full boats into your estimate rules?
 
KnightPower

KnightPower

Member
Location
US
Why not group 2 multi-wires together.. (2 sets of Black, Red, Blue respectively)? 9-#12s in a 3/4" pipe, then you can continue to pipe closer to their locations. I'm jumping a bit at we are considering 120/208.

Sent from my SM-G930V using Tapatalk
 
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
jumper said:
I do not do estimating, but I have a question.

With the common disconnecting means rule (handle ties or multi pole breakers) for MWBCs how are you incorporating full boats into your estimate rules?
Click to expand...

A 3 pole breaker costs about 3 times what 3 single poles cost. I assume that would be taken into account but it still beats the extra labor and material of non-mwbc's. I had that handle tie rule.

I agree with knight, 9 ccc is the magic number for 14 and 12, but that is 3 full boats typically.
 
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follybeacher

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Location
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Estimator
I'm hesitant to answer questions on this forum in the presence of such knowledgeable members, but here goes...

In my sketch I do share a ground but each circuit has a dedicated neutral thus not a MWBC and no need for handle ties. Typically the specs will state "no shared neutrals" which makes this crystal clear. If I wanted to really be aggressive and specs did not prohibit then I would qualify shared neutrals and wheel the homeruns as such.

Never do I takeoff utilizing shared neutrals / MWBCs... I could ask other seasoned estimators if I should be? That would certainly save labor and materials?
 
C

cdslotz

Senior Member
follybeacher said:
I'm hesitant to answer questions on this forum in the presence of such knowledgeable members, but here goes...

In my sketch I do share a ground but each circuit has a dedicated neutral thus not a MWBC and no need for handle ties. Typically the specs will state "no shared neutrals" which makes this crystal clear. If I wanted to really be aggressive and specs did not prohibit then I would qualify shared neutrals and wheel the homeruns as such.

Never do I takeoff utilizing shared neutrals / MWBCs... I could ask other seasoned estimators if I should be? That would certainly save labor and materials?
Click to expand...

If the specs say "no shared neutrals" then what you are doing is correct. If you want a full boat with 6 circuits with no shared neutrals, then you get into derating issues, wire size and conduit size...so yes...the cost goes up.
However, for long home runs there is a point where it becomes a savings.
 
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follybeacher

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Location
USA
Occupation
Estimator
infinity said:
How deep is you 4" box? A standard 1.5" deep 4" box is too small for 13-#12's.
Click to expand...

For a homerun I would typically figure a 4x2-1/8 rather than a 4x1-1/2


electrofelon said:
A 3 pole breaker costs about 3 times what 3 single poles cost...
Click to expand...

this shouldn't be forgotten. thank you


cdslotz said:
If the specs say "no shared neutrals" then what you are doing is correct. If you want a full boat with 6 circuits with no shared neutrals, then you get into derating issues, wire size and conduit size...so yes...the cost goes up.
However, for long home runs there is a point where it becomes a savings.
Click to expand...

If the specs don't prohibit this, under what circumstance would this be acceptable? Could I pack in 6 circuits into a 3/4" (6#12H, 2#12N, 1#12G, 3/4"C)? I suppose there would be de-rating, so should to simplify maybe I just use 10's? That would save an entire 3/4" raceway homerun.

These are the tricks I'm looking to identify in this post. Something I can universally apply to some or most takeoffs.
 
jumper

jumper

Senior Member
Location
3 Hr 2 Min from Winged Horses
follybeacher said:
For a homerun I would typically figure a 4x2-1/8 rather than a 4x1-1/2




this shouldn't be forgotten. thank you




If the specs don't prohibit this, under what circumstance would this be acceptable? Could I pack in 6 circuits into a 3/4" (6#12H, 2#12N, 1#12G, 3/4"C)? I suppose there would be de-rating, so should to simplify maybe I just use 10's? That would save an entire 3/4" raceway homerun.

These are the tricks I'm looking to identify in this post. Something I can universally apply to some or most takeoffs.
Click to expand...

If you are sharing nuetrals then you could get nine 20A circuits in a 3/4” EMT, derate and still use #12. I usually use stranded or use 1” EMT.

9 hots, 3 neutrals, and 1 EGC. Code wise you can use the EMT as an EGC.
 
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
jumper said:
If you are sharing nuetrals then you could get nine 20A circuits in a 3/4” EMT, derate and still use #12. I usually use stranded or use 1” EMT.

9 hots, 3 neutrals, and 1 EGC. Code wise you can use the EMT as an EGC.
Click to expand...

:thumbsup:

I would just add that there is the "nonlinear load" thing potentially making the neuter a CCC, but everyone pretty much ignores that for branch circuits, in my experience.
 
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mstrlucky74

Senior Member
Location
NJ
jumper said:
If you are sharing nuetrals then you could get nine 20A circuits in a 3/4” EMT, derate and still use #12. I usually use stranded or use 1” EMT.

9 hots, 3 neutrals, and 1 EGC. Code wise you can use the EMT as an EGC.
Click to expand...

Where do you get 3 neutrals for a MWBC? 1 per 3 ckts?
 
infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
mstrlucky74 said:
So you guys are running MWBC and using multi pole brkrs or handle ties? Even is spec calls for no shared neutrals?
Click to expand...

Depends, if the developer doesn't specify and wants the cheapest installation possible a bunch of handle ties are much cheaper than separate neutrals.
 
F

follybeacher

Member
Location
USA
Occupation
Estimator
mstrlucky74 said:
Wheredo you get 3 neutrals for a MWBC? 1 per 3 ckts?
Click to expand...
Yes. One neutral per A, B & C phase

infinity said:
Depends,if the developer doesn't specify and wants the cheapest installation possible abunch of handle ties are much cheaper than separate neutrals.
Click to expand...
I still haven’t heard if guys are doing takeoff like this. Iknow you CAN figure it like this, but do you?


Still looking for other tricks and methods to drive anestimate down…
 
C

Chris664

Member
Location
Maryland
How large are these jobs your estimating? I always assume 7#12's for my branch (where applicable) & i do this almost as you pictured, depending on how far they are apart. Doing calculations for this in my opinion is a waste of time; unless these are a good distance away from you BPB. Just my 2 cents.
 
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