A lesson to the learnin'

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George Stolz

George Stolz

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Location
Windsor, CO NEC: 2023
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Hospital Master Electrician
Confession time:

I am an idiot. This may not come as a surprise to many, but it feels good to confess it. :)

On my project, they poured all the foundations for the sixplexes, trenched in all the service laterals, and whatnot, in 2003. At that time, they intended to build in a clockwise rotation through the neighborhood. They (whoever they are) decided to build three in that manner, and then, in their infinute wisdom, spun around and began building in the opposite direction.

As a result, a set of garages sitting in the middle of the parking lot, serving two different sixplexes, had conduit running to the wrong building. The building that was originally intended to supply the garage is not going to be constructed for a long, long time.

Looking at the predicament, I decided the easiest route was to divert the conduit to a nearby transformer, and install a service lateral (instead of an outside feeder).

I got the okay from the POCO, sold the GC on the idea, and called for a trencher. I discovered upon digging down for the conduit that the jac***s that originally installed the sleeve under the street installed a 1" conduit for the garages. I was intending to install a 100 amp service to the garage. I had already picked up the Square-D 100 amp all-in-one metermain with 8-spaces below.

At that point, my mental design changed from a conduit run to direct burial, since the spot marked on the curb was a good two feet from the actual sleeve, and my trench hooked a hard 100?+ turn to find it, on both sides of the street. :roll:

Upon finding the 1" conduit, I checked the fill tables, and found the most I could put in there was a 4-3 URD (USE's). So, now I was going to install 60-amp conductors, which was okay by me, since it was above my estimated load. I thought that since my conductors were sized for the connected load, and service conductors were unprotected at their source anyway, then I could install a 100 amp metermain and forget about it.

I was unaware of the existence of 230.90, and the fact that the service conductors are considered protected by the load side of the conductors. I broke with my habit of trying to fail the unusual installation I was considering before I proceeded.

Then it passed inspection. :mad: Stupid! Stupid! Stupid! :mad:
 
Re: A lesson to the learnin'

I don't bury anything smaller than a 2" for anything, unless it's going to a post light or something like that. Heck, I bury a 2" each for phone and TV cable.

Sorry to hear about your troubles. Glad your POCO is okay with the 60 amp service. In my area, even if it's not a dwelling, they'll do 100A minimum. It seems silly to do a 100 amp service for small stuff like billboards, signs, and parking lighting. Your POCO seems to be more flexible.
 
Re: A lesson to the learnin'

I just wish there was a FPN or a direct reference to 230.90 in 230.31(B). That would have nipped it in the bud, because when I found that, I quit looking. :(
 
Re: A lesson to the learnin'

Hold on a sec George. First, URD would be considered one "conductor" per Chapter 9 tables Note (9. and you would be allowed 53% fill.)


But why can't you run THWN?

40% of 1" Sched. 40 PVC = .333

#4 .0973
#4 .0973
#6 .0726
#8 .0556
________
.3228
 
Re: A lesson to the learnin'

Originally posted by davedottcom:
Hold on a sec George. First, URD would be considered one "conductor" per Chapter 9 tables Note (9. and you would be allowed 53% fill.)
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Really? Is it? When I hear "cable", I think of something encapsulated within an inner sheath. URD is three chunks of USE twisted together, that's it. They are labeled as individual conductors.

On tough pulls, I'll actually twist individual conductors together to resemble URD, to make it easier! :D

But why can't you run THWN?
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I'd have had to install a complete conduit run, and would have had problems:
</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">The conduit was too skinny for other than a straight shot with #4, IMO</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">I would have had at least an extra 90? over 360? without re-digging the whole half-frozen playground</font>
<font size="2" face="Verdana, Helvetica, sans-serif">
I guess what it came down to, is I got in a hurry with all the poles, getting help squared for other work, and having to get the trenching done so I could get the trencher called in for pickup.

I got sloppy and in rolling with the bad turn of events (a way smaller pipe than I had use for, in the wrong spot, half-frozen ground, utilities to hand dig around, embedded golfball-size chunks of concrete every 6-8 cubic inches, lack of sleep) I blew it.

I guess my main purpose in posting was to say, "Hey, I screwed up, pay attention to your work," and to call attention to 230.90 (one spot where conductors are considered protected on their load side), and as a reminder to inspectors to pay attention to details. :D

[ December 31, 2005, 09:32 PM: Message edited by: georgestolz ]
 
Re: A lesson to the learnin'

Originally posted by georgestolz:
Really? Is it? When I hear "cable", I think of something encapsulated within an inner sheath. URD is three chunks of USE twisted together, that's it. They are labeled as individual conductors.
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Well, the Southwire Handbook repeatedly refers to it as "Cable". And I agree it should be because of the fact that it is twisted. That greatly affects the way it pulls through a conduit. (Much less ply-ability!?!) Anytime you have a multi wire cable being pulled through a conduit you have to take the widest part of the cable and use that measurement as if the whole cable assembly was that size (In a perfect circle) then do the calculation to determine if it exceeds 53% of the conduit.

As far as your job site goes...yuk! :(
sorry dude!

uh...tomorrow's a new year!

How's that 'ol lang song go?
...Let allll those pipe runns beee forgot...
:D
 
Re: A lesson to the learnin'

Originally posted by davedottcom:
Well, the Southwire Handbook repeatedly refers to it as "Cable". And I agree it should be because of the fact that it is twisted.
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I would call it a cable as well.

Originally posted by davedottcom:
Anytime you have a multi wire cable being pulled through a conduit you have to take the widest part of the cable and use that measurement as if the whole cable assembly was that size (In a perfect circle) then do the calculation to determine if it exceeds 53% of the conduit.
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Again I agree.

Originally posted by davedottcom:
...because of the fact that it is twisted. That greatly affects the way it pulls through a conduit. (Much less ply-ability!?!)
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Here I have a minor disagreement, assuming the raceway is sized correctly factory twisted cables will bend around corners with less resistance than a group of non twisted.

I am only talking about cables with a even and continuous factory twisting, not just some cross overs from messy feeding.

If you have 4 conductors in a straight 'square' pattern trying to go around a corner the conductors on the outside of the radius need some 'slack' to turn the corner or the inside conductors will have to 'bunch up'.

Try bending a piece of 2 wire NM 'sideways' in the middle of a run leaving say the black on the outside and the white on the inside.

I think you will find it is all but imposable. :p

On the other hand a twisted configuration will turn the corner very easily as the conductors alternate between the outside and inside of the radius.
 
Re: A lesson to the learnin'

Originally posted by iwire:
If you have 4 conductors in a straight 'square' pattern trying to go around a corner the conductors on the outside of the radius need some 'slack' to turn the corner or the inside conductors will have to 'bunch up'.

Try bending a piece of 2 wire NM 'sideways' in the middle of a run leaving say the black on the outside and the white on the inside.

I think you will find it is all but imposable. :D

[ January 01, 2006, 10:41 AM: Message edited by: davedottcom ]
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Re: A lesson to the learnin'

Dave forget about friction for a moment and just concern your self with bending the cable.

Have you ever wondered why they twist multi-conductor cables before wrapping them?

Because if they where laid straight then wrapped you would have a very hard time bending them.

If you doubt this lay four solid 12 AWGs in a straight square pattern for about 24" long than tape them tight.

Now take a equal length of 12/3 NM, strip it than tape it identical to the first one.

Now try bending them and tell me which 'cable' bends easer.

Even with them taped tight the twisted set will bend much easer than the straight set.

Now you say thats only in a cable, if it was separate conductors it would be easer.

Well would it?

Where would the 'slack' come from?

The slack would have to come from the beginning of the pull which means the conductors would need to slid by each other for the length of the run.

OR

The 4 conductors in a square would have to flatten out and be side by side which means jamming into the conduit sides.


You will see that 'flatting out' if you try the what I said above. :)


Bob

[ January 01, 2006, 10:56 AM: Message edited by: iwire ]
 
Re: A lesson to the learnin'

Dave one of the reasons I am very confident in this is I have pulled a lot of 'stripped' MC and NM into raceways.

Sometimes the MCs are as large as 4/0 and go through a few bends.

I can tell you without a doubt that a group of four twisted 4/0 copper will go through the bends easer than the same conductors side by side. :)
 
Re: A lesson to the learnin'

I get hung up on one detail of this: the twisted conductors have less surface area, so they take up less room in a pipe.

Stick a piece of 12-3 UF into a 1/2" PVC. Get a bigger hammer.

Now, stick a piece of 12-3 NM into the same conduit. It rattles around.

This is the effect that I visualize in this discussion, I can't look past it. I can glimpse what you're getting at, Bob, but I lose it. :)
 
Re: A lesson to the learnin'

Originally posted by georgestolz:

Dave one of the reasons I am very confident in this is I have pulled a lot of 'stripped' ... NM into raceways.
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How is that legal? :confused:
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Well, George, since the code is permissive; How is is illegal?

True, the consist of an MC cable is not an article 300 conductor type. Along those same lines, when you pigtail to switches and receptacles when you ruff a home, do you use THHN for your pigtails? or do you use scraps harvested from romex? Same thing. Neither is expressly prohibited.
 
Re: A lesson to the learnin'

Originally posted by georgestolz:
I can glimpse what you're getting at, Bob, but I lose it. :)
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It boils down to the conductors on the outside radius of a bend need to be longer than the ones on the inside radius.

If the conductors are laid straight that extra length does not 'just happen' it must come from the beginning of the pull.

If the conductors are twisted they share equal time between the inside and outside of the radius meaning the length will not change for each individual conductors.

Now with 14 AWG in 1/2" this is not a big deal, with 600 Kcmil in 4" the difference becomes much more of a problem.

Lets say you have a 1" diameter conductor turning 90 degrees on a 36" radius.

That conductor would be 31.14" long through that bend.

Now 'stack' a second one inch diameter conductor on top of that.
The conductor will be making a 90 in a 37" radius.

This conductor would be 32.05" long.

Where did this 'extra' inch come from?

It had to slide by the other conductors all the way back to the start.
 
Re: A lesson to the learnin'

It's listed as a cable assembly; removing the sheathing is not in tune with the listing.

The conductors inside are not marked per 310.
 
Re: A lesson to the learnin'

Originally posted by georgestolz:
It's listed as a cable assembly; removing the sheathing is not in tune with the listing.

The conductors inside are not marked per 310.
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I see. ;)

So what do you run inside your panels? :p

I am kidding around but I am also serious.

Where do you find the difference for cables in a raceway and cables brought into an enclosure?

Also MC comes marked a few different ways, sometimes it is marked on each conductor, other times the marking is on the plastic wrap, it is a simple thing to leave the plastic wrap in place. Which is something I do until the MC is fully installed in the connector, sort of a built-in additional 'red head'.
 
Re: A lesson to the learnin'

At the point that the wires are no longer part of a cable assemply is when they become unmarked and misused.Yes have done it when in a jam.Also of question is what we have when we do a changeover.
 
Re: A lesson to the learnin'

Originally posted by iwire:

Where did this 'extra' inch come from?

It had to slide by the other conductors all the way back to the start.
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Yes, of course! That's exactly why, in my mind, it would make the pull much easier.
Think of the 2 front wheels on a car! They are Not turning the same number of RPMs around corners.
Now picture One big wheel instead.
(like Fred Flinstones car)!
Now tell me, which car would turn the corner easier? :D
 
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