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Joined: Jul 2004
Posts: 625
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Did we ever answer the question about the 10 lamp holders, each on a snap switch and all connected to a single 20a circuit. You will have 11 current carrying conductors in the pipe but it is clear they can never overheat since total current is limited to 20a.
If 15A happens to be enough to supply the load, you could put it all on a 15A circuit, and you'll be good to go. You can have up to 20 #12's in one pipe, if they are derated to 15A.

[This message has been edited by SolarPowered (edited 02-07-2007).]

Joined: Mar 2005
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In other words, the word "supervision" implies an ongoing activity, as opposed to, say, "review", which would imply that an engineer did his calcs, stamped the drawing, and was done with it.

Any other thoughts on this?
Engineering supervision applies to the design process. A PE does not need to personally perform any calculations or draft any drawings to be able to stamp them, provided it is all done under his/her supervision. In this way, you can have large engineering departments that only have one actual PE that stamps everything.

Joined: Jan 2003
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While the NEC contains the phrase "engineering supervision", the national building codes do not.

The national building codes including the NEC portion are simply a set of prescriptions.

You either follow the prescription or you have an engineer deviate from the prescription and stamp the plans.

Conduit fill is a prescription. An engineer can deviate from it.

That again is false.

Sorry George your PE seal does not make you all powerful.

You still must follow the NEC, at least in any of the 5 states I work in.

Where is it that you work?

Here in my area the building code has nothing to do with the NEC.

Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Joined: Aug 2005
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Duh! CCC = current carrying conductors! I just have never referred to it as "CCC". See, I learn new lingo everyday. Sorry about the brain fart. Thanks!

Joined: Apr 2002
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In reply to George's comments:
"You either follow the prescription or you have an engineer deviate from the prescription and stamp the plans.

Conduit fill is a prescription. An engineer can deviate from it."

This does not apply in NJ. (period)

UCC 5:23 et al is our 'Code'; NEC is slightly ammended and adopted as part of the UCC>

John


John
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I was taught to always count the neutral as current-carrying ... shared or not.

George, you also bring up an interesting point ... I was given to understand that current flowing through neighboring wires created an impedance in a conductor, hence the de-rating. Less resistance countering the higher impedance, as it were.

If this is so, does it matter what circuit the current is from? Does it matter to our conductor if the wire next to it is from the same circuit? The same phase? Is it an ideal situation when the two wires are of differing phases - or one a neutral, with the current flowing in the opposite direction?

I always imagined this issue - de-rating - applied to pipe carrying multiple circuits. This thread has me thinking ... what about switch legs? Imagine your typical office, with four lighting "zones," and three-ways to boot. You have one 'power leg' shared between the four switches, and 8 travelers. That's 9 wires in a single pipe. De-rate? I never thought about that situation.

What say you all?

Joined: Jan 2003
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John what you describe is what pretty much the same as what Greg brought up.

The NEC requires those switch legs to be derated.

I agree with Greg that it makes little sense to derate.

However how many AHJ / inspectors are actually forcing compliance in those situations? [Linked Image]


Bob Badger
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Massachusetts
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Bob:
In the real world, I have not encountered a situation that derating switch loops/legs would be an issue.

John


John
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"Here in my area the building code has nothing to do with the NEC."

Perhaps you should review your building code and review the process that adopted that code and the process that adopted the NEC.

You will find they are connected. You will find that my belief outlined above is a reasonable interpretation of that connection.

Joined: Dec 2000
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George
Please show us some substantiation. Something written by someone other than you.

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