Do Electrical Engineers understand three phase reality?

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peter

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I am working on a remodel for a Target store in La Mesa, Calif. I have an opportunity to design and construct the conduit system for the Food Court which is very complicated. I designed some runs of 3/4" conduit with two boats [black, red, blue and white] [#12 guage wire, 20 amp] that I figure was alright.
But my boss says that some Target engineer will reject any conduit containing more than four circuits. I'm pretty sure I understand the concept of three phase wiring, but perhaps this engineer doesn't.
The only thing I can think of is something to do with harmonics. If harmonics were really a problem, I could see using #10 neutrals. But would limiting the number of circuits to four really solve a harmonics problem? Or does this engineer need to be re-evaluated?
~Peter
 
Sounds to me like someone is confused about the derating issue. For a #12 THHN conductor the magic number is 9. This means that you can have up to 9 CCC's in a raceway before derating will drop you below 20 amps. If your circuits were all linear, you could have 9 three phase circuits sharing 3 neutrals and still be within the magic number of 9 CCC's.
 
peter said:
[I had a hard time logging in]
Or does this engineer need to be re-evaluated?
~Peter
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Peter, Peter...

Personally, it has nothing to do with the him/her being an engineer, and everything to do with not knowing what he/she is doing!

I do...thank you..and if you wanna "spar" in the electrical boxing ring bring it on...I might not win, but I'll take you to 12 rounds!!

I'm not an "ELECTRICAL" engineer..I'm an Architectural Engineer, so I guess I should be quiet!

Now back to the orginal question...

I have to agree with infinity...didn't it used to be 4-8 before the most recent update?
 
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Peter I work in a lot of National chain stores (Including Target) and I offer this advice.

Don't try to re-invent the wheel in these places.

They build hundreds of stores, just read and follow the specifications that they provide. IMO you are simply wasting your time thinking to much about the reasons for their specs. No doubt your company took the job tight from the start so there is no time to waste trying to get things changed (they won't budge) or doing things twice.

We had a customer that wanted one two wire circuit per 3/4" EMT.

Why?

I don't know, maybe future circuits but who cares, the specifications are what makes the work and the challenges at least a little different from job to job.:)
 
This is a contract issue, not a technical issue. You would win the technical fight, if it came down to a fight. But what does your contract say? Does it say that you will use a specification written by Target? Does that specification say that you will not install more than four circuits in a single raceway? If both answers are "yes," then you made a contractual error. If either answer is "no," then you fulfilled the terms of the contract, and if they wish they can pay you more to install additional conduits.

By the way, this really isn't about "three phase." It's about counting circuits. "Two boats" is equal to six circuits. It is also equal to six current-carrying conductors (or at most, eight). So you are OK with ampacity and overcurrent protection.
 
I really appreciate the replies.
Right here on the plans, page E-8, Food Service Power & Systems Plan, they have a flex to panel LP-10B for ckts. "1, 3, 5, 7, 9, 11" complete with six short, two long and a long cross with a dot on the end of it [indicating ground wire] lines on the curved homerun arrow. [Incidentally, there is no "k" in the word "circuit".] So maybe a bit of hypocrusy is going on here. Or maybe, somebody doesn't under stand electrical theory. But I do.
I ran a 1" for eight or nine #10s for the two pizza ovens. As the second poster mentioned, nine is a useful limit. One is just a ground which hopefully will be green if we can get it. So two boats or six circuits. But to comply, as I Wire suggested, I am thinking of simply eliminating tow of the circuits. So instead of #4, 6, 8 + N and #24, 26, 28 + N, I will just pull #4 + N and #24, 26, 28 + N. This will conform to the four circuit maximum, will it not? 50% of the pizza's will be rather underdone.
Nobody has commented on the possibility of concern for harmonics. The run is <30' so voltage drop should not be an issue.
I would like to find out the name of this engineer who is responsible for this idiocy and track him down on the Internet and file a complaint with his State Board of Examiners and also send a message to the Dean of his [her] school complaining about their obviously defective alumni.
~Peter
 
Lady Engineer said:
Peter, Peter...
I do...thank you..and if you wanna "spar" in the electrical boxing ring bring it on...I might not win, but I'll take you to 12 rounds!!
I'm not an "ELECTRICAL" engineer..I'm an Architectural Engineer, so I guess I should be quiet!
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Lady...Lady....Lady....Your Hot!!:D Are you busy Saturday night?:cool:

peter said:
I would like to find out the name of this engineer who is responsible for this idiocy and track him down on the Internet and file a complaint with his State Board of Examiners and also send a message to the Dean of his [her] school complaining about their obviously defective alumni.
~Peter
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The engineering could 've been outsourced to ...INDIA?? Ya think?
 
The engineer may have a reason to limit the number of circuits that are in each conduit. Unfortunately :) , there is no comment area on Contract Drawings to tell the bidder or installer why it is shown a certain way. If I had to document a comment each time I drew something requiring more than the code minimum, I would never get a drawing out the door.
I often require oversized conduit for reasons that I do not document on the drawing. Sometimes it is as simple as expected future functionality.
 
Palm Beach county school district apparently specs no more than 3 CCC's per homerun and they want'em in 3/4 EMT. Go figure?

We do what they want even though it seems like a complete waste of money.
 
Hold on a moment.
I work on government buildings and they often have designs that far more restrictive than the NEC, such as minimum size of 3/4" conduit.
Why?
Closet today.
Office tommorrow.
Project money is easier to come by than maintenance money.
Do it right up front. Allow for growth
 
peter said:
I would like to find out the name of this engineer who is responsible for this idiocy and track him down on the Internet and file a complaint with his State Board of Examiners and also send a message to the Dean of his [her] school complaining about their obviously defective alumni.
~Peter
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Peter your joking right?

They are wrong because the design is not what is convenient for you?

As far as harmonics it is a non-issue with the equipment you are supplying.

You have motor loads and resistance heating at the snack bar.

It sounds like this whole issue could be cleared up with an RFI if you have the time.

As the plans show '2 boats' and your being told that they will not accept more than four circuits.

Have you seen that in writing or is it just hearsay?

As much as I will follow their 'rules' I make sure they do as well.....it's kind of fun throwing their own specs back at them.:D
 
Many engineers limit homeruns to one three-phase, four-wire multiwire circuit. Read Section 90.8 and remember that the code is dirt. It is the least you can do. The engineer allowing spare capacity in the raceways is good design practice (see also 90.1(B)).
 
quote by Peter
"I'm pretty sure I understand the concept of three phase wiring, but perhaps this engineer doesn't."

What makes you think his decision is based solely on electrical engineering? It is more likely that you don't understand the direction that the engineer is taking.

second quote
"I would like to find out the name of this engineer who is responsible for this idiocy and track him down on the Internet and file a complaint with his State Board of Examiners and also send a message to the Dean of his [her] school complaining about their obviously defective alumni."

You need to walk a mile in his shoes so to speak, before deciding he/she is an idiot, and describing them as defective. The Target engineer has most likely built more Target stores than you ever will, and certainly knows their needs better than you or most electricians who wire a store.

Jim T
 
Threads like this irks me...people get upset, and blame a person's profession. If I had a nickel for everyone contractor who wanted to prove me wrong or "save the client money", I'd be rich. Or if I had a dime for everytime I had to prove that I put it in the spec, but they lacked to read the spec...I'd be Oprah...

Can't we all just get along. I have a good friend who's an electrical contractor, and he decided to do design...well guess what? He went back into the field...he said "too much stress...and too much to remember". Doing design isn't all that easy, so at least be sensitive.

Send an RFI and be done. This man/women may have a good reason for doing it.

Off the soap box and into the ring...wanna dance pretty boy?? Just Kidding...
 
peter said:
I would like to find out the name of this engineer who is responsible for this idiocy and track him down on the Internet and file a complaint with his State Board of Examiners and also send a message to the Dean of his [her] school complaining about their obviously defective alumni.
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I take great exception to this statement. :mad:

First and foremost, there is no technical error, no code violation, no breach of professional ethics, no threat to the health and safety of the public, no significant variation from industrial standards, in short, nothing wrong with limiting a raceway to four circuits. The State Board of Examiners will utterly disregard a complaint of this nature, and rightfully so. It would waste their time to even read such a complaint.

Secondly, it appears likely that you are talking about two different engineers. One you could locate by name, by reading the seal on the drawings or specifications. That person is known to be real. The other is some theoretical, perhaps real and perhaps not, "Target engineer" who (as you were told by some other party) would reject an installation with more than four circuits in a raceway. You appear to have taken the word of this other party as being gospel truth, and you have found a conflict between this person's statement and the design drawings. How about sticking with fact, and disregarding rumor? How about waiting a little bit before maligning the reputation of an engineer, at least until you know whether you are dealing with one engineer or two, and whether there is any truth to the rumor that one will reject an installation that faithfully followed the design of another?

Finally, and you should already know this, no curriculum for Bachelor of Science in Electrical Engineering includes wiring or raceway design.
 
charlie b said:

I take great exception to this statement. :mad:


Finally, and you should already know this, no curriculum for Bachelor of Science in Electrical Engineering includes wiring or raceway design.
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Amen, Charlie! Actually, Architectural Engineering has CKT design, and building systems...but it's rear..and I stumbled on it. But there are a lot of things as an AE I still had to learn.

Still waiting in the ring....
 
If the engineer over designs a system, why should the installer care? If he's getting paid to do work beyond the scope of the NEC so be it. The only one that should really care is the guy who is paying the bill. He may be getting a lot more than actually necessary and paying for it too.
 
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