Crane feeders

[Bgg321]

We are installing a new feeder for a crane collector rail with a 800 amp breaker feeding four cranes. My question is what size cable should we feed this collector system with?

 

[mgookin]

You're going to need much more information than that. Do you have a local engineer you can consult? Or the manufacturer of the system?

 

[Bgg321]

You're going to need much more information than that. Do you have a local engineer you can consult? Or the manufacturer of the system?

Yes, we have already done a load calculation for the cranes that are on the runway, according to article 610. The feeder is only a 100 feet long. Looking at article 610.14a we can use 500 mcm thhn for this feeder. Do you feel that this is the right size cable.

 

[Bgg321]

Crane feeder

Crane feeder

Come on guy's, someone has an opinion!!!!!

 

[Volta]

Is this a 30-minute crane?

 

[Bgg321]

Crane feeder

Crane feeder

Yes. What this is about is that there is several engineers at the plant. Some feel that the cable should be sized according to 310,15 and others feel that 610.14 is correct. I think 610.14 is correct and was looking for an answer, at least some discussion.

 

[Volta]

I have not read through the article but it seems likely that you are right.

 

[Julius Right]

NEC T310.15(B)(16) refers to continuous loading of a cable. You have an intermittent load[load-pause-load]. So the appropriate table is T 610.14(A).
The problem is 800 A rating of the circuit breaker has to be the current calculated as per 610.14(E) " Calculation of Motor Load" and not as per 610.33" Rating of Disconnecting Means".
:happyno:

 

[Bgg321]

Crane feeder

Crane feeder

Yes, that is what was done for calculating load.

 

[iceworm]

We are installing a new feeder for a crane collector rail with a 800 amp breaker feeding four cranes. My question is what size cable should we feed this collector system with?

Yes, we have already done a load calculation for the cranes that are on the runway, according to article 610. The feeder is only a 100 feet long. Looking at article 610.14a we can use 500 mcm thhn for this feeder. Do you feel that this is the right size cable.

Yes. What this is about is that there is several engineers at the plant. Some feel that the cable should be sized according to 310,15 and others feel that 610.14 is correct. I think 610.14 is correct and was looking for an answer, at least some discussion.

I don't have much help for you - I've never done a crane feeder. But I am interested in learning.

Just to confirm I understand:
If the feeder is sized by 610.14, then 500kcmil is sufficient.

If sized by 310.15, then parallel 500s are a bit small.

Is this the issue? If so, that's a lot of money if it is not needed. Then again, it is only 100 feet of copper and pipe.

Even so, I'd tend to be real cautious about overruling the one saying, "More Copper" with out being absolutely sure I completely understood her position and reasoning. Sometimes there are reasons why a code minimum job, with the accompaning lack-luster performance and poor reliability, just isn't good enough.

ice

 

[mgookin]

... Sometimes there are reasons why a code minimum job, with the accompaning lack-luster performance and poor reliability, just isn't good enough.

ice

I used to do a lot of teaching, especially during code changes. I'd often open with "remember, codes are a minimum, meaning that's as shitty as we're allowed to build".

Code does not require a smoke detector over the clothes dryer or where the christmas tree goes, but I have both in my house.

When you bid you bid the minimum to get the job. When doing engineering we have a fiduciary duty to the client so we use minimums. Only when the client specs above and beyond code, or on our own stuff, do we exceed code. Often we can talk them into it based on our experiences but as a general principle, "as shitty as we're allowed to build" is the norm.

 

[Bgg321]

Crane feeder

Crane feeder

I understand that. But this plant has been here for 25 years with several feeders just like this one. It failed a couple weeks back and is now being replaced. The cable that failed was underground conduit that has been full of water that time. The 500 mcm has held up very good! O do not know why we would feed with parallel after this has lasted this long. Seems like over kill and a waste of money in hard times.

 

[iceworm]

I understand that. But this plant has been here for 25 years with several feeders just like this one. It failed a couple weeks back and is now being replaced..

Bgg -
I'm not taking sides.

I will say that I have looked at installations that were in place, working for years - and I'm wondering why it hadn't failed the first day it was energized, But it didn't. However, even though it worked fine for years, there is no way that I would ever sign my name to an equally poor replacement.

There is a thing called the Double Dumb Shit Syndrome: "We have always done it this way. Everybody else does it this way." I work really work hard at not getting caught up it that.

Still, I don't see the problem. You said several engineers, some engineers one way, other engineers the other. Get the chief engineer to make a decision - that's her job.

I'm wondering if that isn't happening because the dissenting engineer has valid reasoning. Again, I'm not taking sides. But, we have only heard one view - your's. We don't know the engineer's reasoning.

ice

 

[Bgg321]

Crane feed

Crane feed

Yes my side is all you have heard. But, I was hoping someone here knew the code! I sure some of you do. But I am surprised that no one without me leading you through it would even try to answer my question. What a waste of time!

 

[iceworm]

Good point. Except for Julius we are pretty useless. He did as you asked.

The rest of us didn't tell you what you want to hear. Nor did we all pitch in and do a couple of hours of research to advance your case.

I don't think I'll bother talking to me anymore.

ice

 

[kwired]

Yes my side is all you have heard. But, I was hoping someone here knew the code! I sure some of you do. But I am surprised that no one without me leading you through it would even try to answer my question. What a waste of time!

Good point. Except for Julius we are pretty useless. He did as you asked.

The rest of us didn't tell you what you want to hear. Nor did we all pitch in and do a couple of hours of research to advance your case.

I don't think I'll bother talking to me anymore.

ice

I kind of have to agree with what ice said in the last post. Just what do you expect from a free service? If you don't hear the answer you want to hear maybe keep asking elsewhere until you get the answer you want, and don't get mad at us for not providing you with what you want to hear:thumbsdown: If you do find the answer you want to hear, unless it is from an engineering firm and is properly drawn out just who do you think still ultimately takes on the liability of making the design decision you are looking at? (look in the mirror) Any information given here is nothing more than the opinion of the member that posts it, and not any kind of official code interpretation or engineering project.

I won't say nobody here is familiar with cranes, but I would guess there is a fairly low percentage of members that are here quite frequently that maybe are familiar enough that they can answer with some experience behind the answer. Otherwise most of us can read what is in art 610 and give you our own interpretation, but it may not really mean any more than the same printed words mean to anyone else that has little or no experience in this type of install.

It may take some time for someone with good experience in this area to even see the thread.

 

[electrofelon]

Yes my side is all you have heard. But, I was hoping someone here knew the code! I sure some of you do. But I am surprised that no one without me leading you through it would even try to answer my question. What a waste of time!

Why dont you call up the electrical inspector who will be inspecting it and ask him? After all his/her interpretation is the only one that matters.

 

[Julius Right]

I agree 500 MCM is the minimum conductor cross section required. If we follow the IEEE Standard 242-2001 ch. 9.5.2.4 "Development of intermediate characteristics" or better E.P.R.I. POWER PLANT ELECTRICAL REFERENCE SERIES VOL.4 WIRE AND CABLES "Evaluation of Conductor Temperature Under Transient Conditions" [Eq.4-23] and if we'll take Irated[In]=430 A for continuous load as per NEC Table 310.15(B)(16) we'll get approx. 1000 A for 1/2 hour load 90 dgr.C conductor temperature and 30 dgr.C ambient[run in conduit].
But you have to cool the cable-natural cooling, of course-for at least 7 hours before starting again.
:angel: