parallel conductor sizing

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spider2

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A co-worker had a service call the other day, lights flickering, loud rattling etc. when using a piece of equipment. He found the problem, lug on the breaker had melted and broken loose. Now comes the real problem. This a 225A breaker feeding two pieces of equipment in a room where there was originally one. Conduit size 1 1/2" with 3 - 1/0 and 3 - #1 paralleled for this 225A feed. Obviously this is wrong. What are the potential dangers with this setup? I'm thinking lower resistance on the 1/0 will cause it to carry more load than it's capable of handling and minimal on the #1 or would it divide evenly? This will be quite costly to replace plus downtime for them and they don't want to do it.
 
Re: parallel conductor sizing

Are you saying that each phase consists of a #1 and a 1/0 in parallel. If so, yes this is not NEC compliant and your thinking is correct that the amount of current carried over each conductor will be in respect to their resistances.
 
Re: parallel conductor sizing

Originally posted by spider2:
This will be quite costly to replace plus downtime for them and they don't want to do it.
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Ask them which will cost more:
a) a scheduled shutdown done at the most convenient time

b) an "unscheduled" shutdown at any given moment with no notice.
 
Re: parallel conductor sizing

Originally posted by spider2: This is a 225A breaker feeding two pieces of equipment in a room where there was originally one. Conduit size 1 1/2" with 3 - 1/0 and 3 - #1 paralleled for this 225A feed.
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You have me slightly confused. I see that at the source, you have two sets of conductors connected to a single breaker. But are the two sets conductors (i.e., the #1 and the #1/0) also connected to each other at the other end (i.e., the load end)? That is, do the two sets of conductors feed one item of equipment or two? If they feed two items of equipment, do they share a single point of connection?

What I am trying to understand is whether this is a case of ?double-lugging,? using one breaker to feed two separate loads, or a case of ?parallel conductors.? From what you describe, it is clear that either would be a code violation. But the hazards of the two types of violations are different. I can?t answer your first question, until I understand the installed configuration. I refer to the following question:
What are the potential dangers with this setup?
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Re: parallel conductor sizing

charlie b, This is a case of paralleled conductors. I haven't personally seen the installation but if I remember the description correctly it was a feed to a junction box and then tapped to feed a fusible disconnect for one piece of equipment and tapped to feed a transformer for a second piece of equipment. I have spoken with my father about repairing it and he will be speaking to the owners. I know that the owners don't have alot of money right now because of recent equipment upgrades so while I hope they will be convinced of the real need to repair it may be a while before it happens. I believe it has been working for quite a while so I wanted to have some better explanations than "the code book says so" if asked.
 
Re: parallel conductor sizing

Originally posted by spider2: I believe it has been working for quite a while so I wanted to have some better explanations than "the code book says so" if asked.
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Let me suggest the following analogy:
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  • <font size="2" face="Verdana, Helvetica, sans-serif">Suppose that just before you back your car out of the driveway each morning, you put on blinders and earmuffs.</font>
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  • <font size="2" face="Verdana, Helvetica, sans-serif">Suppose that you wait for a random amount of time, and then just back into the street.</font>
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  • <font size="2" face="Verdana, Helvetica, sans-serif">When you get into the street, you can take off the blinders and the earmuffs, and drive to work.</font>
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  • <font size="2" face="Verdana, Helvetica, sans-serif">Question: If you do this ten days in a row, and if you don?t hit anything during those ten days, would you conclude that this is a safe driving habit? Or would it take 20 consecutive days without incident, to convince you it was safe? 30? How many?</font>
<font size="2" face="Verdana, Helvetica, sans-serif">I like to use this analogy, whenever someone tells me, ?It?s never been a problem before.? Everyone is welcome to steal it shamelessly. ;) But give me authorship credit, if you wish to use the following aphorism:
?An accident waiting for a place to happen will, given time, find that place.? Charlie Beck
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Re: parallel conductor sizing

?An accident waiting for a place to happen will, given time, find that place.? Charlie Beck
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I.e., the Charlie Beck combined restatement of Murphy's and the Second Law of Thermodynamics.

Great quote and even better analogy Charlie ;)

I do ocassionally review why ?It?s never been a problem before.? Sometimes theres actually a good reason that becomes the basis for a future NEC Proposal but it usually it tends to be, "Nobody goes near it."
 
Re: parallel conductor sizing

Originally posted by charlie b:
?An accident waiting for a place to happen will, given time, find that place.? Charlie Beck
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I like it and I will shamelessly quote you .

Are you the author of Charlie's rules of technical reading or was that the other one. I give that one a lot of mileage. Students like it.

Thanks
 
Re: parallel conductor sizing

Originally posted by sandsnow:Are you the author of Charlie's rules of technical reading or was that the other one. I give that one a lot of mileage. Students like it.
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I am their author. And I am flattered that your students like it.
 
Re: parallel conductor sizing

Charlie, that goes right along with. "If you don't look at it, it's OK and you won't have to fix it".

Edit: Spell check, Spell check, Spell check, there maybe I'll remember next time.

[ May 17, 2005, 01:01 PM: Message edited by: 69boss302 ]
 
Re: parallel conductor sizing

I keep thinking that's a really good idea Charlie. But I don't usually have a word processor open so I don't do it. And until I start, you're right, it is cheating. :D
 
Re: parallel conductor sizing

Sam
The forum has a spell checker, so am I missing something???

How would you members relate Charlie's 2nd Axiom or Theorem (technical reading being the 1st) to the requirement in Code "...likely to be... or .....likely to become...."
Something "likely to become energized" would occur during an accident. If it's that likely to happen, then why don't we just fix it before it happens.
 
Re: parallel conductor sizing

Originally posted by charlie b:
Originally posted by sandsnow:Are you the author of Charlie's rules of technical reading or was that the other one. I give that one a lot of mileage. Students like it.
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I am their author. And I am flattered that your students like it.
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We start off with your rules, then I ask how many think you can't splice in a panelboard. Then we go to the Code section. I try to get them to let go of all those myths that they have learned and of course look it up when they want to know something.
 
Re: parallel conductor sizing

For those who might not know what Sandsnow is talking about, here it is:
Charlie?s Rule of Technical Reading

It doesn?t say what you think it says, nor what you remember it to have said, nor what you were told that it says, and certainly not what you want it to say, and if by chance you are its author, it doesn?t say what you intended it to say. Then what does it say? It says what it says. So if you want to know what it says, stop trying to remember what it says, and don?t ask anyone else. Go back and read it, and pay attention as though you were reading it for the first time.
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Re: parallel conductor sizing

I haven't seen that before Charlie and I especially like the part about even if you wrote it yourself. :D

By Larry:

Sam
The forum has a spell checker, so am I missing something???
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Why yes, you might be missing something Larry.

The spell check on this forum sucks. That and text editing is just a lot easier with my own programs. Way more features and stuff. For me, the font on the post editor, for some reason, makes it harder for me to see errors. After somethings posted, boing, all the errors pop out at me. That might be just me though.
 
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