Derating wires for amps

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brother

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Ive been on many jobs and i have seen some guys who never derate, they just cram as many wires as they can in some pipe and call it a day. I try to follow as much code as possible and i even do the derating of wires even though i have to admit i have NEVER seen a fire or melt down cause people over stuffed conduits and did not derate.

But just to get your opinion, do you think there should be some leeway in the different sizes of conduit when it comes to derating?? for example if you have 12 wires of size #12 thhn in 1 inch pipe should you get a break from having to do the 50% derating as to if they were 12 wires in 3/4 inch pipe?

Seems like even though it may be a small difference in the heat its still a little different in the in heat in my opinion. what do you think? Reason i asked is because im doing a job that it would be lot easier than having to derate those wires cause the conduit runs to my area i need to go, but cant do it without upsizing everything to #10. Even though the most amps ive seen on any of them is only 6 amps. and this is at full load. ;)
 
brother said:
for example if you have 12 wires of size #12 thhn in 1 inch pipe should you get a break from having to do the 50% derating as to if they were 12 wires in 3/4 inch pipe?
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IMO, the wires in the conduit are still resting on one another.
 
The NEC does not allow 'less' derating for using a larger raceway.

If you think it's a good idea, provide sufficient documentation to back it up & submit a proposal for the '11. Forms are in the back of the '08. You have until November.
 
480sparky said:
The NEC does not allow 'less' derating for using a larger raceway.

If you think it's a good idea, provide sufficient documentation to back it up & submit a proposal for the '11. Forms are in the back of the '08. You have until November.
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Yes i know the NEC doesnt allow for this, but i was just, well shall i say it, "wanted to make my rules/codes' and do what ive seen sooo many times from others that dont derate. lol Please dont crucify me for thinking like this, ive been pretty good boy for the most part.
 
brother said:
Yes i know the NEC doesnt allow for this, but i was just, well shall i say it, "wanted to make my rules/codes' and do what ive seen sooo many times from others that dont derate. lol Please dont crucify me for thinking like this, ive been pretty good boy for the most part.
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I would never 'crucify' someone for thinking out loud. Fact is, sometimes a pretty good idea gets started that way.

Just be careful 'making your own rules', however. Inspectors take a dim view of it.
 
Your confusing conduit fill with derating.You might need larger conduit if you up wire to #10 to get passed derating.You start with the wire size you will be running after derating and then select emt size
 
I have seen many conduits with thermal issues due to fill ampacity issues. from red hot to melt down. The derating is there for more than to sell conduit.
 
Jim W in Tampa said:
Your confusing conduit fill with derating.You might need larger conduit if you up wire to #10 to get passed derating.You start with the wire size you will be running after derating and then select emt size
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No im not confusing it. I know what conduit fill is and i know what derating is. The point im making is that someone who has 10 #12 thhn in a 3/4 pipe has do the same (50%) derating as someone who has 10 #12 thnn in 2" inch pipe.

It just seem that in reality that the 2" inch pipe would be able to dissipate the heat more than a 3/4 inch pipe when dealing with the same number of wires and type. Do you not agree??
 
brother said:
It just seem that in reality that the 2" inch pipe would be able to dissipate the heat more than a 3/4 inch pipe when dealing with the same number of wires and type. Do you not agree??
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Common sense tells you it does.

But the NEC has nothing to do with common sense.
 
brother said:
LOL. Now wait a minute, Ive seem some common sense in the NEC, give me a minute and ill find it and show ya!! ;)
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90.1(C) is the best I can find. It goes downhill from there.....:smile:
 
brother said:
Yes i know the NEC doesnt allow for this, but i was just, well shall i say it, "wanted to make my rules/codes' and do what ive seen sooo many times from others that dont derate. lol Please dont crucify me for thinking like this, ive been pretty good boy for the most part.
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The code rule you have alluded to has been a code rule for a long time.
Installation methods in our industry are constantly on the change.

Maybe your idea has some merit to it. Although I surmise it may be very difficult to inspect for.

A point towards your idea:
Today we see a lot of lighting panels/circuits installed that do not have large loads on the individual conductors. This makes for more conductors installed carrying a small load (hence less of a heating load in the conductor itself), creating many more raceways if installation is conforming to code.
So maybe a study is in order for the powers to be to see if there is any merit to your idea.
 
Here we go again....

Here we go again....

We never got into loads heavily loaded with unbalanced lines. I'll shut up. We can stay away from that for now:rolleyes:
 
Conduits filled to capacity and beyond were the norm in NYC for many years because their electrical code had a maximum derating of 70%. That meant that you could fill a conduit with #12's (THHN) and never encounter derating issues. I don't recall too many buildings bursting into flames with pipes jammed with conductors.
 
76nemo said:
We never got into loads heavily loaded with unbalanced lines. I'll shut up. We can stay away from that for now:rolleyes:
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I still don't get what you have hinted about a few times now. :-? :-? :-?

Start a thread, spell out you question or your view, none of us can read your mind ... well at least I don't think so. :)
 
infinity said:
I don't recall too many buildings bursting into flames with pipes jammed with conductors.
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We could apply that logic to many of the NEC rules, they are only needed when things go bad.


For what it's worth I see what you describe around here as well, I still like to be a rebel and apply the derating rules. I run a lot of 10 AWG for 20 amp circuits.
 
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