Derating wires for amps

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iwire said:
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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Personally I follow the code and derate as required. But for every one guy who's not jamming the pipe with wire there are many who still are doing it without consequence. Makes for an uneven playing field when bidding a job.
 
infinity said:
Personally I follow the code and derate as required. But for every one guy who's not jamming the pipe with wire there are many who still are doing it without consequence. Makes for an uneven playing field when bidding a job.
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It does till the inspector does his job and tags them.Really not hard to catch.When they end up repulling and piping they will learn.
 
Jim W in Tampa said:
It does till the inspector does his job and tags them.Really not hard to catch.When they end up repulling and piping they will learn.
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Unfortunately I don't see anyone getting caught.
 
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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Unless the change can be covered with some general tables, I don't see it happening. The code tries to cover the general cases most of us might encounter, but certainly does not cover everything. While it does not directly allow for this derating, 310.15(C) would be way to get it done and meet code.

The lay of the conductors in the conduit (and the conduit type) does change the impedance and heating characteristics. I don't think it would be worth the money to have it done and cover the liability cost except in rare cases. I certainly don't think you could "make your own brew" and meet code.
 
"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. "

You could use a 15 amp breaker.
 
Pierre C Belarge said:
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.
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This was also my first thought, It is so easy to figure the circuit loads before you pull the wire I don't see why on a new install you would need to "cram" as many conductors in a conduit as will fit.
Getting a dead beat customer to pay is harder then putting the correct number of CCC's in a conduit. :D
 
John25 said:
....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.....
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How does installing 2" as opposed to 3/4" for a dozen 12s make the job easier?
 
480sparky said:
How does installing 2" as opposed to 3/4" for a dozen 12s make the job easier?
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that 2" inch was just an example i pulled out the air. What ive actually ran into is an EXISTING 1' inch that has 9 #12 thhn CCC that goes to my area that new circuits are wanted.

This pipe run would be VERY convient. If i add 2 more ciruits ( 2 hots and 1 neutral) it would be 12 #12 thhn ccc in there, I have to derate 50% amps on all those wires according to code.

Yes i did think about just putting them all on 15 amp breakers (down from the 20 amp), but was STRONGLY recommended not to , because the prints are not up to date and even though i took some amp readings and the load appeared light on some of them, it was just best to leave the 20 amp breakers alone.

So im left with the issue of either pull them all out and pull #10 's for all of them (waste of time and material in my opinion) or run more pipe all the way from the panel to the area and pull my own circuits then. The pipe run is a long run the route one has to go.

When you look at table 310.15(B)(2)(a) for the derating, its just such a HUGE span when you get to the 10 cccs on that chart. It says 10 - 20 ccc you have to derate 50%!! the others before that (7-9) is just done in 3's and its 70% and 80 % .

How we go from 70% way down to 50% wheather i have 12 wires or 20 wires????!! It just got me thinking, ESPECIALLY when i run into sooo many electricians that do not even bother derating. Even though this is a 1' inch pipe, it could have been 3/4 ' inch pipe (3/4 can handle 16 #12's 1' inch can handle 26 #12's) just as easily, but one would have to use the same derating regardless of the size of pipe.

Like others said, i do not know of any inspector that have ever tag anyone for this on jobs. This can be unfair bidding on some projects when some people dont play by the rules!! But the derating looks like it could use some looking into in the new codes. Not to mention the extra 30 degrees you have to add for roof top installations in the 2008 NEC! Were there really that many fires/melting wires on roof tops that caused that change for 2008 on roof tops??!!

As for this project im doing , I know of one guy that told me do not even bother derating it, just pull it in, especially with that bigger pipe.

Ok im done venting. Thanks for listening.
 
I guess you could say it's like cheating on your wife. " lot's of guy's do it and don't get caught." That is when your own personal integrity comes into play yes people do bad and wrong things, but is this how I want to live my life ? You only have control over your self and what you do. It seems that you know it is not code compliant, it is easier, it may never get found out, and it may never cause a problem, but is that the way it should be done ?
Just asking.:)
 
brother said:
So im left with the issue of either pull them all out and pull #10 's for all of them (waste of time and material in my opinion) or run more pipe all the way from the panel to the area and pull my own circuits then. The pipe run is a long run the route one has to go. .
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Your paid by the hour.

Your employer pays for material

Presumably they hire full time electricians to do the jobs within code and keep the facility in good condition.

Whats to even think about? :smile:
 
acrwc10 said:
I guess you could say it's like cheating on your wife. " lot's of guy's do it and don't get caught." That is when your own personal integrity comes into play yes people do bad and wrong things, but is this how I want to live my life ? You only have control over your self and what you do. It seems that you know it is not code compliant, it is easier, it may never get found out, and it may never cause a problem, but is that the way it should be done ?
Just asking.:)
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No it should not be done that way, so yes i will do it code compliant, no matter how much time or costs it take. it just irrates me when i see other electricians do stuff and get these jobs/projects and its because they just didnt follow the rules.
 
brother said:
No it should not be done that way, so yes i will do it code compliant, no matter how much time or costs it take. it just irrates me when i see other electricians do stuff and get these jobs/projects and its because they just didnt follow the rules.
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This comes down to who is in charge of the job and if it turns into melt down who will get blame.If its costing you contracts then lean on the inspector gently as you can.Low bidders usually turn out s--- work and botom line customer only sees $$$$$$$$$ and if it works.Is no easy answer here.Personally i prefer to do jobs the right way and i think you do too.Pick up the phone and call it to inspectors attention.
 
brother said:
What ive actually ran into is an EXISTING 1' inch that has 9 #12 thhn CCC that goes to my area that new circuits are wanted.

If i add 2 more ciruits ( 2 hots and 1 neutral) it would be 12 #12 thhn ccc in there, I have to derate 50% amps on all those wires according to code.
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If this is a 120/240 single phase system, adding this circuit would only add 2 CCC's. And if those 9 conductors that are in the conduit already are 6 hots and 3 neutrals, there are only 6 CCC's. So you would be in fine shape with 8 CCC's.
 
wirebender said:
If this is a 120/240 single phase system, adding this circuit would only add 2 CCC's. And if those 9 conductors that are in the conduit already are 6 hots and 3 neutrals, there are only 6 CCC's. So you would be in fine shape with 8 CCC's.
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The plot thickens.:smile:
 
wirebender said:
If this is a 120/240 single phase system, adding this circuit would only add 2 CCC's. And if those 9 conductors that are in the conduit already are 6 hots and 3 neutrals, there are only 6 CCC's. So you would be in fine shape with 8 CCC's.
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This is not a 120/240! its a 3 phase 120/208 systemin commercial. like i said there 9 wires there, I have to double check monday but i think some circuits they had seperate neutrals for some reason on some of the circuits. Maybe because of electronics/harmonics and things.
 
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