240.4 & T-310.16 Conductor Protection and Ampacity
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- čas přidán 29. 08. 2024
- Understanding Conductor Protection (240.4) and how to use the most common Ampacity Table in the NEC (T-310.16). I also look at several Code sections that relate directly to T-310.16 and consider Insulation Ratings. [All Code Sections from 2020 NEC]
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Bet your electrician said your over thinking it
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Extremely clear explanation of a vital subject
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Ive been looking for someone to explain all these concepts together. Other videos ive found only cover individual aspects of these codes. Thank you
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If you had #2 Al SER from the main to a sub running along floor joist in a basement and then popping through the garage wall into PVC conduit that runs along the outside of the drywall to the sub box. The sub box charges an EV for 8 hours continuously (truck is adjustable from 20 to 80 amps), a hot tub, and a few seldom used 20 / 30 amp outlets. Also the SER Al is about 100’ long total. The sub breakers are 50 amp on #6 Cu for the hot tub, #3 Cu on a 90 amp breaker to the EV Truck, (2) #12 on 20 amps, and #10 Cu on a 30 amp. Note: the 20s & 30 never get used unless the truck is in the driveway NOT charging because there is no room to use power tools with it in the garage.
I ask because my house has a 100 amp breaker on the main 200 amp service that feeds a sub and I feel like they should be 80 amp on both the sub and main, when I review all the code sections an derate for the breakers 75° & continue use due to the EV truck exceeding 3 hours. Note: I’ve been charging at 70 amps max since I think the system shouldn’t have 100 amp breakers & I have NOT tripped a breaker yet. Sometime I want to turn the truck up to 80 to see if it does trip a breaker but I also don’t want to damage the breakers with excessive heat (I’m assuming the wire can handle the tub and truck rocking at the same time since it’s all 90° C rated wire but the poor breaker is only 75° rated for 100 amps and if the hot tub and truck both go full out they would exceed 100 amps (80 plus 50 potential).
Excellent presentation. Great teacher!
Great instructional video, thank you
Thanks for your course it's so interesting
SUPERB, THANK YOU DAVE
Great explanation! Thanks.
Amazing teacher. Thx.
Fantastic video.
4:50 Also, the title of article 310.14 says table 310.16 applies to conductors rated between 0 V and 2000 V.
Very good job, easy to understand
fantastic content
Actually Dave Gordon posting this? If so, we miss you at the school.
Thanks brother.
Excellent
A very good instructional video! However I have a minor correction. The conductor type, for NM, is not actually found in 334.80 although insinuated. It is really not found until 334.112
EXCELLENT VEDIO👌👌
110.14 C with the 100amp rule states that below 100a, we're to default to the 60deg column. But, ay 15:00ish you show where we can use the 75deg column for a 40amp circuit, provided the connections are temp suitable.
What am i misinterpreting?
When you say we can start in the 90 degree column for smaller wire as long as we don’t end up with the ampacity larger than the 60 degree column, I assume you are talking about for your ambient temp and derating adjustments. Is that correct? Otherwise you would go directly to the 60?
Great video!
If more than 3 CCC are ran thru a conduit can u instead of upgrading wire just change out conduit to a bigger size and if so what would b the correct size to use? And what percentage of the conduit fill would be used?
I’m not a technician (though an electrical engineer), but regarding your first question, as far as I know, no, changing the size of the raceway (conduit/tubing) doesn’t change the correction factor for more than 3 CCC.
Regarding your second question, table 1 of chapter 9 says to use up to 53%, 31%, or 40% (sometimes 60% instead), for conduit/tubing carrying respectively 1 wire, 2 wires, or more than 2 wires. And that’s including CCC as well as ground/grounding conductors, signal conductors, etc., because such calculation is for conduit fill, not for thermal reasons.
🔥🔥🔥
Question about PV source circuits. I have a 2 strings run in parallel. Total current calculated 690.8 A and B. 34.81 amps total. The contractor is using # 10 stating that because there is not OCPD between the modules and the inverter that 240.4(D) does not apply and the conductors are rated for 35 amps. Your thoughts I believe they should be #8 CU
The PV source circuits are fine as #10 but the combined PV output circuits should be #8. Hope this was resolved appropriately.
Thank you
Thank you so much
Help.. when does the neutral count as a ccc and when doesnot... thanks
I thought the temp ratings were the current a conductor could carry at that ambient temp. So as long as you don’t have more current on that conductor it’ll never exceed the temp listed regardless of the ambient temp?
Forgive me if I over-explain, but let's first clarify that "temperature ratings" are the maximum temperature that a type of insulation can handle and the "ambient temperature" is the temperature of the surrounding air.
Now let's look at it this a couple ways.
FIRST EXPLANATION: We know that current flow through resistance causes heat and as more current flows, more heat is generated. Conductors are, in a sense, long resistors (see Ch. 9 Table 8). When no current is flowing, how hot is the wire? Well, it's probably the same temperature as the ambient temperature (the air around it). As current starts to flow, the temperature of the wire will increase from ambient temperature. So, if a wire is in a refrigerated room it is starting from a colder point than a wire in a hot factory environment. With the same type of wire in both locations, both running the same amperage, which one do you think would be hotter? I believe the wire that is in the hotter ambient temperature would run hotter.
The temperature ratings heading each of the columns of our ampacity tables are the maximum temperature that those insulation types can handle (see Table 310.4(A)). In order to keep the conductor from damaging its own insulation by the heat generated by its own current flow, we must limit its ampacity (the current allowed to flow on it). If we follow the conditions of use (in the written Sections 310.16 - 21) for each table, the listed ampacities should keep each conductor below its column's maximum temperature rating.
However, if we alter the conditions of use by installing conductors in a higher ambient temperature than 30 degrees C (for Tables 310.16 & 17) or 40 degrees C (for Tables 310.18 - 21), "Note 1" below each of the tables refers us to 310.15(B) for allowed corrections. Essentially, if the ambient temperature (starting temperature with no current flow) is higher than the conditions of use we must restrict current to a smaller amount than the ampacity table states because the wire is starting out at a hotter temperature (less available temperature rise before it hits its limit), but if we are installing the wire in a colder environment we are allowed to run more current because it is starting from a colder temperature (more temperature rise available before it reaches its limit).
SECOND THOUGHT: If a car pulls the same trailer up a hill on two different days, is it more likely to overheat on the cooler day or the hotter day? My money says more cars overheat on hot days (higher ambient temperature) than cold days.
***Coming soon... When my videos on 310.15(B)&(C) are ready I'll paste the links here***
@@davegordon6819 thanks for the thorough reply. I understand what you’re explaining. What are the impacts of additional conductors run in the same or neighboring ducts underground? Say one conductor is run at 90 degrees - if you add a second conductor and run at 90 degrees, will there be additional heat or will the temperature remain at 90 degrees? I’m trying to determine if additional runs of conductors in separate conduits all loaded to 90 degrees would stay at that temperature or is it strictly the maximum that you’d generate based on the “hottest” conductor? So if you had two at 90 degrees and added a third at 100 degrees, the 100 degrees would dissipate and warm up other conductors within a certain radius based on temp, etc.
@@Mike_Rundle This may be getting out of my knowledge band. I have had an experience of running underground service conduits where we were close to an underground steam line, but we were given a specific clearance distance by people of higher rank than I. I also worked with a guy who told me of a large underground duct bank that they needed to redo because of overheating when they initially turned everything on. There are other phenomena that can play into this, but if I remember correctly, mutual heating was a suspected culprit. I believe they then routed all the conduits over head.
The answers you're looking for may be in Article 311, a new article for Medium Voltage Conductors (2,001 V to 35,000 V). Possibly in 311.60 - "Ampacities" and/or possibly in Annex B that include dimensions for duct banks. Unfortunately, both areas where I am not knowledgeable to speak to the specifics.
Sorry I can't be more help on this, but I will give you one more code section that I should have mentioned in my first reply. 300.17 is a general rule that underpins the ampacity and conduit fill rules - "any raceway" could be read as any raceway either on its own or in a group (i.e: duct bank). Thanks for being curious about our trade and trying to find answers.
@@davegordon6819 thanks Dave. Your videos are great and very thorough and informative. I’ve been going through them and learning something from every video which is great. Thanks again for trying to help me find the answers.
Good video but you should put all intel
ie insulation aluminum…etc …or a pic
tnx
😃
Hi Mr Gordon, I Was wondering if I could possibly get your email address from you from you because I have a few questions I'd like to ask and talk to you about
I guess the Federal Pacfic engineers skipped this class 😂
Who else is here from Beluga
NM and NM-B both restricted to 60c?