This is approaching a DIY type project given the lack of understanding that your question itself shows.
Do you really believe this, based on the other the other questions and answers I've posted to this site, or is this just a snarky response? I'm not often required to size SO cable for machines this large. I'm also dealing with a control cabinet I didn't design, so I'm working with the size limitations of the existing terminal blocks. Thus, my question.
I don't know where you came up with the idea to multiply the FLA by 1.2. This is not something supported by any electrical code that i have seen. Normally if it is a continuous load the multiplier to get the ampacity of the cord would be 1.25. 56 X 1.25 = 70 Amps.
Forgive me. I left off the "5" when I typed the question, and did the math in my head. 1.25 is of course the multiplier for a continuous load.
I think that by 2/5 cord you mean five #2 conductors. I don't know why you would need 5 conductors. Normally the 3 phase conductors and a ground would be adequate, although sometimes you might need a neutral which could account for the 5th wire.
I do mean (5) #2 wires. And no, you don't know why I need five conductors. I do in fact need the neutral, but it wasn't germane to the conversation, so I left that part out.
The use of cords is covered in article 400.
Yes. That's the table I have open on my desk right now.
T400.5(A)(1) will tell you what the allowable ampacity of SO cord is. For #2 conductors it is 80 Amps. For #3 it is 70 Amps. At least in the 2017 code.
While #2 is oversized and #3 will work, it's proving mighty hard to find #3 SO cable. Thus, my question. Even the great McMaster-Carr doesn't carry #3 SO cable.
You can make the cord larger than the minimum required.
I'm aware of that.
Regardless of the wire size, you have to protect the wire at its ampacity. Article 240 will tell you what the maximum size circuit breaker or fuse is allowed for the ampacity of the conductors. 240.4 allows you to select the next standard higher rated CB above the conductor ampacity under 800 Amps. T240.6(A) tells you what the standard breaker and fuse ratings are. Since 70 and 80 are standard ratings, you would need to protect #2 SO cord with an 80 A rated device, and #3 SO cord with a 70 A rated device.
I'm aware of that. The conductors feeding the receptacle will be #3 THHN, and protected at 100A.
However, I can ensure that the machine will never draw more than 60A, as that's the breaker in the control cabinet. Thus, my question: do I size the SO cable for 56A, or 56A x 1.25 = 70A?
Incidentally, the instructions that come with the connector will tell you what the maximum size of the conductors can be. It is not whether they will fit or not. It is whatever the instructions say.
The connector will take up to #1 conductors. It's rated for 100A. The connector isn't the concern. It's the terminal blocks in the machine. It's a European machine, and they have different rules for sizing conductors. I can swap out the TB's if I have to, but it's not my first choice to go tearing into a brand new machine.
Personally, I might be looking at using a cord other than SO that has higher ampacity ratings at smaller conductor sizes, keeping in mind that many devices are rated for a maximum of 75 deg C terminations so even if the conductor insulation can go higher than that, as a practical matter you may well be limited to the 75 deg C column. The connector instructions should tell you what the temperature limits are. if they don't say, it is 75 deg C.
I'm aware. I'm looking to use SO cable for its flexibility as well as its availability.
Please be careful to read the notes at the bottom of the tables. The ampacity ratings are different depending on how many of the conductors in the cord are considered current carrying.
I'm aware. I'm using 'Column A' ampacity values, as I will have (3) current-carrying conductors. Majority of the load is heater-based, so no need to count the neutral as a CCC; no harmonics and/or non-linear loads.
Thanks,
SceneryDriver
