How can I safely connect a 2 leg 250v DC panel rated at 1058 FLA when the wire gauge chart doesn’t go that high – could I parallel 90 rated 700 kcmil to each leg, or did they have lower standards in the 60s?
Asked by Daniel Ambrose 
3 months ago
Last Updated: August 25, 2024
Hey there, just a quick question for you all. So, I’m working on hooking up a 2 leg 250v DC panel that’s rated at 1058 FLA, and I’m running into some wire gauge issues. The chart I usually use doesn’t have options for single conductors that high. Do you think it would be safe to parallel some 90° rated 700 kcmil to each leg? I’d appreciate any input you have on this.
On a related note, the original wiring for the crane from the 60s only has 250 kcmil feeding it from the collectors. Do you think they had different standards back then, or were they just being practical since they probably wouldn’t be using all 6 motions at once? Thanks in advance!
Are you referring to the main one or the additional one?
Mentioned the crane, right? The crane is equipped with a magnetic disconnect and the collector shoes are connected to the top of it. I will be running the crane by bringing the +/- from the bottom of it over to this panel. The voltage is 250VDC.
Are the collectors DC or 3-phase AC?
DC, 2 sensors
That statement doesn’t add up, nowadays all cranes are AC.
Thanks for your time 😁
What kind of facility is this going into?
Just hire an electrician and let them handle our job
Ail Bott lol maybe true industrial electrician journeymen, but in house maintenance always messes up when working on a crane.
Ail Bott hopefully they can put it back together 👍
Where are you connecting it to? How far is the distance. We usually use DLO cable in most situations. Parallel 350 should do the trick.
Nice, I’ll definitely check those out, do they bend easily?
Not very bendy.
DLO cable is absolutely lovely to work with. It’s like fancy welding cable. And don’t forget to crimp the ends!
Here are some cables I installed for a 2000a service a couple of years back. They just… sag like a wet noodle 😆
Rzesiek Jaros, that sounds fantastic! Much better than struggling with the 600mcm thhn wire and various cheating devices, ugh.
I think that picture was also taken with a 600s camera.
Rzesiek Jaros, these are the kind of connectors that have worked well for us. We rely on a Dewalt crimping tool without the need for dies.
No content
Has been using those tools, but they lack pizzazz
Is really flexible, but can be a bit heavy.
I’m curious about how heavy that 700 was considering using would be. 🤔
The flare from is really handy for keeping all the strands together. I like to use heavy heat shrink to give it a clean finish.
Needs to grab me a battery-operated heat gun since there’s no AC up there. Thanks for your help!
If you’re not in a restricted area, a MAP torch should do the trick.
Of course, we’ll need to include hot work precautions and have someone on fire watch! 👍
When it’s drawing more amps than what’s on the wire chart…. as per NEC 310-16….. you reach out to an electrician and they can assist you in navigating the complete chaos of the code book!
700 kill is Seriously no laughing matter 😬 amazing
If you have questions like that on , I’ll give you the best advice anyone ever could. Stay away from that piece of junk! 😡
Wynne talked to a few electricians at the plant. They were unsure as well. This is essentially just a query about available products for the two wires entering this panel. I wouldn’t want you guys messing around with my controls either lol
Copy that
You might want to think about using parallel feeds instead, to decrease the wire size to a more manageable level.
Wynne I’m enjoying the DLO 350 x2 for it right now. Just need to run them about 15′
There you have it, just a quick look without seeing everything, I would likely opt for the 400 due to a higher load at the crane’s startup.
Wynne I agree, this should include PE specifications that likely involve a buss for power!
Yeah it’s known as parallel feeds, there are specific rules regarding how and when… but basically you multiply the ampacity of the wire by the number of runs to get the total.
We do this often for building feeds of 3,000, 4,000, etc. We’re currently working on a building where we have 11 parallel runs to achieve 4,000 amps.
I don’t know much about DC motors, but I do know that AC motors require a 6% inrush current.
Machine wiring has different requirements compared to construction wiring.
A lot of this equipment utilizes buss and direct connection. We had salt furnaces that drew 5000 amps, with the high temp reaching 2150 degrees and the contractors (we used high power SCR’s and later IBT’s in a hockey puck style that were water-cooled!) would wear out while running Proportional Integral Derivative (PID) loops. The 2150 degrees was so hot that thermal couples couldn’t be used on it. It employed a Ray-O-Tube or high temp IR calibrated to Aerospace specifications and believe it or not, Boeing was one of the few companies that ever checked the calibration on them haha! Ours was a smaller Chinese model, whereas ours were Ajax and had liquid-cooled bus bars!
Most things are usually rated for X amps with 600V insulation, so just choose something that is rated for the amps, wire it up, and go chill on the roof by the exhaust fan. But definitely don’t do it near the supply air handler, Bob got fired for that.
I might even consider going 3 or 4 simultaneously.
Dealing with 700 CM in tight spots can be tough. Especially when you’re working with quad 350 CM MTW/THHN/THWN copper wire. But there’s more to consider than just the wire size.
The first step is to grab a flash suit and hood.