But before we get to the amazing experience, a little backstory. Well, ok, a lot of backstory.
So I had purchased a miller XMT 304, along with a bunch of other welders; but in order to run the big machines right, you need 3-phase power. Unfortunately when we pulled a the dinosaur that was there before, it was only using single phase 480V and there weren't enough wires to use 3-phase. So a few days later I went and bought some solid #10 wire, and it turned out to be stiff enough that I was able to jamm it up through 30 feet of conduit (with three wires already in the conduit) and down into the outlet box behind the welder. Then I hooked up the wire to the 3-phase shutoff switch, wired in the welder, and it still was only single phase. Finally we broke out a volt-meter and verified that one of the leads feeding that panel was dead also. Sigh.
So, we back traced the wire upstairs to the main panel (which is not labeled), and after turning off just about everything in the shop, we found the breaker that was feeding it. Turns out its a 2-pole breaker, not a 3-pole breaker. Luckily the wire ran all the way to the panel, so the problem was just the breaker. But this was no ordinary namby-pamby breaker, this was a 3-phase 150A I-Line manly-man breaker.
Just to give you some appreciation for the difference in sizes we're talking here: the contact lugs on a normal breaker are designed to connect to a 12 or 14 gauge wire which is about the size of a pencil lead, and can handle a current of 15 to 20 amps. The lugs on this Square D breaker can handle wire so large, they don't have a gauge for it. Just the copper part is about the size of your average garden hose, and then there's a rubber jacket around that. Instead of a screw head, the tightening nut takes a giant 3/8 Allen wrench (the same size you use to unstick a 1/2 horsepower garbage disposal). Not something you're going to find in the average homeowner's toolbox.
Everything about this part is large. Including it's price, which is over $1,400. I found these breakers online in the Square D catalog. Well, almost. What I had was a KAB26150 and what I needed was a KAB36150, but the catalog didn't mention it. All they talked about was a KA26150 (2-pole) which was $1,463 and its big brother the KA36150 (3-pole) which was $1,820; and would supposedly solve all my problems.
Now, not wanting to spend twice as much as I paid for the welder itself, I turned to my solution of all things expensive: Ebay. There I found a wide variety of KA and FA (the smaller brother which goes up to 100amps) breakers ranging in price from $20 to $200. Still no sign of a KAB or FAB, but what the heck, it's probably not important anyways. I finally settled on a FA36100 (3-pole, 100 amp) for $52 and I figured I was good to go. Even that was overkill for the line, as only the single welder is on that circuit and it draws 18.3 amps at maximum power. The original breaker could have run an entire room full of welders and still not have broken a sweat.
So a few days later, the breaker arrived on my back doorstep, and the next day I went down and with the shop teacher took apart the main panel, and stuck the new breaker in. Thankfully I didn't electrocute myself, and after wrestling the main 800 amp shutoff switch back to the on position, we were in business and the welder was happy.
But that part number was still bugging me. What was the B for anyways?
On a lark, I decided to call and ask. So I pulled up the Contact Us page, got the phone number (888-778-2733), and called it. It started off with a typical voice mail routing system, "Press 1 for Motor Control, 2 for Automation and Control, blah blah blah." I pressed 4 for Circuit Protection, and then a guy came on the line.
"Hello, thanks for calling Square D. How can I help you."No redirecting to somebody else, no looking it up, just rattled right off the top of his brain. The explanation, how to use it, and the entire political history behind it. This guy new his stuff.
thinking I'd need to be routed to the right department/person, I started off somewhat high level:
"I have a question about a 3-phase I-Line circuit breaker part number."
"Yes, what is it?"
"I'm changing out a breaker from 2-pole to 3-pole and its currently a KAB26150. I was wondering what the difference between the KAB and a normal KA was."
"The KAB has a bolt on the clamp that attaches to the I-line rails to increase its holding power. This is in addition to the lugs for the wire side. There are a set of black caps at the top, along the I-line edge the pull up and expose the screw head which you loosen to remove the breaker from the panel."
wow, I'm impressed
"But in reality, you don't really need it. What's your application?"
"This is going into a school shop."
"Right. Then the KA should be fine. The KAB was just in response to a holding specification that GE came up with in the 80s to try and lock us out of commercial bids. But the the KA & FA series have been in use for over 20 years now and they've proved themselves in the market. You should be fine."
Yup, there's the cap for the screw head and up inside (way up, look for it ...) is the screw that tightens up on the power rail. How cool is that.