Thread: Fire in the Furnas

So I was running my SB 9A this evening for a couple of hours, doing as I have done for the past nine months since rebuilding it. I turned it on as I had done probably 15 times earlier this evening, and puff. Sparks and Flames from the Furnas reversing switch.

I thought I saw an earlier post where someone had just rebuilt a South Bend an put a brand new Furnas switch on it. In the picture that was posted, it looked like a new switch. Are they still available? Does anyone have a part number and source? Google didn't get me where I wanted to go.

Second question. I'm wondering if the problem with the switch was really a motor problem. Any ideas on how I can tell if it was just the switch, or the motor?

Yea, you can get reconditioned Furnas switches on ebay - that's where I got mine. Can't remeber the seller, but he was in New England, and the switch was cleaned up and shot with clearcoat. Needed a little tweaking but now it works and looks great.

I'm not much of an electrical expert, so my thoughts are probably worth what you paid for them. But here goes my logic. Did the motor smoke? My guess is that if the fire occurred in the switch, and the motor smelled fine, the switch got hotter than the motor. I'd guess the switch was the problem. There's always kind of a rat's nest of wires and springs and insulation crammed into those switch housings, and if any piece of metal bridges the hot wires, you may get a short circuit condition. If you want you could do a post mortem teardown, if you carefully pull apart the switch you might find the cause of death. Usually the insulation burns away but the metal stays the way it was when the fire started. You might find some telltale melted / oxidised metal hot spots as well.

But of course nothing is guarranteed. You might want to test the motor by wiring up the power cord directly to the motor using wire nuts, and plug the motor directly into the wall. Wear a glove in case the plug gets hot. Be careful. Good Luck.

You need to be really careful on how you route the wires in the switch.
You want to avoid having wires cross over another wire.
I had 2 wires that rubbed against each other until the insulation was worn off 1 wire and it started smoking.

Wire that thing with stranded wire and insulated crimp on lugs.Put a junction box somewhere on the back of the table,and run flexible metal conduit to the motor and the switch.Bring the cord into the box and lace everything up with 14 AWG stranded THHN wire.
I personally dont believe in reversing a screw nose lathe,but I have written several diatribes about that nuff said.

so far everyone has been correct in their answers. But there's one thing you should do that no one has mentioned. put a quick disconnect box at the lathe, with a circuit breaker just above the start current of the motor. for instance If your start current is 6 to 8 amps, use a 10 amp breaker. the closer the circuit breaker is to the start current, the faster it will react. just make sure it's not so close that it will trip prematurely. a fuse will also work, just not as convenient. now if something does short out it will throw the breaker. Also if you're using a 110 V motor you can use a ground fault interrupt, GFI. in many cases this will react quicker than a circuit breaker or fuse.

in the home always use a plug to wire up your machinery, regardless of its power requirements. This will allow you to get around many of the local codes when wiring the equipment. you can also unplug it when doing any service. It may keep you from getting hurt.

I know this sounds like a lot, but if it teach your shop from burning down it will be worth it.

stay safe, and keep those chips flying.

promacjoe

Originally Posted by promacjoe

so far everyone has been correct in their answers. But there's one thing you should do that no one has mentioned. put a quick disconnect box at the lathe, with a circuit breaker just above the start current of the motor. for instance If your start current is 6 to 8 amps, use a 10 amp breaker. the closer the circuit breaker is to the start current, the faster it will react. just make sure it's not so close that it will trip prematurely. a fuse will also work, just not as convenient. now if something does short out it will throw the breaker. Also if you're using a 110 V motor you can use a ground fault interrupt, GFI. in many cases this will react quicker than a circuit breaker or fuse.

in the home always use a plug to wire up your machinery, regardless of its power requirements. This will allow you to get around many of the local codes when wiring the equipment. you can also unplug it when doing any service. It may keep you from getting hurt.

I know this sounds like a lot, but if it teach your shop from burning down it will be worth it.

stay safe, and keep those chips flying.

promacjoe

Joe;

Good points. I unplug all the equipment in my shop each night, lathes, mills, drill press, grinders, belt sander, air compressor and so forth.

Many fires start with switched off electrical devices such as kitchen toasters. Just because electric operated devices are switched off does not mean they are safe from switch insulator failure or otherwise when not in use.

Thanks for all of the comments. I was able to pick up a brand new "Old Stock" Furnas switch on eBay.

A friend of mine who builds and wires custom machinery for large companies wired the switch for me, and it ran fine for 9 months, but we started with a pretty worn switch to begin with so it's not a surprise that it failed.

He came over last night and examined the switch and traced the wiring. Doesn't look like there are any shorts in the motor. Although there was a lot of black soot and some charred insulation, we didn't find any shorts in the switch either....but in the process of opening it up and examining the wiring, we may have "fixed" the short.

In any case, I'll wait till I get the new switch. I'm not going to fool around with the old one anymore. I was very fortunate to come up with a new one on eBay right when I needed it.