Good wire gone bad

[ChrisOlson]

And the large electrical house in the area, does not stock ferrules

That doesn't surprise me. The only place that handles ferrules around here is Viking Electric and they only sell to contractors. The contractors usually got 'em in the truck in their tackle box. But no other stores around here carry them either.

[russ]

You need to try finding them here! Everyone just looks at me funny.

[ChrisOlson]

I'm sort of wondering about what happened with Mike's box what would happen if it had a cascade failure. If the bar can get hot enough to melt the standoffs on the bar in a metal box and short out - how big is the fire going to be? You can think you got it fused but DC power is pretty mean compared to AC when that happens.

Years ago when we first started out here we had an old DR-series inverter (I don't think they make those anymore) and a bus in a metal box. We just had marine deep cycles then - 12V batteries hooked in series and parallel. We'd just go to Farm and Fleet and buy a couple more batteries and add them in when we had the money for it and eventually we ended up with 9 strings hooked into that bus box. I had 200A inline fuses on them.

I was working on it one day and had one of those Craftsman hammers with a steel handle with a rubber grip on it. I hung the hammer on the wall by the claw on a nail. Somehow that hammer fell off, hit the top of the box and flipped in mid-air and went inside the box and came into contact with the positive bar. It was not just sparks - it was an instant explosion and the top half of that hammer was instantly turned to molten metal that sprayed me (I still got some burn scars from it) with a brilliant flash of light.

It never blew a single fuse on any of the strings. Every since, I been scared crapless of DC bus boxes hooked to batteries.

[mapmaker]

John Wiles on flexible cables:

http://www.nmsu.edu/~tdi/pdf-resources/CC104.pdf

--mapmaker

[ChrisOlson]

But #4 wire does heat up with just 45 amps continuous through it, so I may move to #2.(

Mike, I sort of wonder about this. AWG 4 does not heat up here with 45 amps in it. I got 6 AWG from my MPPT60's to the bus. Those controllers run that 6 AWG THHN (90C rated wire) at 60 amps continuous for hours and the wire does not get warm. I think you still got a high resistance connection there someplace if 4 AWG is warming noticeably at 45 amps. Maybe fire up your mV meter and check the circuit to see how much drop you're getting across those connections? Something has to be not right there.

Edit:
Like maybe a defective bus bar? Maybe that bus bar is plated aluminum instead of tin plated copper or something? I've seen where you order stuff like that from a vendor and a cheaply made or substandard component gets mixed with the rest in a shipment and gets installed during assembly because it's hard to tell the difference. If something like happened and you got a bus bar that's made of the wrong aluminum alloy or something, guess what you got? A built-in resistor in your panel.

I'd be highly suspect of it when you're heating 4 AWG wire with 45 amps.

[Sunking]

I was working on it one day and had one of those Craftsman hammers with a steel handle with a rubber grip on it. I hung the hammer on the wall by the claw on a nail. Somehow that hammer fell off, hit the top of the box and flipped in mid-air and went inside the box and came into contact with the positive bar. It was not just sparks - it was an instant explosion and the top half of that hammer was instantly turned to molten metal that sprayed me (I still got some burn scars from it) with a brilliant flash of light.

It never blew a single fuse on any of the strings. Every since, I been scared crapless of DC bus boxes hooked to batteries.

Hello from paradise. On Tablet so my response is short as well as time.

Well if it hit the battery terminal buss there was no fuse. That is what is so dangerous about battery systems. Voltage is not high, but available fault current is extremely high.

[Sunking]

Mike, I sort of wonder about this. AWG 4 does not heat up here with 45 amps in it.

Chris it i snot the wire heating up. It is the resistance in a poor connection that is heating up. If you use mechanical clamp connectors, you will have a failure period. It is just a matter of time. Get rid of the buses that use Mechanical Clamp connections and replace it with a copper bus bar wide enough to terminate 2-hole connectors using proper bolts, washers, and lock washers. Terminate wire with compression connectors using th eproper size and tooling to make a UL tested connection. When done properly will last a life time.

See ya down the road, gotta go.

[inetdog]

I was working on it one day and had one of those Craftsman hammers with a steel handle with a rubber grip on it. I hung the hammer on the wall by the claw on a nail. Somehow that hammer fell off, hit the top of the box and flipped in mid-air and went inside the box and came into contact with the positive bar. It was not just sparks - it was an instant explosion and the top half of that hammer was instantly turned to molten metal that sprayed me (I still got some burn scars from it) with a brilliant flash of light.

It may just be a shaggy dog story, but an acquaintance who had worked for Ma Bell back in the day told of a pair of HVAC guys who were putting a new air duct in the battery room of a large Central Office.
The bus bars (@ 48V nominal) were so large that you could easily walk on them. And they did. That was not a problem.
What was a problem was that they dropped the 6' section of duct they were trying to put in place.

Two ends of the duct hit the floor and the middle section vanished in a flash.

[russ]

It may just be a shaggy dog story, but an acquaintance who had worked for Ma Bell back in the day told of a pair of HVAC guys who were putting a new air duct in the battery room of a large Central Office.
The bus bars (@ 48V nominal) were so large that you could easily walk on them. And they did. That was not a problem.
What was a problem was that they dropped the 6' section of duct they were trying to put in place.

Two ends of the duct hit the floor and the middle section vanished in a flash.

I have been on plant start ups where buss connections in the HT switchgear were not properly tightened - torqued - we vaporized meters of heavy copper buss bar - after a somewhat violent indication that something was not right.

[ChrisOlson]

It might be just me, but after learning my lesson with that old bus box we had I don't believe in leaving DC bus bars exposed where people can get at them. And I don't believe in using metal boxes to put them in in the event something would go bad and come into contact with the metal box where you would have virtually unlimited current from the battery able to go to ground and not stop until it was all burned up.

That grey plastic (or PVC) box I put our bus bars in won't burn. It has some sort of retardant in it. It will melt with direct flame or high heat to it, but as soon as you take the flame away it won't continue burning. The box itself is UL Listed. And the bars that are in it were from a UL Listed generator switchgear. But combining the two does not make a UL Listed or even approved bus box. But I feel a lot safer with it than a metal one.

Even so, I never open it up or even hook up a little fused wire in it without shutting everything off. We have a battery combiner with 90A breakers on each string. When I have to work in that bus to hook something up, I start our little generator and flip the manual transfer switch to switch the loads to gen power. Then I shut the entire DC system down and turn off all the breakers on the battery strings so that box is dead and it's safe to work on.