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From reading through this, it appears that some of you think that the point of the short was in the engine wiring harness, that is before the positive post as the current flows, or behind the positive post as you look at the car front it he front. It was not. The arcing to the chassis occurred about 3 inches in front of the positive post when viewed from the front. This pic may help you see where the short was located better.
That is not to say that they are all in the same location, or that you couldn't have a short in the engine wiring harness - you certainly could! Many locations are possible, and as my picture of that engine wiring harness form a 1995 GTS shows, the insulation on these cars is cracking badly.
Pointing at the point where the wire arced to the unibody. This is between the radiator and the positive post on the Right side.
I know it is a long journey to get everything back to normal but I wish you all the best and hope that in the end you come out ahead.
Thank you, Havey928, it certainly has been. I ordered one of those POD things and they came and dropped in on our driveway, and I ordered a metal recycling dumpster too. Then we had to gut the shop - tools went in the POD so it could be locked at night, camshafts and other ruined parts went in the metal dumpster, and trash went in the trash. When the place was emptied out to the bare walls, ServPro came in with a crew of 8 and cleaned everything as best they could. It took them about a week. The soot upstairs in the office was awful, black residue on everything. Then all the walls and ceiling were sealed with Kilz, then painted. Then the electricians came in to re-wire the whole shop, the HVAC guys had to replace the furnace and the AC (they were ruined), and the natural gas lines were all replaced too. After that, I had to run new compressor lines around. There's more - but you get the idea.
We are liking it now. Fresh paint, new lighting, literally better now than it ever was. Here is the shop and office today:
Note that my pictures show my battery in my '91, yours may be different. They come in all kinds of lengths and heights in these cars. I mention in the first page of the instructions that you may have to adapt the installation to fit your battery and car.
Please remember during your installation to check the battery compartment cover - make sure you do not mount anything so high up or so lose that it could ground out on the lid after you close it.
Note that my pictures show my battery in my '91, yours may be different. They come in all kinds of lengths and heights in these cars. I mention in the first page of the instructions that you may have to adapt the installation to fit your battery and car.
Please remember during your installation to check the battery compartment cover - make sure you do not mount anything so high up or so lose that it could ground out on the lid after you close it.
When I installed my Optima, anywhere there was risk of contact (terminals to the top, auxiliary post adapter for heavy gauge wiring to the side) I adhered thick rubber as an insulator - on the side it's cut pieces of trailer fender tread step material and the top is a different thick rubber material. The Optima battery doesn't have have a vent line, so I also sealed up the bottom of the battery compartment to keep it clean and the cutout for the ground strap and in the corner where the extra wires exit allow for the little bit of gas venting needed. It vent to the large compartment below the Sharkwoofer. In my car, that's in the trunk where it's not actually air tight.
With the billet mount, the base plate is bolted to the compartment floor and then the top anchors the battery with the long side rods threaded into the base plate and then the screws through the top plate thread into those side rods. The way it's attached, that battery doesn't move even 1mm.
In this view, the auxiliary side terminal attachments look closer to the top plate than they actually are.
Note that my pictures show my battery in my '91, yours may be different. They come in all kinds of lengths and heights in these cars. I mention in the first page of the instructions that you may have to adapt the installation to fit your battery and car.
Please remember during your installation to check the battery compartment cover - make sure you do not mount anything so high up or so lose that it could ground out on the lid after you close it.
While I've never seen an electical fire in any 928, I think a main fuse kit is a good idea and a good addition to these cars!
I also agree that fuses have their own set of problems. I'm helping a really good friend with some details for his build of a big block early Corvette. On the first start-up attempt, the main fuse he installed (he's a professional electrician and sees lots of electrical shorts with burned wiring) blew....the current draw from the starter was higher than the amperage of the fuse.
i'm guessing that getting the "correct" amperage fuse to protect the car's entire electrical system and still allow the starter to function is a balancing act....and wonder if this is even possible.
Here's my question/thoughts to Carl, who has had months to study this problem and come up with this elegant, well done, solution:
Does a single high amperage fuse protect against a short on a smaller wire? (Like the wires that caused your fire.) Fuses always seem to be sized according to wire size....bigger wires that carry more current always have/need bigger fuses (which is why there are different amperage fuses in our electrical panels.)
My thought is that if you have a short on a 16 guage wire, that wire is going to glow red and burn long before a 300 amp fuse blows....the wire simply can't "draw" 300 amps, to blow that fuse.
In short (pun intended), does a single large fuse protect the 12 gauge wire that shorted to the chassis, or does the wire (which is not capable of drawing 300 amps) burn anyway?
Is a single large amperage fuse a false sense of security?
To really protect the car, it seems like one would need a big fuse (like in your new kit) to protect the starter/alternator sized wire and them smaller fuses to protect the smaller gauge wires that go to the fuse panel.
Glad to see you bounced back Carl. I have a sailing buddy who is basically homeless. He used to have an art gallery long ago, but had a fire, lost everything, threw his hands up in the air, and gave up. I suspect you would have no idea about how to even make a start at giving up.
While I've never seen an electical fire in any 928, I think a main fuse kit is a good idea and a good addition to these cars!
I also agree that fuses have their own set of problems. I'm helping a really good friend with some details for his build of a big block early Corvette. On the first start-up attempt, the main fuse he installed (he's a professional electrician and sees lots of electrical shorts with burned wiring) blew....the current draw from the starter was higher than the amperage of the fuse.
i'm guessing that getting the "correct" amperage fuse to protect the car's entire electrical system and still allow the starter to function is a balancing act....and wonder if this is even possible.
Here's my question/thoughts to Carl, who has had months to study this problem and come up with this elegant, well done, solution:
Does a single high amperage fuse protect against a short on a smaller wire? (Like the wires that caused your fire.) Fuses always seem to be sized according to wire size....bigger wires that carry more current always have/need bigger fuses (which is why there are different amperage fuses in our electrical panels.)
My thought is that if you have a short on a 16 guage wire, that wire is going to glow red and burn long before a 300 amp fuse blows....the wire simply can't "draw" 300 amps, to blow that fuse.
In short (pun intended), does a single large fuse protect the 12 gauge wire that shorted to the chassis, or does the wire (which is not capable of drawing 300 amps) burn anyway?
Is a single large amperage fuse a false sense of security?
To really protect the car, it seems like one would need a big fuse (like in your new kit) to protect the starter/alternator sized wire and them smaller fuses to protect the smaller gauge wires that go to the fuse panel.
Thank you Greg, you have made some good points here. You are right, the 300 AMP fuse will likely never blow if one of the small feeder wires on that battery post were to ground out, and yet if we were to fuse it down low enough to protect those circuits, that little fuse would blow every time you try to start the car! True. I think the only way to protect both circuits would be to install another fuse block that is sized just for the small wires, and then the bigun' that is sized for the larger starter current draw and such. Thinking of the complexity that would require, I opted for this simpler single Master Fuse model. I believe it a damnsite better than nothing at all (which is what we have now) and would agree its not perfect. My goal is to protect as many 928's as possible from experiencing this tragedy, and it wasn't the little feeder wires that started the car on fire. Fusing the primary battery cables was my goal.
That said: the best size of Master Fuse is the one that is only slightly more than you need. After all, during a grounding incident, we want the fuse to blow and quick. I did start my '91 many times with a 250 AMP fuse in the block without incident, but the car was indoors. It was after it was parked outside in the Wisconsin cold that I went to a 300 AMP model as the current draw on cold motor was higher. Makes me think that perhaps the better fuse for the southerner is a 250 AMP fuse... providing greater protection for the car because of the earlier/faster disconnect it would provide? And leave the 300 AMP size to those northern cars parked outside? I also noted BMW was using a 250 AMP fuse on their car, but that was a V6...
What do you think? I could easily make the kit available in 250 AMP and 300 AMP versions if it was felt that was needed.
I'd recommend testing the fuse solution please. Hook the smallest gauge wire that you expect to be protected to the front jumper post, then ground it and see if your fuse blows and how long. Something about the length of that +12 wire from back to front makes me wonder what would cause a fuse to blow and when.
If you really want to fix this, I'd recommend looking into a contactor in the rear battery box. A line that has no power can't short out, and this is what we do for HV cars (where you have pretty plasma fires).
Yes: A fuse should always be rated to blow if the current capacity of the smallest wire or trace or component is exceeded. So if you have a 10g wire (30a) going to a 14 gauge wire it's a 15a fuse max.
And of course a fuse must have an appropriate AIR (Amp Interrupt Rating) for the voltage being carried. For 12v cars this is not a problem, but I can tell you a funny story: One time I was working on the external battery pack for my GE Elec-trak tractor. 20 BB600 cells, each one capable of 1,000 amps current at short, protected by a 100a auto fuse. When I dropped a wrench across the end terminals I felt stupid then thought "No biggie, the fuse will blow". Then I looked as the fuse literally incinerated itself and a 36 volt arc started burning across it. Only stopped when I kicked the wrench loose. That was because auto fuses are rated 12/24 volts, and this was a 36v system. Oops. Now when you get to 300v DC @1,000 amps then you want to get the KLKD class sand filled fuses....
02-21-2019, 12:08 PM
