"Short circuit"

[Barry Wolk]

As a newbie here I've been reading a number of posts here that use the term "short circuit". It is most often misused as a short circuit is a direct connection between the power source and a ground that causes a wire to burn or a fuse to blow.

There are a number of reasons for blown fuses and a short circuit is only one of them. One is the direct connection to ground and the other is consumption of electricity beyond the capacity of the filament in the fuse.

If some device isn't getting current it could be due to an "open circuit" like a blown fuse or a loose connection. In the case of the horn the horn button is an intentional "open circuit" that gets completed to ground when the button contact closes.

Many electrical automotive problems come from loose ground connections. This will cause intermittent operation and can result in fires as loose connections create resistance and resistance causes heat. It's very important that the ground strap from the engine to the body has a good metal to metal connection as it is the return path for the power to return to the battery.

Many other problems come from substituting battery cables that were designed for 12-volt cars. Those cables can only carry half the current of a cable designed for 6-volts and will heat-up substantially during heavy current draw. That heat actually makes the problem worse.

I am an electrician by trade and love problem solving on old cars. Let me know if I can help. And, thanks for the warm welcome here.

[George/Maine]

I found a good one the other day. No head lights.I pulled the headlight switch, and there it was tin foil rapped around the fuse.Turned out the headlight switch was hitting the under side of dash.Wrong switch.

[Barry Wolk]

Here's a case of DIW.

If you know what you're looking at, you'll be "shocked".

[ford1]

Barry, your right but most of the guys in here are all old time restorers or hot rodders, alto some terms may not be correct but in there venicualr they know what it means, kind of a hot rod slang, and in my world a sort circuit is a circuit that goes to ground before it reaches it intended destination,usually before the fuse and burns up the wiring harness at the least, the car at the worst, a short circuit can happen after the fuse with no serious problem, but still a short circuit, in our world a blown fuse is called an over load, to many amps being drawn for the fuse size, and as far as open circuits almost all circuits in a car that are switched are open circuits, head lites, brake lites, radios, turn lites, back up lites, all are open circuits till the switch is operated closing the circuit, what im trying to say is all the terms used in our hobby may not be correct terminolgy but we do understand what is being said, and by the way welcome to our little group

[Frank The Plumber]

I follow the gospel of the guru of electrical automotive wiring. I use Ron Francis products and try to promote his wiring theories, you can argue product if you like but his engineering is sound, I did a complete rewire of my truck, all my wires are integrally labeled, the system is redundantly grounded, the paths are all channeled cased and protected. One of the best investments you can make.

[jboren]

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"If you know what you're looking at, you'll be "shocked"."

Oh my...Looks like a 3 phase fused disconnect but that middle fuse will handle a lot of current! I was looking at a dual 7.5 ton condensing unit one time. I turned the disconnect off and started taking the panel off to get to the control circuit to check out a couple of things. Just about the time I got the panel off the unit started up. The disconnect was as 60 amp and should have been a 100 amp for the size unit and apparently had burned up at some point. Rather than replace it some brighto had just bypassed it. That one scared me and afterward got my blood pressure up...

[V8 Bob]

Originally Posted by Frank The Plumber

I follow the gospel of the guru of electrical automotive wiring. I use Ron Francis products and try to promote his wiring theories, you can argue product if you like but his engineering is sound, I did a complete rewire of my truck, all my wires are integrally labeled, the system is redundantly grounded, the paths are all channeled cased and protected. One of the best investments you can make.

I agree 100%. R.F. also carries about the largest quantity of high quality wiring accessories. The latest catalogs include a wealth of information, and the tech support, both on the phone and Email, is second to none!

[sturgis 39]

I have a car friend and he uses the term dead short. That is always irritating. I just say" will lets look at it". Nice looking ride george from main. Is that a 38 or 39.

HOW DO YOU USE SPELL CHECK WHEN REPLYING ON THIS SITE?

[Brendan]

Brake ohm's law go to jail. that is what you are doing when you use 12 volt cables
with a 6 volt battery. the lower the voltage, the higher the amperage

[4dFord/SC]

All I know is that if you let the smoke out of the wire, the thing it's connected to won't run.

[Barry Wolk]

Originally Posted by sturgis 39

I have a car friend and he uses the term dead short. That is always irritating. I just say" will lets look at it". Nice looking ride george from main. Is that a 38 or 39.

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[Grandpas38]

Barry that is a scary picture reminds of my grandfather sticking pennies in the fuse box. I was a kid and knew this can't be right! Electricity is a mystery for a lot of people.

[Barry Wolk]

This guy should have known better. He was an HVAC contractor mounting a piece of equipment to a rooftop unit. He pierced a wire and it blew the 100-amp fuse at the main instead of tripping the 40-amp breaker.

The contractor had his helper go back to the truck for some Z rail they use to connect ductwork, drilled two holes in it and replaced the 100-amp fuse. Walked away and never looked back.

We would never have known had the helper not lost sleep over it and finally told the facility manager.

Some people.

[41ford1]

And the sad thing is the person that did it is probably lisenced. Crap like that could kill some one. Good to know the helper knew better.

[Barry Wolk]

Having a license does't give you a work ethic.

[Mike51Merc]

Short = loss of all resistance.

Many guys describe any/all electrical failures as a "short circuit".

[Grandpas38]

There should a test and license for "Common Sense".

[Barry Wolk]

As there should be for parenthood. Therein lies the problem.