Any Hazards Associated with a High Current Conductor

Question

For a conductor carrying a low voltage (say 12V) and high current (say >500A), are there any hazards that we should beware of? I assume it is safe to touch the uninsulated conductor even when it is carrying a high current. I know when an inductor is involved, disconnecting the circuit could cause a high self-induced emf. But does that apply to any high current circuit?

Answer 1

The inductive kickback phenomena is related to a rate of current change \$U_L=-L\dfrac{di}{dt}\$, therefor it applies to all voltage ranges.

The hazard of high currents involve risk of fire, burning. The metal vapours are very dangerous since they have a high melting temperature, they are poisonous. The metal vapour blowed in your face, results in almost cases in certain death. The skilled electricians are killed by this vapour, not by electrocution.

Killed by arc: https://www.youtube.com/watch?v=J8auz60ma0A

Answer 2

The danger with high current circuits is short circuits. If the current should get redirected thru another conductive entity which is not entirely capable of carrying the resulting current, that entity could be damaged by the resulting resistive heating or by arcing. Arcing and sparking is possible at low voltages (like 12 volts) when there is erratic contact within the circuit.

An example of low voltage arcing can be seen by disconnecting a cable from the terminal on your car battery and touching it intermittedly to the same battery terminal while the engine is being cranked, the horn is blowing or another high current load is switched on. If you want a real convincing demonstration, short the battery terminals together with a wrench - ONLY KIDDING !!!! (There's a good chance the battery will explode, blasting acid in every direction.)

Another often reported automotive electrical accident occurs when a mechanic wearing a finger ring gets that ring situated between the positive terminal of the battery, or a between heavy positive cable which is carrying the battery voltage elsewhere in the car (e.g. t o the starter motor, or a distribution block), and chassis ground. The ring stands a good chance of getting electro-welded to the chassis with the mechanic held in its grasp, and with a very burnt finger.

Moral to the story: Respect both high voltage and high current!

Answer 3

Adding to already great answers.

It also depends if it is DC or AC. If it's a wire carrying hundreds of amps of AC that can induce significant current in any metals brought close to the conductor, e.g. jewelry, rings and tools.

The latter can get hot very quickly.

If you are unfortunate enough to have a pacemaker or other metallic implants, stay away from high current AC lines.

BTW: That also applies, but to a lesser extent, to switching that 500A on and off too.

Answer 4

This video shows how to go blind/sunburned/dead with short-circuits on 230VAC. Most of the effects would be the same at lower voltage if enough current/power is available. Notice how the infrared blast from the arc causes the dummy's plastic facial shield to warp.

This one here is only 54V, but with enough batteries to fill a small truck... nice fireworks, batteries catching fire, and don't stand near the fuses when they go boom.

It also has a few epic quotes, like "the cable's insulation has fire retardant properties as long as it doesn't melt".

And this one is only 9V but stuff catches fire just fine.