Questions about resistance and ohms law.

[Coolmanjack]

This says that rubber has a resistance of 10^13. I ohms law implies that amperage = voltage/resistance wouldn't there still be some current flow across anything?

 

[Darkbreeze]

Rubber does not conduct enough electricity, unless you're talking extremely high current loads, to be relevant. For most situations you can consider rubber to be non conductive.

 

[Coolmanjack]

So you are saying that there would still me a tiny amount of current flow no matter the resistance?

 

[Darkbreeze]

Anything, including rubber, plastic, wood, air, water, dirt and glass can conduct electricity if the voltage is high enough, electric current can be made to flow through even materials that are generally not considered to be good conductors. With a high enough current there is nothing that electricity cannot flow through. For common current amperages and voltages, plastic and rubber generally won't conduct.

Electricity follow the path of least resistance, so if there is substantially higher voltage/current than the insulator was designed for, it may take a shorter path but will generally choose the path that contains the better conductor. Cracks, splits, tears or any other opening through an insulator may change or reduce the resistance to the point where it becomes the easier path and will flow through the alternate circuit rather than the intended conductor.

 

[Coolmanjack]

i was just thinking that if Amps = volts/ohms that no matter how much reistance an object had, some electricity would flow through it. If an object had a trillion ohms of resistance and there was a voltage source of 12V, 12/1 trillion is still a number, so i am thinking that there would still be some flow of electrons no matter the voltage or resistance, am i correct?

 

[Karadjgne]

Consider your average lightning strike hitting a tree in a field. Generally wood is considered a good insulator, for average household electricity. But because of the size of the current and voltage, and the sap in the tree, all that combines to overcome the woods resistance, lightning strikes, tree blows up.

9/10 of the shorts in household electrical wiring are caused by electricians. It happens when the wire is installed and corners or Staples etc, squash the insulation surrounding the hot wire. This thinner jacket is still the same material, just now much thinner, allowing transmission of electricity from the hot to ground. It will arc, because the voltage and current are higher than the resistance endemic in the thinner jacket.

 

[Coolmanjack]

i know most of what you said karadjgne, my question is more out of curiosity than practical purpose. I was wondering whether there would still be any electrical flow through rubber or any extreme resistor. I realize that if there is then it is incredibly insignificantly small but i am wondering whether there is anyways. Is there a point where an insulator will block out current completely or will ohms law take effect and allow the calculated amount of current through an insulator?

 

[Karadjgne]

It's a hard thing to really answer. The coating on wires is designed with a certain thickness for voltage, not current. If you have a 20amp circuit at 120v, standard thhn-2 wire is plenty well insulated to deal with that. 20amp circuit on 1200v is a whole different ballgame, that 1200v has enough pressure to physically send an arc of electricity through the coating on thhn-2 to the nearest ground. That plastic coating isn't nearly thick enough, and totally the wrong material. You'd need XHHW, which is rubberized plastic, and much thicker insulation. For instance, the 400A 3-phase panel I'm currently working on requires parallel 4/0 wires to each mains terminal. This XHHW is good for @380A. The power company just ran a single 4/0 wire to their terminal, but their wire singly is rated at 600A. The insulation on it is easily 10x thicker than what my wire is covered with. I think it's unfair, but I didn't write the codes I have to work by.

Yes, you can flow electricity through any single resistor, rubber or otherwise. It's all a matter of resistance, just how thick the resistor is. If you look at the gloves a linesman wears, they are thick leather (boot leather thick) covering a layer of padding, covering thick rubber gloves. This is all to prevent the heat of the wire from melting the rubber glove, and to prevent any wire spurs from puncturing it. What you'll never see is a linesman wearing thin surgical gloves, the leather and padding will still conduct electricity at that high voltage, but the rubber/latex is simply not thick enough to prevent arcing. The gloves are also leak tested because the voltages are high enough, that even a pin prick sized hole will allow the voltage to arc through that hole to the sweat on your hand, and considering the temps created, will at minimum blow your hand off, or if you are wet/sweaty will travel tour blood/ sweat and fry you like a twig on a bonfire. Lethal, even at a fraction of an amp.

There is also magnetic fields, they will induce voltage and current, regardless of insulation, if the voltage/current is strong enough and the wires long enough. It's how coils/transformers work. But thats a whole different beast.