electric car hazard

[cacciatorino]

on the fb profile of a historical user of the forum I found this article, in which the problem of the excessive voltage of the batteries that in case of serious accident could expose the rescuers to the risk of lightning. can you comment?
http://www.lifesaonline.it/evidenza...u-auto-elettrica-le-verità-scomode-delle-auto

 

[welcome to the machine]

very interesting. I don't have enough expertise on this, but did you see how the pilots should get off the formula1? must jump down on foot even to not stick to the shell. Some trouble maybe there is...

 

[Lettore espatriato]

very interesting. I don't have enough expertise on this, but did you see how the pilots should get off the formula1? must jump down on foot even to not stick to the shell. Some trouble maybe there is...

Who knows what sophisticated technology could take if (if) all other systems fail?
class 1 gloves from 45 € per pair? too?

 

[Lettore espatriato]

on the fb profile of a historical user of the forum I found this article, in which the problem of the excessive voltage of the batteries that in case of serious accident could expose the rescuers to the risk of lightning. can you comment?
http://www.lifesaonline.it/evidenza...u-auto-elettrica-le-verità-scomode-delle-auto

Um... some, usual, selective asymmetry read in that letter.

For example, from the alarmist tone of the letter seems that:
- the electric car centered from
Tram splits into two, pulling whirlpools made of altoresynthetic and hot-printed steel, but the cables and internal connections of the modules do not interrupt, the passengers resist to 40g of the crash, are saved but die lightning from the current and burned by the battery fire, which also kills rescuers and tram passengers....

- while it seems that the passengers of the car to methane or to gpl that have the cylinders in the rear floor (see panda http://www.greenews.info/wp-content/uploads/2009/12/panda-a-metano.jpg) and attached to the exhaust pipe, with pretensors belts and airbags with pyrotechnic activation, do nothing and descend alone, dusting the jacket, carrying the rescuers, who had passed in front of the event ...

Boh. I had a methane car with the tank in the trunk, in case of a crash with a tram, I don't think I'd be quieter than one with the electric car.

Then I think there are 6-7 more between selective asymmetries or forgetfulness, so much so that the temptation to
put it in the "fake news" basket is very strong.
But I leave someone, for now, the chance to highlight these things, quite obvious.

Sorry, I'll be absent for a moment that I have to go to increase the number of visits on that site .

 

[cacciatorino]

Yes, okay, but think about who does the professional rescuer (infirmary, firefighter, cop) and serious accidents maybe 7-8 a month. Do you say that statistically the risk is irrelevant?

 

[cacciatorino]

Who knows what sophisticated technology could take if (if) all other systems fail?
class 1 gloves from 45 € per pair? too?

you say that the doctor can take heartbeat and pressure to a patient wearing these gloves, knowing that he also has to be careful not to touch with his shoulder the fast door mount? Consider that the doctor does not know, and has no way of knowing, whether security systems have worked or not, and therefore must move as if they had not worked.

 

[exxon]

that it is a new type of risk for rescuers (but also for mechanics in workshops!) is a fact that does not need to be tried: First the 400 v were not there, now there are.

that this is a greater risk, compared to that of one hundred liters of gas ready to spread everywhere or to a gas cylinder (or perhaps hydrogen!) compressed, you could open an endless discussion.

Surely it is necessary to integrate skills for anyone dealing with these new items of everyday work, and at the beginning we will find ourselves faced with a normative deficiency on the matter (if nothing else because the "nomers" still know nothing about the matter).

just to mitigate some excessive and sensational boutade of the journalist in turn, it should be said that if a man touches the two terminals of a 400 v battery with the two hands (one by pole)... his chance to tell the event are almost null, but if in a catastrophic incident that compromises the isolation of cables and battery, one of the poles comes in contact with the body, even touching it would not happen.

the conditions in which a frame should be isolated from the ground, in contact with a pole of the battery, while the other pole should be in contact with a particularly conductive ground or with another part of frame isolated from the ground and the first part of the frame are so resible that it ends up discussing more statistics than anything else.

It must be remembered that 400 v are many (and can cause death) if applied simultaneously to a human body, but they are still "low voltage", meaning that a sheet of paper is enough to isolate these potentials and prevent discharge.

 

[cacciatorino]

just to mitigate some excessive and sensational boutade of the journalist in turn, it should be said that if a man touches the two terminals of a 400 v battery with the two hands (one by pole)... his chance to tell the event are almost null, but if in a catastrophic incident that compromises the isolation of cables and battery, one of the poles comes in contact with the body, even touching it would not happen.

Sorry the question probably scema, but with the current I always had some understanding problem: If I take the positive to 400v in my hand and I stand on the ground to zero potential, my body is not crossed by the discharge?

 

[exxon]

No.

a closed circuit is needed for power passage.
in the situation that you described, with the land to zero potential, the positive of the battery would also have zero potential and the negative pole would assume the potential -400 v (negative potential). between the hand and feet of the person there would be no difference of potential and no current would flow.

if instead the negative pole of the battery was "moved to the ground", then it would be the negative pole to have null potential, the positive pole would rise to 400 v (positive potential) and the body interposed between this potential and the earth (at zero potential) would see a difference of potential and a consequent passage of current.

In this speech, however, a fundamental concept must be inserted: dry soil, as well as the road under the same conditions, are excellent insulation and constitute an invariable obstacle for the current generated by a battery at (soli) 400 v.

 

[cacciatorino]

No.

a closed circuit is needed for power passage.
in the situation that you described, with the land to zero potential, the positive of the battery would also have zero potential and the negative pole would assume the potential -400 v (negative potential). between the hand and feet of the person there would be no difference of potential and no current would flow.

I'm sorry but then what's the point of "putting down" plants if touching only a pole and with feet on the ground nothing happens?

 

[exxon]

the plants are put on the ground "locally".

at your home, all metal parts that can come into contact with an active conductor (phase or neutral), must to read be connected to another equipotential conductor, distributed throughout the building (what is commonly called land). the carcass of the washing machine will be connected to the ground, like the iron plate.

the main motivation of this connection is the operation of the differential switches (save) that intervene when there is a "dispersion" between one of the active conductors and the earth. if for example the heating resistance of the water in the washing machine is for corrosion and the water comes into contact with an active conductor while it is also in contact with the basket and therefore with the frame (mounted on the ground), the differential switch "scatta", interrupting the power supply.

the equipotential conductor is also connected to a disperser stuck in the ground, this imposes the potential null to the equipotential conductor. It should be noted that it is not enough to support the conductor to the surface of the soil, but it is necessary to plant one or more paline in depth, where the soil is perpetually humid and intrigued with mineral salts, otherwise there is no electrical connection.

Since in the place of energy generation, the neutral conductor is also connected to the ground, in case in a house a man touches with one hand the phase conductor and with the other the water tap, the circuit closes through the pipes and the ground because also the water system is normally in good contact with the deep and conductive part of the ground. even in this case (although not the electric discharge) the contact makes the differential switch intervene.

This is a quick and summary explanation, but I hope it might have been helpful. in reality there are different types of electrical connections between the places of generation and those of use, with different systems of management of the earth conductor, but the concepts expressed remain valid.

Note: That's right, if you stand on the wooden floor and don't touch any metal part connected to the ground, you can touch the active conductors (one at a time!) and don't take "the shock".

 

[bip]

to the excellent explanation of exxon I add only a small example to make better understand that to have a current flow it needs a difference of potential and therefore to get hurt you have to touch at the same time two points at different potential: observe the birds laying on the low cables, but also of medium or high voltage, nothing happens because the two legs are leaning on the same conductor, so among them the difference of potential is nothing (*).


(*) in reality the difference of potential between two points of the same conductor material exists, and is the product of electrical resistance between the two points and the current flow that crosses the section, but for a metal material on such short distances is absolutely negligible, the difference of potential on a few centimeters of cable is not even measurable, the discourse changes on lengths of kilometers, where note a fall of potential.

just for lazy, I remember that in reality to do harm is not the tension (or difference of potential) to which the body is subjected, but the current, just a few milliamps to kill.
Further difference should be made between continuous and alternating current, and on the parts of the body crossed by the current (between index and thumb of the same hand the damage is minimal, between hand and hand are much more serious, as the current crosses the heart.

 

[cacciatorino]

to the excellent explanation of exxon I add only a small example to make better understand that to have a current flow it needs a difference of potential and therefore to get hurt you have to touch at the same time two points at different potential: observe the birds laying on the low cables, but also of medium or high voltage, nothing happens because the two legs are leaning on the same conductor, so among them the difference of potential is nothing (*).

Are you telling me that if I hold the positive and hold a foot on the ground my body sees a zero deltav? So why do I touch the cow fence take a superbriscola? You haven't convinced me yet....

 

[bip]

the fence of the animals has just a pitch planted on the ground, to create difference of potential between the soil and the wire.

exactly as if you touch the stage of the conductors you have at home, touching the ground (which is on the ground, 0v) you have the difference of potential that can create damage (if the differential switch did not exist).

do you want the simple and safe counterprove (touch conductors in tension can be dangerous if something is wrong)?
take a 9v battery, the parallelepiped battery to understand, and lean the tongue to one of the two poles, nothing will happen.
Try to touch them both at once, and you will feel a pinch. .

 

[exxon]

the soil is a bad conductor on the surface and a bad conductor in depth.

to overcome the resistance offered by a bad conductor and allow the flow of a current even minimal, it serves a huge difference of potential.

cattle fences have generators capable of producing potential differences of even 10000 v and are placed in areas where normally on the ground there is lawn that ensures excellent humidity even on the surface.

Besides this, the ground connection of the generator (because the generator is connected between the wires and the ground) is normally constituted not only by one, but by many palines, also distributed along the fence, so as to ensure a good connection along the path it serves.

when the soil is dry, the same is deliberately watered and also sprinkled with coal powder before watering, all to reduce the resistance of the ground path.

in a house, the wooden floor is a practically perfect insulator, there is no way to take the shock standing on the parquet. a marble floor can be instead seat of condensation and standing above bare feet can not be enough to guarantee the insulation from the natural land conductors present in the house (water basins, heating, metal structures such as railings, grondes, etc.) that can close the circuit to the ground.

It must also be remembered that in this case the voltage of line is 230 v, tens of times lower than that of an electric fence.

 

[bip]

Are you telling me that if I hold the positive and hold a foot on the ground my body sees a zero deltav?

If you touch the positive pole of a battery and the ground, the difference of potential is nothing, you can easily verify with a multimeter.
if you touch the positive pole and the chassis of the machine that is normally connected to the negative pole of the battery, here is the tension you feel because you are closing the circuit.

 

[cacciatorino]

the fence of the animals has just a pitch planted on the ground, to create difference of potential between the soil and the wire.

exactly as if you touch the stage of the conductors you have at home, touching the ground (which is on the ground, 0v) you have the difference of potential that can create damage (if the differential switch did not exist).

OK, then returning to the initial case: I'm a doctor and I have to save a wounded man's life. If the car has a metal part resting on the ground (for example the suspension arm after a wheel is detached) I touch an uncovered cable is fried, right? But if the car doesn't touch the ground with metal parts, I could handle it. or again: if with the left shoulder I support the door mount and with the right arm I touch the cable discovered the current crosses the heart and are fried again, is it correct?

 

[bip]

back to the case of electric cars, to have risk of lightning you should come in contact with the positive conductor, that has the insulation ruined from the accident, and the frame of the machine (which will most likely be connected to the negative pole of the battery) without the positive conductor has still entered contact with the frame (other than the short circuit happens before) and no burnished battery, to the maximum if no fuse/ can take

 

[bip]

OK, then returning to the initial case: I'm a doctor and I have to save a wounded man's life. If the car has a metal part resting on the ground (for example the suspension arm after a wheel is detached) I touch an uncovered cable is fried, right? But if the car doesn't touch the ground with metal parts, I could handle it. or again: if with the left shoulder I support the door mount and with the right arm I touch the cable discovered the current crosses the heart and are fried again, is it correct?

If you touch the ground and the uncovered positive thread, nothing will happen if the asphalt is dry, it is a good insulating, if you touch the positive thread and the frame both with the naked skin, yes, risk of hurting you.

I ask you a question: who harmed the insulating of the positive conductor? If it has been hit by a metal part of the car, the battery is already short-circuited and you are perfectly safe from lightning, however you may need an extinguisher (as on current cars).

just to give an idea, on the electric prototypes running on the track, there are two detachments (one for the high circuit and one for the low voltage one) that dissect the circuit on the positive pole of the battery, just drive them and all qiello that happens after on the electrical system is no longer a problem.

 

[cacciatorino]

back to the case of electric cars, to have risk of lightning you should come in contact with the positive conductor, that has the insulation ruined from the accident, and the frame of the machine (which will most likely be connected to the negative pole of the battery) without the positive conductor has still entered contact with the frame (other than the short circuit happens before) and no burnished battery, to the maximum if no fuse/ can take

Okay, I think I understand: We say that a conductor could also be handed over from a non-massive part (a tire, a plastic part, a tree), or even simply torn because the part to which it is bitten is removed from a force higher than the mechanical resistance of the cable itself.