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Question About The Third Rail On Outdoor Portions


EE Broadway Local

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What exactly happens, electricity wise, to the third rail on outdoor portions when snow sticks to the ground, accumulates and covers it and is the third rail actually more "dangerous" when it rains and the rain is steady, keeping it wet?

 

Snow acts like insulator. You can step in snow that touches the 3rd rail and nothing will happen to you. As for when it rains, it would only be more dangerous if there is something hanging off the 3rd rail into a pool of water and you step into it.

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A person can even jump onto the third rail and walk on it as long as you don't touch anything else, then jump off to the ground.

 

In theory, yes but I'd never want to try it.

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I see and thank you. So snow, acting as an insulator, has an effect on trains running normally when it accumulates high enough to cover the third rail?

 

I don't think they'd be running at all if the snow gets that high without some plowing being done. I mean, if the snow gets that high you won't be able to see the running rails either.

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EE, there's a huge difference b/w snow... and water, directly.

 

From what I can remember, snow acts as an insulator (not only for the infamous 3rd rail, but for pipes as well) due to the shape of the snowflake(s)....

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EE, there's a huge difference b/w snow... and water, directly.

 

From what I can remember, snow acts as an insulator (not only for the infamous 3rd rail, but for pipes as well) due to the shape of the snowflake(s)....

 

Ok as a former science teacher I have to jump in here.

 

Electrical insulation is totally different from thermal(heat/cold) insulation.

 

Materials conduct electricity because they allow the free flow of electrons. Materials that are electrical insulators do not allow the free flow of electrons. In the case of water, pure water is actually an electrical insulator, but totally pure water is rare, and most water has dissolved particles called ions. They are what conduct electricity because they can flow in liquid water. When water is frozen as in snow these ions cannot flow, and therefore snow would be an electrical insulator. However, if there is any liquid water in or on the surface or bottom of the snow, electricity can flow in this space. Electricity can also arc through the small air pockets between liquid droplets, especially when backed by strong current and high voltage. So in the case of the third rail, I would not count on snow to protect you.

 

The simplest way of explaining thermal insulation is that it works by preventing the flow of heat by creating isolated pockets of air. You are correct about the shape of snowflakes creating thermal insulation. Because they are tiny hexagonal flakes, they create air pockets which prevents the free flow of heat, and is therefore an effective thermal insulator.

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A person can even jump onto the third rail and walk on it as long as you don't touch anything else, then jump off to the ground.

 

Be my guest and try to do it... I just hope you make it out alive.

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what if you are walking on the thrd rail and you touch the wall,then you`re fried?

 

The third rail is positively charged. If you touch anything that acts as a ground, you will "complete the circuit" and 600VDC will go through YOU. Many times when people are shocked with 600 (some survive this, but it's sure not recommended) it is because they are not aware that they have actually grounded themselves to something when working. That's why you'll see Power Dept using rubber mats to stand on when doing third rail work, as a safety precuation to prevent themselves from unknowingly completing the circuit.

 

As for the snow, when it rises above the third rail and a train tries to run through it (slowly), the result is usually a small electrical fireworks display. I think there's a video on Screwtube somewhere that shows what can happen, taken from the J line during a snow storm, so happy hunting if you're interested...

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That's why you'll see Power Dept using rubber mats to stand on when doing third rail work, as a safety precuation to prevent themselves from unknowingly completing the circuit.

 

 

ALL depts. working close to the 3rd rail must use rubber mats.

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A person can even jump onto the third rail and walk on it as long as you don't touch anything else, then jump off to the ground.

 

If I were you, I would no longer carry my house keys with me and would just ring the bell from now on to get back in the house.

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Does NYCT use work cars with sand/salt spreaders like MNR and LIRR do?

 

I don't think so, the only thing that they put down is the stuff the "KY" train puts down during leaf season.

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A person can even jump onto the third rail and walk on it as long as you don't touch anything else, then jump off to the ground.

 

Yeah, I forgot that about electricity... It always wants to get back to the ground so, as long as you don't provide that link, you're safe. That's why birds on power lines don't get shocked. That's also why the 3rd rail is suspended by something that doesn't conduct electricity.

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EE, there's a huge difference b/w snow... and water, directly.

 

From what I can remember, snow acts as an insulator (not only for the infamous 3rd rail, but for pipes as well) due to the shape of the snowflake(s)....

 

Ain't it cause ice doesn't conduct electricity?

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I don't think so, the only thing that they put down is the stuff the "KY" train puts down during leaf season.

 

That's to reduce the slip-slide effect, right? I can imagine wet leaves being a bigger issue than snow or possibly even light ice, especially for trackage such as the Brighton Line.

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That's to reduce the slip-slide effect, right? I can imagine wet leaves being a bigger issue than snow or possibly even light ice, especially for trackage such as the Brighton Line.

 

They the "KY" train puts something down to in cress adhesion. During major snow storms they send out deicer trains. The work motors have scrapper shoes to clean off the 3rd rail and I think the special deicer car might apply some chemical to the rail so ice does not form on the rail head. I'm not 100% sure though.

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