Why do overhead wires appear green?

I was wondering today as I drove to pick up a friend, why do Amtrak's overheard wires appear green? Is this indicating a ground or is it designed for high visibility?

Could the green be oxidized copper?
Mike

What part of the wires? Wouldn't the corrosion on the part that contacts the pantograph be worn off?

The green patina is mostly basic copper carbonate. Here's an explanation from Wikipedia.

"Copper in moist air slowly acquires a dull green coating. The green material is a 1:1 mole mixture of Cu(OH)2 and CuCO3:[1]"

2Cu(s) + H2O(g) + CO2 + O2 → Cu(OH)2 + CuCO3(s)

Copper carbonate decomposes at high temperatures, giving off carbon dioxide and leaving copper(II) oxide.

CuCO3(s) → CuO(s) + CO2(g)

Basic copper(II) carbonate occurs naturally as malachite (CuCO3.Cu(OH)2) and azurite (Cu3(CO3)2(OH)2).

The top wires appear to be greener than the wire the pantograph hits, which is why I thought they might have been a ground.

That is interesting, it does make them highly visible (almost like a positive side effect)

For what it is worth - some of the cat poles are being painted a light blue to light gray - blends in better with the surroundings as opposed to the brown rusty color of the catenary poles. Course most that I've seen are on trains where NJT operates.

yes , Copper wire oxidises to green . Interesting that it s so noticable in an A.c system . When we do D.c systems , the positive wire usually oxidises to green in a moist enviroment , the negative just goes dull brown . I guess in the case of the cantenary , the track and masts are earthed , and the cantenary wire is positive in relation to earth for 1/2 the time , and this is when the oxidisation is occurring .

Good responses, everyone.

Tomorrow: "Why is the sky blue?"

This is not a topic specific to Amtrak, it will be moved.

-otto-

Hi All,

Excellent explanation, and it also answers the question, " Why is the Statue of Liberty green ?"

The top wires are greener because they are generally older. The contact wire is replaced on a regular basis and therefore is either un-oxidized or made from a different alloy that does not contain copper.

Otto Vondrak wrote:Good responses, everyone.

Tomorrow: "Why is the sky blue?"

This is not a topic specific to Amtrak, it will be moved.

-otto-

Id say the air is blue cos the train is late .

Jersey_Mike wrote:The top wires are greener because they are generally older. The contact wire is replaced on a regular basis and therefore is either un-oxidized or made from a different alloy that does not contain copper.

The catenary wire structure has copper strands in steel cable and it turns all the wire green.
The trolley wire is not actual wire but a copper strand in a profile (solid material) and it does not turn green due to fact that its wipped with grafite grease too avoid wear.