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 Post subject: A Full Moon, 5 Light Bulbs, and Some Trolley Wire
PostPosted: Thu Mar 08, 2012 10:56 pm 
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If you're not a trolley car nut you probably have no idea what this picture is about. The simple answer is we had a full moon last night at Orange Empire Railway Museum. But so did everybody else on earth. So what about the five light bulbs. Well the trolley wire is at 600 Volts. The light bulbs are 120 Volt bulbs. 5 times 120 equals 600. So if you string 5 of these light bulbs in series between the 600 Volt trolley wire and ground (the rails) the bulbs will light if the power is on and not light if it is off.

But there is a glitch. What if one light bulb burns out? Like with the cheap mini-Christmas tree lights, the other bulbs go off too because the burned out bulb presents a gap and no current can flow. In other words, the power could be on but the bulbs not lit. Oh, getting across 600 Volts is usually a one time deal.

Hope you like the picture.

http://railfan44.rrpicturearchives.net/pictures%5C24082%5C120307%20OREM,%20Perris,%20CA%205.jpg

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 Post subject: Re: A Full Moon, 5 Light Bulbs, and Some Trolley Wire
PostPosted: Thu Mar 08, 2012 11:08 pm 

Joined: Tue Jul 06, 2010 1:57 am
Posts: 210
When I worked at MATA, they had a string of those in the car barn for indicating whether the barn wire was hot or not. They called them Nemo lights. Does anybody else call those lights by the same name, or does anyone know what it means?


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 Post subject: Re: A Full Moon, 5 Light Bulbs, and Some Trolley Wire
PostPosted: Fri Mar 09, 2012 12:40 am 

Joined: Sun Aug 29, 2004 9:21 pm
Posts: 105
Zak Lybrand wrote:
When I worked at MATA, they had a string of those in the car barn for indicating whether the barn wire was hot or not. They called them Nemo lights. Does anybody else call those lights by the same name, or does anyone know what it means?

That seems like a very bad idea, since dark bulbs indicates one of two things: either the power is off or one of the bulbs is burned out. The difference could be deadly.


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 Post subject: Re: A Full Moon, 5 Light Bulbs, and Some Trolley Wire
PostPosted: Fri Mar 09, 2012 3:31 am 

Joined: Thu Nov 22, 2007 5:46 am
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Location: S.F. Bay Area
Not seeing why that's an issue. Anybody who does wire work treats the wire as if it's hot. 90% of line work happens with the power on. Line cars are pretty immobile if the power is off.

You are right though, the light indicates exactly one thing: that the power is on and you may put a pole on wire, pump up and go. Except at OERM where it does not mean that :)


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 Post subject: Re: A Full Moon, 5 Light Bulbs, and Some Trolley Wire
PostPosted: Fri Mar 09, 2012 10:41 am 

Joined: Wed Jan 05, 2011 5:57 pm
Posts: 58
Wasn't (isn't) the same 5-bulb principle applied to interior lighting in streetcars? I think I can remember seeing a bank of 5 bulbs not lighted on some occasions, indicating that at least one of them was burned out. I also recall seeing "Street Railway" lettered on some of the bulbs but I don't recall any voltage markings on them.


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 Post subject: Re: A Full Moon, 5 Light Bulbs, and Some Trolley Wire
PostPosted: Fri Mar 09, 2012 11:42 am 

Joined: Sun Oct 19, 2008 12:58 pm
Posts: 1346
Location: Chicago USA
Yes, I believe this was the standard way to light interurban and street cars. The bulbs need to be designed for this service because while regular 120VAC light bulbs will work just fine on 600VDC, when one burns out, the open gap gets the full 600V on it and bad things will happen if an arc is struck, possibly exploding the bulb, or worse.

BTW, modern miniature Christmas lights have a high resistance shunt/fuse in the bulb. Under normal circumstances, with 2.4 or 3.4 V across each bulb (segments of 50 or 35 bulbs in series, respectively) the shunt passes little current. When a bulb burns out, there will be the full 120V across it and the shunt melts and creates a by-pass, keeping the string (or string segment) lit but increasing the voltage to each bulb slightly. The string or segment will still go dark if there is any sort open in the wiring, bulb broken or missing, or the shunt doesn't work correctly.

Steve


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 Post subject: Re: A Full Moon, 5 Light Bulbs, and Some Trolley Wire
PostPosted: Fri Mar 09, 2012 11:45 am 
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robertmacdowell wrote:
You are right though, the light indicates exactly one thing: that the power is on and you may put a pole on wire, pump up and go. Except at OERM where it does not mean that :)


Let me explain Robert's comment. During non-operating times OERM keeps 600V on the wire but with a low current power supply. The reason is simple. The price of copper. We want to keep our trolley wire here. Put the pole up and the compressor only makes noises.

Some streetcars use banks of 32V bulbs across the 600V. The bulb sockets short out if a bulb burns out and the remaining bulbs stay on but see a slightly higher voltage.

The Los Angeles PCCs that I have been working on lately do use the five 120V bulb method which can be a real pain because often not all five bulbs are in a row inside the car. For example, the two bulbs in the roll sign box are in series with three bulbs inside near the middle of the car. There may a bulb in a box under the car or in the fuse box in front of the car. If bulbs in more than one series circuit go out, finding and replacing the burned out ones is rather frustrating. The other day in a car that has not been used for a few years three series were out. Somehow, five bulbs were burned out. I bet it took me an hour to get that straightened out.

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 Post subject: Re: A Full Moon, 5 Light Bulbs, and Some Trolley Wire
PostPosted: Fri Mar 09, 2012 11:50 am 

Joined: Thu Aug 26, 2004 2:50 pm
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Location: Northern Illinois
Sure... that was the common way to do it. More interesting is situations where you need only one or two bulbs, such as for marker lamps. ITS 1565, the Illinois Terminal Class B boxcab motor at IRM has a closed box inside that contains six light bulbs. These are the additional three to balance the two bulb classification / marker lamp circuit at each end of the loco. Yes, one should be able to calculate the resistance needed to balance a two bulb circuit, but apparently, this was easier :)

Street Railway bulbs are rough service bulbs with a twist... their filaments are designed to not arc when the bulb burns out, since the potential across the two ends of the burned out filament is 600, not 120, volts.

Which brings to mind a story... during the time 'tween the wars, when AM radios became small enough to carry (not exactly portable, but not a floor model cabinet, either) It became common knowledge that a certain model had the proper electrical characteristic to replace one bulb in a five bulb circuit. So, the guy working on cars could listen to the radio by virtue of replacing one bulb with one of those screw-in receptacles that used to be common. The catch was, when you were done and wanted to take your radio, you had to turn the light circuit off, first. If you just clicked the switch on the radio off, it would explode, since there was no way the switch in the radio was designed to break a 600V circuit.

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 Post subject: Re: A Full Moon, 5 Light Bulbs, and Some Trolley Wire
PostPosted: Fri Mar 09, 2012 12:08 pm 
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Neat exploding radio story Dennis. Here at OERM when changing light bulbs in the five bulb series the interior lights are turned off. Walking back and forth to the front of the car to turn the lights on and off adds to the bulb changing fun. How many guys does it take to change a trolley-car bulb?

The other day the base of a bulb stayed in the socket and the globe was in my hand. The pole was pulled and blue flagged while I fished the base out.

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 Post subject: Re: A Full Moon, 5 Light Bulbs, and Some Trolley Wire
PostPosted: Fri Mar 09, 2012 1:16 pm 

Joined: Mon Aug 23, 2004 3:01 pm
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Location: SouthEast Pennsylvania
Some technical additions that may help new volunteers keep things bright:
The "P.C.C." light bulbs of 30 volts, to run about 20 in series on 600 Volts Direct Current, are designed to short when burnt out like the 2.5 Volt Christmas tree lights mentioned above. They will also short if stolen and used in a 120 Volt house! Also, the bases are spring loaded, designed to short if the bulb is removed. If the spring is weak, you might still get an arc. Street Railway bulbs above 100 Watts need to have "Arc Resist" filaments. With weaker bulbs, it was usually sufficient to have no gas, just a vacuum in the bulb to prevent arcing. The "P.C.C." bulbs are gas filled, the arc formed when they burn out helps melt the lead insulation in the base, allowing the short circuit to form that bypasses the arc and allows the rest of the string to stay lit. Some cars with only 5 high Wattage bulbs for all of their lighting have relays to control resistances to bypass a burnt out or missing bulb and keep the rest of the car illuminated.
Tod Prowell of Railways to Yesterday taught me some of this, other information came from Electric Railway Journals about 1926.


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 Post subject: Re: A Full Moon, 5 Light Bulbs, and Some Trolley Wire
PostPosted: Fri Mar 09, 2012 3:43 pm 

Joined: Mon Aug 23, 2004 12:08 pm
Posts: 255
Location: Western Railroad Museum - Rio Vista
Almost all old trolley cars show signs of fire damage around a few light sockets. If the lamp is loose in the socket, an arc can start between the lamp and the socket. This arc burns through the socket and can continue on car wiring. That's why you should check regularly that vibration or visitors have not loosened bulbs.

Street Railway bulbs have a high vacuum inside to reduce possibility of arcs forming when filaments burn out. Home-type bulbs have nitrogen inside at about 1/2 atmospheric pressure that will support arcs. The nitrogen helps conduct heat away from the filament and it also reduces metal plating on the glass that turns it black. That's why you need to check that helpful volunteers have not replaced a street railway bulb with a regular light bulb in a streetcar. The high vacuum is why street railway bulbs make a satisfactory pop when the glass is broken.

Street Railway bulbs have many addtional filament supports to reduce vibration damage to filaments.

Occasionally companies would wire six bulbs in series for longer lasting lamps. An incandesent bulb operating at 20% under rated voltage lasts almost forever (at least many thousand additional hours).

Many streetcars had an extra lamp underneath the car or inside door motor cabinets
to provide the additional lamps for a five-lamp string.

BTW the strange wattage ratings, i.e. 36 or 56 watts, on street railwy bulbs are left over from the days when light bulbs were rated in candlepower rather than watts.


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 Post subject: Re: A Full Moon, 5 Light Bulbs, and Some Trolley Wire
PostPosted: Fri Mar 09, 2012 10:54 pm 

Joined: Wed Oct 22, 2008 8:18 pm
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today you might be able to get away with a super bright LED and a resistor, prolly safer even.


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 Post subject: Re: A Full Moon, 5 Light Bulbs, and Some Trolley Wire
PostPosted: Sat Mar 10, 2012 2:03 pm 

Joined: Mon Aug 23, 2004 12:08 pm
Posts: 255
Location: Western Railroad Museum - Rio Vista
I wouldn't trust it because when the circuit goes open you will have 600 volts DC present plus extremely high voltage spikes from inductive kick backs. I have seen some studies that show those spikes can be as high as 25,000 volts.

I don't know if a LED would tolerate those spikes without a capacitor across it to shunt the spikes.


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 Post subject: Re: A Full Moon, 5 Light Bulbs, and Some Trolley Wire
PostPosted: Sat Mar 10, 2012 3:55 pm 

Joined: Fri Mar 26, 2010 11:43 am
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Dennis Storzek wrote:
Which brings to mind a story... during the time 'tween the wars, when AM radios became small enough to carry (not exactly portable, but not a floor model cabinet, either) It became common knowledge that a certain model had the proper electrical characteristic to replace one bulb in a five bulb circuit.


That's a cool idea ;) I have several older radios that would actually work quite well that way...but there are a lotta "ifs ands and buts!"

One, is it has to be an AC/DC tube type radio
Two, the radios wattage needs to be close to the watts of the bulb it replaces
Three, the radio will only work with the plug inserted one way, reverse and it won't work (it won't damage the radio, just won't operate)
Four, these old radios had the chassis directly wired to one side of the line cord. (they were one of the major inspirations to the invention of the polarized plugs), so they would only be 'safe' on the LOWEST potential bulb socket in the string. Anywhere else and the chassis (antenna connections, metal knob shafts, screws through the bottom of the case into the chassis itself, as well as the chassis) could be anywhere from 120-600 volts to ground!


These kind of radios were known as an "All-American Five"
http://en.wikipedia.org/wiki/All_American_Five

I always like hearing about these kind of 'hacks', it's a good reminder these people were folks like us just trying to get through the workday!

Robert


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 Post subject: Re: A Full Moon, 5 Light Bulbs, and Some Trolley Wire
PostPosted: Sun Mar 11, 2012 3:22 pm 

Joined: Thu Nov 22, 2007 5:46 am
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Location: S.F. Bay Area
Dennis Storzek wrote:
Street Railway bulbs are rough service bulbs with a twist... their filaments are designed to not arc when the bulb burns out, since the potential across the two ends of the burned out filament is 600, not 120, volts.

It's more than that. AC switches are rated to break AC, which stops flowing and reverses direction 120 times a second. This interruption of current tends to snuff out arcs. Therefore AC switches are lightly built in terms of arc snuffing, they don't have magnetic or air blowouts, nor arc chutes. Once a DC arc is struck, absolutely nothing will extinguish it except interruption of power, melting of conductors, or a widening of the gap so the arc cannot continue. Air blowouts blast away the ionized air. Magnetic blowouts use the collapsing field from interruption of current to bend the arc across an insulator, increasing the length of the arc.


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