Incandescent lamps failing

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Dave_PE

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Here's the deal. 16 unit apartment building completed about a year ago, each unit has 125A, 120/208V single-phase panel fed from a 120/208V 3-phase, 4 wire metercenter. Each unit has #1/0 CU feeder, less than 100' feeder length.

About once a month for the last year, the maintenance crews have to replace every single incandescent lamp that is installed inside the units because they are only getting an average of 25 to 30 days of life. Doesn't matter if its an A-19, PAR20, etc. Same problem month after month.

There are no appliance problems, the fluorescent lamps are fine. Almost all of the incandescent lighting fixtures are installed on dimmers. 1.2 ohms measured at the grounding electrode system. No issues with any house loads.

I have not been to the building to check things out my self. The POCO has done the usually battery of tests and have determined that everything is fine on their end. The power analysis indicates the voltage measured at a random sample location inside one of the units averaged between 124V and 125V over a two day period.....which falls within the POCO + or - 5% range of 114V to 126V that is deamed normal voltages. There were a couple spikes to 127.5V, but I could not tell for how long based on the scale of the graph.

Any thoughts? Are they just getting really cheap lamps rated for 120V and they can't handle the 125V supply?
 
That was my first recommendation was to buy better lamps, 130V rated as that was the simplest solution to me as well. But that was 8 months ago, and I had just heard that they are still replacing lamps. Maybe, they are still buying the same cheap ones, but at a $1000/month, you would think they would spend a few more bucks to get a better quality lamp. They won't release the GC's retainer until they are happy that the problem has been resolved. I'll stop by and see what they have been buying......
 
infinity said:
130 volt lamps will have a noticeable depreciation in light output.
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Trevor-- I use the 130 volts all the time in fact I wont use the 120 bulbs. I have never noticed a difference-- I even put a 120 bulb in next to a 130 and I find it hard to see the difference
 
Assuming they changed lamp types...I have been involved in many projects were on site personnel were directed to change a procedure to assist in determining the possible causes of an electrical anomalie. Only to receive complaints that the issue still exist, make a site visit to find facility personnel still utilizing old methods, having never changed.

Are these recessed?

Are they all the same type of fixtures?

Heat dissipation from the fixture?

Did they buy these lamps from the same lighting company (cheap lamps).
 
A 130 volt lamp operating at 120 volts will have about a 24% lower light output. I certainly can tell when 24% is missing.
 
Dennis Alwon said:
...I use the 130 volts all the time in fact I wont use the 120 bulbs.
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I won't use 130V bulbs unless I have to (generally cause something is difficult accessibility. Power costs are up and as infinity says, light output is down.

carl
 
If they are recessed lights, is it possible the thermal switch is tripping? the switch trips, then they replace the lamp before the switch has a chance to reset.

If this isn't it, I like the 130 Volt lamp idea.
Wouldn't a 75 watt lamp rated at 130 volt have a lower resistance than the 120 unit? Then less power consumption? Inquiring minds want to know.
 
boater bill said:
If this isn't it, I like the 130 Volt lamp idea.
Wouldn't a 75 watt lamp rated at 130 volt have a lower resistance than the 120 unit? Then less power consumption? Inquiring minds want to know.
Click to expand...

A lower resistance would consume more power.

R=E*E/P

130V*130V=16,900/75W=225.33 OHMS

120V*120V=14,400/75W=192 OHMS
 
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If they are recessed lights, is it possible the thermal switch is tripping? the switch trips, then they replace the lamp before the switch has a chance to reset.
Click to expand...

OH NO Mr. BILL, please tell me that is not the case, land fill receiving all those good bulbs.
 
Re: Lamp voltage and output

Incandescent lamps are very non-linear resistors. With a linear resistor, power dissipation is proportional to voltage^2, for P=E^2/R. But in an incandescent lamp, _R_ is not constant. This is simply because of the very wide temperature range that the filament will experience, and the temperature coefficient of resistance of the metal. There are some simple formulas that approximate how things like resistance, current consumption, power consumption, light output, and life will change with temperature.

http://en.wikipedia.org/wiki/Incandescent_light_bulb#Voltage.2C_light_output.2C_and_lifetime
http://www.walamp.com/lpd/files/applicationnotes/isl297a.pdf
http://www.cs.indiana.edu/~willie/lvr.html#anchor00021

(Note the equations are approximate, and the two sources above give different values. But the general overview is similar.)

An incandescent lamp rated 130V and 100W 1800 lumen , when operated at 120V will be 're-rated' to 88W (12% decrease in power consumption), 1360 lumen (24% decrease in light output). Expected life will more than double. Note the key feature of the above equations: efficiency changes much faster than power consumption, and life faster still.

By selecting different lamps, number of lamps, operating voltage versus nominal voltage, etc. you can trade off between total light output, total power consumption, lamp life, and energy consumption.

Using a lamp at lower voltage will reduce both power consumption and efficiency. Because the eye adapts, a human may not notice the change in light output. If the effect is the same (my room is bright enough), then the net result of changing to 130V lamps will be less power consumption and longer lamp life.

On the other hand, if you maintain the same light output, then to go to 130V lamps in 120V service, you will need more lamps or higher wattage lamps, meaning more power consumption.

Given that the voltage in the units is on the high side, 130V lamps are probably a good choice.

-Jon
 
Glad to help. I spent time building bicycle lights, so learned lots about what voltage does to bulbs.

Notice the 'numbers game' hidden in the bulb ratings. The 100W, 130V bulbs are rated for 5000 hour life, but have a lumen rating of 1230. The 100W, 120V bulbs are rated for 750 hour life, but have a lumen rating of 1630.

The 120V bulbs are designed with a hotter filament, and thus operate more efficiently but have shorter life. The 130V bulbs, when operated at 120V, will have even cooler filaments, and thus still longer expected life but lower efficiency.

I estimate that if you use these particular 100W, 130V bulbs at 120V, then they will only produce about 900 lumen of ouput, using about 90W of electricity.

But they will last a good long time :)

-Jon
 
don_resqcapt19 said:
...How do the power costs go up when you use a 130 volt lamp in place of a 120 volt ...
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Don -
I didn't phrase my comment very well. To get the same amount of light requires more power. jon had a lot better explanation.

carl
 
infinity said:
A 130 volt lamp operating at 120 volts will have about a 24% lower light output. I certainly can tell when 24% is missing.
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Trevor, even if the resistance didn't drop as the filament cooled, I don't understand your 24%. Power is voltage squared divided by resistance ... 120/130 squared is about 0.85, or 15% less power. BUT, the resistance will be lower (I don't know how much), so it will probably be between 10% and 15% dimmer.

Is there more to this? Perceived brightness from lower color temperature?

George
 
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