light bulbs blowing

[Buck Parrish]

I had a customer that was watching TV in the living room. The lamp at the end of the couch, it's bulb took off like a rocket and flew across the room
It was very difficult to convince this lady that it was a faulty bulb...

 

[gar]

100131-1641 EST

zappy:

I doubt it.

A typical single phase spinning disk watt-hour meter has one voltage coil, and two current coils. The voltage coil is between the two hot lines, and a current coil is in series with each hot line. The effect of the current coils is effectively summed, and instantaneously multiplied by the voltage. The result is averaged and integrated over time.

See http://www.docstoc.com/docs/635019/Watt-Hour-Meter-Maintenance-and-Testing-January
for a discussion.

To satisfy yourself on this question run some experiments.

.

 

[480sparky]

I had a customer that was watching TV in the living room. The lamp at the end of the couch, it's bulb took off like a rocket and flew across the room
It was very difficult to convince this lady that it was a faulty bulb...

It's always the electrician's fault. Didn't they teach you that in school?

Bulb burns out, it's the electrician's fault.
Switch goes bad, it's the electrician's fault.
Dishwasher quits working, it's the electrician's fault.
Power goes out in a blizzard, it's the electrician's fault.
Roof leaks, it's the electrician's fault.
Taxes go up, it's the electrician's fault.
Die in an auto accident 873 miles from home, it's the electrician's fault.

 

[jwjrw]

It's always the electrician's fault. Didn't they teach you that in school?

Bulb burns out, it's the electrician's fault.
Switch goes bad, it's the electrician's fault.
Dishwasher quits working, it's the electrician's fault.
Power goes out in a blizzard, it's the electrician's fault.
Roof leaks, it's the electrician's fault.
Taxes go up, it's the electrician's fault.
Die in an auto accident 873 miles from home, it's the electrician's fault.

I ALWAYS BLAME the PLUMER!

 

[Riograndeelectric]

here is the latest update from my customer. I will stop by tomorrow to see what is going on. maybe a bad neutral on the fixtures or bad socket on the fixture.


The bulbs I bought (GE) didn't specify the v120 or v130 but were rated double life.
I figured they were a higher quality bulb.
The same sconce blew out immediately.
I would appreciate your stopping by tomorrow.
I'll make arrangements to work from home.

 

[jwjrw]

Almost sounds like a socket short or problem.

 

[flashlight]

...It's always the electrician's fault. Didn't they teach you that in school?

That's true, we just got a service call because water was dripping from
their recessed fixtures... new building, turns out they had a condensation
problem on pan for the concrete roof due to improper insulation.

 

[gar]

100201-0831 EST

If you have three bulbs in parallel, all are the same nominal rating for voltage, and only two burn out immediately on application of power, then it is unlikely that there is a neutral problem. The important point here is that three items are in parallel and one does not burn out. Ask yourself how can this be a neutral problem?

Why would a socket problem cause a bulb to burn out? How would this cause excessive voltage? Could be some unlikely reasons.

Clearly, speculation without some quantitative data is unlikely to provide an answer.

Is the circuit really three items in parallel as indicated in the first post? What is the measured voltage at the input to this circuit?

Some points to keep in mind. An incandescent lamp's life is a function of voltage. Rather substantial over-voltage is required to cause instantaneous burnout.

http://www.experiencefestival.com/a/Incandescent_light_bulb_-_History_of_the_light_bulb/id/1451167 useful but a very poor website.

See "Voltage, light output, and lifetime" about 3/4 down the site page at http://en.wikipedia.org/wiki/Incandescent_light_bulb

V^(-16) for life vs voltage calculates to about 2% life at at 20% over voltage. Thus, on average a 120 V 1000 hour bulb would last about 20 hours at 144 V.

.

 

[480sparky]

I ALWAYS BLAME the PLUMER!

Blame whoever you please.













But it's still always the electrician's fault.

 

[gar]

100201-1026 EST

Some additional points on neutral problems.

For the first part of this discussion assume a 120 V branch circuit originates at a breaker panel. There are two wires, a neutral and a hot, from this panel for the branch circuit. There are no incorrect connections from this circuit to another circuit.

If the voltage at the breaker panel is invariant, is always 120, then no poor connections in either the hot or neutral parts of the branch circuit can cause an increase in the voltage at the load. From a transient point of view, fractional part of a cycle, if there was substantial inductance in the circuit, then on turn off of current in the circuit there could be a momentary increase in voltage. Sufficient energy from this in a residential application is essentially zero relative to an incandescent lamp.

Where neutral problems exist they result from a 240 V center tapped transformer supplying a pair of opposite phases for 120 V circuits. In this case a common neutral part of the system, most likely between the neutral buss bar and the transformer center tap, with high resistance in the common neutral can cause unbalanced supply voltages to branch circuits.

If on the load side of the panel neutral buss bar you share a neutral with two or more branch circuits and at least one of the circuits uses an opposite phase, then a high resistance in the load side common neutral can be a source of problems.

Otherwise a high resistance neutral does not cause high voltage problems.

To visualize this draw a center tapped transformer, a small resistance in the neutral wire, and two load resistances connected to the opposite phases. Now do circuit analysis.

.

 

[jes25]

100201-1026 EST

.....no poor connections in either the hot or neutral parts of the branch circuit can cause an increase in the voltage at the load.

.

Exactly the point I was making earlier. Most electricians I meet seem to blame anything odd on a voo-doo neutral problem.