Light bulbs are constanly burning out

Nick_sr,

I would suggest you contact the landlord or building manager.

The problem could be a loose service entrance neutral conductor.

Have you ever noticed all of a sudden some lights get brighter at times while other go dim?

First call should be to an electrical contractor. The electrician will check line to neutral voltages at the main service. The electrician will determine if the problem is on the load side or line side of the meter/s. And if on the line side of the meter/s he will contact the utility company's service department.

I have this issue in Austin. My voltage is about 127 volts.
09-10-09: Jfrech

127V is too high... For residential customers the utility company is supposed to keep the voltage with-in (+ or -) 5%. 120V being the base line.

You should contact your utility company and ask them to check your incoming voltage. It may be a simple fix of moving the taps on their transformer to lower the voltage.

Can I check the voltage myself with a multimeter? If so how?

Agree with with Al...... But just remember the voltage reading will only be for that moment in time.

I suggest you talk to the other tenants in the 4plex.
See if they are having the same problem with light bulbs as you are.

I asked a question in an earlier post if you noticed if any incandescent light bulbs suddenly get brighter than normal.
With a loose service neutral conductor connection this is typical. The service neutral conductor carries only the unbalanced load back to the source, the utility transformer.

Example, say all Line 1 (L1) to service neutral loads equal 20 amps and all Line 2 (L2) to service neutral loads equal 20 amps. Then 0 amps will return to the source on the service neutral conductor. The two loads are in series with one another. If the loads are constant and do not vary the service neutral conductor could be disconnected and the two loads would continue to operate just fine.

But what if L1 to neutral load increased to 30 amps and L2 to neutral load remained at 20 amps. If the neutral has a good electrical connection back to the source then 10 amps will return on the neutral to the source.

Some simple calculations..... Lets keep it simple.... purely resistive loads. E = I x R

L1 to neutral load 30 amps. Find R (resistance in ohms)
120V / 30 = 4 ohms

L2 to neutral load 20 amps.
120V / 20 = 6 ohms



Here would be a worse case example. The service neutral is completely open, not connect somewhere between the neutral bus at the electrical panel and the source (utility transformer).
L1 to neutral bus loads and L2 to neutral bus loads are in series with one another.

Current is the same in all parts of a series circuit. Find I (current, amps)

L1 loads, 4 ohms total.
L2 loads, 6 ohms total.
R1 + R2 = Rt = 10 ohms

240V / 10 ohms = 24 amps

Find voltage drop across L1 to neutral bus loads.
E = I x R
24 amps x 4 ohms = 96 volts......

Find voltage drop across L2 to neutral bus loads.
24 amps x 6 ohms = 144 volts.....

The above example would be the extreme that could happen in the event of a total loss of a service neutral connection for the given loads.
A loose or corroded service neutral connection will have the same effect but because of resistance within the bad connection the voltage drop variables will change due to the amount of unbalanced load current placed upon it. And just to muddy the water the service
neutral to earth connection integrity becomes part of the equation as well. Most utility companies connect the neutral at the utility transformer to earth ground as well.

So basically in the case of a loose or corroded service neutral conductor where an unbalanced load is present at the electrical panel the Line with the bigger load will have a Line to neutral voltage lower than half the Line to Line voltage, and the other Line to neutral voltage higher than half of the Line to Line voltage. If the balanced load voltage is say 123V Line to neutral, (246V Line to Line), then one might easily see in an unbalanced load condition one side with a voltage of 115V and the other side 131V. And again it all depends how big the unbalanced load is and how loose/corroded the service neutral connection is.

Now you can see why incandescent bulbs could become brighter when the refrigerator kicks on.

So if he has a 3V differential between ac neutral and ac safety ground at the particular outlet he measured, let's make the following rough assumptions:

-- 100 feet of wiring from the outlet to where those two lines are bonded together at the service panel.

-- Negligible current flowing through the safety ground wiring.

-- Wire resistance of 1.6 ohms per thousand feet (corresponding approximately to 12 gauge wire). Which would mean 0.16 ohms for 100 feet.

That would mean, if the resistance through the path is what it should be, that he has 3/0.16 = 18.75 amps flowing through the neutral wiring on that line.

Sounds kind of high, suggesting that perhaps the resistance is higher than it should be somewhere in the neutral run.

Al,

Voltage drop, (VD), would come into play I would think for the 3 volt difference of potential between the neutral and the equipment grounding conductor. And for VD to exist we need a connected load across the hot and neutral conductors of the branch circuit. The greater the load the more VD. ( NEC recommends that the VD drop for a combination feeder / branch circuit should not exceed 5%)

The 3 volts Nick measured from the neut to the grd could of been the result of connected loads on the branch circuit and VD.

We do not have the whole picture though just what wiring method was used for Rick's Condo. I can only assume each condo has its own electric meter. Are the meters all located together in a common meter bank? Is the main disconnect, (breaker), for each condo electrical service outside by its respective meter? If the main disconnect is outside by the meter then I assume the service neutral was connected to earth there. I assume the electrical panel is inside the condo unit. If that is the case then 4 conductors were ran from the disconnect to the electrical panel. 2 hots, 1 neut, and 1 equipment grounding conductor.

At the electrical panel a separated isolated neutral bar is needed and a separate equipment ground bar. What is the distance the main disconnect is from the electrical panel?
So without knowing how rick's condo is wired it hard to give a good answer regarding the 3 volts.

I believe though, from memory, NEC says at the end of a branch circuit there shall not be more than 1 ohm of resistance between the neutral and equipment grounding conductor. To check naturally the branch circuit would need to be de energized and any loads disconnected from the branch circuit.

3 volts....... It could just be his meter registering phantom voltage. High resistance digital volt meters are notorious for giving erroneous readings at times when not connected across a load. Jmho you can't beat a good old analog meter.
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If I take a reading on that plug the voltage drop is from 123.8 to 110. (measured across both vertical slots). However, if I measure from the short vertical to the ground then it reads 116v. If I turn off the kettle the reading goes back to the 123.8.
09-12-09: Nick_sr

VD is definitely more than 5%....

I would check around for a good electrical contractor. Preferably a commercial/industrial electrical contractor. The contractor will send out a service driver electrician with trouble shooting experience and find and fix the problem. One hour of labor probably around $100 - $150 bucks.... If the problem is by chance on the Line side of the electric meter the electrician will call the utility company's service department.

Jim