Lighting Flicker

[cdcengineer]

Folks, I got a strange phenomena happening at the house. My lights are flickering when certain loads are turned on. It doesn't seem to matter which phase these loads are on or whether it's a cord and plug load placed in any room.

I spent some time as a licensed repair tech and thought I'd seen this before. It usually always ends up as a loose neutral. I checked the panel (main and branch ckt's), but no solution. I called a friend at the utility and they came down and checked the connection on the transformer - A-OK. I don't have any voltage drop issue, and the house hasn't had any recent repair and/or modification. We've lived here for over (6) years. Voltage measurements from A to neutral 108V, B to neutral 135V with all loads on. With all loads off, we have 124V (A Phase) and 120V (B Phase).

I'm cracking up a bit. I've pulled every device on circuits in the rooms with flicker) to verify connection. I've tightened the connections in the meter housing, checked the grd'g electrode conductor connection.

Without typing for another page or so, does anyone want to toss out any ideas?

Thx,

CDC

 

[cpal]

do you have a well pump or sump elec heat?
108 and 135 doesn't sound right. If a large load pulls in it should dip even more.

 

[gar]

110107-1948 EST

In my opinion you have a neutral problem somewhere.

The key indicator is that your voltages are close to equal under no load, but not as close as I would expect. My own voltages under whatever are my current loads are 123.1 and 123.4 volts.

Then with your load, but clearly not very balanced, your voltages are 108 and 135 volts. This is horrible.

As an electrical engineer you should be able to draw a circuit diagram and clearly see the problem. With changing loads you should be seeing some lights brighten and others dim. Assuming you have lights on both phases.

I can go into how and where you look for the cause, but you should try to see how you would troubleshoot the problem now that I have stated that the problem is a neutral problem.

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[hurk27]

Try turning off all "B" phase loads(every other breaker in the panel) also turn off the main before doing this and only turn it back on after all "B" phase is off, and any 2-pole breakers, then take a measurement, if you have city water with copper pipes ((don't try this unless you are sure no one is around that could contact anything that is grounded and earth or a concrete slab)), very dangerous test, but I find it helps me show the utility guys and speeds up locating the lost neutral, but turn off the main, and every breaker on "B" phase, lift the water ground with only one phase loaded, again I must stress that you have control on everyones where abouts and make sure they do not touch anything connected to the electrical system, and be careful yourself, if you have a lost neutral or a bad connection and you lift the water ground you should loose the power or close to it, on the phase you have loaded, but remember the grounding now will have 120 volts to Earth!!! so only do this when you have control over the area, check this to see if this happens, then be there to show the utility guy to help him find the bad connection. I have had to do this a few times because the bad connection would not show up, and most utility guys around here don't carry a clamp on amp meter to check the neutral when one phase is loaded, which is a safer method to use for this test.

I have to add: if you have a cable connection to the house make sure its not bonded to the house grounding when you do the above test as it can burn up the cable shield.

 

[LarryFine]

In my opinion you have a neutral problem somewhere.

Mine, too. That one phase has a low voltage could be a resistance almost anywhere. That one phase is well above nominal must be due to a neutral issue.

The trick is to find the point of resistance. Somewhere between the utility transformer and your panel's neutral bus, there is an unwanted voltage drop.

 

[jumpingspidermedia]

Flickering of lights is normal, and it happens for a number of reasons:


1. Wires have resistance, meaning that when current flows through them, some amount of voltage gets 'used up' to make the current flow. This means less voltage for your various loads (lights, toaster, etc.). If you have loads that turn on and off, then the voltage supplying your lights will change, and the lights will flicker.

2. Many loads have 'inrush current,' and draw lots more current when they are first turned on; on startup they will cause significant voltage drop in the supply.

3. Proper design of your electrical system can minimize but not eliminate flicker. For example, large loads should be on their own circuits, and should be on 240V circuits. Since your main supply wires have some resistance, you will still get some flicker even when these loads are on different circuits. Properly designed, you may not be able to notice the flicker, but it will still be there.

Flickering of lights is essentially a measure of the resistance of the circuit that feeds both the lights and the load causing the flickering. If the flickering is large, or if the amount of flicker has changed without any intentional changes in the electrical system, then this could be an early indication of a problem.

 

[ptonsparky]

Light flicker can be normal. Yours is not. IMO anyone that has that large of voltage difference is just a blink or two away from smoking appliances.

 

[cdcengineer]

Yeah - no joke about smoking appliances. When my wife was vacuuming I heard the motor wind down with the voltage drop. That got me scrambling to figure this out ASAP. It's got me scratching my head. I know it's a neutral issue, but can't find it in the house. I really thought it would've been outside at the pole, but XCEL assures me they checked it. This all started not long after a neighbor called XCEL out to check our shared XFMR due to a buzzing hissing noise.

The search continues. I'll post findings as they become available.

 

[LarryFine]

I know it's a neutral issue, but can't find it in the house.

You need to measure the L-N voltages everywhere: The panel, the main (if separate), the load- and line-side meter terminals, the point-of-attachment connections, etc.

Somewhere, you'll find a point where the voltages will suddenly be normal upstream and bad downstream. These voltages must be measured while the service is under load.

 

[gar]

110107-23540 EST

cdcengineer:

You have a potentially dangerous condition, at least for equipment, and possibly for people. In the tests I am going to suggest i would recommend electrically insulated boots and gloves, and other clothing that would prevent your body from making electrical contact with anything.

Use a meter like a Fluke 27 or 87. These can resolve 0.1 V at 120 V level.

Make some insulated probes. I used 10" screwdrivers with plastic handles. Create some 6 to 10 foot test leads from the meter to the probes. 135 minus 108 = 27 V. Divide by 2 and resulting in 14 V. You might expect some fraction of this between points in the earth 12 to 20 ft apart. This will be angle sensitive.

Internal to your house put a lot of resistive load on one phase to neutral. Several 1500 W heaters if possible. Have everything else turned off. This should produce a high unbalanced voltage between the phases and neutral.

Assuming this does and that you have what appears to be a good connection between neutral and your grounding electrode (your house ground rod or equivalent), then measure the voltage between your load side neutral, neutral in a suitable outlet, and the ground electrode. The result should be well under 1 volt. Really only a few millivolts. If not a low voltage investigate the cause. But this is not the source of your problem.

Next, connect your test lead to the ground electrode at your service entrance. Quite likely you have a ground rod at this point. In my house it is the city water line so it is not actually outside for access. Measure the voltage across the 12 to 20 ft span of the probes in several directions. Ideally this is going to be in the millivolt range. I believe mine gets into the range of 50 to 100 millivolts.

If you see modest voltage relative to the above said 14 V or more unbalance, then my guess is that some or all of your neutral current is flowing thru the earth system. Now get a long roll of wire to extend one test lead toward the pole transformer. Get as close as reasonable to the ground rod at the pole. If you can get to the pole and read a large fraction of the unbalanced voltage, then there is a neutral problem between the pole and your service entrance. There could be other points of the problem.

If there is only a volt or so, depends upon length, of voltage difference between the pole and your service entrance, then the neutral wire from the base or some ways up the pole to your service entrance is probably OK. But you could have a high resistance in the neutral at the transformer above or inside the transformer relative to the point where the ground wire from the pole ground rod connects to the transformer neutral. This connection point might be a few inches to a few feet from the transformer neutral post.

Be aware that if you are fed from a Y primary supply that the Y primary neutral is also connected to your low voltage 120-0-120 secondary neutral. Be careful. You can spot severe problems by making voltage measurements as you approach the pole.

Its bed time.

.

 

[ptonsparky]

Underground or overhead service?

 

[cdcengineer]

Underground lateral which is approx. 125'. I'll try some testing once it warms up a bit. I'll post more as I go.

Thx

 

[wptski]

The Ideal 61-165 Suretest can measure impedance of a circuit. There is a adapter to replace the normal three prong plug cord used for testing which has clips. Turn OFF all loads to Phase "A", clip to that phase, take a reading and repeat on Phase "B".

If you don't have a Ideal 61-165 then somehow introduce a good sized load at the panelbox on each phase with the loads turned OFF and measure the voltage then.

This should tell you if your problem is before or after your panelbox.

 

[ptonsparky]

Underground lateral which is approx. 125'. I'll try some testing once it warms up a bit. I'll post more as I go.

Thx

Have fault locator, will travel.

 

[tryinghard]

Underground lateral which is approx. 125'. I'll try some testing once it warms up a bit. I'll post more as I go.

Thx

Isn't this the utilities? I think your voltage drop is on their side.

 

[ptonsparky]

For this area it could be owners responsibility. Depends on where the meter is located.

 

[tryinghard]

For this area it could be owners responsibility. Depends on where the meter is located.

Not the service disconnect? Residentially here we install the OH service entrance (from the drop to the service disconnect) and the utility installs the lateral UG, the customer manages the service entrance while the utility manages the UG (even if installed by others).

 

[gobblerhuntr]

Under load check the voltage at the bottom side of the meter if the meter is on the house. This should tell you if it is your problem or the utility's problem.

 

[cadpoint]

Under load check the voltage at the bottom side of the meter if the meter is on the house. This should tell you if it is your problem or the utility's problem.

OK and...

I might have missed where they broke the meter seal!

If they passed this load side test on the OP's house, could it still be the neighbors service that failing due to neurtal (ground) tied at the transformer.

It'd be intresting to read the voltage at the neighbor's panel and meter as well...

The POCO need to come and meggar thier circuits,(if both houses fail) if they balk, notify chief POCO engineer, then up the pecking order...

 

[gar]

110108-1651 EST

If the voltages are good at the meter of the house in question under the load test, then the neighbor has nothing to do with the problem.

On the other hand if the neighbor is willing to let someone into their home, then that neighbor can be useful. If the problem is inside the transformer, at its terminal, or in a neutral connection common to both houses, then a load change producing a large unbalanced voltage at home A resulting from a problem closer to the transformer than the common neutral connection point for the two houses will also produce a large voltage change at house B.

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