Lights dimming for a fraction of a second when well pump or heat pump starts.

[hockeyoligist2]

A friend called me last night, wants me to check out his mobile home service. I don't do residential work, so I don't know if this is common.

He has a 200 amp service, the well and heat pump are on breakers at the service pole. He said the well is 1 hp, 120v 50 foot run with #10, heat pump 240v #10 about three foot run. He said that they have always dimmed when either one started. He has had it for 5 years and never thought anything about it.

He had the in-laws over for Thanksgiving and his brother-in-law noticed it and said he needed to have it checked out.

Is this normal? I figured I would check the torque on the connections and check for voltage drop. Any other things I should look for?

 

[roger3829]

A friend called me last night, wants me to check out his mobile home service. I don't do residential work, so I don't know if this is common.

He has a 200 amp service, the well and heat pump are on breakers at the service pole. He said the well is 1 hp, 120v 50 foot run with #10, heat pump 240v #10 about three foot run. He said that they have always dimmed when either one started. He has had it for 5 years and never thought anything about it.

He had the in-laws over for Thanksgiving and his brother-in-law noticed it and said he needed to have it checked out.

Is this normal? I figured I would check the torque on the connections and check for voltage drop. Any other things I should look for?

You could check all the connections but you are probably going to find them all OK. This is a rather normal occurance when a motor starts.

 

[ptonsparky]

I agree, very common.

 

[StephenSDH]

Pretty Common. My sister was able to have her utility transformer upsided and moved a couple poles closer to reduce the voltage sag.

 

[brian john]

Voltage drop as little a 3 VAC can result in light flicker, how this is perceived is dependent on the individual. In my experience women seem to be bothered more by flicker.

Take your DMM (best if it has a min max feature), check each phase at the main as the loads cycle on and off. Sometimes other contributing factors such as washers, dryers and refrigerators can be isolated to one leg and all lighting on the other, won't eliminate it completely but will minimize the effect..

 

[brian john]

I posted this a while ago.

Light flicker (dimming and restoration of light to near pre-flicker level) of lights from motor inrush) is a byproduct of several factors and generally is difficult to over come.

AC motor loads (in particular compressors) but all motor loads have inrush currents. These inrush currents result in voltage drop in the branch circuit, panel bus, service laterals, utility transformer and possibility the utility HV feeders.

Flicker is in addition user dependent; some people are more susceptible to flicker. For some reason flicker seems to bother women more that men (based upon personal experience).

A Voltage Drop (VD) as little as 3 volts on a nominal 120 VAC system is noticeable (by me), 2.5% VD.

We have had cases were the VD was all a byproduct of primarily single phase 120 VAC loads, in these cases we were able to put the lighting on L1 and all the motor loads on L2, the HVAC compressors were something the homeowner had to live with. This minimizes the flicker.


To test for this VD and resulting flicker to determine the source of the inrush, use a min max amp clamp and min max multimeter at the main service watch the lights(it may take two workers) and correlate to the meters.

 

[gar]

101201-2043 EST

Assuming there is no circuit problem, then try GE dimmable CFL bulbs. These have a more constant light output with a varying sine wave excitation than a tungsten incandescent. See photos P9 and P14 at my website http://beta-a2.com/EE-photos.html .

Note: with sine wave excitation these fail to light around 100 V.

.

 

[kwired]

Size of POCO transformer and distance from home as well as size of service drop or lateral are a big factor in a lot of this kind of thing in many residences. Some POCO are pretty reluctant to do much about it if it is a problem.

 

[ceb58]

Just have him tell his BIL its a redneck strobe light in a disco.

 

[KTM2005]

Ktm2005

Ktm2005

Have you resolved the Flickering problem?

Mark

 

[dasv]

The flicker is due to the transformer on the pole is sized to small therefore when a motor load starts it drags the voltage down momentarily. To solve this issue call your local power provider and tell them about issue and they will install a meter and monitor the voltage and current for a week. Power companys have a minuim flicker allowable based on the duration of the low voltage. They may upsize the transformer but in most cases they won't

 

[paulgarett]

Lights dimming when motor starts

Lights dimming when motor starts

This is an interesting problem. The first thing that comes to mind is voltage drop. As current increases, voltage drops; ohms law. So motor start-up may momentarily cause the voltage to drop on the feeders.
Second, there may be a loose neutral conductor for the lighting circuit.
Third, try increasing the size of the conductors for the motor to accomodate for voltage drop.
Fourth, contact the utility company to increase the incoming voltage to the residence, maybe as much as 10 volts; generally common practice to accomodate for voltage drop.
Fifth, try rearranging the circuit breakers in the panel. See my forum post "Circuit breaker location in panels," second from the most recent post on this forum.
thank you,
Paul

 

[gar]

101222-1142 EST

paulgarett:

Increasing or decreasing the supply voltage will have negligible effect on lamp flicker. The turn on of a motor still causes a change in voltage to the lamp whatever the source voltage.

Loose connections are not always on a neutral. Can just as well be on a hot line. If some lights brighten and others dim, then it is most likely a high impedance in the neutral.

.

 

[Dennis Alwon]

It is not always a utility issue. I wired a house about 15 years ago with absolutely no issue with the heat pumps dimming the lights. The a/c guys came in this year and replaced the units with these energy efficient higher seer units and the dimming of the lights started. Homeowner called me and asked what could be done. I said get the a/c guys back. They did everything possible to fix the problem and ended up replacing the units with another brand and the issue was resolved.

Go figure.

 

[hockeyoligist2]

Have you resolved the Flickering problem?

Mark

No, everything checked out OK. The voltage drop was only 1.3 volt for a split second when they started, then back to normal. Too close for the meter to react but showed up with the high-low setting. I even turned off all breakers except the well and heat pump, same reading, 121.6 to 120.3.

The only lights that you could see dim was the incandescent and I had a hard time seeing that. I told him to keep his Bro-In-law away from the incandescent to prevent further brain damage.........

 

[paulgarett]

Another thing to check is the insulation integrity of the motor circuits. Use a megometer or megger to check this. This will most likely effect the motors. But if the insulation is not damaged to the point of malfunction, the old insulation may cause a current loss and cause the motors to have to work harder. There also may be some harmonic effects or lead/lag of the current and voltage sine wave.
Any comments about harmonic currents and lead/lag of sine wave?

 

[realolman]

....I even turned off all breakers except the well and heat pump, same reading, 121.6 to 120.3.

........

That doesn't seem low enough to cause any problems.

In laws, however, can cause lots of problems...

 

[kwired]

Another thing to check is the insulation integrity of the motor circuits. Use a megometer or megger to check this. This will most likely effect the motors. But if the insulation is not damaged to the point of malfunction, the old insulation may cause a current loss and cause the motors to have to work harder. There also may be some harmonic effects or lead/lag of the current and voltage sine wave.
Any comments about harmonic currents and lead/lag of sine wave?

Why should this problem only effect conditions during starting? A motor with failed winding insulation is not only going to have starting problems it will have running problems too.

The problem here is voltage drop when the motor load starts up. The solution to the problem is to increase the size of conductors supplying the load to include service and feeders and/or increase the size of the source(POCO transformer) to a size that can handle the demand put on without dropping voltage too much it even if it is only for an instant in duration.

Remember - a motor that draws around 20 amps while running may draw 100 or more for just an instant when that motor is starting. Throw 100 amps into any voltage drop calculations for your circuit and you will see a big change from what 20 would give you.

There will always be losses in conductors and there will always be a drop in voltage in the source - you have to decide where to draw the line on what is acceptable amount of voltage drop or find a way to reduce instantaneous starting current. Though not a suggested practice an undersized branch circuit will actually help with the problem because its resistance will limit instantaneous starting current - it will result in starting current (at a lower peak level) lasting for longer duration. Undersized feeders and service conductors will make voltage problems with other circuits worse.