Dimming Lights

Most of us have seen our lights get really dim or see them flicker. We will see words like “dirty power” or “unstable power”. In this article I want to go over some of the common causes of dimming lights and explain what this is. It is important to know that voltage and current work hand in hand. One goes up, the other goes down. It is also important to know that current (load) is drawn by the user, the electric utility only provides voltage. As a user you must make sure that from your point of service (residential customers is typically the top of the weather head or meter can) that your system is up to par.

Now what does this mean. Think of your largest loads in your house, most will say their A/C unit. Looking on your AC unit nameplate data (any motor nameplate data), you will see LRA and RLA. LRA stands for Locked Rotor Amps and RLA stands for Running Load Amps. What this means is the power (amps) needed to get the motor moving from a locked (still) position. RLA means the power (amps) needed to keep the motor moving once it is at speed.

Going back to what was said earlier, current goes up, voltage goes down, the current (LRA) going up for a start up event will cause voltage to go down throughout your house, thus is seen with dimming lights. This is one reason to ensure that your AC unit has a high SEER rating or soft start kit. There are also other ways to ensure that the voltage drop scenario is less drastic, such as having a larger wire size, transformer size or shortening the distance of any wire ran. This will ultimately reduce the impedance/resistance of the voltage and the voltage drop/dimming will be less drastic.

Knowing the basics of this aspect and how it applies to residential applications can convert to commercial and industrial applications as well. Throughout larger facilities, think of the larger loads, maybe elevators, HVAC units, conveyor lines, etc. All of these different types of equipment will have LRA values with high power (amp) draw on start up. It is vital that these type of customers install soft start, provide proper wire size, XFMR size and various other aspects that can affect voltage drop. When thinking of the modern industrial and commercial facilities you will see a lot of logic, PLC (Programmable Logic Controllers), VFD (Variable Speed Drives) and robotics.

All of this modern equipment is extremely sensitive to power anomalies and must have a proper source. We are seeing a lot of overseas equipment that have a very tight voltage tolerance, as tight as 2.5% of nominal. This is where Alpha Power Systems can assist in ensuring that your facility can handle these bound to happen power anomalies, to ensure that your facility stays running throughout these voltage drop/dimming scenarios.

For more information contact APS at 813-805-9506.

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