Commercial Power Quality and Surge Protection for San Antonio Buildings

Commercial power quality and surge protection is a subject most business owners only think about after something fails. A point of sale system reboots in the middle of a lunch rush, a compressor controller dies after a storm, or the same breaker trips every afternoon and nobody can say why. In most of these cases the power did not go out. It arrived in a shape the equipment did not like. This guide explains the common problems, what protects against them, and when it is worth measuring before spending money.

What power quality means in a commercial building

Utility power is supposed to arrive as a steady voltage at a steady frequency. Inside a building, that ideal gets bent. Large motors starting pull the voltage down for a moment. Electronic loads such as computers, LED drivers and variable frequency drives draw current in short pulses instead of a smooth wave. Lightning and utility switching send short, high energy spikes down the line. Each of these is a power quality issue, and each has a different cause and a different fix.

The reason it matters more now than it used to is that so much of a modern building is electronic. Controls, network gear, refrigeration controllers, security systems and even lighting all run on circuit boards that tolerate far less disturbance than an old motor or an incandescent lamp did.

Surges: where they come from and how protection is layered

A surge is a short burst of voltage well above normal. Some come from outside: lightning nearby, or the utility switching its lines. Many come from inside the building, when large loads such as HVAC compressors, lifts or kitchen equipment switch on and off. Inside surges are smaller but happen constantly, and over time they wear down electronics.

Surge protection works best in layers. The 2023 National Electrical Code covers surge protective devices in Article 242, and the usual approach in a commercial building looks like this:

• A surge protective device at the service entrance, to take the largest outside surges before they reach the distribution.
• Devices at the panels that feed sensitive equipment, such as the panel serving a server room, a kitchen line or a medical suite.
• Point of use protection at the equipment itself for the most sensitive loads.
• Good grounding and bonding throughout, because a surge device can only send energy to ground if the path is there.

A device at the service alone does not stop surges created inside the building, and plug strips alone do not stop the big ones from outside. The layers cover each other.

Homes get the same idea at a smaller scale, which our whole house surge protection page explains. For a business, the layers are planned around the panels and the equipment that matter most.

Voltage sags and why equipment trips without an outage

A sag is a short drop in voltage, often lasting only a fraction of a second. The lights may flicker or may not visibly change at all, but a drive, a controller or a computer can drop out and restart. Sags often come from large motor loads starting inside the building, from a fault elsewhere on the utility system, or from a service or feeder that is undersized for the load it now carries.

When sags come from inside, the fix is usually on the building side: soft starters or drives on large motors, moving a sensitive load to a different circuit or panel, or correcting a feeder that has grown overloaded as equipment was added. When the cause is outside, the conversation is with the utility, and in most of the San Antonio area that utility is CPS Energy.

If the cause turns out to be a service that has simply outgrown the building, our guide to a commercial electrical service upgrade walks through how that work is planned with the utility.

Harmonics and the neutral conductor

Electronic loads draw current in pulses, and those pulses add distortion called harmonics to the electrical system. In a building full of computers, LED lighting and drives, harmonics can heat transformers and conductors beyond what the load on paper suggests. On three-phase systems that serve many single-phase electronic loads, some harmonic currents add up in the shared neutral instead of cancelling, so the neutral can carry more current than expected.

Signs that harmonics may be part of a problem include a transformer or panel that runs hot at moderate load, a neutral that measures higher current than the phases suggest, and nuisance trips that do not line up with any obvious overload. These are worth measuring rather than guessing at, because the fixes range from rebalancing circuits to equipment rated for nonlinear loads.

Grounding and bonding come first

Every protective device in this guide depends on the grounding and bonding behind it. A surge device sends surge energy to ground, so a loose or corroded grounding connection, a missing bond at a water or gas line, or a separate structure grounded on its own can leave the device with nowhere useful to send it. Poor bonding also lets small voltage differences show up between pieces of equipment that are connected by data or control cables, which can damage the ports on both ends.

For that reason a power quality visit begins at the service: the grounding electrode conductor, the bonding of the service equipment, and the bonding of any separately derived system such as a transformer serving a group of panels. Fixing a grounding fault is often the least expensive improvement on the list, and it makes everything installed after it work as intended.

When monitoring makes sense

Buying surge or power conditioning equipment without knowing what the power is doing is a common way to spend money on the wrong fix. A power quality recorder connected at the service or at a problem panel for a week or two shows the voltage, the current on each phase and the neutral, the sags, the swells and the distortion, with times attached. Lining those times up with when equipment failed or tripped usually points straight at the cause.

• Repeated trips or resets with no clear overload.
• Equipment failures that cluster after storms or at the same time of day.
• Hot panels, transformers or neutrals at moderate load.
• A building that has added a lot of electronic or motor load since it was built.
• A new tenant with sensitive equipment moving into an older space.

What the work looks like

A typical power quality and surge job starts with a walk through the electrical room and the problem areas, a look at the panels, the grounding and the bonding, and a list of the sensitive equipment. If the cause is not obvious, monitoring comes next. The recommendation then names the surge devices and where they go, any circuit or panel changes, and anything that needs to go to the utility. Every item gets a written price before work starts, and installation in an occupied building is scheduled around your hours so the short shutdowns happen when the space is closed.

Surge devices and connections are also checked during scheduled service, which our maintenance agreements cover. For everything else we do for businesses, see our commercial electrical services page.

Mistakes to avoid

• Relying on plug strips alone and calling the building protected.
• Installing a surge device at the service without checking that the grounding and bonding give it a good path.
• Adding conditioning equipment before measuring what the power is actually doing.
• Ignoring a hot neutral or transformer because the phase currents look normal.
• Forgetting that surge devices wear out and need to be checked like any other part of the system.