You’re reviewing a quote for a new electrical panel and one of the line items reads “whole-home SPD.” You know what a panel is. You’re not sure what that other thing is, or whether you actually need it. It’s a reasonable question. The answer matters more than most homeowners expect, especially now that New Hampshire law requires one whenever a panel is replaced.
A surge protective device (SPD) is not a power strip. It’s a hardwired unit that mounts at your main electrical panel and intercepts voltage spikes before they reach any circuit in your home. At Garneau Electric, we’re licensed in New Hampshire and Massachusetts and install SPDs as part of panel upgrades throughout Windham and southern NH. What we see regularly: homeowners who skip this step pay for it later, usually through a failed HVAC control board or a fried EV charger that nobody connects back to a surge.
What a Whole-Home Surge Protector Actually Does
An SPD connects to your main electrical panel and monitors incoming voltage. When a transient voltage spike (a brief, intense overvoltage event lasting microseconds) hits the line, the device diverts the excess energy to ground before it can travel into your circuits. The response happens in nanoseconds, faster than any appliance can react on its own.
Here’s the part most homeowners don’t know: more than 80% of residential voltage surges originate inside the home. Every time a large motor cycles on or off, it creates a small voltage disturbance on your electrical system. HVAC compressors, well pumps, and refrigerators are the most common culprits. These internal events don’t blow fuses or trip breakers. They just quietly degrade the control boards and circuitry inside your appliances over months and years, until something fails and there’s no obvious reason why.
Why Windham Homes Are Especially Exposed
The internal surge problem exists in every home. Windham adds external risks on top of it. Summer thunderstorms bring lightning strikes and tree-on-line events that send high-energy spikes through utility lines directly into your service entrance. Winter ice storms cause outages that require utility switching during restoration, and that switching process produces its own surge events when power comes back online.
The equipment common in southern NH homes makes this more consequential than it used to be. Variable-speed heat pump compressors, EV charger control circuitry, and well pump variable-frequency drives are all highly surge-sensitive. A single significant event can destroy any of them, and replacing an EV charger or a heat pump inverter board costs far more than a whole-home surge protector ever will.
There’s one more risk that often gets overlooked in homes with standby generators. When a Generac generator transfers from grid power to generator power and back again, the transition creates its own voltage disturbance. A panel-mounted SPD intercepts that transfer surge before it reaches your appliances, which matters because those transitions can happen multiple times during a single outage.
It’s Now Required When You Replace Your Panel in New Hampshire
New Hampshire adopted the 2020 National Electrical Code in 2022. Under NEC Article 230.67, a Type 1 or Type 2 SPD is required at the service panel for all new residential construction, service upgrades, and panel replacements. Full enforcement became effective October 1, 2025, per the NH Office of Professional Licensure and Certification.
If you’ve recently had your panel replaced or upgraded, confirm with your electrician that an SPD was included on the permit. If it wasn’t, you’re not up to current code. If you’re planning a panel replacement now, an SPD isn’t optional language on the estimate. It’s a legal requirement under NH law.
Panel-mounted SPD installation must be done by a licensed electrician. DIY installation is unsafe, won’t pass a New Hampshire inspection, and voids the device warranty. This isn’t a job for a long afternoon and a YouTube video.
What a Power Strip Can’t Do
Point-of-use surge strips (the kind you plug your TV or computer into) are useful as a secondary layer of protection for sensitive electronics. They aren’t a substitute for a panel-level SPD. A power strip can only protect what’s plugged into it, and it’s rated to absorb only a fraction of the surge energy a panel-mounted device handles. More importantly, your hardwired appliances have no access to a power strip at all. Your HVAC system, water heater, well pump, and EV charger connect directly to circuits with no point-of-use protection available. Without a panel-level SPD, those systems have zero defense against either internal or external surge events.
The most complete protection combines both layers: a panel SPD as the primary defense covering every circuit in the home, and quality point-of-use strips on computers, televisions, and other sensitive electronics as a backup. Neither layer alone does what both together accomplish.
What to Know Before Installation
SPDs are classified by where they connect in the service equipment. A Type 1 device installs on the utility side of the main breaker, at the service entrance itself. A Type 2 installs on the load side of the main breaker. For most homes in Windham, a Type 2 provides sufficient protection and is the more common installation. The work typically takes one to two hours when scheduled alongside or immediately after a panel replacement.
Every surge protective device has a finite lifespan. The metal oxide varistors (MOVs) inside the unit (the components that actually absorb surge energy) degrade with each event they handle. Quality SPDs include a status indicator light that changes state when the device has reached the end of its useful life. You’re looking at roughly ten years under normal conditions, though a single major surge can exhaust a device sooner. When the indicator changes, the unit needs replacement. An SPD that has absorbed its rated surge capacity provides no protection at all, even if it still has power to it. The voltage protection rating (VPR) is the number to watch when comparing devices. It measures the maximum voltage that passes through to your equipment during a surge, and lower is better. We can walk you through what the specs mean for your specific home and equipment when we provide your estimate.
Protecting What You’ve Already Invested In
A whole-home surge protection device costs a small fraction of what it protects. A new HVAC system, a heat pump inverter, a well pump controller, an EV charger, or a Generac generator transfer switch are all orders of magnitude more expensive than the device that keeps them running. When you factor in that New Hampshire’s weather produces external surge events regularly and that your own appliances create internal ones every day, this isn’t a precautionary add-on. It’s basic protection for equipment you’ve already paid for.
If you’re planning a panel replacement or have recently completed one, Garneau Electric can confirm your SPD status and handle the installation with upfront pricing and no surprises. Call us at (978) 915-7860 to schedule a free estimate.