SPD

Updated: September 2026 · CNC Electric Pakistan

AC SPD vs DC SPD — The Single Most Important Choice

Type 1 vs Type 2 vs Type 3 — When to Use Which

How to Size an SPD — 3-Step Method

Step 1 — Match Voltage Type

AC system → AC SPD. DC system (solar PV string, battery bank) → DC SPD. Never mix them.

Step 2 — Match Voltage Rating

For AC: Uc ≥ 1.2 × nominal AC voltage. For 230V AC use 275V Uc. For 400V AC use 440V Uc.

For DC: Uc ≥ PV string Voc. For 350V Voc use 500V DC SPD. For 700V Voc use 1000V DC SPD. For 1100V Voc use 1500V DC SPD.

Step 3 — Choose kA Rating (Imax)

• 20 kA — most Pakistani homes, light commercial, residential rooftop solar
• 40 kA — higher-exposure: rural sites, hilltops, buildings with external lightning rods
• 65 kA+ — industrial PV plants, telecom towers, critical infrastructure

SPD Installation — Critical Rules for Pakistan

1. Install AS CLOSE as possible to the protected equipment — within 0.5 m of the main DB or inverter input.
2. Earth wire length less than 0.5 m, cross-section ≥ 6 mm² copper, going directly to earth bar (not daisy-chained through other devices).
3. Always install an upstream overcurrent device — a 32A or 63A MCB / MCCB protects if the SPD fails short. Use CNC MCBs for this.
4. Replace the cartridge when the wear indicator turns red. CNC SPDs have a window on the front showing green (good) or red (end of life). SPDs are sacrificial — each surge degrades the MOV slightly.
5. For solar: install both DC SPD (between panels and inverter) AND AC SPD (between inverter output and main DB).

SPD Frequently Asked Questions — Pakistan

Q1: What is an SPD and why do I need one?

An SPD (Surge Protection Device) diverts dangerous voltage transients to earth, protecting your appliances, inverter, and wiring from lightning surges and switching spikes. Pakistan's 40-60 lightning days per year, plus frequent WAPDA switching transients, make SPD essential for any modern installation.

Q2: What is the price of an SPD in Pakistan?

AC SPD: Rs. 1,500 for 2P 230V 20kA (home main) to Rs. 6,500 for 4P Type 1+2 (commercial). DC SPD: Rs. 1,800 for 2P 500V (small solar) to Rs. 8,500 for 3P 1500V 40kA (industrial PV). Replaceable cartridges: Rs. 650-1,200.

Q3: Where should I install the SPD?

Within 0.5 m of the main DB box, with earth wire less than 0.5 m and 6 mm² cross-section. For solar: one DC SPD near inverter DC input, one AC SPD near inverter AC output.

Q4: How do I know if my SPD is still working?

Every CNC SPD has a wear indicator window. Green = working, Red = end of life (replace immediately). SPDs are sacrificial — typical life is 5-10 years depending on surge frequency.

Q5: Can the same SPD work for AC and DC?

No. AC and DC SPDs use different arc-quenching designs. AC SPD on a DC line cannot extinguish the arc — often catches fire. Always match SPD type (AC or DC) to circuit type.

Q6: Do I need Type 1 or Type 2 SPD?

For 90% of Pakistani homes and small commercial (no external lightning rod): Type 2 is correct. Type 1 only if your building has a metal lightning rod with down-conductor. Type 1+2 combined units cover both for commercial buildings.

Q7: Is CNC SPD PSQCA certified?

Yes. All CNC YCS6 series SPDs carry IEC 61643-11 (AC) or IEC 61643-31 (DC) compliance and PSQCA approval.

Q8: What warranty does CNC offer?

1-year manufacturer warranty on the SPD body and unused cartridges. Replacement cartridges sold separately at Rs. 650-1,200 each.

Protect your electrical systems from unexpected voltage surges, spikes, and lightning strikes with high-quality Surge Protection Devices (SPDs) from CNCelectric.pk. Our SPDs are designed for residential, commercial, and industrial applications, providing reliable protection for sensitive electrical and electronic equipment.

Key Features of CNCelectric.pk SPDs:

• Overvoltage & Surge Protection: Safeguards electrical circuits from lightning strikes, power spikes, and voltage fluctuations.
• Fast Response Time: Immediately diverts excess voltage to ground, preventing damage to connected devices.
• Durable & Reliable: Built with premium components for long-lasting performance and continuous protection.
• Versatile Applications: Ideal for solar systems, electrical panels, industrial machines, home appliances, and office setups.
• Easy Installation: Compact, modular design for quick mounting in distribution panels and enclosures.
• Indicator & Alarm Features: Some models come with LED indicators to show operational status and fault conditions.

Benefits of Using CNCelectric.pk SPDs:

• Protects valuable equipment like inverters, transformers, motors, and electronics from sudden voltage spikes.
• Reduces downtime caused by electrical faults and surges.
• Enhances the longevity of electrical systems and connected devices.
• Available at competitive SPD prices in Pakistan, combining quality, safety, and affordability.

With CNCelectric.pk SPDs, you get trusted, tested, and efficient surge protection, ensuring the safety and reliability of your electrical and electronic systems.

Frequently Asked Questions (FAQs)

What is an SPD (Surge Protection Device)?

An SPD (Surge Protection Device) is a critical electrical safety device designed to protect electrical systems from voltage spikes or surges caused by lightning, power surges, or other transient voltage events. SPDs divert excess voltage away from sensitive equipment to prevent damage.

Why do I need an SPD?

SPDs are essential for protecting electrical equipment and systems from damage caused by transient voltage events. They help:

• Prevent electrical fires
• Protect sensitive equipment such as computers, servers, and industrial machinery
• Enhance the reliability and lifespan of electrical systems

How does an SPD work?

An SPD works by diverting the excess voltage caused by a surge or spike to the ground. When a surge occurs, the SPD detects the excess voltage and channels it safely to the ground, preventing it from reaching sensitive equipment. This is achieved using components such as varistors, gas discharge tubes, and metal-oxide varistors (MOVs).

Where should I install an SPD?

SPDs should be installed at:

• The main distribution board to protect the entire electrical system
• At the point of entry for electrical wiring
• Near sensitive equipment such as computers, HVAC systems, and machinery to provide localized protection

What is the difference between AC SPD and DC SPD?

• AC SPD (Alternating Current SPD): Used in systems powered by AC electricity, such as residential and commercial electrical grids.
• DC SPD (Direct Current SPD): Used in systems powered by DC electricity, such as solar ower systems, battery storage, and DC circuits.

Both types serve the same purpose but are designed to handle different types of current.

What types of SPDs are available for AC and DC circuits?

• AC SPDs: Typically used in residential, commercial, and industrial applications to protect against surges from the electrical grid or external sources.
• Types: Type 1 (for direct lightning strikes), Type 2 (for surge protection at the distribution board), Type 3 (for final protection near sensitive equipment).
• DC SPDs: Used in renewable energy systems, particularly solar installations, to protect the system from surges caused by lightning or other transient events.
• Types: DC SPDs are available for both photovoltaic (solar) systems and battery-powered systems, with specific protection against high-voltage surges.

What is an SPD cartridge?

An SPD cartridge is a replaceable unit within an SPD device that absorbs and diverts surges. It contains the surge protection components, such as varistors, and can be replaced after it has absorbed a certain amount of energy. Cartridge-type SPDs are commonly used in industrial and commercial settings where frequent surges might occur.

Are there different cartridge types for AC and DC circuits?

Yes, there are separate SPDs for AC and DC circuits, and the cartridges for each type are designed to handle the specific characteristics of the respective currents:

• AC SPD Cartridge: Designed to protect against AC surges, these cartridges often come with components that are specifically rated for alternating currents.
• DC SPD Cartridge: Specifically designed to protect DC systems, such as solar systems, from voltage spikes and surges.

How do I choose the right SPD for my system?

Choosing the right SPD depends on factors such as:

• The type of system (AC or DC)
• The level of protection needed (Type 1, 2, or 3)
• The voltage and current specifications of your system
• Installation environment (residential, commercial, or industrial)

It’s essential to consult with an electrician or electrical engineer to select the appropriate SPD for your system.

How can I ensure the effectiveness of an SPD?

To ensure your SPD is effective:

• Make sure it is properly installed by a certified electrician.
• Regularly inspect and maintain the SPD to ensure it is functioning properly.
• Replace the SPD cartridge as recommended by the manufacturer or when it shows signs of wear.

What are the benefits of using an SPD in my system?

• Increased Equipment Longevity: Protects sensitive equipment from damaging voltage spikes.
• Improved System Reliability: Reduces the risk of downtime due to surge-related failures.
• Fire Prevention: Helps prevent electrical fires caused by surges.
• Cost Savings: Prevents costly repairs or replacements of damaged equipment.

Related Guide: SPD Full Form: What Is Surge Protection?

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