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📱 EPISODE 4 — Article 242 (Part 4 of 4... almost!)

Part III Begins — Surge Arresters Over 1000V

SLIDE 1 — Intro to Part III
⚡ NEW TERRITORY: SURGE ARRESTERS ⚡

Once you're above 1000V nominal, SPD terminology goes away and we start talking about surge arresters instead. Same mission (protect against voltage surges), different voltage class, different rules.

🚫 USES NOT PERMITTED (242.40)
A surge arrester can't be installed anywhere its rating is LESS than the maximum continuous phase-to-ground voltage available at that point. Undersized protection = no protection.

SLIDE 2 — Surge Arrester Rating
📊 DUTY CYCLE RATING (242.42)

The duty cycle rating must be AT LEAST 125% of the max continuous operating voltage at the point of application.

How you calculate that voltage depends on the system:
🔹 Solidly grounded systems → use the phase-to-ground voltage
🔹 Impedance-grounded or ungrounded systems → use the phase-to-phase voltage

This is a classic exam trap — solidly grounded vs. ungrounded changes which voltage you reference!

SLIDE 3 — Number Required & Location
🔢 NUMBER REQUIRED (242.44)
Just like SPDs, a surge arrester at any point on a circuit must connect to EVERY ungrounded conductor. One installation CAN protect multiple interconnected circuits — as long as no circuit gets left exposed while disconnected from the arresters.

📍 LOCATION & ROUTING (242.46 / 242.48)

Indoor or outdoor placement is fine

Must be inaccessible to unqualified persons (unless listed otherwise)

Conductors to the arrester should be as SHORT as possible with minimal bends — longer runs mean bigger reflected voltage waves back through the protected equipment

SLIDE 4 — Exam Question + CTA
🧠 TEST YOURSELF

Q: A surge arrester is being sized for a solidly grounded system. Which voltage should be used to determine the max continuous operating voltage?

A) Phase-to-phase voltage
B) Phase-to-ground voltage
C) Line-to-neutral voltage x 2
D) System nominal voltage only

(Comment your answer 👇)

FOLLOW — one more episode to fully close out Article 242! ⚡ #JoshTheSparky #NEC2026 #ElectricianLife

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