Let's break down 700.17(1) and 700.17(2) and clarify the requirements

Understanding 700.17 (1) and (2)

Both sections of 700.17 of the National Electrical Code (NEC) address acceptable means of supplying emergency lighting circuits to ensure that emergency lighting remains functional even when the normal power supply fails. However, they focus on different aspects of wiring and power sources. 700.17(1) Independent Wiring

This section mandates that the wiring for emergency lighting circuits be kept physically separate from the wiring of the normal lighting circuits, especially if the emergency lighting source is the normal power source. The separation requirement is intended to prevent a fault in the normal lighting circuit from disabling the emergency lighting circuit.

700.17(2) Two or More Separate and Complete Systems

This section is about having two completely separate electrical systems. One system powers the normal lighting, and an entirely different system powers the emergency lighting. These systems have separate wiring, power sources, and often separate distribution equipment.

Decoding "upon the event of failure of the normal lighting branch circuit" (700.17(1))

This phrase refers to any situation where the normal branch circuit supplying the regular lighting fails to provide power. This failure could be caused by: A power outage from the utility company. A tripped circuit breaker in the normal lighting panelboard. A short circuit or ground fault in the normal lighting wiring. Damage to the wiring or components of the normal lighting circuit.The key idea is that whatever causes the normal lighting to fail, the emergency lighting must remain operational.

Does it mean two circuits for lighting?

Yes, in effect, it means you will have two circuits serving the same or overlapping physical areas: Normal Lighting Circuit

This circuit powers the regular lights used under normal operating conditions.

Emergency Lighting Circuit

This circuit powers the emergency lights that activate only when the normal lighting circuit fails. These emergency lights might be dedicated emergency fixtures or select fixtures normally powered by the normal lighting circuit that switch over to the emergency circuit.

How 700.17(1) Differs from 700.17(2)

The major difference between 700.17(1) and 700.17(2) lies in the degree of separation and the source of power for emergency lighting. 700.17(1)



Focus

Physical separation of wiring to prevent a fault in the normal lighting circuit from affecting the emergency lighting.

Power Source

The emergency lighting can originate from the same normal power source if the wiring separation requirements are strictly followed. This is common in buildings where a generator or UPS system automatically starts upon a power failure. The emergency lighting comes on, but it's ultimately powered from the same utility source (via the generator/UPS). The separation is critical because a short in the normal lighting panelboard upstream of the emergency circuit breaker could knock out everything if the wiring wasn't separate.

Example

A normal lighting panelboard also feeds an emergency lighting circuit breaker. When utility power fails, a generator starts and powers the entire panelboard, including the emergency lighting. The key is the wiring from the emergency circuit breaker is run separately from the normal lighting circuits.

700.17(2)



Focus

Complete electrical independence between the normal and emergency lighting systems.

Power Source

The emergency lighting must have a completely independent power source, often a separate generator, batteries, or UPS that is not connected to the normal power system.

Example

Normal lighting is powered by the utility grid. Emergency lighting is powered by a dedicated generator or battery system that only powers the emergency lights. There is no shared infrastructure beyond the building grounding system.

In simpler terms



700.17(1) is about wiring separation to prevent a fault in the normal wiring from knocking out the emergency wiring. It's like having two pipes running side-by-side, but one is reinforced so if the other bursts, it doesn't affect the reinforced one. They could share the same water source, but the pipes themselves are separate. 700.17(2) is about complete system independence. It's like having two completely different water supplies for two different buildings. If one water supply fails, the other building still has water.

Why are both options allowed?

The choice between 700.17(1) and 700.17(2) depends on the specific application and the level of reliability required. Higher Reliability

700.17(2) provides a higher degree of reliability because the emergency lighting system is completely independent. This is often required in critical facilities like hospitals or data centers.

Cost and Complexity

700.17(1) can be less expensive and complex to implement if a generator or UPS system is already in place for the entire building. However, the wiring separation requirements must be strictly followed.

In conclusion:700. 17(1) requires separate wiring for emergency lighting circuits to prevent a failure in the normal lighting circuits from disabling the emergency lights, even if both circuits originate from the same power source (like a generator). 700.17(2) requires two completely independent systems: one for normal lighting and one for emergency lighting, with separate power sources and wiring.Always consult with a qualified electrical engineer or inspector to ensure compliance with all applicable codes and standards. These sections are often misunderstood and require careful consideration of the specific application. Flag for review