You are correct. Using both EM battery packs and an ELCU (Emergency Lighting Control Unit) on the same fixture is generally redundant and often unnecessary. Here's the breakdown: Emergency Battery Packs

These are self-contained units within or adjacent to the light fixture. They provide power directly to the lamp in the event of a power failure. They are simple and do not require additional control wiring.

Emergency Lighting Control Units (ELCUs)

These monitor normal power and switch fixtures (often a group of fixtures) to emergency power from a central battery system or generator when normal power is lost. ELCUs require dedicated emergency circuits and control wiring.

Why They Are Typically Mutually Exclusive



Redundancy

Both systems accomplish the same goal: powering the light fixture during a power outage. Using both is overkill.

Cost

Implementing both adds unnecessary expense (equipment, installation, and maintenance).

Complexity

An ELCU adds complexity to the emergency lighting system.

Potential Interference

The switching mechanisms of the ELCU might conflict with the battery pack's automatic operation.

Possible Exceptions (But Uncommon and Should Be Clearly Specified)

While rare, there might be specific circumstances where you could theoretically combine them, but these would be highly unusual and require clear justification and detailed specifications:

Specific Run Time Requirements

Perhaps the battery packs provide a minimum run time, and the ELCU extends that run time by switching to a generator after a certain period. However, even in this case, a larger battery pack might be a simpler solution.

Specific Control Scenarios

Some highly specialized applications might have complex control needs where both are used, but this is very atypical.*

Local Code/Authority Requirements

In very rare cases, a local authority might have specific requirements that dictate this configuration, but this is unlikely.

In Summary

Your intuition is correct. If the lights are already specified to have emergency battery packs, the ELCU detail is likely an error or a misunderstanding.

What to Do


Clarification

The best course of action is to clarify the intent with the drawing's author (architect, engineer, or whoever created the detail). Ask them to explain why both EM battery packs and an ELCU are specified for the same fixtures. There might be a specific reason you're unaware of, but it's important to understand the rationale.2.

Point Out Redundancy

Explain your understanding of the redundancy and ask if the ELCU can be removed from the specification for those fixtures with battery packs.3.

Review Specifications: Double-check the overall project specifications to see if there's any mention of specific emergency lighting requirements that might justify this configuration.By clarifying the intent, you can avoid unnecessary costs and complexity during installation and ensure the emergency lighting system functions correctly. Flag for review