ERCES Authority · Educational Reference

UL 2524: What the Listing Standard Means for Your BDA Equipment Selection

Zion Fire Protection | ercesauthority.com | Updated June 2026

When an AHJ approves an ERCES for installation under IFC §510, one of the baseline requirements is that the bi-directional amplifier (BDA) and associated active components must be listed to a recognized standard. That standard is UL 2524: In-Building 2-Way Emergency Radio Communication Enhancement Systems.

UL 2524 listing is not a marketing designation — it is a third-party certification that a specific BDA model has been tested and verified to meet defined safety, performance, and reliability criteria. This article explains what UL 2524 tests for, what it requires for enclosures, and how to verify that a BDA is actually listed rather than merely "compliant."

What UL 2524 Tests

UL 2524 is published by Underwriters Laboratories and referenced in both IFC §510.4 (2021 IFC) and NFPA 1225 §18.12.1.3 as the required listing standard for BDA equipment. The standard covers:

• Electrical safety: The BDA enclosure, power supply, and wiring must meet UL safety requirements for building-installed electrical equipment.
• RF performance: The BDA must deliver the amplification levels and frequency accuracy specified by its design without overloading the donor path or the public-safety network.
• Environmental durability: Variable voltage, temperature, and humidity tests consistent with NFPA 72 fire alarm system requirements.
• Battery backup: The secondary power source must sustain the BDA under load for the required 12-hour duration at full system load.
• Monitoring output: The BDA must provide the supervisory and trouble outputs required by IFC §510.4.2.5 and NFPA 1225 §18.14, with visual and audible annunciation within 200 seconds of fault for most fault types.
• Automatic gain control (AGC) and oscillation detection: The BDA must include built-in oscillation detection and control circuitry, and must not introduce interference when donor signal levels are high.

Enclosure Requirements — What UL 2524 Actually Specifies

A critical aspect of the UL 2524 standard is its enclosure requirement. UL 2524 requires:

> All repeater, transmitter, receiver, signal booster components, external filters, and battery system components are contained in enclosures which comply with the requirements for a NEMA Type 4 or Type 4X enclosure.

> Batteries requiring venting are contained in enclosures complying with the requirements for a Type 3R enclosure.

This requirement applies to all covered components regardless of installation environment. UL 2524 does not differentiate between conditioned and non-conditioned spaces for this purpose — NEMA Type 4 or 4X is required universally for active components.

NFPA 1225 §18.3.1.2 carries forward this same requirement: all active signal booster and filter components must be in NEMA 4 or NEMA 4X enclosures. IFC §510.4.2.4(1) and (2) (2021 IFC) also requires NEMA 4 for BDA enclosures and NEMA 3R for battery enclosures.

Class A and Class B — What These Terms Actually Mean

The terms "Class A" and "Class B" appear frequently in ERCES specifications and proposals, but they are not UL 2524 equipment classifications. The correct source of these definitions is FCC 47 CFR §90.219, and they refer to filter bandwidth, not installation environment:

FCC Class A Signal Booster (47 CFR §90.219)

A signal booster designed to retransmit signals on one or more specific channels. A booster is Class A if none of its passbands exceed 75 kHz. Class A boosters are channelized — they amplify specific, pre-programmed channels with narrow filters. They are also known as narrowband or channelized BDAs.

FCC Class B Signal Booster (47 CFR §90.219)

A signal booster designed to retransmit any signals within a wide frequency band. A booster is Class B if it has a passband that exceeds 75 kHz. Class B boosters amplify all signals within a broad frequency range. They are also known as wideband or broadband BDAs. Class B installations must be registered in the FCC signal booster database before activation.

The Class A/Class B distinction has nothing to do with where the BDA is physically installed. A Class A BDA installed in a parking deck requires the same NEMA Type 4 or 4X enclosure as a Class A BDA installed in a conditioned IT closet — the enclosure requirement comes from UL 2524 and NFPA 1225 §18.3.1.2, not from the FCC class designation.

The AHJ and frequency license holder typically specify which FCC class is appropriate for the installation based on the local public-safety network's channel structure and interference environment.

Why AHJs Require UL 2524 Listing

IFC §510.4 (2021 IFC) and NFPA 1225 §18.12.1.3 require BDA equipment to be listed by a nationally recognized testing laboratory (NRTL) to UL 2524. AHJs rely on the listing because:

1. Independent third-party testing: UL tests production samples from the manufacturer — not just prototypes. A UL 2524 listing means the specific model has been tested under controlled conditions.

2. Consistency across projects: Every BDA on a jurisdiction's inspection circuit carries the same listing baseline, giving inspectors a defined standard.

3. Ongoing oversight: UL conducts follow-up inspections of manufacturers' production facilities. A manufacturer that changes production processes affecting listing can have the listing suspended or revoked.

4. FCC alignment: UL 2524 RF performance testing aligns with the operational parameters required by FCC 47 CFR §90.219.

UL 2524 listing became mandatory under IFC §510 with the adoption of the 2021 IFC (equipment listing was not specifically addressed in IFC §510 prior to the 2021 edition).

"Compliant" Is Not the Same as "Listed"

A manufacturer can claim a product is "designed to meet UL 2524" or "UL 2524 compliant" without having submitted it for third-party listing testing. These claims are not equivalent to a UL listing.

A product is only listed to UL 2524 if:

• It has been submitted to and tested by UL or another authorized NRTL.
• UL has issued a listing certification for the specific model number.
• The physical device carries the UL listing mark on the enclosure.
• The model appears in UL's online product database with active status.

AHJs increasingly request listing documentation as part of the plan review submittal. A BDA that arrives on site with manufacturer marketing material instead of a verified listing record can be rejected before installation begins.

How to Verify a BDA Is Actually Listed

UL maintains a publicly accessible product database at www.ul.com/database (UL Product iQ). To verify:

1. Search by manufacturer name, product category ("In-Building 2-Way Emergency Radio"), or UL file number.

2. Confirm the specific model number appears with an active listing status.

3. Confirm the listing is to UL 2524 and that the frequency bands covered match the AHJ authorization letter.

You can also request the UL certification document from the manufacturer. A legitimate document includes the UL file number, the specific model numbers covered, the standard (UL 2524), and the date of listing. If a manufacturer cannot produce this document, the product is not listed.

Do not rely on spec sheets or brochures.

Common Misconceptions

"FCC certification covers the same thing as UL listing."

FCC authorization (Part 90) confirms the device does not cause harmful interference and operates within authorized frequency bands. It does not test electrical safety, environmental durability, battery performance, or monitoring output. Both are required; neither substitutes for the other.

"If the BDA was UL-listed two years ago, it's still listed."

Listings are maintained through UL's follow-up service program and can lapse if the manufacturer changes the product without UL notification. Always verify against the current database.

"Class A means it's rated for conditioned space; Class B means it needs a heavier enclosure."

This is incorrect. Class A and Class B are FCC designations based on filter bandwidth — they have no bearing on enclosure or environmental requirements. UL 2524 and NFPA 1225 §18.3.1.2 require NEMA Type 4 or 4X enclosures for all active BDA components regardless of FCC class or installation environment.

Equipment Selection Checklist

Before specifying or accepting a BDA for an ERCES installation:

• [ ] Confirm UL 2524 listing via UL Product iQ using the specific model number.
• [ ] Confirm the listing is active (not lapsed or superseded).
• [ ] Confirm the listing covers the frequency bands required by the AHJ authorization letter.
• [ ] Confirm FCC Class A or Class B matches the AHJ/licensee requirement and, if Class B, that FCC registration will be completed before activation.
• [ ] Confirm the BDA enclosure is NEMA Type 4 or 4X (required for all active components by UL 2524 and NFPA 1225 §18.3.1.2).
• [ ] Confirm FCC Part 90 authorization for the model.
• [ ] Verify the physical device carries the UL listing mark on the enclosure.

Having this documentation prepared before plan submittal avoids a resubmit cycle.

Use our free Building Signal Check tool to see if your building is in scope: https://bda.zion.us/bda/check

This article is provided as educational reference. It does not constitute a code interpretation or legal opinion. Confirm current code adoption and amendments with your local Authority Having Jurisdiction (AHJ) before applying any of this to a specific building.

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