Component Snapshot At-a-Glance

• Model: A4H124-24FX; Foxboro OEM marked part #: P0973JN
• Alt. P/N: Cross compatible A2H124-24FX(P0973BJ), alternate factory part P0973BL
• Product Series: Enterasys SecureStack A4 industrial managed switch lineup, factory pre-configured for Foxboro I/A DCS control networks
• Hardware Type: 19-inch standard 1U rack mount Layer2+ stackable fast ethernet fiber switch
• Key Feature: 24 fixed MT-RJ multimode 100BASE-FX ports + 2×1G RJ45 stacking ports + 2×hot-swappable Gigabit SFP uplink slots
• Primary Field Use: Terminate multimode fiber runs from Foxboro FBM field I/O modules inside refinery, power generation DCS rack cabinets

A4H124-24FX

Hard-Numbers: Technical Specifications

• Protocol Support: 802.1Q VLAN, 802.1p QoS, RSTP/MSTP, SNMPv2c, RMON, LACP port trunking, IGMP Snooping, port ACL
• Port Count: 24×MT-RJ 100BASE-FX multimode fiber; 2×10/100/1000BASE-T RJ45 stack/uplink; 2×Gigabit SFP; 1×RJ45 RS232 console port
• Baud/Data Rate: Fixed 100Mbps optical on all base fiber ports; SFP auto-negotiate 1Gbps SX/LX/T copper/fiber uplink
• Operating Temperature: 0℃~+50℃ continuous cabinet running; -40℃~+70℃ warehouse non-operating storage
• Isolation Rating: 1500V surge isolation between front fiber transceiver PCB and main ASIC board for MCC cabinet spike protection
• Power Draw: Max 62W full load; universal 100–240VAC 50/60Hz input, supports external redundant RPS backup supply
• Switch Fabric: 12.8Gbps switching capacity, 9.5Mpps wire-speed forwarding rate
• MAC Table Depth: 16384 fixed onboard MAC address entries, non-volatile flash storage
• Stack Limit: Max 8 identical A4-series switches chained via dedicated RJ45 stacking ports into single logical switch domain
• Form Factor: 1U rack chassis, 442(W)×44(H)×368(D) mm standard EIA rack sizing

The Real-World Problem It Solves

Copper Ethernet cabling routed adjacent to large induction motors and MCC bus bars picks heavy industrial EMI, triggering recurring CRC errors and unplanned Foxboro FBM field controller dropouts during unit startup cycles. Scattered standalone fiber media converters eat critical rack U-space and inflate plant spare parts inventory counts.

Where you’ll typically find it:

• Refinery CDU/FCC process rack rooms aggregating dozens of remote FBM analog/digital I/O fiber drops
• Coal-fired power boiler DCS auxiliary cabinets collecting feedwater and turbine controller fiber communications
• Chemical process outdoor control shelters where fiber spans exceed CAT5 100m maximum distance limits

Integrated fixed MT-RJ fiber ports eliminate discrete media converters and block electrical noise from disrupting mission-critical DCS interlock traffic.

Hardware Architecture & Under-the-Hood Logic

Unit uses split-isolation dual PCB construction; front-panel optical transceiver board is galvanically separated from main CPU/ASIC section to block field cabinet surge spikes from frying core switching logic. It occupies edge tier between field Foxboro I/O hardware and plant core DCS backbone switches.

1. Inbound 100Mbps optical signals from remote FBM controllers feed directly into fixed MT-RJ multimode transceivers mounted on front I/O PCB.
2. Optical transceivers convert incoming light waveforms to standard electrical Ethernet frames before passing payload to central switching ASIC.
3. Factory preloaded QoS rules tag all proprietary DCS control and Modbus TCP packets to highest forwarding queue above historian background data.
4. ASIC either switches local peer-to-peer FBM traffic across base fiber ports or forwards uplink traffic out SFP/RJ45 stack ports toward core network.
5. Stack protocol syncs active running-config and firmware revisions across all chained A4 units to operate as unified single switching plane.
6. Onboard nonvolatile flash retains startup VLAN and QoS configuration through full AC power loss events.

A4H124-24FX

Field Service Pitfalls: What Rookies Get Wrong

Improper SFP transceiver mixing in gigabit uplink slotsNew field techs plug single-mode LX SFPs into uplink bays intended for multimode SX; mismatched optical wavelength causes constant uplink flapping and spontaneous stack splits during live production.

• Quick Fix: Restrict uplink SFPs to 850nm multimode SX transceivers matching OEM Foxboro specification only.

Stacking live insertion with mismatched firmware revisionsField crew adds spare into running stack without matching firmware build; version mismatch locks new switch offline with all front port LEDs fully dark and breaks master stack election.

• Field Rule: Configure and verify firmware match on bench offline before stacking cable connection into live DCS stack.

Poor MT-RJ fiber termination triggering vibration induced link faultsInstallers over-strip fiber core inside MT-RJ connector; cabinet cooling fan vibration shifts fiber alignment leading to intermittent DCS PV signal dropout and unstable closed control loops.

• Quick Fix: Re-terminate faulty fiber per MT-RJ spec, validate transmit optical power with handheld fiber power meter before returning to live service.

Commercial Availability & Pricing Note

Please note: The listed price is for reference only and is not binding. Final pricing and terms are subject to negotiation based on current market conditions and availability.