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what JB/enclosure required for fire alarm installation

Tom D

I am not an expert but re fire alarm systems but I need to split my fire loop due to modular project requires that.

Once the whole project delivered on site everything will be connected back and stays for years.

I have come across conflicting opinions about this.

Some say that this has to be done by using fire resistant plastic JB with ceramic terminals whereas other says that it need to be steel box not plastic.

I have fount both of them plastic and SS JB and they both actually "fire resistant" so I am confused completely.

 

  • 0

    Well, the plastic one says, "fire resistant" and the steel one says, "fire rated". BS 6387 refers to cables, not JBs.

    I suspect that the fire resistant one will char, and burn eventually.

  • 0

    Hi Tom, what are all the other enclosures/back boxes in your system made of?

  • 0

    Hi Tom. My first question is have you carried out a cost comparison between this product and an adaptable box equipped with a DIN rail and connectors?

  • 0

    Hi Tom,

    I think I can offer some help here, though just to be fully transparent I work for Hensel, one of the junction box manufacturers you’ve mentioned.

    To answer your question directly, if you need to use a junction box on a fire alarm system it’s important that the connection terminals inside it can withstand fire conditions for at least as long as the cable it's connecting.

    BS 5839-1 requires that fire alarm cables maintain integrity for a minimum of 30 minutes, and up to 120 minutes for enhanced systems. The standard also states that terminals must withstand similar temperature and duration as the cable.

    As you’ve noted, we have a fire-resistant range of polycarbonate enclosures that use ceramic terminals and an internal metal support plate, tested and approved to maintain circuit integrity for up to 2 hours (PH120). So although the outer enclosure is plastic, the whole system (including terminals and mounting) is designed and tested to perform under fire conditions.

    Since we already specialise in polycarbonate enclosures, we’ve been able to keep key benefits of our standard enclosures (like quick installation and cost-efficiency) and still meet the fire performance requirements set out in the standards.

    Hope that helps!

  • 0

    BS 5839-1:2025

    "35.4 Cables should be installed without external joints wherever practicable."

    BS 8519:2020

    17.1 "Where the life safety, fire-fighting or other critical circuits require the use ofjoints or junction boxes
    to house terminations and other critical system components, they should provide the same level of
    fire performance as that offered by the cable."

  • 0 in reply to W B X

    most of them mild steel

  • 0 in reply to AMK

    Cost is one thing but rules are rules so I if more expensive box is required as per reg. or BS it doesn't matter how cheap the other one would be as it can't be simply used.

  • 0 in reply to Matt Bailes

    Thanks for your reply Mark. We are aiming to use mild steel box with ceramic terminals inside. The only thing I am not sure of is the colour of the box as it will be standard white (not red/orange). Moreover it won't be only dedicated for the fire detection system but some other 12/24V circuits will be connected in the same box. Do you think that would be okey?

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