A fire alarm panel that blinks out for two seconds during a blackout test will be written up. Detection has to continue while the ship transfers between supplies, and the arrangement that makes that possible is specified in far more detail than most retrofit packages allow for.
Power supply is also the part of a detection system most likely to be replaced like for like, without anyone revisiting the calculation behind it. That is where compliance quietly erodes.
Why Does A Fire Alarm Panel Need Two Power Sources?
The FSS Code requires not less than two sources of power supply for the electrical equipment used in operating a fixed fire detection and fire alarm system, one of which must be an emergency source. Supply runs through separate feeders reserved solely for that purpose, terminating at an automatic change-over switch situated in, or adjacent to, the control panel for the fire detection system.
The reasoning behind the duplication is straightforward. Detection is the service that has to survive the loss of the very system whose failure may have started the fire, so the Code separates the feeders physically and requires the transfer to happen without crew intervention. For ships built on or after 1 July 2014, resolution MSC.339(91) added a further condition on the switch itself, requiring it to be arranged so that a fault will not result in the loss of both power supplies.
How Long Must The Emergency Supply Actually Last?
The FSS Code does not state a single figure. Paragraph 2.2.4 requires the emergency source, supplied either by accumulator batteries or from the emergency switchboard, to be sufficient to maintain operation of the fire detection and fire alarm system for the periods required under SOLAS chapter II-1 regulations 42 and 43, and then to be capable of operating all connected visual and audible fire alarm signals for a period of at least 30 minutes.
Those SOLAS periods differ by ship type, which is why a generic standby figure taken from a shore specification tends not to survive contact with a marine plan approval.
| Ship type | Emergency supply period | Additional alarm requirement |
| Passenger ships | 36 hours | 30 minutes operating all connected visual and audible alarm signals |
| Cargo ships | 18 hours | 30 minutes operating all connected visual and audible alarm signals |
| Passenger ships on short international voyages | Reduced period as permitted by SOLAS II-1/42 | 30 minutes operating all connected visual and audible alarm signals |
One figure in this part of the Code is regularly misread. Chapter 9 requires the supply to sustain continued operation of the system with all detectors activated, but not more than 100. That is a sizing rule for the power supply, and treating it as a ceiling on loop capacity leads to systems specified against the wrong constraint. Where a supply needs replacing on a marine fire detection system, a Tyco power supply module matched to the panel it serves keeps that calculation intact, and we stock these in Singapore for vessels working the regional trades.
What Has To Happen During Changeover?
Operation of the automatic changeover switch, or failure of one of the power supplies, must not result in loss of fire detection capability. Where a momentary loss of power would degrade the system, a battery of adequate capacity has to be provided so that operation continues through the transfer. This clause catches ageing installations more often than new ones, because a panel that rode through changeover cleanly at commissioning may not do so once its internal battery has aged, and the annual test of emergency power switchover is exactly where that surfaces.
How Are Standby Batteries Sized And Sited?
Batteries have to be located in or adjacent to the control panel for the fire detection system, or in another location suitable for use in an emergency. The rating of the battery charge unit must be sufficient to maintain the normal output power supply to the system while recharging the batteries from a fully discharged condition, and that second requirement is the one most often missed on like-for-like replacement, where a higher capacity battery is fitted to an unchanged charger.
Load calculation drives the sizing. The two architectures compared in addressable vs conventional fire alarms draw on the supply in quite different ways, and the quiescent load of an addressable loop card bears little relation to a conventional zone card of similar vintage, so a panel upgrade almost always changes the battery duty even when the detector count is unchanged. Record the calculation with the system documentation so it can be reproduced at the next survey instead of being reconstructed from memory.
What Type Testing Applies To Marine Panel Supplies?
Marine fire panels and their power supplies are type tested against a different specification from shore equipment. IACS Unified Requirement E10, the test specification for type approval, applies to electrical, electronic and programmable equipment used in control, monitoring, alarm and protection systems on ships, and its schedule takes in external power supply failure, power supply variations, dry heat, damp heat, vibration, inclination, salt mist and a full set of electromagnetic compatibility tests.
The power supply failure test is specific: three interruptions during five minutes, with a switching off time of 30 seconds in each case.
One point needs care here. UR E10 does not include an ingress protection test, so a type approval certificate issued against it does not establish the enclosure rating. An ingress protection (IP) rating, defined in IEC 60529, is a two-numeral code describing how well an enclosure resists solid objects and water, and it has to be specified separately against the space in which the panel or supply is actually mounted.
Get The Supply Specified Before The Panel Arrives
Power supply arrangements are cheap to get right at specification stage and expensive to correct once a panel is on the bulkhead and a surveyor is on board. Atlas Technologies Corporation is an authorised distributor for Tyco, Federal Signal and Solo, supplying certified fire detection equipment, power supply modules and spares to fleet owners and ship managers across Singapore, Malaysia, Indonesia and beyond. Speak to our team about your panel, your load figures and the duty your emergency source has to carry, and we will help you match the parts to it.
