Sizing of Fire Department Connections (FDC)
Automatic Fire Sprinkler Systems
Fire department connections (FDC) are required on NFPA 13/13R designed automatic fire sprinkler systems but are not required to be sized for flow or pressure. Automatic fire sprinkler systems are “automatic” and automatically provide the required design flow and pressure.
NFPA 13 Standard for the Installation of Sprinklers simply requires an FDC to supplement the system if needed. In the case of a NFPA 13 automatic fire sprinkler systems, the standard requires a single two x 2 ½ in. FDC for all systems with risers greater than 3 in.
In those situations where the riser is 3 in. or less, the FDC is allowed to be a single 2 ½ in.
NFPA 13R Standard for the Installation of Sprinkler Systems in Low-Rise Residential Occupancies only requires a single 1 ½ in. FDC.
Standpipe systems are different, in that the FDC can be used to supplement a standpipe system. This requires the FDC to be sized for the highest system demand and requires two x 2 ½ in. inlets on a building, as a minimum. The FDC is sized by one 2 ½ in. inlet for every 250gpm of system demand to a maximum system demand.
The maximum number of inlets required on a building is based on whether the building is equipped throughout with automatic fire sprinklers. In a building protected throughout with automatic fire sprinkler systems designed to NFPA 13, the maximum system demand is 1000gpm or four x 2 ½ in. inlets, all others must be sized to a 1250gpm demand or five x 2 ½ in. inlets at the FDC.
In combined systems where the water supplied is shared between the standpipe and automatic fire sprinkler system, the FDC is sized for the greatest system demand. It must be based on either the sprinkler system demand, including any hose stream allowances or the standpipe demand, whichever is greater. In most cases, standpipe demand is used to size the majority of combined system FDC inlets. Combined systems are subject to the same maximum as standpipe only systems, or 1000gpm for buildings protected throughout by an automatic fire sprinkler system meeting NFPA 13, or 1250gpm for all others.
In buildings with combined systems that are equipped with partial automatic fire sprinkler systems, the flow rate is increased by an amount equal to the calculated sprinkler demand or 150gpm for light hazard, or by 500gpm for ordinary hazard occupancies, whichever is less.
It must be noted that both installation standards, NFPA 13 and NFPA 14, allow listed four in. or 5 in. large diameter quick connect threadless FDC to be used, but neither gives guidance on sizing.
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