Is it a Main or Branch Line (for Seismic Bracing)?

Can a branch line tee to multiple sprinklers?

Please see the attached example. I'm trying to figure out if a branch line that has a tee to multiple sprinklers would then be considered a main or still part of the branch line.

This question also applies to looped branch line systems.

The classification of branch lines and mains can have a major effect on the amount of seismic bracing required.

NFPA 13 defines branch lines as "The pipes supplying sprinklers, either directly or through sprigs, drops, return bends, or arm-overs."

NFPA defines arm-overs as "A horizontal pipe that extends from a branch line to a single sprinkler or a sprinkler above and below a ceiling."

Therefore, others that I have talked to have argued that the branch line will become a cross main since it is now feeding two sprinklers off of one line. This as a result would require additional seismic bracing.

NFPA defines a cross main as "The pipes serving the branch lines, either directly or through riser nipples." In my opinion, the pipe would remain a branch line because it still aligns with the branch line definition.

Moreover, there is nothing in NFPA that says that branching/teeing from a branch line automatically reclassifies the branch line as a main. Just because a pipe is no longer serving as an arm-over doesn't categorize the pipe feeding it as a main. The distinction between branch lines and cross mains is primarily based on their roles within the overall system, branch lines serve individual zones or areas, while cross mains supply multiple branch lines.

​What do you think?

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