UL 1971 vs UL 1638

W@ttson

W@ttson

Senior Member
Location
USA
Hello,

I have a Horn/Strobe that is rated 15/75 cd. It is 15 cd per UL 1971 and 75 cd per UL 1638. It is not selectable, its rating is just different based on which listing is governing.

My question is regarding the change from UL 1971 to UL 1638. Looking through the editions of NFPA 72 UL 1971 seemed to be the go to until the 2019 or so edition when UL 1638 seems to have started to take over regarding requirements for Visual indication. Now at the 2025 edition, UL 1971 is only mentioned in 1 place which is for tactile requirements, everything else is UL 1638.

I need a 60cd strobe, I assume since the code has drifted toward the UL 1638 requirements, my horn/strobe listed for 75cd per UL 1638 is fine.
 
When I think of UL 1638 I think of 'Private mode' or
"applications are those where a signal is known to be in place and where someone is trained to take additional action upon notification
from the alarm signal", I.E nurses’ stations and front desks.
Such emergency signaling applications do not need to meet ADA requirements.

Though when I look at the scope of UL 1638 it says " These requirements cover visible signal devices for use in ordinary (non-hazardous) indoor locations and outdoor locations. This includes:
a) Flashing visual devices used for fire alarm or emergency signaling in both public mode and private mode as defined in the glossary;"

UL 1791 I think of as "public mode operation" buildings where someone is not present or trained to take additional action upon notification emergency-signaling then the system needs to meet ADA for the hearing/visually impaired etc.
And the scope reflects that.
 
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