hello i have a customer who has primary and secondary lines in a fire alram. they want to use the same lines for another fire alarm. we are in calif. does anyone know if this is leagal. thanks dave

Always check with the "Authority having jurisdiction". In our county, fire alarms need 2 lines, with the 1st one being dedicated, the 2nd can be shared on the output side of the RJ-31. It can be used as the input to a burglar alarm, and then the output can be used for whatever the customer wants.

However, in the county seat's city, BOTH lines must be dedicated, and not shared with anything.

Like TTT said you need to check local codes but 2 alarms will not work on a line together. The line seizure of one alarm would override the other.

What about a fire alarm and burglar alarm sharing the same line?

I wouldn't recommend sharing the lines for fire alarms. Like Merritt said one will over ride the other. I seriously doubt any Fire Marshall would approve of that if they were aware of it.
Is it possible to connect the two panels together and use one to report signals? That is fine in many jurisdictions (in Texas anyway).

Jeff, I've seen burglar alarms share fire alarm lines but it's not a good situation for the same reason as the fire alarm situation but it is the lesser of the two evils.

In Denver, the requirement for Fire Alarms are two dedicated lines for each alarm. This seems to be a standard code almost everywhere. I have seen a setup where 3 alarms shared the backup line, but all had dedicated main lines. Burgalar alarms are optional pieces of equipment, so they can share lines.