Okay, it is a long story so I won't get too detailed but the just of it is that a fire marshall told one of my builders today that I can't do the smoke detectors in the house because NEC says they have to be 120v. Now I have had some tough inspections before, and have talked at length to several fire marshalls that said as long as I had smokes with horns in them I was okay. I do not have a copy of the NEC, so I was wondering if Larry, Tom, or someone with more electrical experience knew what the NEC said about smoke detectors.

NEC will only specify how or how not to install a 120v smoke detector. Fire and building codes determine what kind of detectors must be used in your locality.

That is what I thought, but the builder swore he said NEC. I am cool not installing them because I don't want the added headaches when something goes wrong.

You can use the alarm smokes. I will follow up with the NED Code number at a future date.

BUT! The NEC code also says that a local electrical inspector or the local fire marshall can make his own ruling.

I'm with you, who wants the liability.

Mike

You could always double up and put the alarm system detectors in addition to the 120v ones. I don't see how that could be a code violation under any circumstances, but it would be a waste of a little bit of money.

In the mountain towns in Colorado they all need to be low voltage alarm system smokes with 24 hour back up and tied in to a central station with an outdoor strobe and keyswitch.

Ask the inspector if it is a battery back up issue.
As long as there is battery back up as well as horns to cover the proper DB level you should be fine.
Also I dont think this comes from the NEC side but the BOCA code.

Here in NC the smokes can be low voltage as long as the power supply is in a security enclosure (locked enclosure around transformer). Meaning that not only do they have battery back-up, but that they also have a permanent 120v power source, which cannot be disconnected.

But even this varies from city to city, to county. City requires a permit, county does not.

PIA to keep up with this stuff, as we deal with several cities and counties.

Actually, the NEC doesn't directly address smoke detectors at all, except for the outlet box that 120v models are attached to and powered from. Everything else is building code.

There may well be different rules for new installations (120v w/battery backup) and for existing premises (grandfathered as long as the original met code when it was new).

And of course that you aren't supposed to connect a 120v smoke detector to a GFCI protected circuit. :-)

In Massachusetts all new construction has to have 120v smoke detectors wired together with back up. Battery ones are grandfathered for existing structures. Also, in a few communities around here sprinklers are required for new residences as well. YMMV, check with the local fire inspector of the community you are working in. Bob

You will need to refer to NFPA 72. You may need to take it up with the local fire marshall. Unfortunatley what the local inspector is the ahj so what he says goes no matter how wrong he is. Unless you really want to piss him off that is. There are ac smokes with relays to tie into a low voltage system.

Perfectly legal to install low voltage smokes provided they have your standard 80db of sounder and battery backup. Let the inspector know that these smokes are of the same caliber and performance of smokes that are installed in commercial applications. In some jurisdictions, you may be required to hard wire a transformer in a sealed enclosure to satisfy code requirements.
Also, pull an 18 gauge wire for all of the smokes. Just walked a house that another low volt company pulled 22/4 for the primary smokes. No 110 smokes, just low volt smokes. 15 smokes on a 22/4 loop, what a bunch of jamokes.

I am not a big fan of tying in relays to 110 smokes. If there is a problem then who is responsible and who do you call? Low volt company or sparky? I won't touch anything that sparky installs.

Got to ask what fire district was this in, I have never had a problem with using LV smokes around here. I use a 24 power supply with a reversing relay setup to sound the smokes on alarm. I would go and talk to the fire marshall and ask the their requirements and explain (nicely) that the NEC does not address the requirement for 120 smokes. Most district require interconncted smokes and 80db of sound in bedrooms with door closed and battery backup. WHen you go to see the FM be able to full explain the system you are going to install most the time they just don't seem to understand and seem to think LV means battery powered..
.When I did my own home I had to spend a couple of hours showing the FM what my plan was and by the time I was done he was completely satisfied that I was above the level of protection they wanted.