Douglas Krantz - Technical Writer - Describing How It Works

Can a Strobe be Connected to a Horn Circuit?

A strobe should never be connected to a horn only circuit, and the strobe has to be compatible to be used with the panel it is connected to.

Can a Strobe be Connected to a Horn Circuit?

Greetings Douglas,

Can I connect a strobe onto a horn circuit from panel, or do the horns and strobes need separate circuits for horns-only and strobes-only?

Thank you, DL

When figuring out whether or not a strobe can be used on any horn circuit in a fire alarm system, there are some questions to ask yourself:

As the building is currently wired, does the system use separate horn and strobe circuits?

If the answer is yes, then out of common practice, all strobes go on the strobe circuit and all horns go on the horn circuit. No strobes should ever go on the horn-only circuit because the system was designed to have separate circuits.

In the future, if there are any changes, mixing strobes in with the horns now will cause problems later.

Is the strobe compatible?

To be compatible doesn't mean "It is lawful to use it", to be compatible means "It has been tested to actually work with what it will be connected to".

This is a life safety fire alarm system; people depend on the system to work. If the strobe is not compatible, it has not been tested and might not work at all, or it might not work reliably, and it will probably flash at the wrong rate (possibly causing epileptic seizures).

The strobe should be the same make and model as all the other strobes in the building. If it's a different manufacturer than the other strobes in the building, it probably isn't compatible.

Check with the manufacturer's technical support to find out if the strobe is compatible. It won't hurt to call them, and they might have more ideas.

Will adding the strobe overload the panel?

Make sure that the panel isn't close to being overloaded with the horns and strobes that are already connected.

This is an issue. In a few cases, the panel actually turned off the horns and strobes during a fire alarm because they drew too much current. That doesn't happen very often, but be aware that that could happen.

Will the NAC circuit in the building support an extra strobe?

The strobe is going to be connected to the strobe circuit (Notification Appliance Circuit or NAC), or it's going to be connected to the horn/strobe circuit (also a NAC).

This doesn't have anything to do with the panel's ability to handle the current in the building's NAC; this has everything to do with the current in the wire of the NAC. No, the wire isn't going to get hot and burn up if there's too much current. It's just that some of the horns or strobes at the end of the NAC won't work if the wire is too long or too small to handle the current.

In essence, if the wire is too long or too small, the wire will slurp up a lot of the voltage so there won't be enough voltage for the last few horns or strobes on the circuit.

Whether adding it to a strobe circuit or a horn/strobe circuit, the additional wire and the extra current used by the strobe can easily be a problem. One time, to find a problem with strobes that weren't flashing correctly, I had to sound off the horns and strobes in a courthouse early one Saturday morning. I found out the problem. The problem was that when extra strobes had been added, the wiring couldn't handle it.

Because of the small size and the length of the wire, even though the panel gave out enough voltage at the start of the NAC, the voltage was too low at the end of the NAC to power the added strobes.

If a lot of wire is going to be added, there could easily be a problem. Even if the wire is the largest diameter copper that can be used, something somewhere else might not work. Be careful when adding an extra strobe.

Douglas Krantz
Life Safety
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