Fuse Selection for AC Motor and Lights - Safety

[jeremypw]

I'm designing a circuit that will control turning on/off two rotating emergency lights. The specs for the rotating lights are linked below. Should I include a fuse in my design and how do I select the proper fuse? I want to ensure that the circuit is is safe to have in the home and it won't cause a fire or shock anyone.

Brief Description of Circuit:
Arduino with IR receiver will switch on the AC power source through a relay that will provide power to the two lights in parallel. If a fuse is recommended it will be connected to the phase side of the power source before the relay.

Rotating Warning Light

 

[ScottyUK]

You don't say which rules you're working under, but yes a fuse is probably mandatory and is certainly good practice. I'd suggest about 1.6A - 2A assuming the Arduino board takes very little power, but you may have specific national codes to comply with.

 

[jeremypw]

Thanks for the response. I live in Ohio, U.S.

Should the fuse be slow blow or fast and can you help me understand how you decided on 1.6A to 2A?

 

[ScottyUK]

Based upon the very limited information to hand I would choose a slow-blow fuse given that there are motors to turn the beacons; if you have a small transformer or SMPS hidden in there then a slow blow make even more sense. Sizing was essentially an educated guess selected from the standard sizes, based on the loads declared, with sufficient margin to make sure there is no realistic possibility of nuisance blowing.

 

[jeremypw]

How do I determine what I2t rating and breaking capacity at rated voltage I will need for the fuse?

I'm narrowed my search for fuses down those in the link below:
Fuses

 

[BrianPetersen]

You say that this circuit should be safe to use in the home.

Then I will assume that it is being plugged into a 110V outlet - which already has fused protection (probably 10 amps).

Your vacuum cleaner, blender, lamps, etc don't have their own fuses ... they rely on the fused protection from the outlet.

But ... this means the various cables, switches, relays, etc have to be good for handling the full current from the receptacle, in the event that something goes wrong.

 

[jeremypw]

I called the manufacturer and one of their technicians said they don't believe any of their customers use a fuse with these lights. However, the weakest link in my circuit is rated at 2.5 Amps... well below the 10 amps Brian mentioned.

The motor for the light is a Synchron brand single-phase synchronous motor that runs at 60 rpm. The clocks these are used in don't have fuses but they may have components that can handle up to 10 Amps.

http://www.decodesystems.com/help-wanted/simplex-clock.html

Based on the information you provided me, I think I need a fuse. I'm not sure how to determine what I2t rating and what rated voltage I need.