Mini Circuit Breaker Ratings

[Engineer85]

Hello everyone,

We have designed a Lamps testing board with 4 holders. Firstly, we used fuse of 3 Amps in it as a protection device. We would like to replace the fuse with circuit breaker as it blows up every other day.

The load on this testing board will vary from 5W to 300W depending on the lamp we use. What rating of (mini) circuit breaker would be suitable for this purpose?

Regards,
E

 

[gepman]

What is the voltage?

 

[burnt2x]

Assuming 120V, and the worst case scenario of testing 4 X 300W, you have 1200W. If you are going to test luminaires which on average the power factor is 0.8, will give you an operating amps of 12.5A. You need a 15A breaker(80% loading).

 

[rovineye]

Yes, a 15 amp breaker, IF your cable and wires are rated for that current.

 

[jraef]

Actually if it is a testing board, you should size the wire for the expected maximum current load, then size the breaker to protect the wire. The voltage and power factor is irrelevant.

If you want to protect each of the different sized lamps when plugged in to the board, you will then need separate breakers for each size and some sort of selector switch to make sure you have the right one in the circuit. In that case, determining the exact nature of each individual lamp load would be more critical. Might be easier to use some sort of programmable electronic current sensing relay for that though, and just rely upon the breakers to cover any maximum load and/or short circuit scenario, in which case you would go back to the first method I mentioned.