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wildybill · May 31, 2016, 01:18 PM

Will a 10amp in-line circuit breaker installed before the equipment with the 15amp fuse protect said fuse from blowing?

ebaines · May 31, 2016, 02:19 PM

Maybe, maybe not. If a fault occurs that is between 10-15 amps the circuit breaker should trip, but it may take several minutes to do so. For a fault around 20 amps the circuit breaker could take 30 seconds or longer to trip, and during that time the 15A fuse may heat up enough to blow. For very large current faults both the circuit breaker and fuse may blow essentially simultaneously.

wildybill · Jun 1, 2016, 03:30 AM

Hey cheers for the help, I was under the impression circuit breakers were instantaneous much like an RCD?in any case the problem isn't fault related but rather when attempting to operate a 10 amp item which has a high initial load current.simply starting a brick saw has blown my fuse previously.

hfcarson · Jun 1, 2016, 04:42 AM

bill,
Circuit breakers and fuses come in many different configurations, that is to say some operate faster or tolerate higher current levels before they operate.
Now, put a circuit breaker and a fuse in series and you will be adding a dynamic impedance to the circuit which can effect the speed or level of fault current that will cause either to operate.

It sounds like you have a motor or similar device with a high inrush. If the FLA or Full Load Ampere rating is "10 amps", then a dual element / time delay fuse rated at 175% can be used. Theoretically this will allow the inrush without tripping...
If using a circuit breaker, a "15 ampere" HACR rated breaker should be appropriate.

Try using one or the other....not both,

wildybill · Jun 1, 2016, 04:50 AM

The fuse is built into the machine, I have no choice but to use it, I'm trying to protect it externally to prevent 30-60 minutes of downtime dismantling the machine whenever it blows.

hfcarson · Jun 1, 2016, 05:10 AM

Are you replacing the fuse(s) with "exactly" the same fuses as original? What kind of fuse is it? Do you have the catalog number?

wildybill · Jun 5, 2016, 10:59 PM

Yea, straight from manufacturer, its PAT equipment so I have to keep it 100% to spec.The fuses in question are 2x 500V 16A Ceramic Cylinder Fuses.There is no fault with them or the machine, Any blown fuses would likely be to my negligence, so I was interested in using a switch with a lower threshold to eliminate any risk to the 16A fuses.If that idea isn't reasonably practicable then I will have to do without, I'm no worse off and I don't want to be wasting everyone's time with wishful thinking.Cheers for the help.

hfcarson · Jun 6, 2016, 04:01 AM

what is "PAT" equipment?

wildybill · Jun 7, 2016, 04:55 AM

Originally Posted by hfcarson

what is "PAT" equipment?

Portable Appliance Tester.

Used for running a variety of tests on electrical equipment to ensure it conforms to Australian safety standards.

I will test anywhere from 0-200 items in a day, 99% of items will include a leakage test which involves powering the item via my PAT machine.
If I believe the test to pose any safety issues I can skip it

The problem is if I don't know an item is faulty or has a high load current and blow the fuse, I have to work late without pay to finish the quota.

hfcarson · Jun 7, 2016, 05:21 AM

I would expect a more successful method of protecting the 16 ampere fuses would be to put in series another set of fuses as closely matched as possible to the existing ones but with a lower current or trip threshold. The greater the difference between their ratings the more likely the lower rated fuses will blow first...
You could try using a lower rated circuit breaker but I think using fuses would give a more predictable outcome...
Good luck