Class t fuse question

Re: Class t fuse question

offgrid me wrote: »

Would a class t fuse blow faster than a circuit breaker. The reason I ask is that my 150amp class t fuse blew today. I was doing some wiring and had a faulty light fixture, neutral to hot short. When I switched the power on the inverter made a very loud buzz then everything shut down (cc, battery monitor and inverter). The light was wired threw a 30amp 120v breaker that did not pop. I tested the fuse for continuity and found it had blown. I dont have a spare. What would be the least dangerous way to bypass the fuse while a new one comes in(I ordered a spare this time).
Thanks Ned

First a comment about fuses versus circuit breakers: Class T fuses are extremely fast blow and are designed to try to protect equipment which could be damaged by high current as well as interrupt really high short circuit currents safely.
They will blow within a short time (10-20 seconds) from a current which is only 50% above their rating. A circuit breaker will usually have two time characteristics, one the instantaneous trip value which for a 20 amp breaker will be somewhere over 300 amps, and the other the current over time (thermal) trip. The latter for a 20 amp circuit breaker carrying 30 amps can be on the order of minutes. Remember that 20 amps at 120 volts AC corresponds to 200 amps or more at 12 volts DC.

The least dangerous way to bypass the fuse is to not do it. In your case if the fuse had not been there, you could easily have done damage to the inverter which would cost hundreds of dollars to repair if repair was even economical. Not to mention the chance of fire or worse.
I can't in good conscience advise you to do anything other than replacing it with an identically rated fuse, or a smaller (lower current) fuse of the same type.

The class T fuse used in the inverter is also rated so safely interrupt DC, which many normal fuses cannot do.

PS:

Transistors are devices which blow rapidly under overload conditions to protect any fuses that might be in the circuit.

Unfortunately the type of transistors used in an inverter tend to fail as a short circuit rather than failing open, making the fuse even more important.

Re: Class t fuse question

offgrid me wrote: »

The inverter is 48v with a 12k surge rating. The fuse was not in the inverter it was one that I put in between the battery and positive bus bar. I dont know if the inverter has its own internal protection or not.This is my only source of power so not using it is not an option. Whats the fusing rating of a piece of 14awg copper.

Check out this reference: http://www.litz-wire.com/New%20PDFs/Fusing_Currents_Melting_Temperature_Copper_Aluminum_Magnet_Wire_R2.011609.pdf
It will give you a ballpark figure. If the wire is insulated, it will blow sooner, but may melt or ignite the insulation in the process, so I would use bare wire, and at least an inch or two of it to make sure the it does not leave a self-sustaining arc, one of the hazards of DC fusing and battery voltages like 48 volts.

Re: Class t fuse question

Blackcherry04 wrote: »

Yeah, you'll get some heat, you're supposed to.

Just be careful to keep combustibles out of the immediate area of the fuse wire and make sure that molten copper will not fall or vaporize onto anything important. :-)