Class t fuse question

offgrid me
offgrid me Solar Expert Posts: 119 ✭✭
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

Comments

  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    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.
    SMA SB 3000, old BP panels.
  • offgrid me
    offgrid me Solar Expert Posts: 119 ✭✭
    Re: Class t fuse question

    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.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    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.
    SMA SB 3000, old BP panels.
  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Class t fuse question

    Don't quote me , I think it's 166 amps / 14 awg . Been there myself. If you run naked with out it, it's bigger chance. I'd put a a drop away on the wire so you get a clean break if you were to have a short.
  • offgrid me
    offgrid me Solar Expert Posts: 119 ✭✭
    Re: Class t fuse question

    Thanks thats what I am going to do. The 14awg will be the weak link as all other wire runs are 2/0. I may get some heating under load but my normal highest loads are less than 2kw when I am not using the shop. 2 new fuses on the way. Does anyone know if the xantrex 6048 has internal fusing.
    Ned
  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Class t fuse question
    offgrid me wrote: »
    Thanks thats what I am going to do. The 14awg will be the weak link as all other wire runs are 2/0. I may get some heating under load but my normal highest loads are less than 2kw when I am not using the shop. 2 new fuses on the way. Does anyone know if the xantrex 6048 has internal fusing.
    Ned
    Not for what your trying to fuse, they might have something small on the control board or they use to anyway. You should be fine, I see inverters that never had fuse for 10 years. A Class T, is fast like the dog said, it's spring loaded . Yeah, you'll get some heat, your supposed to.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Class t fuse question
    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. :-)
    SMA SB 3000, old BP panels.
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    Re: Class t fuse question

    Hii ogm,

    Would think that a Class-T 150 amp fuse is too small a value for your XW 6048's surge rating.

    Thanks for adding your Signature line, it sure helps ... Here, the predecessor Xantrex inverter -- SW+ 5548 -- uses factory-supplied 250 amp DC Circuit Breakers. Believe that these older inverters will surge more than the XWs, but you could have some more nuisance fuse bowing incidents with a 150 A Cl T fuse. It IS true that a 175 A circuit breaker would provide no real protection for the inverter. Always trade-offs.

    Just opinions, YMMV, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Class t fuse question
    Vic wrote: »
    Would think that a Class-T 150 amp fuse is too small a value for your XW 6048's surge rating.

    Right you are, Vic; 150 Amp is too small for the 6048's continuous rating.
    6000 / 48 = 125 Amps * 1.25 = 156 Amps.

    Should indeed be a 250 Amp fuse on an XW6048 if you want full surge capacity. Check the manual: it recommends 4/0 wire and 250 Amp Breaker/Fuse