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Thread: Jay see 1997 GU build up

  1. #431
    Smart like tractor Ben-e-boy's Avatar
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    Quote Originally Posted by PeeBee View Post
    I am sure they will trip at a point well before the insulation is compromised is perhaps the message. They are a cheap generic design and I have them in use and they certainly have worked for me when i have replicated the short circuit fault.
    No, the message is get the breaker to trip instantly in the event of a fault, dont give it a chance to wait around and trip whenever, hoping it doesn't damage other stuff. That just increases the chance of it not working and damaging other stuff.
    General overloading on the other hand needs a bit of room to move.

    How did you replicate the short circuit fault?
    96 GQ coil/Cab
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  4. #432
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    Shorted to earth. I think we are talking in circles. If you have a main cable feeding a sub board, protect the feed cable as suggested with the 60 amp breaker, and the accessories off that board are protected by their correctly sized breaker or fuse per circuit The main breaker should be sized to protect the cable and the accumulated maximum load it might see if every accessory was drawing their maximum current. ie, if you blow a fuse on a circuit with a 5amp draw, the main breaker of 60a is not going to trip. If you damage the main feed cable between the battery and the sub panel,and it feeds to earth, the main cable breaker will trip.
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    Legendary jay see's Avatar
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    Thank you gentleman. Good information there.

    So a 60 amp breaker and I should be good.

    Just on wire size. The wires going to the fuse box is trailer wire. Used for radio., Uhf, a couple of 4.2 amp dual USB and cig plugs. Do you see any problems with that.

    Suppose I should make sure that I'm using correct size fuses as well.

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    Should be fine as cables are typically rated at 10a although there is a 15a cable avail for trailer wiring as well.
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    Legendary jay see's Avatar
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    Quote Originally Posted by PeeBee View Post
    Should be fine as cables are typically rated at 10a although there is a 15a cable avail for trailer wiring as well.
    Pretty sure it's 10a wire, so I shouldn't have fuses bigger than the wire. Max fuse 10a correct.

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    You should be protecting the device first then the wire. If the device calls up a 2amp fuse, thats what you install. If the device is calling up a 15amp fuse and you have 10amp cable, upgrade the cable.
    Manufacturer of the Complete Camp Oven System

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    Have just read the past few posts about fuse/circuit breaker sizing & thought I'd add a couple of comments.

    Firstly a summarising comment which I think both BB & PB will agree with. Assuming correctly sized cabling for intended loads is fitted, the fuse or contact breaker should have the minimum current capacity you can fit without being blown/tripped by the appliance in normal use. That way the cable is protected in as wide a range of circumstances as possible. In the event of a short circuit you want the protection as 'instantly' as possible. The fuse/CB should be fitted as close to the battery as possible to protect as much of the cable as possible.

    If you find, as I did, that normal use of an appliance blows the fuse or trips a contact breaker, so long as your cable is adequately sized for the appliance's current draw, you can safely increase the current rating of the fuse/CB up to the next size. Example. I run a Makita fast charger off my inverter to charge 18v lithium batteries. My inverter is rated at 350w which at 12v equates to a tad under 30amps max, so I fitted a 30amp circuit breaker. However I found that it kept tripping. The combination of the fast charger's current draw & the inverter's ability to operate over it's rating had shown me that during the charge cycle the the fast charger was at times pulling up to 33amps. The next size CB available to fit the housing I had was a 50amp which I had no qualms about fitting. It no longer gets tripped by the Makita charger & I am confident the cables are still protected from overheating in the event of a short. In short (pun intended) if unsure start smaller & increase if required rather than the other way around ...as a general rule.

    Secondly ... something BB made reference too. I claim no expertise, but became aware that different fuses & CB's have different 'trigger' times. Ben-E-Boy referred to "(<0.4sec) of 10×Rated current". In situations where higher currents are involved the fuse or CB rating is only part of the story, the designed 'trigger' speed is important too. Some fuses are designed to withstand a certain current for x period of time before they blow. An example - in my car I have cable which connects my bank of aux batteries (in the rear canopy) to the crank battery (under the bonnet). It is a 70mm2 cable which allows me to parallel all the batteries for extended winching if needed. The winch on 'full noise' can pull 450amps. As the cable runs in part along the chassis, suitably protected, the risk of sustaining damage on rocks or similar could not be ignored. Current running through the cable from 360Ah of Aux batteries & shorted against the chassis would be sufficient to vapourise metal. So I fitted a 450A fuse in the belief I was doing the right thing. However I later learned that this was not offering me the instant protection I thought I had as it was a 'slow blow' fuse, which could take up to 20 seconds at 450 amps to blow, less at higher amps but still too long in a 'rock damage short' scenario. I took expert advice & fitted a 225A fuse of the same type. It has never yet blown with normal winch use. Others here with better electrical knowledge than me might like to clarify. My main point is that there are pitfalls for the unwary to fall into when it comes to 'electrical protection' .

    One other thing, based upon personal experience...... I prefer manually re-settable circuit breakers - auto reset types make electrical problem finding a nightmarebecause by the time you have the multi meter out to do your checking they have reset. I will never fit another!!!
    Last edited by Cuppa; 15th December 2019 at 04:37 PM.

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  14. #438
    Smart like tractor Ben-e-boy's Avatar
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    Quote Originally Posted by PeeBee View Post
    Shorted to earth. I think we are talking in circles. If you have a main cable feeding a sub board, protect the feed cable as suggested with the 60 amp breaker, and the accessories off that board are protected by their correctly sized breaker or fuse per circuit The main breaker should be sized to protect the cable and the accumulated maximum load it might see if every accessory was drawing their maximum current. ie, if you blow a fuse on a circuit with a 5amp draw, the main breaker of 60a is not going to trip. If you damage the main feed cable between the battery and the sub panel,and it feeds to earth, the main cable breaker will trip.
    Not in circles yet. I'm probably not explaining my point regarding fault current and instantaneous trips properly.
    96 GQ coil/Cab
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  16. #439
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    Quote Originally Posted by Cuppa View Post
    Have just read the past few posts about fuse/circuit breaker sizing & thought I'd add a couple of comments.

    Firstly a summarising comment which I think both BB & PB will agree with. Assuming correctly sized cabling for intended loads is fitted, the fuse or contact breaker should have the minimum current capacity you can fit without being blown/tripped by the appliance in normal use. That way the cable is protected in as wide a range of circumstances as possible. In the event of a short circuit you want the protection as 'instantly' as possible. The fuse/CB should be fitted as close to the battery as possible to protect as much of the cable as possible.


    Correct. But in order to get an instantaneous trip you need to have a circuit impedance (ohms) low enough to actually generate a high enough fault current. To use the previous 120A breaker @ 10 x In example, your circuit Impedance needs to be a maximum of 0.01ohm to achieve an instantaneous disconnect. There is much more to it.

    If you find, as I did, that normal use of an appliance blows the fuse or trips a contact breaker, so long as your cable is adequately sized for the appliance's current draw, you can safely increase the current rating of the fuse/CB up to the next size. Example. I run a Makita fast charger off my inverter to charge 18v lithium batteries. My inverter is rated at 350w which at 12v equates to a tad under 30amps max, so I fitted a 30amp circuit breaker. However I found that it kept tripping. The combination of the fast charger's current draw & the inverter's ability to operate over it's rating had shown me that during the charge cycle the the fast charger was at times pulling up to 33amps. The next size CB available to fit the housing I had was a 50amp which I had no qualms about fitting. It no longer gets tripped by the Makita charger & I am confident the cables are still protected from overheating in the event of a short. In short (pun intended) if unsure start smaller & increase if required rather than the other way around ...as a general rule.

    Secondly ... something BB made reference too. I claim no expertise, but became aware that different fuses & CB's have different 'trigger' times. Ben-E-Boy referred to "(<0.4sec) of 10×Rated current". In situations where higher currents are involved the fuse or CB rating is only part of the story, the designed 'trigger' speed is important too. Some fuses are designed to withstand a certain current for x period of time before they blow. An example - in my car I have cable which connects my bank of aux batteries (in the rear canopy) to the crank battery (under the bonnet). It is a 70mm2 cable which allows me to parallel all the batteries for extended winching if needed. The winch on 'full noise' can pull 450amps. As the cable runs in part along the chassis, suitably protected, the risk of sustaining damage on rocks or similar could not be ignored. Current running through the cable from 360Ah of Aux batteries & shorted against the chassis would be sufficient to vapourise metal. So I fitted a 450A fuse in the belief I was doing the right thing. However I later learned that this was not offering me the instant protection I thought I had as it was a 'slow blow' fuse, which could take up to 20 seconds at 450 amps to blow, less at higher amps but still too long in a 'rock damage short' scenario. I took expert advice & fitted a 225A fuse of the same type. It has never yet blown with normal winch use. Others here with better electrical knowledge than me might like to clarify. My main point is that there are pitfalls for the unwary to fall into when it comes to 'electrical protection' .

    Fuses and C/B's have a 'Trip Curve' graph (posted below). Selecting an appropriate device should be based on application. Winching for instance, is not exatly a constant load, it is susceptible to spikes in current and possibly even a very short time at locked rotor situation. There is circuit protection available for that intended use that will deal with it appropriately.

    One other thing, based upon personal experience...... I prefer manually re-settable circuit breakers - auto reset types make electrical problem finding a nightmarebecause by the time you have the multi meter out to do your checking they have reset. I will never fit another!!!
    Some responces in red
    I will add that protecting the cable is first and foremost.

    Attached is a random trip curve graph plucked from the internet. The darker section is the area where the breaker will trip, everything below that is normal working conditions.


    images (6).jpeg
    96 GQ coil/Cab
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  18. #440
    Legendary jay see's Avatar
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    Quote Originally Posted by Cuppa View Post
    My main point is that there are pitfalls for the unwary to fall into when it comes to 'electrical protection'
    Yeap, that's me to a tee.

    Sent from my A1601 using Tapatalk
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