Fuse taps using the hot side aka wrong side

CDNinHH

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OK, well from some of the videos I have seen of GTA a camera is probably a good idea ;-)
 

Rajagra

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Surely the aim of a fuse tap is to take an actual 12V ("hot") line out then pass that line through a new fuse to the new equipment.
That way you don't affect the existing layout, and you use the correct fuse for the new stuff.

If instead you take your output from the protected side of an existing fuse, then the current of the new equipment is added to the current of the existing equipment. This might tip the balance and cause the original fuse to keep blowing.
The only reason for doing this is for extra protection if you're doing a messy installation or using untrusted connections. Otherwise it's not the proper approach.

I suppose if the original circuit has an overrated fuse - or if the relevant equipment is never used - then it doesn't matter which way round you do it. But I think you should understand the difference between the 2 options and make an informed choice, not leave it to chance.
 

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Why do you think almost everyone is using fuse taps rather than direct to the battery, are we all in danger of being incinerated?
We use fuse taps because it is the easiest source of power and provides a reasonable clean install. Running a power line through the firewall on a modern car is a major task on its own.. and.. there is no nice way to attach a light gauge wire to the battery.
I think the bulk of this conversation was about the right and wrong way to add a fuse tap and, why it matters.
 

CDNinHH

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Mountains out of mole hills here guys......the OP was talking about 2 amp fuse addition. I stand by my earlier comments that IN THIS INSTANCE it really makes no difference!
 

CDNinHH

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Think about it this way.. Suppose you used a tap on a 3o amp circuit to ADD another 30 amp service. One way would work and the other way would see 60 amps go through the original circuit and fail. In the image (above) the left hand side circuit "could" see a 35 amp load across the 30 amp fuse. The right hand picture will not see a combined load.

This has been bothering me for a while Ralph. You are suggesting that 2 fuses in series would double the rating. That is completely wrong. Only 2 fuses in parallel would do that. If you have 2 fuses in series of 30 amps each and the load goes to 31 amps ( theoretically) one of the fuses would blow. Now if you have 2 30 amp fuses in parallel then yes, theoretically it would take more than 60 amps to blow. Remember a fuse is simply a conductor that at a certain temperature will melt, if you draw more than what it is rated for it will blow.
 

Ralph2

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Let me try it again. :)
In the pictures shown by CDNinHH (post #6) the left hand sides shows a setup where a load of 30 amps out to the original load and a 5 amp additional load will pass 35 amps through the 30 amp fuse. The right hand side will only ever have a 30 amp load across the 30 amp fuse.
There is a right and a wrong way to install a fuse tap.. but in this case it will work both ways, the additional load is almost negligible in the big picture.
 

CDNinHH

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Ralph, lets for a minute say that I put a solid piece of 12 gage copper wire in the bottom slot. Then a 5 amp fuse in the top. Then I apply a load of 10 amps to the wire coming out of the top of the tap. Do you not think that 5 amp fuse will blow?
 

CDNinHH

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the left hand sides shows a setup where a load of 30 amps out to the original load and a 5 amp additional load will pass 35 amps through the 30 amp fuse.

That makes no sense. What if I didn't put a fuse in the top slot at all, are you saying the original load would not be supplied? Ok, now I think I understand what you are driving at. Yes, in the one situation you are trying to draw more load thru the 30 amp fuse, that's true. But it has no bearing on the protection of the camera or ITS function.

I think we may have been talking about 2 different things here or I didn't grasp what you were getting at.
 
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Ralph2

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:) Okay.. another way to look at it. Take the 30 amp fuse out. put a 100 amp fuse in the top. In one of the pictures this would work.. in the other it will not. Put the 30 amp fuse back in.. now what will happen when you put a 100 amp load on the top? One way will still work.. the other way will blow the 30 amp fuse. :)
 

CDNinHH

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it would still work but if you put it in the wrong way the second outlet won't be protected by the fuse, original outlet works either way

I think this where it went off the rails :p
 

CDNinHH

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Basically the tap in one way creates a whole new circuit with its own protection. The other way you are adding additional load to the existing circuit, but again with its own separate protection. So protected by the 5 amp fuse either way. So if you were talking about combined load to the original equipment then I see your point.
 

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...But it has no bearing on the protection of the camera...
That is true, it also has no bearing on the protection of the original load, the issue is the protection of the supply.

If you start off with a 5 amp fuse supplying a 5 amp load and you add a fuse tap with another 5 amp fuse and a camera that consumes 5 amps then if you connect the fuse tap one way around you can draw 10 amps total, the other way you can only draw 5 amps total. If the original fuse is supplied by 5 amp wire then one way you can not overload the supply wire, the other way you can double the rating of the supply wire at which point the plastic insulation will start to melt, become very thin, and then start to short circuit to the metal it is attached to, the sparks from the short will then ignite the already melted insulation and your car will turn into smoke and flames. Of course our cameras don't take 5 amps so normally this will appear to work fine, until something goes wrong like the lithium battery getting an internal short, then it can start consuming the 5 amps and that is when you car gets destroyed, possibly with you inside it.

Connect the fuse tap the correct way around and everything is safe, even if something goes wrong.
 

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If you start off with a 5 amp fuse supplying a 5 amp load and you add a fuse tap with another 5 amp fuse and a camera that consumes 5 amps then if you connect the fuse tap one way around you can draw 10 amps total

Nigel, that is all wrong, as I stated before putting fuses in series does not double the value, you can not draw 10 amps.

If you use the fuse tap taking power for the camera from the side supplied by the original fuse you will just be "preloading "that fuse.

Let's say we use what was originally a 30 amp fuse location that supplies the rear window defroster. Lets say that the window defroster uses 25 amps when 'on", now we add an additional 5 amps to the camera. Theoretically that would blow the original fuse, protecting everything, the rear window defroster, the camera and the supply wires.

Either way you use the tap you have no danger in melting anything. The only problem is possibly now not being able to supply the original load ( the rear window defroster) with enough current.
 

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Nigel, that is all wrong, as I stated before putting fuses in series does not double the value, you can not draw 10 amps.

If you use the fuse tap taking power for the camera from the side supplied by the original fuse you will just be "preloading "that fuse.

Let's say we use what was originally a 30 amp fuse location that supplies the rear window defroster. Lets say that the window defroster uses 25 amps when 'on", now we add an additional 5 amps to the camera. Theoretically that would blow the original fuse, protecting everything, the rear window defroster, the camera and the supply wires.

Either way you use the tap you have no danger in melting anything. The only problem is possibly now not being able to supply the original load ( the rear window defroster) with enough current.
I am suggesting that you should put the fuse tap the correct way around for the fuses to be in series and thus have everything correctly protected, but if you put it the other way around then the fuses will not be in series and the source will not be protected.
 

CDNinHH

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Lets try this one last time....
Regardless of which way you put the fuse tap in the supply is protected by the original value of the original ( bottom) fuse. Again, you do not add the value together of fuses in series.

Please stop trying to scare people into thinking that IN REGARDS TO PROTECTION there is a right or wrong way to insert the fuse tap.
 

CDNinHH

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CDNinHH

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Thanks jokiin......finally a voice of reason ;)
 
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