fuse box

[bob dunn]

I am re doing my fuse box and would like to know what rateing I will need for each circuit.Maybe 10 fuses.

[mpbarrett]

all depends what is on the circuit....
For example for the main lights then the lamps are usually 44 watts each that's 88 watts divide by 12 to get the current. the current determines the fuse rating and the cable size. The function of the fuse is to cut the current off if the circuit gets a short and it has to do this before the cables  fails (cable catches alight, car burns out...).
So what are you putting onto your 10 fuse circuits?

cheers
mike

[bob dunn]

I know very little about fuses . So to split into groups, gauges ,lights(head and other) , ignition ,overdrive,wipers, air horns.radio.aux lights.

[bob dunn]

http://cdn.instructables.com/F6S/LV21/GG4A6GRH/F6SLV21GG4A6GRH.LARGE.jpg

[bob dunn]

http://www.12voltplanet.co.uk/fuses-guide-uses.html

[bob dunn]

I got 2 fuse boxes each takes 4 fuses, One could be live and the other live with the ignition. I got 30 15 and 10 amp fuses .So next is what is the rating of the circuits for each fuse .Is it as simple as connect up a big fuse and measure the power used then fit an apropriate smaller fuse. If so how do you measure power used.

[bob dunn]

Just read "If current draw is 10amps and cable size is 25amps, then a 15amp fuse is ok ".Sounds good.

[bob dunn]

Fitted the horns , they run at 15amps (checking ammeter in line),When I wired it up I guessed at 15amp for the fuse ,it does not blow, so I will leave it at that for now.

[bob dunn]

Anyone know about the oil for the Harry Moss London Maserati air horns .It says oil monthly with vaseline oil.

[bob dunn]

Wired up ignition ,it takes 6 or 7 amps at turn on then 15 at starting then down to 0.0 running, horn reads 0.0 while car is running. but I guess still 15 at the horns. Next lights and guages.

[RobPearce]

If you're getting readings of 0.0A then I suspect your measurement technique is faulty. How are you doing it?

[bob dunn]

As you have guessed I don,t know what I am doing . The plan is to split up the functions of the electrical system and put them on the smallest fuse that will not blow . First was the horn (15amp fuse)(it blows a 10amp) then ignition 30 amp at the moment but is running at a max of a little over 15 amps on start up and blows a 15 fuse after a few starts(so maybe a 20) . I have split the lights front and rear and instruments all on 10 amp (at the moment ) I will check these to see there running loads. The position of the ammeter is in series next to the fuse. What ever you know of these things is more than me . I have used some new wire of sim size or a little bigger ,the lights look a little brighter ,I am guessing because of better earthing and newer less resistant wire ( 40 year old wire can get no better with age).

[bob dunn]

Wireing now complete just checking of fuse rate to go.

[bob dunn]

http://3.bp.blogspot.com/-B4b450vmbxQ/VQdnfjF5ODI/AAAAAAAAAMg/KVQL5eSJsXI/s1600/DSCF7448.JPG

[bob dunn]

http://3.bp.blogspot.com/-B4b450vmbxQ/VQdnfjF5ODI/AAAAAAAAAMg/KVQL5eSJsXI/s1600/DSCF7448.JPG

[bob dunn]

Like the idea above,a bit steam punk.

[Saltddirk]

Hi Bob,
I have wired up the spit with 3 separate fuseboxes
The first one is in between the connectors at the A post and the loom, it protects the lighting circuits to the rear and the indicators (tail, stop, reverse, indicators both front and rear 1 fuse per side)
The second one protects the relays for headlights and horn plus the wires to the headlights ( I previously suffered a beginning of a fire because I only fused the relays and not the output to the headlights and one of the headlights had shorted)
The third one runs off the white wire at the ignition switch and protects the circuits that are life after ignition, the box I had had 10 circuits, which is possibly an overkill but it separates the circuits nicely, heater, wipers, accessories, ....

As said it is possibly an overkill, but I wanted to apply some logic to the fusing and separate as much as possible the common circuits.

D

[bob dunn]

It would help me to know the fuses that you are using on theses circuits.

[Saltddirk]

Hi bob,
A 55W bulb draws appx 5 Amps continuous so I have 15A on all lighting circuits with 2 bulbs, Indicators are 20A, 10A on the steering side of relais and 25A on the power side.

Actually the load is not important, what you want to protect is your loom against shorts and overheating while still allowing your normal loads to operate. Normal wire size in cars for general use (lights, relays, etc) is generally rated for 9A continuous draw so as a rule of thumb your fuse should not have a higher rating than 18A "blow", which in practice means a 20A fuse. Headlight wires are heavier gauge wires and have a rating of 17A, hence a maximum fuse size of 34A, or in practice again 30A.

Autosparks actually has a good table to identify the maximum load on their wires, in summary it reads for normal wire: mm square/amps: 0.65mm/6A, 1mm/9A, 2mm/17A, 3mm/25A or if you use their Thin wall wire(which has a greater number of strands for the given diameter) 0.5mm/11A, 0.75mm/14A, 1mm/17A, 2mm/25A 3mm/33A . Again this is the continuous load the wire can carry

As you can see I can not give you a one answer suitable for all situations, not knowing the size or quality of your wires, but except of the Starter motor (which is not normally fused ) and horns you should not need any fuses above 30A

and as they say, Caveat something, the above is simplified and if in doubt ask somebody more qualified than I am  

[Saltddirk]

I should have added for clarity sake that there are 2 ways to rate a fuse,
by the maximal current it can carry continuously or
by the peak current that causes it to blow
generally the little plastic blade fuses used in cars are identified by Amps "Blow" and they have generally a continuous carrying capacity of half the "Blow" value

I guess that did not help much 🙁

[esxefi]

you need a bit of leaway in the fuse rating as some components may cause a spike when activated which could lead to fuses blowing unnecessarily.

also I don't think that ignition circuits are normally fused,but that may have changed in todays current thinking.