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Would it be a good idea to use a thicker wire for the battery ground of an A65? Possibly a 12 gauge wire or 10 gauge wire?

Thank you in advance

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It wouldn't hurt , but 10 gauge would be over-kil ... unless you happened to already have the wire hanging around .
and it wouldn't hurt to use a high-strand wire . ( more flexible and resistant to strain )
but its not necessary either .
... because the resistance of a wire ( it's ultimate ampacity )
has a lot to do with the length of the wire ( as well as it gauge )
... so smaller gauges of wire , at shorter lenghts
work fine for harness work .

Lucas properly sized the minimum gauge necessary for a bike harness ( to meet a price point )
as an owner , editing a harness , or building from scratch , the only 'harm' from running larger gauge wire is the expense
... and eventually the bulk diameter of any particular harness run

Last edited by quinten; 08/26/22 5:14 am.
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I have started fusing my wires from the main “ground” bolt on the frame to the battery. With this I can buy a bladed fuse holder with wire (in red) which is capable of carrying 25amp at 12v

This is a little overkill as nothing on an A65 should exceed 15 amp but you want the fuse to be the weakest link in any circuit.

As I make my own harnesses, I tend to use 17amp for the main wiring feed then all the rest of the wires in the loop at 16.5amp thin wall. (The 17amp being standard pvc cable and I switch between the two to try and obtain the colours where possible, and keeping the thin wall as a preference).

After having had a bike where part of the wiring loom set on fire because a previous owner used multiple sections of wire (in one section) made up of difference colours and gauges leading up to the H4 headlight using 55watt.

As I make them now the only issue I have ever had was with the plastic type glass fuse holder which eventually melted after 10 years pushing the fuse away into the softened plastic holder till it cut out…. Hence why I now use the blade fuse, and on the earth side as it’s now in one length, with fewer connections and the right colour.

Some may disagree with its placement but having tested it with a front brake cable switch that used to pop the fuse when applied, it showed that it worked fine for me.

Sorry if it over answered your question…


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It's well to remember, the 50c fuse will always protect itself
by allowing the $10,000 equipment to blow up first.

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No real point in running a heavier wire to ground but it won't hurt either
I like to fuse both sides of the battery having had a side cover on the B50 make contact with an exposed battery terminal
FWIW I now bolt a pigtail to the battery leads then paint over the terminals & bolts with liquid electrical tape.
If nothing else it prevents corrosion at the terminals and accidentially hooking the battery backwards
When rewiring alternator bikes I instal a fuse box which allows lower amperage fuses to be fitted to individual circuits which provide better protection than a big fuse
On the return line from the Zenner ( or whatever you use ) put ina fuse, just under the maximum output of the alternator.
So many times I have been on runs where a short inside the headlight, on the front brake switch or stop/tail light has melted all of the insulation off the wires while the rider was blissfully unaware till the smoke excaped
The single large fuse prevents the battery burning down the bike if shorted but does nt stop the alternator current destroying the entire loom


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When rewiring alternator bikes I instal a fuse box which allows lower amperage fuses to be fitted to individual circuits which provide better protection than a big fuse

That's interesting and when I rewired my Norton the other year I also fitted a main fuse from the battery and also a blade fuse box.

The main fuse from the battery is 15 amp whilst the fuses in the fuse box are 10 amp. The fuse box individually protects the ignition, tail light, headlight, and horn.

Recently, the main 15 amp fuse blew, which was puzzling as I thought the lower 10 amp fuse in the box would blow first. I then fitted a 20 amp main fuse and it was only then that the 10 amp fuse blew and showed that the problem was a wire to the ignition.

I don't know what size the main fuse should be but I'm getting the feeling that 15 amp is a bit on the low side, so I'm going to use 20 amp in future.


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I don't know what size the main fuse should be but I'm getting the feeling that 15 amp is a bit on the low side, so I'm going to use 20 amp in future.

fuses are not that precise . They are designed to melt when overheated . ( Current squared x the tiny amount of fuse resistance x milliseconds )
... but a particular fuse May diffuse Heat better or worse ... under certain conditions

Overheating can be from the current flowing through the fuse , ( the fuse design melt )
or the fuse itself , run in a hotter environment . ( which requires some de-rating from the fuse label )

a 15 amp fuse may blow at 11.25 amp ( above 25C , 77°F) ( 75% rating )
and a 20 amp fuse May blow at 15 amps ( above 77°)

fuses are generally ...or may need to be ... "oversized"
to prevent nuisance blowing . ( but never fused higher than the wires rating )

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All fuses are not created equal
There are fast blow, slow blow and everything in between.
A fuse protecting a delicate electronic circuit will blow instantly, as soon as the current exceeds the fuse rating
A fuse protecting a motor starting on load may take over double the fuse rating for maybe a minute


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fuses are generally ...or may need to be ... "oversized"
to prevent nuisance blowing . ( but never fused higher than the wires rating )

Quote
All fuses are not created equal
There are fast blow, slow blow and everything in between.

Thanks for the info, the way I wired the bike was to use 25 amp (2mm section) between the battery earth (positive) and negative connection to the fuse box. The main fuse is in the connection from the negative terminal to the fuse box and is of the mini blade type.

The fuses in the fuse box are also of the mini blade type, and the output wires from the fuse box use 16 amp (1mm section) wire leading to the components.

These mini-blade fuse boxes are really good and have a LED to show which fuse has blown, so a worthwhile mod over the standard wiring. I'm not sure whether these mini blade fuses have a slow or fast blow rating but they are a standard automotive product.

I've now fixed the problem which was simply a badly routed wire chafing against the frame, so all is well again and I had a great spirited ride today.

I think I've got the wire rating and fusing correct, so hopefully, the fuse box fuses will blow first if there is another problem.

Last edited by gunner; 08/29/22 6:15 pm.

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Originally Posted by gunner
That's interesting and when I rewired my Norton the other year I also fitted a main fuse from the battery and also a blade fuse box.


I don't know what size the main fuse should be but I'm getting the feeling that 15 amp is a bit on the low side, so I'm going to use 20 amp in future.


Blade fuses are marked with their continuous rating so a 15A blade fuse should blow at around 30A and 40A for a 20A fuse etc.
https://www.arc-components.com/durite-standard-automotive-blade-fuse-15a-blue.html
"Durite 15A blue automotive standard blade or spade fuse.

Blue colour coded for easy identification.
15 Amps continuous rating, 30 Amps blow rating."

"Durite 20A yellow automotive standard blade or spade fuse.

Yellow colour coded for easy identification.
20 Amps continuous rating, 40 Amps blow rating."

However, the Lucas system was to describe fuses by the blow rating although occasionally fuses are marked with both.
[Linked Image from i.postimg.cc]


The standard Lucas glass fuse for Commandos and other British vehicles for instance was 35A blow rating (17A continuous) which is why it's important not to replace a 35A blow fuse with 35A continuous as it won't blow until 70A.

https://www.arc-components.com/durite-standard-automotive-blade-fuse-35a-aqua-green.html
"Durite 35A aqua green automotive standard blade or spade fuse.

Aqua green colour coded for easy identification.
35 Amps continuous rating, 70 Amps blow rating."

https://triple-c.com/Products/GLASS_FUSE_35A_1-1_4__PACK_OF_5/FUSE35%7C5

https://triumphtr6.info/Manuali/fuses.pdf

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Thanks LAB for the very useful info, based on what you mentioned, I think I should be safe using a 20 amp main fuse which is slightly oversize compared the Commando 35 amp blow rating.

In comparison, the 20 amp blade fuse is rated as 20 amp continuous rating, 40 amp blow rating. The Commando glass fuse is 17 amp continuous, 35 amp blow rating.

With any luck, the 10 amp continuous fuses in the fuse box will now blow first if there is an issue.


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Originally Posted by gunner
Thanks LAB for the very useful info, based on what you mentioned, I think I should be safe using a 20 amp main fuse which is slightly oversize compared the Commando 35 amp blow rating.

In comparison, the 20 amp blade fuse is rated as 20 amp continuous rating, 40 amp blow rating. The Commando glass fuse is 17 amp continuous, 35 amp blow rating.

With any luck, the 10 amp continuous fuses in the fuse box will now blow first if there is an issue.

Originally Posted by gunner
The fuses in the fuse box are also of the mini blade type, and the output wires from the fuse box use 16 amp (1mm section) wire leading to the components.

Why are you using a fuse which is higher rated than the wiring loom it’s trying to protect?

If you have a fuse box and have a wire for each type of component, especially for electronic ignition and another for the regulator/rectifier.

If I remember right the average EI, can reliably rated for a 7amp fuse. The reg/rec would be fine at 15amps if using a 180w unit, you could get away with a 10amp if using a standard 120w setup, lighting would be next fuse size up from what they calculate out at with a 60w main beam, stop and tail 7 or 10 amp would be fine. 10 amp being better still - you can wire the stop light in that or fuse it separately, probably alongside the horn.


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68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (now rebuilt)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

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What those fuses do not state is the time factor.
IE how long will a 17a cont 35a blow fuse take to blow at say 25a?
They are 10c items and are about as accurate as a smiths tacho.......

Andy was dead right it's all about fuse types, to effectively protect semiconductors
say on an EI, a 'T' type should be used, lights require gf type etc. Automotive fuses,,,,,,,,who knows?

Still,, any of them are better than none at all.

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Why are you using a fuse which is higher rated than the wiring loom it’s trying to protect?

Good point and for clarity, the wires leading from the fuse box to the headlight, Pazon Ignition, Horn, tail light, etc. use a thin wall 1mm cross-section with 32/0.20 strands, the wire is rated at 16.5 amp continuous.

The fuses currently protecting each of these circuits are rated at 10 amp continuous, and 20 amp blow. Perhaps this is a little too high and won't protect the wiring or components sufficiently, so I will change to a 7.5 amp continuous, 15 amp blow version.

The wiring from the battery to the fuse box is also a thin wall type but 2 mm cross-section with 32/0.30 strands, rated at 25 amp. The closest fuse with a blow rating lower than 25 amp is the 10 amp which blows at 20 amp. This seems a little low so I'm now considering doing away with the main fuse altogether as its not really needed, the fuse box fuses should do their job.


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Originally Posted by gunner
Good point and for clarity, the wires leading from the fuse box to the headlight, Pazon Ignition, Horn, tail light, etc. use a thin wall 1mm cross-section with 32/0.20 strands, the wire is rated at 16.5 amp continuous.

Original late model British bike harness (including the Commando) including the main battery wiring was usually 14/32 SWG (14 strands of 0.0108" dia.) with an Amp rating of, I believe, around 7.5A - 8A.* and usually, with the one (17A continuous) 35A blow main fuse that I know from experience blows before damage is done to the wiring.

*The slightly larger gauge modern equivalent standard PVC cable is 14/0.30 1.0mm², 8.75A...

https://www.autoelectricsupplies.co.uk/product/66/category/11

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Originally Posted by L.A.B.
Originally Posted by gunner
Good point and for clarity, the wires leading from the fuse box to the headlight, Pazon Ignition, Horn, tail light, etc. use a thin wall 1mm cross-section with 32/0.20 strands, the wire is rated at 16.5 amp continuous.

Original late model British bike harness (including the Commando) including the main battery wiring was usually 14/32 SWG (14 strands of 0.0108" dia.) with an Amp rating of, I believe, around 7.5A - 8A.* and usually, with the one (17A continuous) 35A blow main fuse that I know from experience blows before damage is done to the wiring.

*The slightly larger gauge modern equivalent standard PVC cable is 14/0.30 1.0mm², 8.75A...

https://www.autoelectricsupplies.co.uk/product/66/category/11

Probably also where Lucas got their reputation for failure from? 🤷‍♂️


Originally Posted by gunner
Quote
Why are you using a fuse which is higher rated than the wiring loom it’s trying to protect?

Good point and for clarity, the wires leading from the fuse box to the headlight, Pazon Ignition, Horn, tail light, etc. use a thin wall 1mm cross-section with 32/0.20 strands, the wire is rated at 16.5 amp continuous.

The fuses currently protecting each of these circuits are rated at 10 amp continuous, and 20 amp blow. Perhaps this is a little too high and won't protect the wiring or components sufficiently, so I will change to a 7.5 amp continuous, 15 amp blow version.

The wiring from the battery to the fuse box is also a thin wall type but 2 mm cross-section with 32/0.30 strands, rated at 25 amp. The closest fuse with a blow rating lower than 25 amp is the 10 amp which blows at 20 amp. This seems a little low so I'm now considering doing away with the main fuse altogether as its not really needed, the fuse box fuses should do their job.

With the clarification, I’d stick with what your doing now, the continuous rating is below that of the wire, and that works fine for me. I had a bike where the PO used a 30a bladed fuse in the system. The loom set on fire before it blew. The only time it did blow was when the zenner failed, it was pretty darn hot then!


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71’ A65 823 Thunderbolt (now rebuilt)
67’ D10 sportsman (undergoing restoration)
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Originally Posted by NickL
What those fuses do not state is the time factor.
IE how long will a 17a cont 35a blow fuse take to blow at say 25a?
They are 10c items and are about as accurate as a smiths tacho.......

Andy was dead right it's all about fuse types, to effectively protect semiconductors
say on an EI, a 'T' type should be used, lights require gf type etc. Automotive fuses,,,,,,,,who knows?

Still,, any of them are better than none at all.

Nothing stopping you using slow or fast blow 20mm fuses, but you start to run a system which is more sensitive than any mass produced vehicle today and of which probably protects more sensitive semiconductor/components.


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Fast and Slow blow fuses are not the same as T or gf i'm afraid.
Those are made to a standard, not like 99% of automotive junk.

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