# 2nd battery wire and fuse size



## joedenise (Jul 20, 2007)

help 

confused about wire size and fuse size

Clive's diagram show 25amp fuses but reading old posts people recommend 20 amp wire 

only need about 1 metre cable between batteries.

joe


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## CliveMott (Mar 10, 2008)

Its not the amperage capability of the wires thats important but the voltage drop. When you only have 12 volts to start with loosing half a volt is nearly 5% loss.

If you are not running aditional equipment like an inverter for example and the linking wires are short then 6 sqmm should be OK. If they are longer than a couple of feet then 10 sqmm copper.

Howzat?

C.


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## joedenise (Jul 20, 2007)

Thanks Clive. Where can I get fuses for that thickness of wire?

Joe


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## Tezmcd (Aug 3, 2009)

current capacity depends on the type of cable

6mm will easily get you 30Amps and 10mm will easily get you 40amps on almost any cable

With some types of cable 10mm will get you damn near 100A with the right cable type and grouping factors


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## sallytrafic (Jan 17, 2006)

Fuses from here

>Vehicle wiring products<

Normally size cable for load then you fuse for cable protestion and hence match the fuse closely to the current carrying capability of the cable in this case you are putting heavy cable in to lessen volt drop so fuse for highest charging current or load rather than for ultimate current carrying spec of cable.


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## teensvan (May 9, 2005)

Hi.

I would suggest 10-16mm cable. An inline fuse holder can be bought from most car accessory shops. Get the spade style fuse holder same as car fuses. You then have a fuse range from 5 to 40 amp. Or go for the large spade fuse which goes up to 50 amp.

steve & ann -------------- teensvan


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## Spacerunner (Mar 18, 2006)

Halfords sell ready-made battery leads in an assortment of lengths.


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## joedenise (Jul 20, 2007)

Thanks all for your replies. Just ordered all I need on-line from Frank's link.

Joe


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## CliveMott (Mar 10, 2008)

I advise not to use any bigger than 25/30 amp fuses in normal blade holders. I know they are specified up to 40 amp but the long termreliability of them is not good at these currents. Use the next size fuse and holder up.


C.


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## joedenise (Jul 20, 2007)

Hi Clive

Ordered megafuses - 20 amp continuous, 40 amp max. The fuse in the MH is 50amp so went for one lower. Do you think this is OK?

Joe


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## sallytrafic (Jan 17, 2006)

Mega fuses and fuseholders don't come in that range have you ordered maxi?

I used midi for my installation


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## joedenise (Jul 20, 2007)

frank

on the site you recommeded look at mega blade fuses

joe


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## sallytrafic (Jan 17, 2006)

No sorry I can only see maxi blade fuses at 20A mega start at 100A


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## joedenise (Jul 20, 2007)

sorry frank to much vino calapso
should be maxi-blade 

joe


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## sallytrafic (Jan 17, 2006)

Then I tend to agree with Clive. Lets face it the fuse is put in this position to cater for a catastrophic short circuit. In the event that happens a lot of energy will have to go somewhere when the fuse blows. An enclosed fuse holder is best. I wish I had given more advice when you asked - sorry.


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## CliveMott (Mar 10, 2008)

Last week I answered a readers letter. He had a fried fuse and fuse holder for the main battery fuse once a year. Each time the wire was cut back and new fuse and holder fitted. The fuse size was 40 amp. Its just too much! The heat generated causes oxidation of the metal components which increases the surface resistance. So they get even hotter. So they oxidise more. etc. etc.

The Fuses marketed as "MEGA FUSES" on that web site are actually to a DIN standard on 50mm stud centres and fuses to fit it are available down to 35 amps. I used these in our previous motorhome and also for powering significant "add on" bits in our new motorhome.

Your local Fork Lift Truck repair man will keep stocks of these. Google or your local Yellow pages.


C.


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## joedenise (Jul 20, 2007)

thanks Clive. 

I know a very good fork lift truck man, will see him Monday, if not will rob the fork lift truck I drive!

Joe


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