Cable for 12 volt

[Manxcat54]

Hi

What is the cable size generally used in narrowboat wiring, I watch a lot of build video's and some seem to overkill the size, appreciated you need to consider the volt drop, also whilst on, what seems to be the preferred fuse type for both heavy cables ie battery, and fuses for lighting etc, are automotive blade fuses the norm?

Edited March 2 by Manxcat54

[BEngo]

The cable size is the size that produces an acceptable volt drop at the length and  working current in use.  This will usually mean a cable which could  safely carry more current than is needed.

 

Battery fuses are usually midi or mega fuses rated for the load and cable size Very few seem to pay any  attention to the interrupt capacity (AIC) of the fuses but this should be thoughh about, particularly if a large Lithium battery is installed.

 

Distribution fusing is often through  proprietary or bespoke panels which switch  and fuse the subsidiary circuits.  Sometimes a domestic consumer unit can be adapted, but then one needs to watch the DC ratings of the breakers.

 

There are also CAN bus solutions but these are not common.

 

N

[Quattrodave]

You need to calculate the guage if wiring using maximum ampage length of run and acceptable voltage drop.  Most people vastly under estimate 12v wiring.  Give us an example of what you want to power and how long the cable run is...

 

I was going to carry on but BEngo beat me to it 😁

Edited March 2 by Quattrodave

[Tony Brooks]

53 minutes ago, Quattrodave said:

You need to calculate the guage

 

That might be confusing to some because it is usually used for solid conductors. For boat work you should use either the number of strands and the thickness of each strand (28/0.30mm), or the conductor cross-sectional area. Confirming that the cable size needed is usually far greater than the safe current rating would suggest.

[ditchcrawler]

There is a useful calculator here ,Cable Size Calculator - Cable sizing and selection | 12 Volt Planet  but if you are installing a 12 volt fridge that doesn't follow the rules and needs a much heavier cable, normally calculated at 1mm CSA per meter run, so if the fridge cable run is 10 Mts then 10mm CSA cable is required'

[Tony Brooks]

5 minutes ago, ditchcrawler said:

There is a useful calculator here ,Cable Size Calculator - Cable sizing and selection | 12 Volt Planet  but if you are installing a 12 volt fridge that doesn't follow the rules and needs a much heavier cable, normally calculated at 1mm CSA per meter run, so if the fridge cable run is 10 Mts then 10mm CSA cable is required'

 

Usually only the length of EITHER the positive OR negative run, so 0.5mm CSA per metre for the length of the total run.

[Alan de Enfield]

1 hour ago, Manxcat54 said:

Hi

What is the cable size generally used in narrowboat wiring, I watch a lot of build video's and some seem to overkill the size, appreciated you need to consider the volt drop, also whilst on, what seems to be the preferred fuse type for both heavy cables ie battery, and fuses for lighting etc, are automotive blade fuses the norm?

 

Don't forget when using on-line calculators that you often need to enter the 'run-length', AND the run length is from the battery to the appliance and back to the battery NOT just from the battery to the appliance.

[Ronaldo47]

Automotive fuses continue to use the old practice of rating fuses by the current that will make the fuse blow. For other applications, such as the fuses in your 13A plug or domestic electronic equipment,  fuses are rated by the maximum current they can carry without blowing, which is normally half the automotive fuse rating. 

[GUMPY]

The only thing that I would use blade fuses for is feeds to battery monitoring equipment and the like.

[MtB]

1 hour ago, Ronaldo47 said:

Automotive fuses continue to use the old practice of rating fuses by the current that will make the fuse blow. For other applications, such as the fuses in your 13A plug or domestic electronic equipment,  fuses are rated by the maximum current they can carry without blowing, which is normally half the automotive fuse rating. 

 

And 

 

5 hours ago, BEngo said:

Battery fuses are usually midi or mega fuses rated for the load and cable size Very few seem to pay any  attention to the interrupt capacity (AIC) of the fuses

 

 

The more one reads up on fuses, the more one realises how complex and how misunderstood the subject is.

 

 

 

 

[ditchcrawler]

5 hours ago, Tony Brooks said:

 

Usually only the length of EITHER the positive OR negative run, so 0.5mm CSA per metre for the length of the total run.

The calculator I listed states "One-way circuit length (m)"

[cuthound]

2 hours ago, MtB said:

 

And 

 

 

 

The more one reads up on fuses, the more one realises how complex and how misunderstood the subject is.

 

 

 

 

 

And that is before you include slow blow, motor rated and the various specialist fuses.

 

The largest one I have ever come across is a 5000 amp one, used to protect a 15,050Ah battery, similar to the one below.

 

A little known fact is that they can provide much tighter protection than circuit breakers.

 

Edited March 2 by cuthound
Clarification

[Sailbadthesinner]

3 hours ago, cuthound said:

 

And that is before you include slow blow, motor rated and the various specialist fuses.

 

The largest one I have ever come across is a 5000 amp one, used to protect a 15,050Ah battery, similar to the one below.

 

A little known fact is that they can provide much tighter protection than circuit breakers.

 

That would do nicely for my planned upgrade to my LiFePO4 battery bank ; )