What size/amperage wire to use.

[Tony Brooks]

2 minutes ago, ditchcrawler said:

I read another report last month of a fridge that played up due to the Loom wiring. He didn't say who made the loom.

all too common when "professionals" think they know better than manufacturers. I think there is some excuse when boaters do it but why they don't RTFM I don't know. maybe back to "electrcics are hard."

[Alan de Enfield]

2 minutes ago, ditchcrawler said:

I read another report last month of a fridge that played up due to the Loom wiring. He didn't say who made the loom.

I guess that why the vast majority of boats do not have pre-made up looms. The loom manufacturer does not know what 'use' the end user will actually use the cables for.

 

Someone could ask for a loom that does not include cabling for a fridge, the (new) owner of the boat decides to install a fridge and just taps-into a convenient cable and complains when it doesn't work properly.

 

I have done just that, but realised why it wasn't getting cold and could rectify the problem - maybe not everyone does and can.

[Tony Brooks]

18 minutes ago, Alan de Enfield said:

I guess that why the vast majority of boats do not have pre-made up looms. The loom manufacturer does not know what 'use' the end user will actually use the cables for.

 

Someone could ask for a loom that does not include cabling for a fridge, the (new) owner of the boat decides to install a fridge and just taps-into a convenient cable and complains when it doesn't work properly.

 

I have done just that, but realised why it wasn't getting cold and could rectify the problem - maybe not everyone does and can.

I know of one "professional" inland marine loom maker who uses his own calculation for fridge cable size, ignoring Danfoss, and

 when his "error" was pointed out seemed to conspire with the fridge converter to alter the fridge settings rather than admit they were wrong and supply the correct size cable. In thsi case they did know the cable was for a fridge. I very much doubt this one instance was an isolated one. I also know of a "scouse land" boat where the build fitted new batteries under warrantee to cure what was essentially and undersized fridge cable problem causing the boater to think they had flat batteries.

 

 

[Mad Harold]

16 hours ago, Mad Harold said:

Many thanks for the link.

All is much clearer now.

Used the calculator on the link.

Heater draws 10amps on start up,then 12amps,then briefly 14amps when the fan,fuel pump,and fan are going at full blast.Then settles to 1.4amps at cruise.These figures are from U Tube as I don't have an ammeter.

The manual states that the voltage required is 11.5  to  12.6.

Using the calculator for my boat ;IR 14amp (7m×.005W/m) the answer comes out as 8.5mm cable.

This thread has been most interesting and educational,and I am sure most helpful to others.

I don't think I am the only electrical thickie on CWF, (or am I?)

[Keeping Up]

When our boat was built, I specified the size of wiring that I wanted for both the fridge and also the stereo system (which would take high current peaks and was to be at the front of the boat). The builder assumed I had missed out a decimal point and used wire that was 10 times too small in cross-sectional area; despite his protests that it was now the same size as he normally used, I made him replace it with the size I had originally specified and it has never caused any volt-drop problems - even after we got a bigger stereo and a less tolerant fridge.

[Boater Sam]

With volt drop, I tend to think 'if in doubt, double it' and have never had a problem.

[nicknorman]

Just to summarise then, there are 2 separate considerations when selecting cable size: 1/ heat generated by cable and thus effect of temperature on cable insulation; 2/ voltage drop in cable. You have to select cable to satisfy both those issues.

 

Typically one issue will dominate and which one depends on circumstances. 1/ for short runs and or high voltage systems, and 2/ for long runs and or low voltage systems. But so long as you consider both issues, you can’t go wrong.Simple!