Battery cable - one size ???

[sarabande]

In a perfect world, battery cables would be sized according to the load and other specs.

However, in the interests of economy and logistics, if one had to go for one size battery cable on an ordinary 12v boat (32ft, two domestic battery banks, one engine battery, all usual sizes) would it be practical to use just one size, and if so, would that be 35, 50, or 70mm² ?

I am looking at 12v Planet as a possible supplier of c10m each of red and black, Any other recommended dealers please ?

 

[john_morris_uk]

In a perfect world, battery cables would be sized according to the load and other specs.

However, in the interests of economy and logistics, if one had to go for one size battery cable on an ordinary 12v boat (32ft, two domestic battery banks, one engine battery, all usual sizes) would it be practical to use just one size, and if so, would that be 35, 50, or 70mm² ?

I am looking at 12v Planet as a possible supplier of c10m each of red and black, Any other recommended dealers please ?

No recommendations for supplier or size, but if you want to borrow my hydraulic crimping tool for battery cables please ask... It copes with most sizes. I've also got some red and black heat shrink to make the crimped ends look very professional. (In fact the end result is exactly what the professional would produce...)

 

[PaulRainbow]

In a perfect world, battery cables would be sized according to the load and other specs.

Not a perfect World, all Worlds. Cabling has to be rated high enough for the loads that it has to carry, and take into account voltage drop.

However, in the interests of economy and logistics, if one had to go for one size battery cable on an ordinary 12v boat (32ft, two domestic battery banks, one engine battery, all usual sizes) would it be practical to use just one size, and if so, would that be 35, 50, or 70mm2 ?

I am looking at 12v Planet as a possible supplier of c10m each of red and black, Any other recommended dealers please ?

You can just use one size battery cable, in fact you should just use one size, in most applications, as the domestics are usually required to be able to start the engine in the event of a flat/dead battery. So, if you size all battery cables (between batteries, between banks, up to the isolator switches and to the starter motor) to be capable to carry starter motor currents, you only need a single size. From the domestic isolator you can down size to cater for domestic loads (again allowing for voltage drop).

Typical 10m yacht with a smallish diesel (usually less than 50hp) would be OK with 35mm cable, in terms of current rating, providing the cables aren't running great distances.

Lots of suppliers out there, 12v planet are pricey for battery cables. This Ebay seller is reputable if you don't mind un-tinned cable https://www.ebay.co.uk/itm/Flexible...ef65e5215:m:mtAQ2ZxS3Ex26dCs-JDL8-Q:rk:3:pf:0

Tinned is not much more https://www.ebay.co.uk/itm/Marine-T...af0747b32:m:mmBbRxeTmwHahdrsEAUgbYQ:rk:1:pf:0

Just examples Tim, have a shop around.

 

[Alex_Blackwood]

In a perfect world, battery cables would be sized according to the load and other specs.

However, in the interests of economy and logistics, if one had to go for one size battery cable on an ordinary 12v boat (32ft, two domestic battery banks, one engine battery, all usual sizes) would it be practical to use just one size, and if so, would that be 35, 50, or 70mm² ?

I am looking at 12v Planet as a possible supplier of c10m each of red and black, Any other recommended dealers please ?

Usual suspects, work out your max volt drop charging current etc. and size everything for that. May mean you are oversized on one bank.

 

[Red Panda]

I'm working through the same exercise myself, and for my 32" boat with a little Yanmar 2GM I've calculated that 35mm should be fine.
I'm also putting together a large order with 12v Planet. I find they're a little more expensive than you could possibly get if you split your order over lots of different vendors, but as a one-stop shop they have nearly all I need.

 

[prv]

Not a perfect World, all Worlds. Cabling has to be rated high enough for the loads that it has to carry, and take into account voltage drop.

Yes, but it doesn't matter if some of it is too big, which is his point, in order to only buy one reel of each colour instead of precisely the correct size for each run.

Pete

 

[Graham_Wright]

It;s worth looking at volt drops. All the cables, breakers, switches and connections contribute to loss. You might find 8 volts at a light fitting as I did. Work back to the cause.

A salutary experience!

 

[PaulRainbow]

Yes, but it doesn't matter if some of it is too big, which is his point, in order to only buy one reel of each colour instead of precisely the correct size for each run.

Pete

Indeed, which is why i said ;

You can just use one size battery cable, in fact you should just use one size, in most applications, as the domestics are usually required to be able to start the engine in the event of a flat/dead battery. So, if you size all battery cables (between batteries, between banks, up to the isolator switches and to the starter motor) to be capable to carry starter motor currents, you only need a single size.

 

[TQA]

Just make sure that whatever you buy is marine grade tinned wire.

 

[Boathook]

I would use one size cable that is big enough for existing loads and any new loads.

 

[PaulRainbow]

It;s worth looking at volt drops. All the cables, breakers, switches and connections contribute to loss. You might find 8 volts at a light fitting as I did. Work back to the cause.

A salutary experience!

I would use one size cable that is big enough for existing loads and any new loads.

Worth noting the OP is asking about main battery cables. 35mm battery cable is rated at 240 amps, doubt if he'll fit anything that draws more current than that

 

[RichardS]

Worth noting the OP is asking about main battery cables. 35mm battery cable is rated at 240 amps, doubt if he'll fit anything that draws more current than that

That's reminiscent of a recent discussion about domestic appliances and wire gauges over in The Lounge. I've just installed a 10.8kW single appliance and we were discussing whether there is anything any larger than that possible in a house. If that appliance were 12V it would draw a steady 900 amps .... which puts our boat wiring into perspective, sort of.

Richard

 

[pvb]

I've just installed a 10.8kW single appliance and we were discussing whether there is anything any larger than that possible in a house.

We have a 15kW pool heater....

 

[PaulRainbow]

That's reminiscent of a recent discussion about domestic appliances and wire gauges over in The Lounge. I've just installed a 10.8kW single appliance and we were discussing whether there is anything any larger than that possible in a house. If that appliance were 12V it would draw a steady 900 amps .... which puts our boat wiring into perspective, sort of.

Richard

Mira shower ?

Not many things in a house that use more power, some cookers can be a few kw higher.

I have a customer whose boat has a full electric cooker, electric hob, dishwasher, washer dryer, TV's in every cabin, microwave and two showers. Try running that from your 16a shore power

 

[RichardS]

Mira shower ?

Not many things in a house that use more power, some cookers can be a few kw higher.

I have a customer whose boat has a full electric cooker, electric hob, dishwasher, washer dryer, TV's in every cabin, microwave and two showers. Try running that from your 16a shore power

Yes, a Mira shower.

The cooker comparison is why the subject came up. I thought that cooker spurs in UK homes are usually 30A which would equate to about 7kW but I wouldn't be surprised if some cookers with a leccy oven and leccy rings need more than 30A.

As for PVB's pool heater .... that certainly is a monster although I'm not sure whether is classifies as a domestic appliance.

Richard

 

[PaulRainbow]

Yes, a Mira shower.

The cooker comparison is why the subject came up. I thought that cooker spurs in UK homes are usually 30A which would equate to about 7kW but I wouldn't be surprised if some cookers with a leccy oven and leccy rings need more than 30A.

Used to be mainly 6mm cable and a 30a fuse, some of the fancy oven/hob combos would need 10mm cable and 40a MCBs.

As for PVB's pool heater .... that certainly is a monster although I'm not sure whether is classifies as a domestic appliance.

I'm guessing it's not on a 13a plug

 

[NorthUp]

My preference (for what its worth) would be for 50 mm sq. cable. Tinned would be nice, but is not essential if you use heat shrink sleeving on the terminals- colour coded so you just need to buy black cable.
Any decent engineering supplier will have double insulated welding cable at a reasonable price.

 

[pvb]

I'm guessing it's not on a 13a plug

Correct! Before we installed it, the electricity people kindly laid on 3-phase power to the house.

 

[PaulRainbow]

My preference (for what its worth) would be for 50 mm sq. cable. Tinned would be nice, but is not essential if you use heat shrink sleeving on the terminals- colour coded so you just need to buy black cable.
Any decent engineering supplier will have double insulated welding cable at a reasonable price.

If there's one thing i really hate, it's using all one colour cable, with heat shrink on the ends !

35mm cable is 240a, not many 10m yachts need more than that to start a small engine.

 

[Poignard]

.... I've also got some red and black heat shrink to make the crimped ends look very professional. (In fact the end result is exactly what the professional would produce...)

That's true, and you can buy adhesive-lined heatshrink that gives even better protection against moisture.

Here's one I did earlier:

View attachment 75621

(Before anyone comments, the small wires have since been properly clipped up )