straps BATTERY STRAPS.

[Guest]

or pi d²/4 If my memory serves me correctly?

[Chewbacka]

Area of a circle is the radius squared multiplied by pi (3.14)

so 7mm diameter is a radius of 3.5mm

 

Area=3.5*3.5*3.14=38mm2

 

Assuming the diameter to be about 7mm, then the nearest standard size would be 35mm2

[MHS]

 

 

Which skool did you go to?!!

Oops. A very good comp actually, but too many years since I studied/skived at skool!!

 

No, that's the circumference. Area is πr²

Guilty as charged. Is there a pi symbol on an iPhone? Edited February 5, 2017 by MHS

[WotEver]

Everyone is assuming that the 7mm is the diameter of the copper. From the OP it sounded to me that it was the OD of the cable. Assuming 2mm thickness for the insulation gives 3mm diameter for the copper, or 7mm² cable as was suggested very many posts back.

[GUMPY]

Whatever it is its to thin.

[GUMPY]

This seems an unduly pessimistic rating, even in a poorly ventilated engine space, given that 35 Sq mm cable is nominally rated at 240 amps.

Can you show a reference for this, seems remarkably optimistic.

Normal industry ratings are 178amps single core in free air derated to 154amps when 2cables bunched and 131amps 3 cables bunched.

[Chewbacka]

Can you show a reference for this, seems remarkably optimistic.

Normal industry ratings are 178amps single core in free air derated to 154amps when 2cables bunched and 131amps 3 cables bunched.

and don't forget to derate if the cable is in a hot engine room, the derate factor at an ambient of 60c is 50% - see post 22

[MtB]

My batteir

 

Whatever it is its to thin.

 

 

The OP hasn't clarified whether the 7mm diameter included the insulation or no.

 

I've just measured a piece of 35mm² cable and the outside diameter including the insulation is 11.7mm

[JACK FELL]

TO ALL RESPONDENTS,

 

GOOD EVENING.

 

OOPS!!! I OPENED A CAN OF WORMS HERE AND I CANNOT GET THE LID BACK ON .

 

MUST GO NOW I'VE GOT A "PI" IN THE OVEN.

 

BEST TO ALL,

JACK

[Guest]

TO ALL RESPONDENTS,

 

GOOD EVENING.

 

OOPS!!! I OPENED A CAN OF WORMS HERE AND I CANNOT GET THE LID BACK ON .

 

MUST GO NOW I'VE GOT A "PI" IN THE OVEN.

 

BEST TO ALL,

JACK

Best pies are in Wigan if you are ever passing through

[WotEver]

I've just measured a piece of 35mm² cable and the outside diameter including the insulation is 11.7mm

Yup. 7mm diameter copper with 2mm insulation.

 

Ish.

[Keeping Up]

Can you show a reference for this, seems remarkably optimistic.

Normal industry ratings are 178amps single core in free air derated to 154amps when 2cables bunched and 131amps 3 cables bunched.

Well there's this one for example

http://www.acornengineer.co.uk/tinned-battery-starter-cable-240amp-black-cut-to-length

[GUMPY]

Well there's this one for example

http://www.acornengineer.co.uk/tinned-battery-starter-cable-240amp-black-cut-to-length

looks like a cable rating version of peak music power, at 240amps continuous 35mm cable would be very very hot and the insulation would be starting to melt!

This link is to a data sheet for cable ratings from a manufacturer rather than a reseller

http://www.aeicables.co.uk/cgi-bin/getds.pl?docid=C12.pdf

It does seem to me that automotive companies just use fantasy ratings for their cables...........

Edited February 5, 2017 by Loddon

[Chewbacka]

looks like a cable rating version of peak music power, at 240amps continuous 35mm cable would be very very hot and the insulation would be starting to melt!

This link is to a data sheet for cable ratings

http://www.aeicables.co.uk/cgi-bin/getds.pl?docid=C12.pdf

It does seem to me that automotive companies just use fantasy ratings for their cables...........

I suspect they are working on the assumption that big currents are only transient on a boat - engine cranking, Inverter surges etc and the rest of the time the 'working' current is much lower. Not many battery banks could manage 240A for more than a few minutes. But it is wrong to state 240A as a continuous rating when it isn't. Likewise they don't mention derating in hot engine bays.

[Keeping Up]

They aren't the only retailers who assume this rating of almost 7 amps per sq mm, I admit I only looked at two, them and Marinestore, as I have purchased items from both in the past so had them bookmarked.

 

Luckily all my cables are 70 mm to avoid voltage drop so I never gave much thought to their current rating.

[Neil Smith]

My battery links are 50mm and battery to inverter charger are 70mm.

 

Neil