Battery cable temperature rating only 70 degrees C?

bedouin said:
I would have thought 70C was fine anyway. That is hot enough to burn your skin and there is no where in my engine space that is anywhere near that hot except actually touching the engine.
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I tend to agree. My engine bay is warm when I open the door to look at the fuel filters or whatever, but it’s not roasting hot. From memory I think 68°c is a common threshold for extinguisher capsules to activate, so if people’s engine spaces were reaching these kinds of temperatures many of them would be full of dry powder or FE36.

Pete
 
syvictoria said:
Sadly my cable does run very close to the engine - it's practically unavoidable in such a small space and the engine connections are, naturally, on the wrong side! Also I have a 70A alternator which I guess will be working hard at least some of the time. (If you've seen my other recent posts, I also have an engine which overheats!!!!! Although at least now only if it's ran for over 1.5hrs!)
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Surely 35mm2 cable must be rated at 200A+ so really won't be worried about 70A (don't forget power/heat is proportional to the square of the current as at 210A it is generating 9x as much heat as at 70A).

But I am not trying to talk you out of uprating it if you feel happier doing so.
 
pvb said:
Why not just get some proper cable from Germany? The 120ºC rated stuff I linked to in post 12. I've bought a few things from SVB and their service and delivery are excellent.
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Because it's not only already purchased, but also fitted! Anyway, I thought we were all supposed to be buying (Great) British these days! :rolleyes: :p :devilish:

(I have bookmarked SVB as a potential for any future purchases, thank you.)
 
syvictoria said:
Because it's not only already purchased, but also fitted! Anyway, I thought we were all supposed to be buying (Great) British these days! :rolleyes: :p :devilish:
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Well, as long as it isn't showing signs of melting, why are you so worried about it? There are more important things to worry about. In olden days we just used to use battery cable, I don't remember any of it having temperature ratings on it. As for buying British, virtually every website I've looked at today for tinned battery cable has been selling Oceanflex, which it seems is misleadingly marketed, so it's hard to know what you're buying.
 
pvb said:
Well, as long as it isn't showing signs of melting, why are you so worried about it? There are more important things to worry about. In olden days we just used to use battery cable, I don't remember any of it having temperature ratings on it. As for buying British, virtually every website I've looked at today for tinned battery cable has been selling Oceanflex, which it seems is misleadingly marketed, so it's hard to know what you're buying.
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Wise words I think. I love this forum, but it can make one (well, at least this one!) a little paranoid about doing everything perfectly!
 
syvictoria said:
Wise words I think. I love this forum, but it can make one (well, at least this one!) a little paranoid about doing everything perfectly!
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I wouldn't give it a second thought. If the engine bay is hot enough to heat the battery cables to in excess of 70 degrees you'll have more to worry about than battery cables.
 
Battery cables for normal vehicles rarely run at high currents for very long.
So a starter motor will only be used for a few seconds, an alternator will only charge at high current for a short time before the current tails off.
Boats are often different, a house bank can take a big charge for along time, relatively speaking.
Most boats run with very fat cables and low drops, so IsquaredR heating is not a problem.
But it's worth a thought.
70degC cable sounds a bit light for anything automotive though.
If in doubt, do the maths.
 
prv said:
I tend to agree. My engine bay is warm when I open the door to look at the fuel filters or whatever, but it’s not roasting hot. From memory I think 68°c is a common threshold for extinguisher capsules to activate, so if people’s engine spaces were reaching these kinds of temperatures many of them would be full of dry powder or FE36.

Pete
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We have a 4.4l Perkins in our engine room. With ventilation on it gets to 40degC here in the tropics with an air temperature outside of circa 30degC. Turn off the vent (or have the fan fail) and our engine space gets to 60degC. I suspect this is fairly typical. The water in the Perkins block runs at 88-90 degC according to the gauge so there will be a high radiant temperature off the engine block that might heat up the cables further
 
geem said:
We have a 4.4l Perkins in our engine room. With ventilation on it gets to 40degC here in the tropics with an air temperature outside of circa 30degC. Turn off the vent (or have the fan fail) and our engine space gets to 60degC. I suspect this is fairly typical. The water in the Perkins block runs at 88-90 degC according to the gauge so there will be a high radiant temperature off the engine block that might heat up the cables further
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You'd have to look at the maker's data sheet, but under those conditions, a cable rated for 90degC conductor max temp might typically be de-rated by 40% due to the temperature and again by 20% or more if the cable is bundled.
So a 35sqmm cable could be nominally rated at 150A, but only 70A or even less in a harsh situation.

But it's quite likely the alternator would either reduce its output or die first under heavy load with failed ventillation.
 
lw395 said:
You'd have to look at the maker's data sheet, but under those conditions, a cable rated for 90degC conductor max temp might typically be de-rated by 40% due to the temperature and again by 20% or more if the cable is bundled.
So a 35sqmm cable could be nominally rated at 150A, but only 70A or even less in a harsh situation.

But it's quite likely the alternator would either reduce its output or die first under heavy load with failed ventillation.
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The cable being discussed here is rated at 240a
 
PaulRainbow said:
The cable being discussed here is rated at 240a
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240A nominally, perhaps. But real world rating will depend on duty cycle, ambient air temperature, maximum allowable conductor temp, whether the cable is in free air or is bundled with one or more other cables, etc.
 
lw395 said:
You'd have to look at the maker's data sheet, but under those conditions, a cable rated for 90degC conductor max temp might typically be de-rated by 40% due to the temperature and again by 20% or more if the cable is bundled.
So a 35sqmm cable could be nominally rated at 150A, but only 70A or even less in a harsh situation.

But it's quite likely the alternator would either reduce its output or die first under heavy load with failed ventillation.
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Fortunately my boat is 24v so square law applies for current on mm2. Wiring is mostly the original high quality tinned stuff and is excellent condition. Its unusual in that it is tinned, then insulated then rubber insulated them pvc sheathed. A friend with similar age cable on his boat has insulation problems. The cable is tinned, insulated then rubber insulated. The insulation has degraded in to what feels like mush. Its horribly sticky and needs replacing
 
geem said:
Fortunately my boat is 24v so square law applies for current on mm2. Wiring is mostly the original high quality tinned stuff and is excellent condition. Its unusual in that it is tinned, then insulated then rubber insulated them pvc sheathed. A friend with similar age cable on his boat has insulation problems. The cable is tinned, insulated then rubber insulated. The insulation has degraded in to what feels like mush. Its horribly sticky and needs replacing
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The current rating of a cable does not depend on the voltage of a system. Obviously you get power proportional to the voltage for a given cable size.
If it's really rubber insulated, it could well be past its sell-by date.
Rubber cables often have a max life of 25years.
How old is the boat?
The other problem with older boats is often that they were designed around a particular use pattern and nowadays we use our boats differently, with fridges, heating, radar and other demands taken for granted.

Tinning is not at all unusual in rubber cables, it is required when using vulcanised natural rubber, to avoid the copper being attacked. Possibly an indication that it's natural rubber and due for the bin?
 
pvb said:
240A nominally, perhaps. But real world rating will depend on duty cycle, ambient air temperature, maximum allowable conductor temp, whether the cable is in free air or is bundled with one or more other cables, etc.
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There are so many variable conditions that the only possible rating is "nominal".

It was stated in post #22 "a 35sqmm cable could be nominally rated at 150A"

I corrected that, by posting that is was rated at 240v, i expected it went without saying that was a nominal rating.
 
lw395 said:
The current rating of a cable does not depend on the voltage of a system. Obviously you get power proportional to the voltage for a given cable size.
If it's really rubber insulated, it could well be past its sell-by date.
Rubber cables often have a max life of 25years.
How old is the boat?
The other problem with older boats is often that they were designed around a particular use pattern and nowadays we use our boats differently, with fridges, heating, radar and other demands taken for granted.

Tinning is not at all unusual in rubber cables, it is required when using vulcanised natural rubber, to avoid the copper being attacked. Possibly an indication that it's natural rubber and due for the bin?
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The boat is 39years old. The boat originally had a fridge, radar and heating. I have stripped out some redundant cables over the years and never found anything that would suggest insulation failure. Even the black rubber under the pvc sheath is perfect, possibly due to the protection of the pvc. The rubber doesn't contact the tinned cable. Each tinned core has its own coloured coded insulation.
 
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