# Best way to join thick and thinner cables?



## Christine600 (Jan 20, 2011)

From my battery I have a finger thick cable. With large cable lugs on both ends. 

From my solar controller I have a short 6mm2 cable and a fuse.

We have temporarily joined the two cables by threading the lugs onto a bolt and tightened the nut. So we can see that the solar system works.

But how do the pros do this? One fat and one much slimmer cable?


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## gillnpaul (Jan 6, 2007)

Hi Christine...
The easy answer is DONT !
A heavy duty cable is capable of carrying a very heavy current, a thin cable is only for a lighting circuit. 6mm cable is very light compared with battery cable.
Seek advice from a qualified sparky is my advice

Hope this helps (or at least stops a fire )
Paul


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## olley (May 1, 2005)

You need to join them via a fuse. 6mm cable I think is rated at about 45amps, but you only need one bigger than the load you solar panels will impose on it.

Ian


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## rayrecrok (Nov 21, 2008)

Hey up.

You don't join cables, you take them back to the battery terminals and fix them on there straight onto the battery.

ray.


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## ovalball (Sep 10, 2008)

Hi just had the same dilemma.Ended up replacing my battery clamps with a clamp with 3 bolt on connectors,1 large and 2 smaller ones.Worked perfectly.Just remember to put an inline fuse as near as possible to the battery for eac wire.For your solar panel I would think a 20 amp would be right.The fuse is there to make sure you don't overload the cable so you will be well in if using a 6mm cable.If you look at my thread about battery clamps(posted earlier this week)there are a few pictures of clamps available.I went for the one in the final picture,the one with 3 bolts on.Arrived the following day and was really easy to fit.Good luck!


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## pippin (Nov 15, 2007)

Read the OP carefully again.

Quite clearly she states that the thin cable HAS A FUSE.


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## bigtwin (May 24, 2008)

There is insufficient information available in the original post to be able to answer the question with any degree of confidence.

There are circumstances when it would be perfectly acceptable to join two differently rated cables in series. 

Ian


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## Christine600 (Jan 20, 2011)

gillnpaul said:


> The easy answer is DONT !


Good advice, but the thin cable is heavy enough. It just does not have the right connector. But the fat cable has. It's overkill but it has this nice lug.


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## Christine600 (Jan 20, 2011)

Here is a picture - probably easier to understand than my ramblings:










This is how we connected it to test that the solar panel and the Ctek box work. It was just a test and was disconnected again.

The fat red cable from battery+ to a thinner 10mm2 cable (not 6 like I said earlier) and then a fuse and finally a cable to the Ctek. The 10mm2 cable is thick enough. But the fat red one had the right lug for the battery.

When we have the right cable it will go along the wall to the other battery+ to the far left in the picture.

We used a fat bolt and nut - but how would a pro do this?


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## sideways (Jun 2, 2008)

The wire that's carrying the fuse holder has a yellow eye crimped on it use a longer piece with a yellow eye with an 8mm hole and bolt it directly to your battery doing away with the red cable.


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## BillCreer (Jan 23, 2010)

If the bolt were not sticking out too much at the back I'd just insulate the connection you have made with some "heat shrink"
I'm not a "professional" but I do know that it would make it a safe connection.


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## Christine600 (Jan 20, 2011)

You are very helpful, guys! 



 BillCreer said:


> If the bolt were not sticking out too much at the back I'd just insulate the connection you have made with some "heat shrink"


I have googled heat shrink and see the tubes before and after. But what do you use to heat them up so that they shrink? Boiling? Hairdryer?


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## philoaks (Sep 2, 2008)

Hairdryer!

To be honest that would still be a temporary fix. Best thing as mentioned earlier is to get some 10mm cable to extend from the fuse to the battery and fit the appropriate crimp connections at each end. If you haven't got a crimping tool then you could probably get an auto electrical engineer to do it for you for the price of a pint!

Just in the interim (IMO) you could leave it with the bolt connection but make sure it's well wrapped in insulating tape and strap the cable down to stop it rubbing against anything. 

Phil


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## kimbo4x4 (Jun 29, 2008)

Heat shrink. Use a hot air gun ( paint stripper)


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## Christine600 (Jan 20, 2011)

Oh we have plenty of 10mm2 cable. Only the thick red cable had this nice lug that fitted the battery. 

We have talked about using the nut connection, but running the cables along the wall and connecting to the second battery+ just behind the green battery watch box.

Then we could lead the cable trough a box so that the nutty connection were isolated inside the box. And cable fastened to the wall elsewhere. Electricity wise we think the current cables are OK. How does that sound?


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## philoaks (Sep 2, 2008)

> Then we could lead the cable trough a box so that the nutty connection were isolated inside the box. How does that sound?


To be honest that sounds like a bodge job to me. Sorry if that sounds harsh but I'm being honest 

In your first post you asked how the pro's would do it. My career in auto electrics ended many years ago but in my DIY opinion I'd say that a pro would have a single cable run with the correct lugs fitted to enable connection to the battery. Ideally the fuse would be located as close to the battery as is practical.

Having said all that, it's your van and the way that you suggest doing it sounds as though it would be safe :wink:

Phil


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## Christine600 (Jan 20, 2011)

Thanks Phil - it's what I wanted to hear. Don't want a bodge job.


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## tony50 (Oct 16, 2007)

Christine600 said:


> gillnpaul said:
> 
> 
> > The easy answer is DONT !
> ...


If there is no reason why you are joining a large cable to a thinner cable we always solder them together if possible if easily got at , then make sure we clean off flux and then insulate with shrinkage tube with heat.

Tony A


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