DC - high current and heat (1 Viewer)

Jan 27, 2013
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If like me you run lots of kit via an inverter it's worth checking that you have good contacts on all the electrical connections. Last year a fuse holder began to deform and melt causing me some angst on a hot day!

When replacing this is fuse block I tinned the end of the multiple strands on the thick cables to ensure a good contact.

Today I was checking there's no overheating!
 

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Techno

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I crimp a tube lug on the end then cut off all but the crimp, this makes a really solid object for screw terminals to bite on.
 

Fireman Sam

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If like me you run lots of kit via an inverter it's worth checking that you have good contacts on all the electrical connections. Last year a fuse holder began to deform and melt causing me some angst on a hot day!

When replacing this is fuse block I tinned the end of the multiple strands on the thick cables to ensure a good contact.

Today I was checking there's no overheating!

You’d be horrified by the number of fires caused by resistance heating (loose or bad connections). Good, helpful post Sidney.

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scotjimland

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I crimp a tube lug on the end then cut off all but the crimp, this makes a really solid object for screw terminals to bite on.

Sorry Techno.. but If I am understanding this method correctly.. I have to disagree.

Modern terminal blocks don't have screws biting on the strands, rather the strands are compressed between two small plates..

A solid copper sleeve does not make a good connection.. the plates cannot compress it.

I worked offshore on oil and gas platforms as an instrument tech, this would not be allowed, nor would soldering the stands together ..same effect.

Even if it's the bog standard chocolate block connector the same principal applies. Soft strands make a far better connection than a solid piece of copper.
 

Techno

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DC fuse holders either have a stud (preferable) or a grub screw terminal. This is not Merlin Gerin :roflmto:
The flat face of a Hexagonal crimp is perfect for a large grub screw
BTW instrumentation does not carry huge currents which is the point of this topic
Example
CA_10191217522913-L.jpg
 
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scotjimland

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DC fuse holders either have a stud (preferable) or a grub screw terminal. This is not Merlin Gerin :roflmto:

a stud is not what you were describing in your first post ..
screw terminals to bite on.
and a screw terminal shouldn't have a solid copper lug in it ..

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pappajohn

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a stud is not what you were describing in your first post .. and a screw terminal shouldn't have a solid copper lug in it ..

in an industrial installation (i know this isnt industrial) we ALWAYS terminate stranded wire with either a soft copper or aluminium furel if it enters any kind of screw terminal equipment/plant.
Domestic, we simply twist and double back then terminate
 

Techno

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Grub screw terminals on fuse holders do not have metal plates to protect the copper

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scotjimland

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in an industrial installation (i know this isnt industrial) we ALWAYS terminate stranded wire with either a soft copper or aluminium furel if it enters any kind of screw terminal equipment/plant.
Domestic, we simply twist and double back then terminate

two schools of though on this John.. some say ferrules maker a neater and better connection.. others say they are more prone to vibrating loose..

off shore and in the Shell oil refinery.. they were banned.. yet in the SSEB power station I worked on they were mandatory :Doh:

Only reason I can see is.. one is high risk(refinery) .. other is not.. (power station)

this is a similar argument as the PTFE tape .. banned offshore .. yet ok in most other places..
 
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SMB

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I have no idea what any of you are talking about :ROFLMAO:
 

TheBig1

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many many years! since I was a kid
soft crimp ferrules are mandatory for MOD installations, or at least they were a few years back. even then there were discussions about whether they were mechanically safe in hazardous environments. vibration or constant snatching and pulling on connections were prone to failure

in motorhomes, its hardly a hazardous environment and other than charging circuits and inverters they tend to be low current connections. some installations are dire, i agree, but going too OTT is pointless and adds expense and complexity where its not needed
 

Techno

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I crimp a tube lug on the end then cut off all but the crimp, this makes a really solid object for screw terminals to bite on.

I'm now in a position to supply explanatory pictures.
Clearly if welding cable was put into a screw terminal it would simply part down the middle and crush under a grub screw. So for fuse holders
CA_06051412155669-M.jpg

CA_06051412162941-M.jpg

No arguments make your own choices :thumb:

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Apr 9, 2013
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If like me you run lots of kit via an inverter it's worth checking that you have good contacts on all the electrical connections. Last year a fuse holder began to deform and melt causing me some angst on a hot day!

When replacing this is fuse block I tinned the end of the multiple strands on the thick cables to ensure a good contact.

Today I was checking there's no overheating!

From what I've read (and experienced), tinning is actually a bad idea as it converts the wire end into something that's relatively soft and "plastic" with no elastic properties. Repeated heating and cooling cycles due to current load lead to a gradual loss of contact pressure that accelerates the heating due to falling contact pressure.

I'm no electrician but I've heard this from several sources and it makes sense to me. I think you need to recheck the temperature periodically to check that it isn't overheating.

Tim
 

scotjimland

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I'm now in a position to supply explanatory pictures.

No arguments make your own choices :thumb:

Yes indeed I will.. and I won't be using a solid copper end in a screw terminal block..

your first picture clearly shows the screw biting into the copper.. a small moon shaped crescent.. very poor contact area and liable to overheat.. and vibrate loose.. your choice.. :winky:
 

Techno

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Yes indeed I will.. and I won't be using a solid copper end in a screw terminal block..

your first picture clearly shows the screw biting into the copper.. a small moon shaped crescent.. very poor contact area and liable to overheat.. and vibrate loose.. your choice.. :winky:

That's not the ONLY point of contact, the whole lug is pushed hard against the back of the receptacle :Doh:

BTW I've just removed that after nearly a year and NO it did not get the slightest bit loose nor did it get hot.

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Ed Excel

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Perhaps you could take a lead from electrical accessory manufacturers? Socket outlets have grub screw terminals, for termination of general wiring cable. Connection units have grub screws, for supply general wiring cable and compression clamps for load flexible cable.

Also, as electrical designers we would never use single strand cables in grub screw terminals, because the screws are intended to cut into the conductor.

All of which makes me wonder if using flexible cable for accessory wiring in a motorhome is the best advice.
 
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Oct 29, 2008
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Re soldering the end that goes into the block. I ran a business refurbishing TVs etc a few years back and one of the causes of blown power supplies was an arching mains plug and 9 out of 10 times it was a soldered ends that had flattened over time and become loose. So dont solder the tails.
 
May 29, 2013
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In the Gas Industry hazardous areas, you put stranded cable into ferrules then into the connector. Solid strand cable goes directly into the connector.

Tightness of all connections is checked every two years while doing an audit of the electrical / instrumentation equipment.

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Sep 24, 2013
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Just to put in my 2p worth. I've just taken the charger out of my Sargent PSU2007 unit to replace the fan with a ball bearing fan old one was noisey). All connections to the charger (including the 13.5V 14.5A output) had ferrules on the cable ends. Termination was by clamping between two plates.
 

cmcardle75

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Personally, I think most clamps/screw terminals work best with stranded, un-tinned, un-ferruled cable. This is because as stranded cables compress and have far more spring, they aren't susceptible to any slight backing off due to pressure or corrosion.

This is provided that the terminal provides some sort of enclosure to push back against. A simple screw against a plate is useless and basically requires a crimp onto a ring to be reliable.

A softish ferrule on stranded cable is not so bad, as it still has enough elasticity, but any solder and it is pretty much guaranteed to fail in a few years unless it is actually soldered to the fitting itself.
 

oldun

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You’d be horrified by the number of fires caused by resistance heating (loose or bad connections). Good, helpful post Sidney.

Are there more or less overheating problems cause by overloading the wire when compared to poor connections?

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