Fire

[nb Innisfree]

Smell of burning and quite a bit of smoke last night while charging off alternator.

 

Turned out to be a crimped connection overheating, replaced it with another crimped length of cable and added solder. A case for soldering?

 

Smoke was from melted mega fuse and fuse holder, didn't activate smoke alarm but soldering did later.

Alarm is ionisation type, maybe optical needed alongside.

 

Dreadful smell, only just about gone 24 hrs later.

 

[twocvbloke]

I'm sure you're in for the "You didn't crimp it right" flak, but that said, I too would have soldered it to get a more solid connection, and now I'll be in for flak too...

[nb Innisfree]

I'm sure you're in for the "You didn't crimp it right" flak, but that said, I too would have soldered it to get a more solid connection, and now I'll be in for flak too...

 

I can't remember when and who did the crimping, maybe it was me, but I guess it was the design of crimper that was to blame as you can only put it in the crimper and squeeze until it stops! This crimp was triangular shaped, the only one I would want to use in future is the hydraulic type that crushes cable into a solid bar, failing that back it up with solder to give a good electrical connection.

 

Edited to add: This was the cable from the alternator, nice and thick but no use with a poor connection.

Edited February 26, 2010 by nb Innisfree

[springy]

Not completely convinced it was the crimp at fault - difficult to tell from a piccie but the heat seems to

have been concentrated around the bolt tab - any chance that it had worked loose ? Probably difficult

to tell in the aftermath. Clearly the copper strands have been hot but the tube part of the crimp doesn't

shows much heat marking, where the tab of the megafuse obviously does ?

 

springy

[twocvbloke]

Not completely convinced it was the crimp at fault - difficult to tell from a piccie but the heat seems to

have been concentrated around the bolt tab - any chance that it had worked loose ? Probably difficult

to tell in the aftermath. Clearly the copper strands have been hot but the tube part of the crimp doesn't

shows much heat marking, where the tab of the megafuse obviously does ?

 

springy

 

Looking at it, I think I'd have to agree there, it looks like there's been arcing issues, that can cause a lot of heat build up to the point of failure, a similar situation I can think of is the aluminium wire problems in the US, the alu, if not connected properly, comes loose through expansion and contraction, and causes arcing and in some cases fire in a rather similar manner to what I see in the pics, so, yeah, may have been a loosened nut, especially if there was no locking nut behind the main one...

[nb Innisfree]

Not completely convinced it was the crimp at fault - difficult to tell from a piccie but the heat seems to

have been concentrated around the bolt tab - any chance that it had worked loose ? Probably difficult

to tell in the aftermath. Clearly the copper strands have been hot but the tube part of the crimp doesn't

shows much heat marking, where the tab of the megafuse obviously does ?

 

springy

 

Connections were tight as I checked them over fairly recently, as you say difficult to tell from the pic and also in the flesh, I wonder if initial overheating caused some carbonisation between fuse and crimp creating resistance and transferred heat to there. Got rid of the fuse and holder for now but I wonder if one is more bother than it's worth, as it is the alternator cable it really needs one both ends to be totally effective, more connections = more weak points, I would like to do away with the isolator but it's very handy when doing any work on the alternator

 

Edited to add: All connections have s/s shakeproof washers and bolt head fits in plastic moulding to prevent turning when tightening.

 

Lesson is to feel all connections for heat when engine is running.

Edited February 26, 2010 by nb Innisfree

[Timleech]

What does the other side of that crimped lug look like?

It looks rather like a 10mm bore lug on an 8mm terminal, shouldn't be fatal but wouldn't help matters.

 

Tim

[nb Innisfree]

What does the other side of that crimped lug look like?

It looks rather like a 10mm bore lug on an 8mm terminal, shouldn't be fatal but wouldn't help matters.

 

Tim

a

 

About the same, slightly cleaner but I think some came off when I unscrewed it to remove.

 

Yes 10mm bore on 8mm lug.

 

I have another maxi fuse holder of the same type and I think I will replace with a better one, perhaps Blue Sea

Edited February 26, 2010 by nb Innisfree

[Arnot]

Smell of burning and quite a bit of smoke last night while charging off alternator.

 

Turned out to be a crimped connection overheating, replaced it with another crimped length of cable and added solder. A case for soldering?

 

Smoke was from melted mega fuse and fuse holder, didn't activate smoke alarm but soldering did later.

Alarm is ionisation type, maybe optical needed alongside.

Here's my take FWIW. Bear in mind that this is hypothesis based merely on the photo...

 

First the crimp tool used for the terminal in the first place didn't do the job properly. the evidence (or lack therof) is in the fact that the tubular end of the terminal is not deformed in the slightest.

 

This then when subjected to prolonged high current started to warm up.

 

At a certain temperature the heat of the terminal was transferred to the stud on the fuse holder and it got hot enough that the thermoplastic base that held the stud captive melted and effectively allowed it to migrate through the base thus loosening the contact pressure exerted by the nut and shakeproof washer.

 

When this pressure was released it then allowed the contact area between the terminal and the fuse to corrode. This was accelerated due to the elevated temperature.

 

This corrosion then in turn acted as extra resistance in the connection and generated more heat and more corrosion.

 

Once the temperature and corrosion reached a critical level, the resitance rose to a point where an arc developed between the terminal and the and of the fuse.

 

The effect is known as "Chernobyl mode".

 

My guess is that if the crimp had been good in the first place this would never have happened.

 

Is it a case for soldering? Personally I think it's a better case for proper crimping. If the terminal had been soldered other than perfectly it would have warmed up, the solder would have melted and the same thing would have happened. The hexagonal die crimpers when used with sufficient presssure deform the strands of the cable and compress them to the point that they cold weld together, these almost never fail even when under extreme load and temperature.

 

It does highlight a problem with these fuse holders where the thermoplastic base is part of the contact pressure but most of them seem to be of this design.

 

Hope this helps,

 

Regards

 

Arnot

[nb Innisfree]

Here's my take FWIW. Bear in mind that this is hypothesis based merely on the photo...

 

First the crimp tool used for the terminal in the first place didn't do the job properly. the evidence (or lack therof) is in the fact that the tubular end of the terminal is not deformed in the slightest.

 

This then when subjected to prolonged high current started to warm up.

 

At a certain temperature the heat of the terminal was transferred to the stud on the fuse holder and it got hot enough that the thermoplastic base that held the stud captive melted and effectively allowed it to migrate through the base thus loosening the contact pressure exerted by the nut and shakeproof washer.

 

When this pressure was released it then allowed the contact area between the terminal and the fuse to corrode. This was accelerated due to the elevated temperature.

 

This corrosion then in turn acted as extra resistance in the connection and generated more heat and more corrosion.

 

Once the temperature and corrosion reached a critical level, the resitance rose to a point where an arc developed between the terminal and the and of the fuse.

 

The effect is known as "Chernobyl mode".

 

My guess is that if the crimp had been good in the first place this would never have happened.

 

Is it a case for soldering? Personally I think it's a better case for proper crimping. If the terminal had been soldered other than perfectly it would have warmed up, the solder would have melted and the same thing would have happened. The hexagonal die crimpers when used with sufficient presssure deform the strands of the cable and compress them to the point that they cold weld together, these almost never fail even when under extreme load and temperature.

 

It does highlight a problem with these fuse holders where the thermoplastic base is part of the contact pressure but most of them seem to be of this design.

 

Hope this helps,

 

Regards

 

Arnot

 

Yes I think something on those lines, it looks as if melted plastic has seeped between lug and fuse and then heated up and carbonised.

 

Agree with hex crimpers, I saw a hydraulic one and was really impressed with the result, the lug looked like a solid bar similar to an allen key shaft after it was crimped.

Edited February 26, 2010 by nb Innisfree

[blackrose]

Is this a potential issue only with badly crimped terminals on big cables carrying heavy loads or can it happen on a any size cable/terminal?

[bag 'o' bones]

Could have been a faulty component or a bad crimping - difficult to tell when the thing is fried especially from a photograph. As others have already mentioned you can't beat checking over the 'lectrics for heating effects when energised, most components 'warm up' and give warning before they fail, well at least some of the time!

 

Interestingly house wiring sockets some times burn out for no apparant reason, until you learn that 50hz mains has been known to loosen terminal screws over time.

[Arnot]

Is this a potential issue only with badly crimped terminals on big cables carrying heavy loads or can it happen on a any size cable/terminal?

The short answer is that it can happen to any terminal - but is most unlikely to.

 

There are a few factors that lead to terminal failure of this sort.

 

First you have to realise that any electrical terminal has a resistance. When it carries current that generates heat.

 

This heat is then dissipated into the metal mass of the terminal and from there into the surrounding structure and air. If the heat generated is in excess of the ability of the surrounding to dissipate it then excessive temperatures occur.

 

When terminals (that consist of differing metals and insulators) heat up, they corrode quickly and the resistance increases and thus the heat generated - "Chernobyl mode".

 

Some electrical loads are irregular and of limited duration such as pumps, starter motors, horns etc and although they draw quite high currents the short duration doesn't allow the wiring and terminal temperature to rise far until the load is switched off so there is no problem with overheating even if the wire or terminals carrying this current are a bit on the small side.

 

Other loads such as lighting and charging tend to be of a longer term or continuous nature and so even if the heating effect is quite minor, over time it leads to high temperatures and failure.

 

There are other external environmental factors that also have an effect such as the local temperature such as in an engine compartment, short and long term effects of damp and other forms of contamination and vibration.

 

It is calculating this sort of thing that is where electrics becomes a bit complex and relies on the knowledge and experience of the designer and installer of the system. There are no easy answers.

 

I realise that this answer probably doesn't help much apart from explaining what is going on here but it's a start...

 

Regards

 

Arnot

[nb Innisfree]

Could have been a faulty component or a bad crimping - difficult to tell when the thing is fried especially from a photograph. As others have already mentioned you can't beat checking over the 'lectrics for heating effects when energised, most components 'warm up' and give warning before they fail, well at least some of the time!

 

Interestingly house wiring sockets some times burn out for no apparant reason, until you learn that 50hz mains has been known to loosen terminal screws over time.

 

We once had a very faint hot plasticcy smell in our house that persisted on and off for a year or more, too faint to trace. I then had occasion to unplug the washing machine and found the front of the socket totally burnt away but hidden behind the plug! Too damaged to look for cause but does go to show how easily it can happen, an optical smoke detector should be able to pick it up at some point, but if it is very a slight and slow burn? Human nose takes some beating

 

Edited to add: The example in my photo has worked perfectly for nearly 5 years.

Edited February 27, 2010 by nb Innisfree

[Timleech]

We once had a very faint hot plasticcy smell in our house that persisted on and off for a year or more, too faint to trace. I then had occasion to unplug the washing machine and found the front of the socket totally burnt away but hidden behind the plug! Too damaged to look for cause but does go to show how easily it can happen, an optical smoke detector should be able to pick it up at some point, but if it is very a slight and slow burn? Human nose takes some beating

 

That sort of thing sometimes starts with a poor fuse contact in the 13A plug.

 

Tim

[nb Innisfree]

That sort of thing sometimes starts with a poor fuse contact in the 13A plug.

 

Tim

 

Our w/m was a 3kW model, 3kW appliances are a bit thin on the ground these days. I remember the clamping force on 3 pin plugs was increased some years ago, difficult to pull one out nowadays, I assume this was in response to overheating problems + a change to lower wattage appliances?

[smileypete]

Is this a potential issue only with badly crimped terminals on big cables carrying heavy loads or can it happen on a any size cable/terminal?

I've seen something similar on my own boat with insulated blue crimps on wires that get damp/wet/somewhat overloaded.

 

The crimp heats up enough for its vinyl sleeve to gradually creep over time and it smooths out and loses the marks from the crimper.

 

Seems to indicate the copper strands in the crimp are suffering from oxidation and/or electrolysis. These are crimps done with a reasonable ratchet crimper.

 

The best cure I've found is to use wire with already tinned strands, in the same conditions they hold up fine.

 

For thick cables where tinned strands aren't available I'd work silicone grease well into the bare end before crimping it. Some heatshrink over the top as well wouldn't hurt.

 

cheers,

Pete.

Edited February 27, 2010 by smileypete

[ditchcrawler]

Our w/m was a 3kW model, 3kW appliances are a bit thin on the ground these days. I remember the clamping force on 3 pin plugs was increased some years ago, difficult to pull one out nowadays, I assume this was in response to overheating problems + a change to lower wattage appliances?

Again back to my apprentice days 1970 ish. The only plug-top we would fit to wash boilers,3 Kw kettles etc was a MK one, we found all the others we tried suffered from heat at high loads.

[Guest]

I doubt if a properly crimped and suitably sized crimp connection would overheat. I believe it was either loose on the mega link,improperly crimped, or maybe the joining faces on the link and fuse were oxidised leading to resistance.

 

Soldering has had bad press both on this forum and elsewhere. It is POOR soldering that leads to failure. That said it is easier, quicker, safer and more reliable to use a crimp. I would never bother with soldering these days. Again crimping must be done properly, not with a hammer or vice! It is quite cheap and easy to make a tool, so no fancy 100 quid crimpers are needed.

 

Connections were tight as I checked them over fairly recently, as you say difficult to tell from the pic and also in the flesh, I wonder if initial overheating caused some carbonisation between fuse and crimp creating resistance and transferred heat to there. Got rid of the fuse and holder for now but I wonder if one is more bother than it's worth, as it is the alternator cable it really needs one both ends to be totally effective, more connections = more weak points, I would like to do away with the isolator but it's very handy when doing any work on the alternator

 

Edited to add: All connections have s/s shakeproof washers and bolt head fits in plastic moulding to prevent turning when tightening.

 

Lesson is to feel all connections for heat when engine is running.

I am not inferring that you used the "star" type of shakeproof washer but:

 

I think it was Snibble (apologies Snibble if it wasn't you) who had discovered that relay connections on Durite relays were cured from overheating by NOT using the "star" type shakeproof washers provided with same. Just a thought.

Edited February 27, 2010 by Guest

[nb Innisfree]

I doubt if a properly crimped and suitably sized crimp connection would overheat. I believe it was either loose on the mega link,improperly crimped, or maybe the joining faces on the link and fuse were oxidised leading to resistance.

 

Soldering has had bad press both on this forum and elsewhere. It is POOR soldering that leads to failure. That said it is easier, quicker, safer and more reliable to use a crimp. I would never bother with soldering these days. Again crimping must be done properly, not with a hammer or vice! It is quite cheap and easy to make a tool, so no fancy 100 quid crimpers are needed.

 

 

I am not inferring that you used the "star" type of shakeproof washer but:

 

I think it was Snibble (apologies Snibble if it wasn't you) who had discovered that relay connections on Durite relays were cured from overheating by NOT using the "star" type shakeproof washers provided with same. Just a thought.

 

Used the split ring type.

 

Edited to add: Earlier we noticed crimped connectors on alternator isolator getting a bit hot so shut the engine down and flicked the isolator on and off several times and now it's ok, time for a new one I think.

Edited February 27, 2010 by nb Innisfree

[Guest]

Used the split ring type.

Can't see a problem there, they are what I woulld choose.

[Timleech]

I am not inferring that you used the "star" type of shakeproof washer but:

 

I think it was Snibble (apologies Snibble if it wasn't you) who had discovered that relay connections on Durite relays were cured from overheating by NOT using the "star" type shakeproof washers provided with same. Just a thought.

 

Stainless is actually not a good choice for the job anyway, its resistivity is something like five times that of 'ordinary' steel and forty times that of copper

 

Tim

Edited February 27, 2010 by Timleech

[nb Innisfree]

Stainless is actually not a good choice for the job anyway, its resistivity is something like five times that of 'ordinary' steel and forty times that of copper

 

Tim

 

Shouldn't matter as it isn't between the two conductors, just tensioning the clamping action of the nut and bolt.

[Timleech]

Shouldn't matter as it isn't between the two conductors, just tensioning the clamping action of the nut and bolt.

 

Surely it's a good idea to use the stud/bolt and nuts as conductors also, to reduce the reliance on one contact face?

 

Tim

[nb Innisfree]

Surely it's a good idea to use the stud/bolt and nuts as conductors also, to reduce the reliance on one contact face?

 

Tim

 

I placed fuse straight on top of crimped connector and then washer followed by nut.

 

I will need to think about that.