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Un-Fused Brown wire inherent fire risk


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A friend recently had (a lot of) smoke from under the dash and was smart and quick enough to disconnect the battery before anything actually caught fire. (N.B. This was done quickly as he has a screw off earth islolator, very fortunate! and his bonnet catch was not near the source of the smoke). He is now fitting a new front loom.

This post is to question why Joseph Lucas decided NOT to put a fuse in the always ON brown wire (and subsequently the ignition switched white wire). 

I believe it was because in the early days engineers did not have confidence in fuse holders so they were avoided for important circuits.

The problem is that if a brown wire is shorted to earth that wire from that point back to the Battery will become red hot and melt its insulation, melting the insulation of adjacent wires in the loom. If not disconnected from the battery fire will ensue.

Does anyone have a logical argument why we should not fit fuses in the brown wire circuits as close to the battery as possible. My 74 TR6 CR has 4 brown wires going under the dashboard. 

I have never had a fuse holder fail and if one of the brown wire fuses should blow and the car stops the alternative would have been smoke from under the dashboard.

Am I wrong?

 

Brown wire shorted to earth.jpg

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Maybe fuses were perceived to be unreliable, hence the minimalist approach  fuse usage in early cars.

I really should have a 60A fusible link in the brown wire to my ammeter.

I'd also be interested to see if there is a reason not to install this protection.

 

 

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There have long been two schools of thought on automotive fusing (for classics, anyway).  One camp believes that certain critical circuits--like headlights--should not be fused.  The other thinks that just about all loads should be fused to protect the wiring.  Even in this camp, the main starter circuit is usually not fused, nor is the alternator circuit. 

I don't know, but I'd assume that modern cars have better over-current protection.

Ed

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In both of my cars I have installed a 50 amp strip fuse in the main feed. I used a fuse holder from Autosparks.

https://www.autosparks.co.uk/strip-fuse-holder-accepts-5mm-ring-terminals.html

The 4A has been like this for 14 years with no problems.

You could also use a circuit breaker like this.

https://www.carbuildersolutions.com/uk/50-amp-panel-mount-circuit-breaker

Cheers

Graeme

Edited by graeme
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I'm not happy with the unfused brown circuits either so plan to fit a heavy duty blade fuse box (pictured).  This will have a supply lead from the battery (unfused - I know) with returns to coinnect with the four brown wires currently connector to the starter feed, plus fuses for the fuel pump main supply, headlight mains supply and the electric booster pump (all via relays).

The box will sit on a plate secured via existing fasteners and will have the clear cover seen to the side of the box.

Cheers

Gavin

 

 

20181018_194932_resized.jpg

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1 hour ago, KiwiTR6 said:

I'm not happy with the unfused brown circuits either so plan to fit a heavy duty blade fuse box (pictured).  This will have a supply lead from the battery (unfused - I know) with returns to coinnect with the four brown wires currently connector to the starter feed, plus fuses for the fuel pump main supply, headlight mains supply and the electric booster pump (all via relays).

The box will sit on a plate secured via existing fasteners and will have the clear cover seen to the side of the box.

Cheers

Gavin

 

 

20181018_194932_resized.jpg

Not really a good place to fit a fuse box as that area often gets wet in heavy downpours, I have had to remove those before now due to eventual corrosion, thats why the original fuse box was mounted vertically.

Stuart.

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Had the same issue on my TR6 some month ago:

Wire from Ammeter to ignition lock and back into the loom got a short at the vent housing -> Wire from ammeter turned from brown to bright yellow :-) and found it´s way straight thru the oil pipe connected to the oil pressure gauge

what a show!

 

Next day i fitted 10 extra fuses + 6 relais...

http://translate.google.com/translate?hl=&sl=auto&tl=en&u=https%3A%2F%2Fwww.straightsix.de%2Fdoku.php%3Fid%3Dstart%3Atr6%3Aelektrik&sandbox=1

Edited by Kamphausen
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I've fitted an 8-way blade fuse box vertically on the inner wing, overlapping the position of the original. It was also useful when splitting various circuits across to fit a terminal block next to the new fuse box.

Nigel

SAM_2760.JPG

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23 hours ago, stuart said:

Not really a good place to fit a fuse box as that area often gets wet in heavy downpours, I have had to remove those before now due to eventual corrosion, thats why the original fuse box was mounted vertically.

Stuart.

Don't you know it never rains in NZ Stuart!!  Valid point although the mounting plate will be elevated above the body panel, possibly vertically. a project for next winter at this stage.

Gavin

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Hi Folks,

                    Prefect asks 'is there a logical reason not to have fuses in the brown wire'.

Difficult that. Old cars and logic do not often go together.

It is accepted that old fuses and fuse boxes can be a bit iffy. Thus no fuses for Brown wire or headlights.

How about new fuses and fuse boxes. Well there are good ones (Durite etc) and there are cheap ones (I have noticed quite a lot of TR people like cheap:P)

 

How often do you hear of the brown wire going 'phut'. Compared to fuses it is a rare event.

Should the brown wire short out and start to combust this could be a very bad situation.

Should the brown wire fuse (if fitted) go pop then perhaps a worse situation.

Why is the brown wire buried in the loom? It can protect it from mechanical damage.

Why isn't the brown wire on its own.? 

Where do you stop being sensitive to major problems.????

 

I prefer no fuse on the brown wire but have everything else fused.

Ensure that the brown wire is positioned so that it is free from mechanical danger 

 

If you fit a fuse make sure it has a good, known rating. That the fuse and box are quality items and protected from the elements.

Inspect the fuses at least annually (start of the season in the spring) and replace if there is ANY trace of corrosion.

AND while your at it inspect all those bl**dy inline connectors for the rest of the loom - they go rusty as well.

 

Roger

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Roger makes some very good points. If you do fit a fuse in series with the battery, don't get carried away and fit one which has too high a rating.  We have covered this recently in a couple of threads but basically if a fuse is rated for (say) 50 amps then unless it states that this is the 'blow' current  you must assume this is the service current and that it will carry 50A continuously without failing. In order for such a fuse to blow in a few seconds it needs many multiples of that current - perhaps 200A or more which is quite capable of cooking the insulation on your wiring while it is waiting for the fuse to blow.  Better than nothing perhaps but not the cure you may be seeking.

The original cartridge fuses are supplied in both forms and you need to be sure which type you are fitting. Modern blade and strip fuses are only available in 'service' rating as far as I am aware so if you are using those don't fit anything too big.

Of course much will depend on the loads you have since cooling fan, uprated headamps, petrol pump etc can pull considerable currrent which must be allowed for if you use them with the engine stopped.

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Hello, I think Roger has hit the nail on the head, the danger is 'mechanical damage' or the wire being allowed to rub against a hard, probably metal surface and damaging the insulation, grommets are there for a reason and I would, in the first instance, check the run of all the wires.  For example I have a few extra wires around the fuel tank, for fuel pump, isolation switch and fuel cut-off, where they are near a hard surface I have encased them in blocks of foam to stop any chance of vibration, elsewhere I make sure looms are cabled tied together with foam or rubber between the wires and a hard surface, I think the chance of spontaneous combustion is nil, there has the be a cause, and an earth!!  Cheers, Andrew

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Planning to wait until after the weekend before drawing any conclusions.

My gut feeling is to never leave any circuit unprotected.

I may make an allowance for the brown cables to the Starter and to the Alternator but those two brown wires that run under the dash need consideration. 

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10 minutes ago, Prefect said:

Planning to wait until after the weekend before drawing any conclusions.

My gut feeling is to never leave any circuit unprotected.

I may make an allowance for the brown cables to the Starter and to the Alternator but those two brown wires that run under the dash need consideration. 

Hi,

    you could always fit a voltmeter and do away with those brown cables under the dash.

 

Roger

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I had to replace a loom as a three foot length was fried behind the dash. Very lucky it did not take out the car.

Fusing the brown wire to the ignition switch has also been a consideration.

In a perfect world positioning the cables so that mechanical damage can be avoided would have merit. However, what of the risks of:

Aged insulation,  someone been in there before (very likely) and rodent damage?

I never did find the cause of the short due to the extensive damage.  The core itself acted as a fuse, blew, and cut of power from the battery.

A fuse close to the battery should prevent this.... However, while I was testing my new installation thought I would be clever and place a temporary 15amp fuse in the supply to the switch.  Well, got smoke, and had to replace the white wire to the voltmeter. Luckily I disconnected the supply before more damage.

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A thought, in the event of smoke escaping from the wire, any wire, isolating the battery, earth or live must remove the source of combustion, I accept if left to late and the smoke turns to flame then you have real problems.  Would it work fitting a high current relay, say 100 Amps between earth or live with a switch on the dash.  When the car is left, switch off, battery isolated, rodent problem sorted, when car in use, switch on, electrical circuit complete, in the unlikely event of a major short, switch off, battery isolated.  The relay could be positioned anywhere so no need for heavy duty wires behind the dash, any thoughts?  Cheers, Andrew

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Hi Andrew,

               yes, you could use a relay with a small switch in the cockpit. But you introduce another level of complication.

Why not have an isolator switch in the cockpit. More reliable than a relay.

It shouldn't matter about having the fat brownies behind the dash because you have the switch at arms length.

 

Roger

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To avoid the complexity of additional relays, one option would be to install this Battery Cut Out switch with cable pull in the Positive Lead from the Battery post.

In a Rally / Race car the red handle would be accessible from the outside, but we don't need that (all sorts of problems in a public street!) so we could mount this next to the Clutch Master cylinder (useful to isolate the battery when working or storage), the pull cable could terminate under the dash on the right hand side similar to the bonnet pull on the left of a UK car. Any sign of a problem pull handle and isolate the battery.

In addition I would install a fuse in each of the two brown wires to provide automatic isolation in the event of a short circuit. If one looks at the wiring diagram http://www.advanceautowire.com/tr2506.pdf you will see that part of the lighting circuit is also not fused. The brown wires don't just go to the ammeter (on a CP) they go to the ignition switch and the fuse box and then after the ignition as an un-fused white wire. All of this would now be protected by the two new fuses in the Brown wires which could be placed just after the Battery Cut Off Switch in the area next to the Brake master cylinder.

With the above installed I think we have all bases covered.

N'est pas?

 

Automotive Plumbing Solutions FIA Master Cut Out Switch and Pull Cable Kit

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O this talk of ..smoke escaping frae the wires is the real problem

the wires rely on smoke inside the wire insulation to carry the current along smoooothely, like oil in yer engine

 

smoke gets oot, then friction starts,

So ye need t,replace the lost smoke,, simples,:P:D

KGrHqJHJDkE63ZdY3VBO6dvFhgW60_12.JPG

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IMG_5252.thumb.jpg.6b0362fc0656ddddb4084631ceafc9e0.jpgMike CIMG_5252.thumb.jpg.6b0362fc0656ddddb4084631ceafc9e0.jpg

Excellent idea Mike thanks, I now have a plan:

Battery Cut off in the Earth Wire adjacent to the battery post (with remote lanyard) and fuses in the two brown wires that head under the dashboard..

There are so many British Cars that have the same issue, I am concerned that as this problem has been identified and accepted by a number of owners (probably not for the first time) there are many other classic car owners who are taking a risk of molten wires and possible fire without knowing it.

If it can happen to an experienced TR owner, it can happen to anyone, the question is will they be as quick thinking..... 

 

74481A50-6968-4F5E-AE0C-7378ABF1657A.JPG

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