S1 Fusewire

Barrie Warrener · Posted: Sun Aug 30, 2015 5:30 pm Post subject: S1 Fusewire

Can anyone please tell me what amps the fusewire should be in the S1 fuse box?
Thank you.

John Murch · Posted: Sun Aug 30, 2015 7:36 pm Post subject:

The manual suggests a single strand of 28 swg tinned copper wire. The horn fuse is 25amp of a cartridge type.

The 28swg should expire at 20amp load and have a continuous rating of 10amp.

The above is from various sources that I had to hand, but do double check!

John

Barrie Warrener · Posted: Sun Aug 30, 2015 7:46 pm Post subject:

Thank you John.
The fusewire I have at the moment in the one that keeps blowing is 5amp and looks a bit weedy for the job.
What you say makes sense but hopefully another Forum member will add to what you say as I'm particularly allergic to electrical fires!

I do not understand the difference between expiry at 20 amp and continuous load of 10 amp.
I've looked and looked but nowhere gives a definitive statement as to what amperage fuse wire is to be used.

John Murch · Posted: Mon Aug 31, 2015 4:03 am Post subject:

Barrie,
http://rrtechnical.info/sc/sc1/wshop/1.pdf
Section A1 page A6 refers to the fuse box, and this web page gives some info on fuse wire,
http://www.gxk.org.uk/info/wire.htm
Hope it's helpful.
John

Ps
As you know which fuse is blowing, can you add up the wattage of all the items on that fuse and calculate it's expected load? This would give a good idea of if there is a problem lurking or if your current fuse wire is just to thin.

Christopher Carnley · Posted: Mon Aug 31, 2015 8:40 am Post subject:

Barrie,

Worrying about "Much Ado About Nothing"!

The handbook states that each fuse, apart from the horn fuse, a 25 amp cartridge, is one strand if 31 SWG tinned copper wire. This has a fusing rating of 12 amps, but a fuse rate of 7 amps.
C.

Barrie Warrener · Posted: Mon Aug 31, 2015 8:56 am Post subject:

John Murch · Posted: Mon Aug 31, 2015 10:43 am Post subject:

Barrie, I don't know what size your fan is, but even the smallest Kenlowe draws 5amps, the 10" one on my 3ltr draws 7 amps and I'm sure yours will be bigger. What else is on that circuit? Until you know the total load I don't think you can make a good decision on what fuse wire to use.
If the total likely maximum load is say 15 amps I would go for a 20 amp fuse, Usually one is just protecting against a short circuit.
John

Barrie Warrener · Posted: Mon Aug 31, 2015 12:42 pm Post subject:

All agreed with John and thank you again.
I had almost more or less come to the same conclusion myself but my natural (over?) caution which prevented me from just increasing the amperage of the fuse was due to concern of not knowing what the capacity of the 1959 wiring.
I didn't want to just put in a 20 amp fusewire in case there was a real problem with the fan or controller because that would just overheat the wiring.
I have to consider why this has become a problem whearas all worked well previously.
My first step is to consider what is the maximum fusewire value I can use to support the electric fan, hence the original question.

Paul Spencer · Posted: Mon Aug 31, 2015 3:23 pm Post subject:

I once knew something about the theory of fuses, but it is in the dim and distant past. Basically, the time taken for the fuse to blow depends on the current. So a fuse will have a rated current at which it will work reliably for a long period. It might take substantially more current to blow in 1 second, and more than that to blow in 1mS. You can get fuses in different speed ratings for different applications. But there is no real need to worry about that here - it just explains why a fuse may have diffeent figures associated with it. If you were looking at cartridge fuses, I would be looking for slow-blow as you have a fan motor starting and hence taking a high current for a short time while stationary.

It seems pretty clear that 10A is not going to be too high, so I would just sling some in and see it if blows. If not, job done. If it does, then you need to decide whether to investigate or try a higher rating.

Usual disclaimers - don't sue me when the car catches fire! It must be 40 yars since I learnt this stuff.

Christopher Carnley · Posted: Tue Sep 01, 2015 7:08 am Post subject:

Barrie,

The fusing current is that at which the fuse, "blows". The safe continuous current is the fuse rate.

The best advice would be for you to consult an auto-electrician, and let him have the worry.

Barrie Warrener · Posted: Tue Sep 01, 2015 11:50 am Post subject:

Thanks Chris, a helpful explanation.
It was an auto electrician who put me in this situation so before I go back to him I want to understand the situation better so I'm informed.
The puzzle is that the new underbonnet thermostatic fan controller worked well for two weeks but now keeps blowing the fusewire.

The 5 amp fusewire is clearly not man enough for the job as I've established that the fan draws 24amps.

Another problem is that whilst the fusewire blows when the fan is switched on automatically it does not blow when I operate the underdash manual control! Thinking about it it sounds as if the new thermostatically controlled switch may have become faulty.
Firstly I'll try new fusewire.

Robert Craven · Posted: Tue Sep 01, 2015 2:17 pm Post subject:

Maybe the fault took two weeks to appear because during those two weeks the fuse was regularly getting stressed and became weakened and eventually just couldn't take any more. But then you say it "keeps" blowing the fuse now, so perhaps I'm wrong.
24 amps for the fan sounds a lot. I assume your wire is thick enough.
No doubt there could be some strange fault with the thermostatic switch which causes the fuse to blow even though the manual switch doesn't have the same effect, but it seems unlikely. Could it be that when you use the manual switch the fan is already rotating from the effect of the wind so that there is then no great surge of current on starting?

PS fuse ratings can be puzzling because (whatever the theory) it's not always clear what suppliers mean when they specify a particular figure. AES helpfully make it fairly clear by giving two figures for each fuse: continuous and "blow". see: http://www.autoelectricsupplies.co.uk/product/290/category/243

Christopher Carnley · Posted: Tue Sep 01, 2015 6:10 pm Post subject:

If the switch contacts start to arc, then the current surge will exceed the fusing rating,and the fuse will blow.

Barrie Warrener · Posted: Thu Sep 03, 2015 8:46 am Post subject:

This thread continues to throw up new information.
One of the difficulties has been establishing that I had the correct 28swg fuse wire and not being able to obtain it from any motor factors in my area..
Whilst waiting for some to arrive from eBay I gave the problem a 'damned good looking at' and saw something loose at the bottom left hand corner of the fuse box.

So I reached down and pulled it out.

An unused cartridge of 28swg fuse wire!
How many of us know it's there, I certainly didn't. It's probably remained undisturbed there since the car was new and isn't mentioned in the hand book.
Anyway the upshot is I used the wire and the fuse blew when the thermostatic control kicked in so the new control unit is at fault.
Problem solved!
Thank you everyone

John Murch · Posted: Thu Sep 03, 2015 9:37 am Post subject:

Easily missed, but on page A11 on the manual, it mentions the spare fuse wire. But perhaps not in the handbook!
Are you sure that your problem is really solved, the fuse is rated at 20amps (so probably won't blow with a little more load), but if your fan draws 24amps won't it blow again if the fan is running and you switch on something else on the same circuit? Would using a slightly higher rated fuse be an idea?
John.
PS
Nice quality photo!

Barrie Warrener · Posted: Thu Sep 03, 2015 12:56 pm Post subject:

John, when my parcel from Mr eBay arrives it will contain some thicker than 28swg wire as well as part of the package so I'll use the chart mentioned above to ramp things up a bit.
I am, however, not hopeful of a result as for the two weeks or so since the new controller was installed it worked perfectly well.
I think something in the new controller has failed.
We shall see........

Christopher Carnley · Posted: Fri Sep 04, 2015 8:24 am Post subject:

Handbook p23, "Fuse Boxes", para 3,

"Spare fuse wire is provide on a special holder within the large fuse box".

Barrie Warrener · Posted: Wed Sep 23, 2015 2:42 pm Post subject:

At last something definitive!

From a late S1 handbook.
The fuse rating for all circuits in the main fuse box is 30 amps.
Although my picture doesn't show it the SWG (standard wire gauge) of the fuse wire is 31.

I'll try and get a more inclusive picture later

Barrie Warrener · Posted: Mon Jan 04, 2016 10:09 pm Post subject:

At last the more inclusive picture. 31 SWG equates to 30 amps

Christopher Carnley · Posted: Tue Jan 05, 2016 8:30 am Post subject:

"If it works, its in".
To paraphrase the "Witches of Eastwick".