conFUSEd about sizes

corazon

corazon

Well-Known Member
It has been well documented on here about the incorrect size fuses being detrimental to the fusebox, melting down etc :shock:
But what is the correct size?
I've read 30mm are too small, 32mm are correct
I've also read 28mm are too small, 30mm are correct :?
32mm is the equivalent of 1.25" which are listed on ebay
31mm are also listed, is this just a mistake?
One thing that I'm sure about is I have a couple of 28mm fuses in my box which are definitely too small :wink:

Jim
 
Just measure the distance on the fuse box from the top of the top blade to the bottom of the bottom blade and that's the length of the fuse you need, which IIRC is listed as 32mm, but in real money is 1.25".
 
Thanks, that does sound like the best idea.
Ebay sellers are listing 1.25"(30mm) fuses :?
So I'm guessing 30mm fuses might be non existant, they're just calling them 30mm for metric ease when they should really be listed as 32mm? :roll:
Jim
 
Hi Jim,

32mm is correct size for the S2 fusebox. 30mm ones are available, as I have seen plenty with a small slip of Lucas paper in them to denote the amp rating.

Since you're under there, it's a really good idea to give your fusebox a bit of an overhaul. We ran an article in the latest issue of Driving Force about this - if I can find them, I'll post some pictures for you (or ChrisYork can if he sees this before I get back).
Essentially, the S2 fusebox is made of a very experimental plastic and is worryingly prone to heating up and melting. Just pointing a domestic hairdryer at the lid is enough to get it smoking a bit! :shock:
If you're not careful, the chain of events goes: fuse too short causes heat in the contacts, contacts melt plastic around them and start opening up. Electrical connection gets worse (you may loose a headlamp intermittently) and/or it shorts to something nearby. Fusebox material starts getting hot and may combust!

So....
Start by unscrewing the box from the bulkhead and crimping the wires tightly on to the connections at the back. The S2 looms were completely new over the S1 versions and the quality of crimping seems to vary between car to car, so squeeze em on tight! Then give each of the U'shaped connectors a little squeeze in towards each other so they make a nice tight contact on the fuse. Some very very fine emery cloth on the contacts wouldn't go amiss either. If you do all that and fit 32mm fuses, you should be fine!

Obviously, relays on the headlamps, etc, is belt and braces. P6s aren't famous for bursting into flames but the S2 under-dash fusebox is a less-than-ideal weakpoint, so needs to be in tip top order.

Michael
 
The fuses most likely to melt the fusebox are the heater and the main beam fuses. I put an infra red thermometer on the main beam fuse of my 3500S with main beam on and the temp got up to 90 degrees C.

Useful thread here illustrates the problem.

Dave
 
Dave3066 said:
The fuses most likely to melt the fusebox are the heater and the main beam fuses. I put an infra red thermometer on the main beam fuse of my 3500S with main beam on and the temp got up to 90 degrees C. <=== Whoa! That's HOT!!

Useful thread here illustrates the problem.

Dave
Click to expand...

How long did it take to get to that temperature?
 
Thanks for all the replies,
Correct 32mm mixed pack on their way to me now.
I don't think sellers should be able to list modern 30mm ones as 1.25" :x

My heater blower hasn't worked for ages and sure enough some browning has occurred at the fuse.
Also a while back I noticed my inner headlamps weren't working as they used to..

High time for a fusebox refreshment
Jim
 
corazon said:
My heater blower hasn't worked for ages and sure enough some browning has occurred at the fuse.
Also a while back I noticed my inner headlamps weren't working as they used to..

High time for a fusebox refreshment
Jim
Click to expand...

Definitely! Let us know how it goes.
Michael
 
darth sidious said:
Dave3066 said:
The fuses most likely to melt the fusebox are the heater and the main beam fuses. I put an infra red thermometer on the main beam fuse of my 3500S with main beam on and the temp got up to 90 degrees C. <=== Whoa! That's HOT!!

Useful thread here illustrates the problem.

Dave
Click to expand...

How long did it take to get to that temperature?
Click to expand...

That was only after around 5 minutes of continuous main beam.

I have relays in the main beam circuit now so much cooler :D

Dave
 
Dave3066 said:
darth sidious said:
Dave3066 said:
The fuses most likely to melt the fusebox are the heater and the main beam fuses. I put an infra red thermometer on the main beam fuse of my 3500S with main beam on and the temp got up to 90 degrees C. <=== Whoa! That's HOT!!

Useful thread here illustrates the problem.

Dave
Click to expand...

How long did it take to get to that temperature?
Click to expand...

That was only after around 5 minutes of continuous main beam.

I have relays in the main beam circuit now so much cooler :D

Dave
Click to expand...

An average of 18C per minute then, or .3C per second then.... wow, glad you now use relays! :)
 
I got a mixed pack of correct 32mm fuses today and had a very brief play.
Straight away I have all 4 headlamps again! :D
The heater fuse was indeed in the worst state, and it's the only holder to have slightly melted the plastic.
The heater wiring was actually disconnected behind the speaker housing, that's sorted apart from the lever earth strap.
Where is it meant to be connected to?
Thanks
Jim
 
Back in the 1990s, my heater (blower) stopped working on a hot Summer's day. Investigation revealed that the contacts that retained the fuse had become so hot that the plastic retaining them had melted.. :shock:

A friend who is an electronics technician checked behind the fuse box for a possible problem with the connection, such as a dry joint etc. He removed and resoldered the wire in question, and the contacts were moved back so as to hold the fuse in the appropriate manner. Testing revealed the blower to be working fine again, although having read of melted fuse boxes and fires etc on the forum, I have been somewhat reluctant to use it ever since. On the occasions that I did, placing my fingers on the fuse while in use showed no obvious increase in temperature.

I also have a fuse box that I removed out of a 1972 Rover 3500 that was being dismantled. I'll post some pics of both that fuse box and my own for comparison of fuse sizes and their location.

Ron.
 
Can anyone enlighten me on the lever earth connection?
Does it have a dedicated connection, I can see a couple of possibilities.
A light blue wire with bullet coming from up near the ignition, or a purple/brown wire connected to a braided wire with inline fuse

Jim
 
The fuses used in the series 2 fuse box, of different lengths were no doubt in the main fitted that way when Lucas was manufacturing them for installation into the Rover.

Ron.
 
Hi Ron

Not so. As manufactured all fuses were 32m length, which is an imperial size (forgive me if I don't calculate what that actually is!). 30mm fuses came along much later with the advent of SI units in the UK (adoption lagged substantially behind the "official" introduction around 1971 - both systems were in use for a lengthy period). I believe continental manufacturers always used blade and similar modern type fuses, so the 30mm fuses - and the fuse boxes to match - were probably just the Prince of Darkness trying to hitch a lift on the metric bandwagon. Just a pity that, at first sight, they appear to fit 32mm holders!

Chris
 
Hi Chris,

Now I am confused as most of the fuses in my fuse box are the originals, and they are all of different lengths. I have attached some photos,....
The first is that of a fuse box from a 1972 3500, a direct import from the U.K rather than via New Zealand.

PB250123.jpg

Only fuse 13-14 is the full length.

The next two photos are from my Rover.

PB250124.jpg

Fuse box

PB250125.jpg

I have replaced a couple of fuses over the years, the heater fuse being one of them. The replacements don't have the Lucas paper within.

Ron.
 
Ron,

My 1973 V8 fusebox looked exactly like the first pic you posted - all 'original' looking Lucas fuses with paper inserts, but too short nonetheless. Odd that the wrong fuses should have been installed at the factory, but this was British Leyland at the pinnacle of their daftness in the 70's. The P6 didn't win the AA 1974 Square Wheel award for nothing!

My own board had melted the headlamp fuse in a spectacular fashion, so I swapped it over for a good secondhand unit several years ago and changed all the fuses to new ones of the correct length, 1 1/4".
 
Hi Rp,

May be the problem isn't so much the fuse but rather the soldered connection behind it.... :?

I am thinking that if the fuse itself was the problem, then would not there have been a problem right from the word go? The first time the headlights or the heater for argument sake are switched on, there would be a problem if the current through the fuse was such that the surface area between its terminals and the contacts that retain it were less than sufficient to carry the circuit current. To work with no issues for years and to then give problems suggests that something has changed. If the fuse and the contact surface area has not changed, then what about the resistance of the soldered joint that links the wires to the fuse box contacts?

If the resistance of the soldered joint should increase, dry joint being a prime example, then that will see an increase in temperature as power is dissipated in the joint. The fuse box terminals retaining the fuse will increase in termperature as a direct result.

Ron.
 
I have just noticed a major difference between the fuse box from the 1972 3500 and my own. In the case of the former, the wires a clamped into terminals on the reverse side, they feed straight in. With my own fuse box, the wires turn at right angles on the reverse side and are all soldered in place.

Anyone who has had a fuse box melt, how were the wires connected on the reverse side,..clamped in or soldered in?

Ron.
 
I thought a relay in a lighting circuit was just to stop the current flowing through the switch, in which case it will have no effect on the current and hence temperature at the fuse? Normally you wire the relay so that the light switch only operates the relay, switching the power to the lights. You would need a separate in-line fuse for the lights and bypass the fusebox completely for it to have any benefit.
 
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