Glass to Blade fuse ratings

Hi,

I've googled this but just want to check I have this correct and, as I see that a number of people have switched their fuses from glass to blades, I'm hoping someone can confirm.

My understanding is that glass fuses used in old British cars are rated at the current they are designed to blow while modern blades are rated at what they are designed to hold at.

When I started trying to compare the fuses in my Ninety to the blade ratings I come out with the following. Are these correct?

Glass Blade
17A 7.5A
12A 5A
10A 5A
8A 3A
2.5A 1A

The ratings that do not exist when divided by 2 I am assuming are the next 1 down.

So, do I have this right or have I got it all wrong and going to set fire to the Landy? I'd hate to do that having spent my whole holiday getting it ready for the MOT!

I don't know whether the older fuses are HRC (high rated cartridge) fuses or not, but if you plan to change them for the blade types you've listed then you're unlikely to set fire to you Landy; all the new ratings are well down on the old ones.

It's worth a try at the fuse ratings you have, but be prepared for some to pop and then you can replace them with the next rating up.

Fires generally start in the electrics if a circuit has no fuse or the fuse is way too big for the job.

As a rule of thumb a circuit should be fused, and if you have a multimeter then you can measure the current drawn by the circuit and fuse it accordingly.

I found that when I changed mine over to blade fuses if I used new fuses to the same rating as the old glass ones they tended to blow, more so the headlights. Changed to the next rating up and they've been fine

the_wolf said:

I found that when I changed mine over to blade fuses if I used new fuses to the same rating as the old glass ones they tended to blow, more so the headlights. Changed to the next rating up and they've been fine

Click to expand...

Hmmm. Interesting. This adds to my confusion just when I thought I might have figured it out

Kev@kenninghall said:

Hmmm. Interesting. This adds to my confusion just when I thought I might have figured it out

Click to expand...

Then there are the ones that have a different rating between constant and "pulse?" Raisins.

I've found blade fuses to be more sensitive. Where items are protected by both a glass one and a blade fuse it's always the blade fuse that blows first, assuming similar ratings. Maybe the glass ones take a little while longer to heat up.

If you post what circuit in turn you have wired then some one will tell you what fuse they use ,
I mean its been done so some one will know

10amp and 25amp should do

I haven't done any yet. I'm planning on doing the lot this weekend. 10A seems a little high when some are currently 2.5A.

I guess I'll start with the amp metre and see what they draw and go from there.

A lot of appliances draw a high current briefly when they start up, and then settle down to their rated current once they've heated up or a bit of 'back emf' has had a chance to build up. The old fuses, where the fuse is a bit of wire in a glass tube might be a bit slower to blow than blade ones. So it might be rather like with domestic wiring where the old rewirable fuses were more forgiving of high start currents than modern MCBs.

I just did mine, and I just put the same rating in not had any problems so far, the only one I had issue with, was that one of the glass fusees was rated at 60amp and the blade fusees only went up to 30 that I had so I have one of them in but its not gone yet...


20130819_144304 by Abhorsen The Final Death, on Flickr

I wouldn't expect blowing fuses if stuck the same sizes back in though, more like a fire!

That's my point, a 10A old glass fuse is not meant to same 10A as a modern blade fuse.

My understanding is that a 10A glass automotive fuse actually blows at 10A whereas a 10A blade fuse is expected to work at 10A and blow at some level over that. So, if I just replace like with like I'm possibly risking wire damage before the fuse goes.

I'd rather get the right values in there. I'll to some comparisons with wiring diagrams and see what newer landies use.

Anyone know when they started to use blade fuses in new landies?

200tdi I think.

try this...

fuse tyres ratings and capacities

and possibly this

blade fuse curve

Should give you the info you need to make the decision...

first ones a PDF...

Thanks for the suggestions and links. In the end I asked the auto electricians I bought the fuse box from and they recommended just using the closest rating at or below the ratings that should be there.