Blade fusebox

[michaeldavis39]

I have recently bought a blade fusebox which will still take the original Lucas fusebox cover- so it looks original but has the more modern blade fuses for reliability. The fuses shown are just what came with it and won't be suitable so are being replaced. I havent seen anyone mention this item for sale anywhere so thought I would post a link to it on here for anyone interested.

https://www.torquerestoparts.com/product-page/triumph

 

[DRD]

I've got one of those, very easy to switch it over.

[Richard71]

Is there a UK based vendor?

Richard 

[Andy Moltu]

They supply pretty quick from the USA. 
Make sure you get the TR one. The MG/Mini one  has the two middle fuses linked pre fuse. The link is easy to cut but caused Me a bit of head scratching. They offered to send me a replacement but declined asI had sorted it.

[michaeldavis39]

Took just over 2 weeks from USA- no UK supplier.

[barkerwilliams]

If you fit one please remember that the rating of the old glass fuse is the current it will continuously pass, so a 15 amp glass fuse will blow at 30 amps, a blade fuse of 15 amps should blow at 16 amps. 

So a little experimentation and a few spare fuses needed.

Alan

[RobH]

5 hours ago, barkerwilliams said:

If you fit one please remember that the rating of the old glass fuse is the current it will continuously pass, so a 15 amp glass fuse will blow at 30 amps, a blade fuse of 15 amps should blow at 16 amps

Sorry Alan - that is wrong, you have it muddled.   Fuses are not precision devices. A 15A blade fuse will probably not blow on 16 amps, and might not on 17 or 18 either. It should at 20A though maybe after some minutes, exactly the same as for a glass one of the same rating.   

A fuse blows because of the heat generated due to the current through its internal resistance. (I^2 R heating).  It has to become hot enough for the element to melt and the time taken for the heat to build up will be very long if the overload is small.  The makers publish curves of overload versus time e.g this one (for illustration only - these are not automotive fuses):

ALL fuses rated  at a  continuous current  might eventually blow on a higher current but the time it takes to do so depends on the degree of overload,  and that applies to blade and glass fuses equally..   They will both require a load of around twice the continuous rating in order to blow quickly  - in under a second. 

Lucas caused confusion by giving their fuses two numbers - the 'must blow' rating and the 'continuous' rating - all other fuse types quote only the 'continuous' number.   The UK car makers compounded the confusion by only using the 'must blow' number in their literature and circuit diagrams for our cars.  A circuit calling for a '30A blow'  Lucas fuse requires only a 15A modern one - glass or blade. 

 

Edited August 10, 2025 by RobH

[RogerH]

Simples 

[Chilliman]

Another useful bit of education, thank you Rob.

[GreatOldOne]

So I almost bought one. Then saw that shipping was almost the same as the cost of the fuse box… I’m thinking I might investigate creating something similar in CAD and making my own. For now the blade fuse holder adaptor plate I have is working fine, so no rush. 

[Mike C]

12 hours ago, GreatOldOne said:

So I almost bought one. Then saw that shipping was almost the same as the cost of the fuse box… I’m thinking I might investigate creating something similar in CAD and making my own. For now the blade fuse holder adaptor plate I have is working fine, so no rush. 

For interest, I was looking for a gearbox top cover gasket last week. The price from most UK suppliers was about five pounds for the gasket with around 50 pounds postage to Australia. International postage costs have never reset after the  covid increases.

[michaeldavis39]

Fitted USA fusebox today. All went well.

 

Edited September 3, 2025 by michaeldavis39
Update for more detail

[GreatOldOne]

So I’ve been busy in Fusion, and come up with this using readily available parts:

Ignore the blue plastic; that’s just what I have loaded in the printer. Once finalised it’ll be black ABS or something similar. Is it a one to one, exact copy of the original Lucas? No, but it looks like it, and all the important dimensions (fixing points etc) are correct.

I’m toying with the idea of adding LED ‘fuse blown’ indicators, if I can work out how they work. And I’ll also do a lid for it, as the original won’t fit currently due to the stem. All in its about 5mm bigger in all directions bar height, where it’s only a couple of mm higher. 
 

Once everything is done I’ll publish the files on Printables. The fuse holders a quid or so each, and the twin adaptors are again not much for a bag of 20 or so. 
 

Cheers

Jason

[michaeldavis39]

Well done- but factoring your time and the equipment you have obviously for most people its cheaper to buy from USA. Perhaps you would think about making and selling them here?

[RobH]

1 hour ago, GreatOldOne said:

I’m toying with the idea of adding LED ‘fuse blown’ indicators, if I can work out how they work.

LED fuse indicators are simple.   You just need the LED and a resistor in series, connected across the fuse - though the LED has to be the right way round.    The resistor is to limit the current - 5milliamps ought to be enough so for 3v LED and a 12v supply the resistor is 1800 Ohms ( written as 1k8 ).   

When the fuse is intact, the LED is shorted out.  When the fuse blows, the LED and resistor have 12v across them so it lights up. 

 

 

[GreatOldOne]

Thanks Rob, I’d found similar online. 🤓

Now I have to see if I can shoehorn them in. 3mm leds should fit between the blades, and then I need pockets for the resistors. And I might be able to add a hole for the stem of an original lid.

[PodOne]

1 hour ago, GreatOldOne said:

Thanks Rob, I’d found similar online. 🤓

Now I have to see if I can shoehorn them in. 3mm leds should fit between the blades, and then I need pockets for the resistors. And I might be able to add a hole for the stem of an original lid.

Nice project more so if you can fit in the LEDs and keep it looking original. Suspect there would be a ready market for it over the glass fuses.

Andy

[JohnC]

1 hour ago, PodOne said:

Suspect there would be a ready market for it over the glass fuses.

Particularly if it's available for free via Printables. So many people have (or know somebody who has) a 3D printer. I totally love your work. Wish I could contribute in the same way.

JC

[GreatOldOne]

I have one of each printing at the moment. 

I thought it might be fun to have my name on it... 'Jason, Viscount of the Slightly Overcast" 🙃

[PodOne]

Sorry to spoil the party but what about these?

 https://www.etsy.com/uk/listing/1378662754/us-cars-vintage-4-sizes-available?gpla=1&gao=1&utm_source=connexity&utm_medium=cpc&utm_campaign=shopping_uk_google&utm_content=Cj0KCQjwzt_FBhCEARIsAJGFWVmnmBHRPsXTcJdoPtiZ_OZ_srvPfJ7WDjgmuXVUp3zeCKsC9mCIZFUaApoCEALw_wcB&gad_source=1&gad_campaignid=17258071114&gbraid=0AAAAAD_PDJk6OfZMG7NXbU3I9ds-T__ec&gclid=Cj0KCQjwzt_FBhCEARIsAJGFWVmnmBHRPsXTcJdoPtiZ_OZ_srvPfJ7WDjgmuXVUp3zeCKsC9mCIZFUaApoCEALw_wcB

What length are the glass fuses in the Lucas box?

Andy

[RobH]

30 minutes ago, PodOne said:

Sorry to spoil the party but what about these?

What an odd thing .  How is that better than just keeping the glass fuse?  They are still relying on the less-than-wonderful round fuse clip, which is often the weak point. 

[PodOne]

7 minutes ago, RobH said:

What an odd thing .  How is that better than just keeping the glass fuse?  They are still relying on the less-than-wonderful round fuse clip, which is often the weak point. 

True Rob. 

I was thinking that after I posted as any corrosion is going to be just the same potential hot spot. I wonder if they could be soldered into a new Lucas box with no corrosion?

Still someone wanting rid of the glass fuses while keeping the original look. 

[michaeldavis39]

I think the best option for keeping the original look with blade fuses is still the option from the States- if you look at my photos its very hard to tell with the cover on- which does fit perfectly too.

[DRD]

13 hours ago, michaeldavis39 said:

I think the best option for keeping the original look with blade fuses is still the option from the States- if you look at my photos its very hard to tell with the cover on- which does fit perfectly too.

+1

[GreatOldOne]

Prototyping done. It now has pockets for fuse out led indicators, and can be used with the original lid or a printed one. I need to grab some black ABS and print one out for actual usage.

Edited September 6, 2025 by GreatOldOne