Fuses

[CapRic]

What size Lucas fuses should I be using in my 1971 TVR Vixen?

There are 4 or 5 on the firewall (& 1 under the dash for horn, lighter, & hazards).

Are they all the same size, like the TR6 (35amp) ??

My car has *30A USA* fuses & I know that's too high for a LBC, right?

So, would *35A LUCAS* be appropriate for all fuse locations?

Thanks!!

[CapRic]

Exactly.

Altho Amps=Amps on both sides of the pond.......

The British fuses are rated at the "instantaneous blow" rate. A British fuse of 35A will blow at 35A & therefore the wiring design only needs to carry up to that load.

The USA fuses are rated at a "continuous load" rate, & will blow at a much higher amperage (although they will carry the *rated* amps continuously without blowing). A 35A fuse may need something like 45A or more to actually blow.

The TR6 takes all 35A British fuses. The Triumph guys are careful to use British fuses.

My TVR Owners Manual doesn't give the specs on the fuses. So I was going to change them all out to 35A British fuses.

What are you guys running in your older TVRs? I have a '71 Vixen 2500 (non-M era).

Edited by CapRic on Tuesday 16th January 03:18

Edited by CapRic on Tuesday 16th January 03:19

[CapRic]

OK, thanks for all the info.

Seems like the easy way out would be to use all Lucas 35A fuses.

Actual Amp measurement might be a good tinkering project when the weather warms up.

However, it's more a question of, "What amperage will melt the wires & switches on a 70's TVR?" Then, of course, restrict the Amps (fuse) to something below that, regardless of the actual Amp draw of components.

I would guess that the wiring & switching is a bit more robust than what the components on any circuit actually need. (Probably like the TR6, the TVR electrical design will support up to 35A.)

[CapRic]

Penelope Stopit said:

The chances are that your TVR is mostly wired with 14/0.30 8.75 Amp and 28/0.30 17.5 Amp cable
The fuses are of a higher rating than the cable which means that the cable can begin to melt before blowing the fuse that protects it

If that's the case, then the 35 [instantaneous blow] Amp fuses originally designed into the system, basically do *nothing* (since the wire will melt/burn up, before the 35A fuse will melt/burn up/"blow"). That's as good as NO fuses at all.

In 46 years, my TVR has survived with, effectively, no fuse protection?

To put it another way, .....No fuse has ever blown on an original TVR? (Since, for *that* to happen, one would have to draw a level of amps across the fuse from wires that won't support that level of amperage!)

I'm not disputing anything here, I'm just trying to understand this.

What about other LBCs with the 35A British fuse design? The TR6 has more fuses than the TVR, but they're all 35A British. Did Triumph also use wires capable of only 8.75A & 17.5A ??

[CapRic]

Penelope Stopit said:

The whole idea of building a good wiring harness is to use cable that is sufficient to carry the current of its particular circuit allowing for volt drops that are dependant upon length, there is no point in using cable that is bigger than needed as it will be adding weight to the vehicle
<snip>
Now you know why cars of today have more fuses, manufacturers slowly learnt the hard way, <snip>

That makes sense. I get it now.

The problem isn't insufficient size cable, ....it's fuses that are too large (I suppose due to the *few* number of fuses/circuits used).

The solution, as pointed out above: Design a greater number of fused circuits, with the appropriate [lower amp] fuses.

Ah, another project on the drawing board!