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MG TD TF 1500 - TD Fuses

The fuse that controls the accessories in my 52 TD has blown, and inseeking to replace it I checked the MG shop manual. It tells me to replace with a like rated fuse. The PO had a 15 amp fuse in place. The parts catalogue for Moss lists 50 amp fuses. Is there a correct fuse?
Thanks.
K Martin

Martin,
I think the correct fuse is a lucas 17amp fuse with a 35 amp blow rate. I got mine from The MGB Hive in NC.
Dave
Dave Kalp

British made fuses are described differently. A 50 amp British fuse is 25 amp hold. That is: its continuous current capacity is 25 amps. It will blow with an overload of 50 amp or a surge which exceeds 50 amp. You can use the American designated 15-17 amp (30-35 amp British) slow blow fuse. The generator is only capable of 17 or 19 amps on the TD-TF and most of that goes to the lights which aren't fused. A 15 amp slow blow fuse is intirely adequate except for the horns. Depending on their condition and adjustment a 15 amp may blow.
Blake

The generator capacity has nothing to do with fuse ratings. Your battery can generate instantaneous currents of hundreds of amps and THAT is what the fuse is there for. To protect your components and wiring loom from disgorging all of the factory installed smoke sealed into the wires, as we all know when the smoke gets out the wires are useless.
Phil Stafford

K Martin, You should check your electrical system to see why the fuse blew. Remember LUCAS!!

Don
Don

Phil:

A fuse's main function is to keep the current in a wire below the wire's capacity. A contiuous draw of 20 amps in a wire designed to carry only 15 amps is just as much a hazzard as a direct short.

What I meant was there is no need to use any fuse greater than the output of the generator: 17 or 19 amps. If the electrical demand is greater than 19 amps you'll be draining the battery and having to recharge the battery at home. A 17 or 19 amp Buss fuse will more readily blow on a slight continous overload than will a larger fuse. This would then save that 50 year old wiring where a larger fuse would not.

I have fused the lighting ciruit on my TD with a 15 amp BUSS fuse. This summer I made a 200 mile trip at night using 50 watt halogen heads and a 50 watt driving lamp. After about 1 hour, the fuse blew. Thus a fuse also protects against over loading while the wires will still carry the current. In the USA the fuse rating in a circuit is quite often 1/2 the carrying capacity of the wire.

G.day
Blake

Pardon the input from a "TF" owner (not TD)....but it seems to me I have seen a lot of talk on this BBS concerning the "test jacks" on the dash of the TD.
Would it be a good idea to have a "look" at that one before replacing the fuse? I added a "test jack" to my TF ...but on the advise of several TD owners I did not use the "orginal style" jack as they had told me these are prone to shorts. I used a more modern type jack as the "isolation" was better and hid it under the dash... switched and fused it does fit my old "period" lighting toys that have these plugs on them.
I'm sure those that have TD's will have a better knowledge of this...but wouldn't that be a good one to check first?
Cheers,
David 55 TF1500 #7427
David Sheward

Dave:

The "Inspection Lamp" (accessory plug in) socket is not fused on the TD. A short here won't blow fuses, just burn up the wiring. It is wired directly from the main power supply coming from the starter switch. I also added a fuse to that circuit.

G'day
Blake

Bottom line is you need wire of sufficient thickness, and robust switch contacts, to take the amps.

You can calculate the amps using the formula Amps x Volts = Watts so in Blake's case two head lamps at 50W each and a driving lamp at 50W consumed 150W. With a TD's 12V system this would have drawn about 13A. Add into this a little extra for heating of the feed wires (and possibly the side and tail lamps - if they were on the same fuse)and it's obviously why the fuse blew.

Thicker cables can take more amps. Cables are normally specified in terms of the number of strands and the diameter of each strand. For info I list some of the more common sizes

9 strands x 0.30mm diameter = 5 Amps
14 8
28 17
44 27
65 35

Don't know how many amps T series headlamp switches can take but am sure someone will be able to advise us.


Jan t
Jan Targosz

This thread was discussed between 06/01/2003 and 08/01/2003

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