Lotus Elan

Fuse Ratings

PostPost by: KevJ+2 » Sat May 02, 2015 12:55 pm

I have now connected my new 6 way fuse box to replace my 2 way box in my '68+2. I have also fitted 4 fused relays.
Could anyone give me the correct fuse ratings for the items listed below. These are blade fuses not glass
Thanks in advance.
Wiper motor & stop light circuit.
Heater motor, reverse lights, indicators & gauges.
Fuel pump (5 amp I think)
Window motors main feed via relays
Interior lights, window switches, cigar lighter (purple circuit)
Fused relay - twin air horns
Fused relay - Radiator cooling fan (general rating as not bought yet)
Fused relay - High beam (may use halogens?)
Fused relay - Low beam " "
Light pod motors (via changeover relay)
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PostPost by: TroonSprint » Sat May 02, 2015 1:18 pm

Wiper motor & stop light circuit.
Heater motor, reverse lights & gauges.
Fuel pump (5 amp I think)
Window motors main feed via relays
Interior lights, window switches, cigar lighter (purple circuit)
Fused relay - twin air horns
Fused relay - Radiator cooling fan (general rating as not bought yet)
Fused relay - High beam (may use halogens?)
Fused relay - Low beam " "
Light pod motors (via changeover relay)

I have fitted a 12 fuse block on my Sprint and can tell you what I have used. You can calculate the amperage if you know the wattage of the item. For example, the main beams are 2x65 watt = 130 watt. 130 watt/12 volts = 10.1 amps. You want a bit of redundancy, so I would use 20 amp fuse.

On my car I have arranged the circuits differently as follows:
Fuel Gauge, Wipers, Washers, Indicators, Rev Counter - Fuse 1 - 15 amp.
Heater Fan, Brake Lights, Reverse Lights, Hand Brake Switch - Fuse 2 - 15 amp.
Fuel Pump, Ignition Coil - Fuse 3 - 15 amp.
Cooling Fan & Thermostatic Switch - Fuse 4 - 20 amp.
Headlamp Flash, Courtesy Lights - Fuse 5 - 20 amp.
Horn, Hazard Lights - Fuse 6 - 20 amp.
Cigarette Lighter Socket, Headlamp Pod Motors - Fuse 7 - 20 amp.
Side and Rear Lights - Fuse 8 - 15 amp.
Main Beam Lights - Fuse 9 - 20 amp.
Dip Beam Lights - Fuse 10 - 20 amp.
LH Window Motor - Fuse 11 - 20 amp.
RH Window Motor - Fuse 12 - 20 amp.

Like you, I am also using lots of relays to take the load off the switches. I haven't had a fuse blow yet!!! I hope this of some help.

Mike
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PostPost by: Bud English » Sat May 02, 2015 5:38 pm

The primary function of a fuse is to protect the wire, connectors or "load" from overheating and starting a fire. The fuse won't protect the load from itself. A radio protected by a 2 amp fuse is no safer than one protected by a 20 amp fuse.

The wire and fuse size should be determined by the smallest wire gauge in the circuit and the nature of the hazard posed by the load, not the load's normal operating current. Your wire size has been determined as you have the harness already installed so your fuse size can be chosen based on that. There's no need to limit the fuse size for, say the headlights, to something lower than the rating for the wire used as they themselves don't pose a fire hazard.

http://www.engineeringtoolbox.com/amps- ... d_730.html

Right about now is when Billwill will chime in and set us all straight. I think he's the resident guru on auto electrics and knows what's what. :D
Bud
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PostPost by: billwill » Sun May 03, 2015 11:33 pm

Bud English wrote:The primary function of a fuse is to protect the wire, connectors or "load" from overheating and starting a fire. The fuse won't protect the load from itself. A radio protected by a 2 amp fuse is no safer than one protected by a 20 amp fuse.

The wire and fuse size should be determined by the smallest wire gauge in the circuit and the nature of the hazard posed by the load, not the load's normal operating current. Your wire size has been determined as you have the harness already installed so your fuse size can be chosen based on that. There's no need to limit the fuse size for, say the headlights, to something lower than the rating for the wire used as they themselves don't pose a fire hazard.

http://www.engineeringtoolbox.com/amps- ... d_730.html

Right about now is when Billwill will chime in and set us all straight. I think he's the resident guru on auto electrics and knows what's what. :D


What Bud says sounds fine to me. The wires need protecting, but also any wires in the devices need protecting too and they are usually much finer than the harness wires, especially in motors (windows and washers and heater fan) and relays & solenoids, so you can't go entirely by the harness wire size, so a rule of thumb of 1.5 to 2 times the normal operating current of the device will serve as a guide.

Fires are unlikey to start in a headlight, but can start in motors or solenoids/relays.
Bill Williams

36/6725 S3 Coupe OGU108E Yellow over Black.
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