Master switches & fusible links ??

[Ohio Blue Tip]

Some folks seem to be well versed in electrical systems, what and where do you recommend master fuses or fusible links and what capacity for general street rods.
I have, over the years, done a fare amount of rod wiring and usually use a master disconnect switch in the battery positive cable. The last car I did we used a master fuse in the battery, alternator, starter loop. I would like more of this protection incorporated into wiring systems and as I do most jobs from scratch, I would like to know capacity and location that would be best to protect most rods.

[HOTRODSRJ]

Some folks seem to be well versed in electrical systems, what and where do you recommend master fuses or fusible links and what capacity for general street? I would like more of this protection incorporated into wiring systems and as I do most jobs from scratch, I would like to know capacity and location that would be best to protect most rods.

I would like just to throw my general response in for this purpose.

First, automotive wiring has become more and more complicated as it grows toward the more modern auto designs with the likes of power everything, EFI and high capacity batteries, charging systems and wiring to go with and even EMI/RFI and sophisticated alarm issues coming to the surface. As we all know it used to be a simple 8 or 9 circuit issue and pretty straight forward.

I would like to address the subject of capacity first and I could easily write many pages on this, but others I am sure will chime in with their experiences and takes as well. This depends more or less on your system's design or application's demand. As I have pointed out, some applications such as roadsters and others with little or no auxillery power needs, have a very simple demand and relatively light loading compared to modern day vehicles. The way I figure demand is do a balance sheet of peak load then add another 50% for main fusing. Lightly loaded systems often require no more than a 100 amp fuse (keep in mind that I ONLY USE mini starters and do not use the old boat anchors/starters of yesteryear which take more current ...alot more current!). I jump from there to a 150amp main fuse on most applications up to 100amp peak/nominal DC current loads. I locate all my main fuses within 18" of the battery itself regardless of location. This protects all but 18" of the main feed wherever it goes.

My 57 Belair is just about as power burdened as you can get and I have never exceeded 100 amps peak (I actually have a DC shunt that can easily measure this accurately) nominally. This includes a 25 amp cooling fan, 1200watt stereo, six-way power seats, high wattage headlights, air, yadda yadda yadda. The 150amp main fuse is what protects the total system.

But, fusible links or the more modern maxifuses are necessary too to compliment the main protection system. Again, the capacity of the fusible links depends on the alternator and bus demand. I put my links nearest the feeding source. This protects the whole bus branch. So my fusible link from the alternator is at the alternator. My maxifuse(s) is located at the source of the feed for the fuseblock and/or relay bus.

I do have some wiring/electrical system suggestions to keep things more with modern OEM designs and specifications. These are MY suggestions.

1. Always located your main fuse within 18" of your battery....actually the closer the better.
2. On-off switches offer no practical protection for system dynamic situations. Plan accordingly.
3. Aux relay any circuits that are over 10 amps external to the interior, if possible (you will have brighter headlights, more output from fans and less voltage drops due to length of wire and connections).
4. Always use fusible links or maxifuses accordingly.
5. Use high quality automotive/appropriately rated wire/insulation for all circuits. This includes battery cables. (and this will open up a can of worms...I know alot of guys out there using rubber coated welding wire/cable and while these are great conductors and very flexible cables.... if not installed correctly with the ends completely sealed from the elements they will wick water up in the cable itself and eventually fail...quickly. Notwithstanding that fact, the coating/insulation is NOT rated for fuel fires and/or heat and can easily be compromised in a high heat or fire situation adding another problem in a simple fuel fire to becoming an electrical issue as well. There is just too much other engineered cables for this purpose and I highly recommend them albeit more $$$).
6. Use only quality crimping tools, skip the cheap ones. Usually gas tight connections are wanted for all applications. With quality crimps, soldering is not necessary at all!
7. When replacing an old battery, consider a newer technology such as a spiral-cell technology (Optima). These do not leak acid, no gassing, provide a longer shelf charge (meaning no tender necessary), and can be mounted in any attitude you can invent.
8. Dump your old fashion field-wound starters. These take tons of current, are hard on your battery, require large conductors/connectors, heat soak easily, weigh a ton and are now relatively huge compared to perm mag starters....what else do you need to know?
9. Use quality automotive relays that are rated at least 30 amps and most preferably 40amps and in some cooling fan situations....70amps! Pay attention to the nominal currents of these devices for reliable designs.
10. Use "bucking" diodes on cooling fans of more than 15amps. This will eliminate large inductive spikes on your system.
11. Relay sockets (not PC board ones!) are preferable to just relay wires with terminal connections.
12. Do not put any mechanical stress or torsion or at least minimize such on any electrical wire or connection.
14. Screw clamping/termination type fuse blocks are prone to heat cycling issues and failure. I highly recommend against them. The GM block designs/types are as good as it gets.

I am sure others will have more to offer on this subject.

[Jokester]

The rule is to use 4 numbers smaller than the gauge of the wire being protected.  For example, a 10 gauge wire should use a 14 gauge fusible link.  

OE manufacturers seem to put them on the positive battery cable's auxiliary leads.  

My 2 cents.


.bjb

[enjenjo]

Another thing, Maxifuses fail instantly, fuesable links are more of a slow blow fuse. Keep this in mind when designing your system.

[HOTRODSRJ]

Another thing, Maxifuses fail instantly, fuesable links are more of a slow blow fuse. Keep this in mind when designing your system.

Well...that can be a good thing in most cases.  Their (maxifuses) failure curves are more "designed" and "specific" than the old fusible links which were relatively poor in performance as far as predicting exacting current capacity over time.

Maxifuses (mid 80s design) and the cartridge style fuses known as JCASE (mid 90s design) were designed for the purpose of replacing fusible wire and fusible links and are in fact the preferred product of application over wire fusible links. The maxifuses are much slower in "blow" time than the JCASE styles.  Typical "blow" times are about a second for maxifuse applications at five times the current as opposed to about one-third of a second for a comparitive JCASE cartridge.  These devices will NOT drop the voltage like fusible links inherently do. This is a good thing in all circuits.

But......in applications larger than 100 amps...you will still need to stick to master fuse technology and/or wire fusible links.

[enjenjo]

My point was , for something like a master fuse for anything including a computer, a maxifuse might be the right answer, but for an alternator, a fuseable link may be better. FWIW, I have been using a maxifuse on all my wiring jobs for tha last several years, 50 amp mostly, and that seems to be big enough. I have had one blow with a short circuit, so I know they are working.

[HOTRODSRJ]

My point was , for something like a master fuse for anything including a computer, a maxifuse might be the right answer, but for an alternator, a fuseable link may be better.

Yep....exactly.  With the high currents involved, maxifuses are not available for alts etc.  Your point is well taken.

[Ohio Blue Tip]

Good discussions.  Now could you help educate an old school rodder that's a little out of date?
What is the deference between a "Maxifuse" and a "Master Fuse"?
Do you buy your "Fusible Links" or make them?
What size, type and location protection would you use on a street rod with the following;
Optima battery
100A  alternator
High power electric fan
Power windows
Power trunk lift
Electric wipers
Heat & Air
Electronic cruse control
CD changer and stout sound system
Power seat
Thanks, Ken

[rooster]

Good discussions.  Now could you help educate an old school rodder that's a little out of date?
What is the deference between a "Maxifuse" and a "Master Fuse"?
Do you buy your "Fusible Links" or make them?
What size, type and location protection would you use on a street rod with the following;
Optima battery
100A  alternator
High power electric fan
Power windows
Power trunk lift
Electric wipers
Heat & Air
Electronic cruse control
CD changer and stout sound system
Power seat
Thanks, Ken

Ken, Maxie fuse is a brand name, you can get them and luseable links at a parts store. The fuseable link wire you use is determined by the guage wire your connecting it to, the fusable link will allways be smaller.

As for what size Maxie fuse to use in your descibed system I will have to say 30 amp. The Maxie Fuse is connected close to the battery where you can get to it in case of a blow. It protects the main power feed to the fuse box in the car.

If you make additional wiring harness's for the lights, alt, fan, you will need to protect them also. I see no reason why these additional circuts should not be protected with a additional maxie fuse. You could also use a Fuseable link. The Maxie fuse would be much easyer to replace. Additional if you needed to place a charger on the battery you could just pull the maxie fuse to protect the diodes in the alt.