Wire sizes and Fusing

[Janncwebb]

Oh, I’m so confused! What gauge of wire do I need to go from battery to inside the van?

 

[John61CT]

Calculated by round-trip distance and the maximum amps you expect to flow through the wires.

Minimum gauge is for safety, minimizing voltage drop, say to 1%, requires thicker wire.

Blue Seas Circuit Wizard app is an excellent tool

 

[Weight]

Tell us what length, positive and negative, two wires. Tell us what you will power with those wires. Just alternator charging? Running the inverter? Or in between. Then we will show you where and how to look up your requirements. That includes AWG (american wire gauge), Cable ends, fuses and fuse holders. Maybe switches. STSP (single pole single throw), DPST (double pole single throw), Well I know what I am talking about even if others don't.

 

[highdesertranger]

thanks Weight for including definitions with your abbreviations. highdesertranger

 

[poot_traveller]

Just a question about a pulling a fuse under load.

I have a fuse between the panel and controller, I know I can't disconnect under load but I'm wondering if I can pull the fuse under load? That's in the event I won't be using solar for a few days, that's why I ask if I can pull the fuse.

 

[MrAlvinDude]

Just a question about a pulling a fuse under load.

I have a fuse between the panel and controller, I know I can't disconnect under load but I'm wondering if I can pull the fuse under load?  That's in the event I won't be using solar for a few days, that's why I ask if I can pull the fuse.

You can pull a fuse under load, but expect to see a spark (or worse, an arc).  So it is not advisable, but in can be done. 

So if you do need to pull a fuse under load, do it quickly, and if possible use a tool, preferably a plastic fuse pulling tool.

Sparks (or an arc) happens with switches as well (but inside the switch).
Most switches will be designed so they can endure being used many times, as in; the spark can happen many times before the switch degrades. Also, the switch design will protect the user from potentially getting in contact with the spark.

When pulling a fuse under load, the design does not include this same user protection, and thus it is advisable to use a tool (so as to keep ones fingers out of the way), and to pull it quickly (so the spark/arc will have a shorter time to exist). 


The best advise is of cause to include a switch somewhere in the circuit.

 

[bullfrog]

Covering the panel and then pull the fuse works best for me. I just throw one of those fee Harbor Freight moving quilts over the panel. I pull the fuse in case the quilt falls off while working.

 

[B and C]

A properly set solar charge controller shouldn't need to be disconnected. It is a good way to maintain the batteries unless I forgot that you have LifePo4 batteries. And yes, you can pull a fuse under load. When a fuse blows it is under load and in and of itself doesn't cause a problem. By pulling the fuse it is the same in the circuit as if the fuse blew. Just pull it out firmly and not let lt reconnect immediately, electronics don't always like the fast reconnect.

 

[Yohan]

Can anybody tell me if I still need to put an inline fuse between my starter battery and auxiliary battery if I'm already going to have a class T fuse between inverter and auxiliary?

 

[Yohan]

If I'm running 6 gauge wire from my relay to my auxiliary battery. Is it ok to run 4 gauge from my auxiliary to my inverter or should all wiring be the same gauge throughout system? The guy at Samlex told me 6 gauge was fine with their Samlex 100 amp class T fuse. They don't offer a lower amp one. However, both their diagram and this diagram say I should use a 80 amp fuse for 6 gauge wire.

 

[Trebor English]

Can anybody tell me if I still need to put an inline fuse between my starter battery and auxiliary battery if I'm already going to have a class T fuse between inverter and auxiliary?

Every wire needs to be protected from too much current at every point where power can be applied.  This can be a circuit interrupter like a fuse or it can be a current limited source. 

For example,  on a 65 chevy (pre computer) there is a wire from the left headlight to ground.  The left headlight, about 60 watts, will only pass about 5 amps.  If that wire chafes on a sharp edge and shorts there is no problem if it is big enough to carry the full current from its source, the light bulb.  No fuse is needed. 

Batteries are generally not current limited as they store energy.  However, if the wire really is big enough, if the wire chafes on a sharp edge and shorts it can carry the current.  The cold cranking amps rating of the battery may be helpful as a lower bound in deciding how much current the battery can produce.  The CCA rating is not a short circuit current and your system failure will probably not happen at zero degrees.  I suggest using 10 times the CCA for at least 30 seconds when picking the wire size to make sure the wire doesn't need a fuse to protect from the full current of the battery. 

My Ford has no fuse in the big fat red wire from the battery to the starter motor.  Part of it is protected by corrugated plastic tube. 

When the wire connects one battery to another it needs protection at both ends.  The wire can chafe on a sharp edge and short anywhere along its length.  That will, of course, only happen when the charging switch is on.  There is no place between the two ends where a fuse will protect the entire wire.  

To fuse or not to fuse is a question.  If you understand the issues and select the battery size and wire size, it's up to you.  Personally, my choice is to put in fuses not breakers.  

The Wikipedia AWG chart has current recommendations based on insulation temperature rating and time, continuous and 1 second fuse blowing.   These are worth considering.  
https://en.m.wikipedia.org/wiki/American_wire_gauge

 

[Trebor English]

If I'm running 6 gauge wire from my relay to my auxiliary battery. Is it ok to run 4 gauge  . . .

You can put a fuse at the auxiliary battery then connect from the one fuse to both the inverter load and the alternator/starter battery.  If you use a 100 amp fuse make sure that all the wires are big enough to withstand the 100 amps long enough to blow that fuse.  Following the 100 amp fuse with more fuses like a fuse box full of 10, 20, and 30 amp fuses is perfectly reasonable.   

The wire from the auxiliary battery fuse, 100 amps, could also get current from the starter battery.  If you put a 100 amp fuse at the starter battery then the fuse box cable needs to be big enough to blow 200 amps of fuse.  That's not a continuous rating just a 10 second fuse blowing rating.   AWG #12 would be enough for that and you would want a bigger wire to give good voltage drop performance.

 

[happyVanderer]

This is helpful information. I read this, though, and for me it isn't as easy as people make it sound. However, I will keep learning so I can put fuses in my system so I don't burn my rig up. Keep the info coming!