Can you give a practical example where you'd want/need to do this?

 

Sure. My water pump is rated at 7.5 amps. It is round trip 40' from my fuse box. The AWG sizing calculator I'm using (faroutride) says to use a 10 gauge wire. On all my wires, just to be safe, I'm going one size larger than recommended (maybe overkill?) - so there's the 8 gauge wire. The wires coming out of the pump look to be about 16 gauge (they're slightly smaller than the 14 gauge that I'm using).

 

There are "step down" butt connectors available, but if it were me I'd just find a size the smaller one still works with, and remove some strands from the larger one until it fits.

If you want to solder, size doesn't matter much.

You might also consider some sort of intermediate junction board/box, but I suspect that's more than needed.

 

Thanks Sparky961. I was thinking with such a big step-down I could maybe use a 12 gauge bridge wire in the middle and go with multiple step-down connectors? 8 => 12 => 16? But as you say, if I just solder them then size doesn't matter. So may just do that. Thanks for the ideas.

 

I'd avoid multiples. Every connection is adding a potential failure point, plus the chance of higher resistance than the original wire (depending on how it's done).

 

Good point, thanks!

 

Two options (I've done the same water-pump thing): fold the water-pump wire over and you should be able to put it into a butt-connector with the 10-gauge; preferred method (for me) is using disconnects. A 10-gauge disconnect will often fit the 16-gauge disconnect (M/F) depending which type you're using (bullet or blade, for example).

Also an option to twist them together and use a closed-end crimp connector. I often use those for temporary or odd-ball connections.

 

Because water pumps do fail eventually, along with many other devices, I used tab connectors for situations like the one you described above. I'm not a huge fan of them in-general, but if crimped properly and if the female tab has sufficient bite for a nice snug fit, then they work well enough. To get a smaller size to fit in a larger size tab crimp end, you just strip 2-3 times as much bare wire, then fold it over 2-3 times. That nearly always does the trick for me. Sometimes I'll solder a connection if the situation warrants, but soldering has issues like potential wicking if you get too much on.

This guy's technique and general advice are good. Worth the view even if not exactly the topic you're asking about:

Cheers.

 

Engineering wire size for Continuous Duty loads with 3% voltage drop makes sense. A water pump is an intermittent load, so a 10% voltage drop plan is adequate. see: 3% Voltage Drop & 10% Voltage Drop
Ring lugs will also work in joining the wires gauges you are considering, #8 & #14. The #14 you have should be fine for the pump motor even at lower battery voltages. If on the other hand, the load was electronics with a low voltage cutout, I would feed this type of load with a 3% voltage drop design.

Sparky, please add what I may have missed. I agree with sparky, "avoid multiples".

 

Delphi weather pack is your answer

easier to disconnect. Secure weathertight connection, connectors are all the same regardless of gauge wire. Get the whole set. You’ll use it

folding wires over or twisting them together is hacking it. Do it right. Do it once

 

Lol. Only $230 and you too can have space-grade tech for wiring up a simple van water pump. Hacker is a badge of honor in my book. I think I paid $1.49

Cheers.

 

lol you can buy a much smaller kit. I got the $300 kit and wired several vehicles with them. And still have plenty left over.

if your going to be working on vehicle wiring it’s good to have to make a much better finished product in the end

 

The best connection is a well done solder joint (use flux) covered in heatshrink tubing. If it's exposed to the weather, cover the solder joint with silicone or die-electric grease before installing the heatshrink. It will never ever ever ever fail.

 

Big wire IN small wires Out. You can get them at lowes, HD, Electrical supply places. They make them for all sizes of wiring.

https://www.alliedelec.com/product/marathon-special-products/1421570/70193131/

 

Big wire to fuse block and any size wire out from the fuse block. Pump wiring should be fused.

I used cords and did not have any splices in wiring. Used 14/3 for 120 volt AC, 12/2 for 12 volt DC outlets, 14/2 for water pump and Maxxair fan and 16/2 for LED lights. Two wires to every DC load.

Used two fuse blocks. 12 position one on driver side and 6 position one on passenger side powered from the 12 position. Only one DC cord from driver side to passenger side.

 

This is probably a silly question with an obvious answer:

Among some other reasons, we select wire size based on amps and distance. But why doesn't the step down in size (from 8ga to 16ga) affect this? Seems the 16ga wire should be included in the total amp load and distance that we impose when we select the 8ga wire, no?

 

Good question. I'm by no means an expert in this, but in my case, the 8a gets the current all the way to the appliance (pump, in this case) with a little drop in voltage as possible (hence the big fat 8a wire), but once there, it just connects to the 16a wires coming off the pump. If the pump were connecting directly to the fuse box or battery it could be connected directly with its 16a wires. No need for the big fat wire in between. I'm sure I screwed up lots of terminology there LOL.

 

The pump likely has wires that are sized for the length that's supplied. If you were to hook this directly to a power supply it would be fine. But when you're wanting those electrons to travel farther than the length of the supplied wires, you need to take the resistance of the wire into consideration. The longer the wire, the larger it needs to be to be the same resistance of a shorter length.

It's the same reason why the cross-sectional area of printed circuit board traces can be much smaller than the wire that carries current to or from the board. It's a very short distance, and thus the resistance is kept to a minimum.

 

Many have already said it. Fuse blocks!

 

Sizing up to 8AWG for a water pump that runs intermittently seems like overkill even with your 40' wire run. I used Ancor marine crimp connectors throughout my build. They are fast, strong, waterproof and pretty adaptable for different wire sizes. If you use 10AWG for this circuit, you'd make the splice with the 10-12AWG (yellow) connector. As others have suggested, you'll want to double up the 16 gauge wire by folding over the bare wire before inserting it in the connector and crimping it.

 

While searching for something else, I came across this document that has a bunch of interesting and presumably "Ford Approved" splice/crimp methods in graphic detail.

http://www.fordservicecontent.com/ford_content/catalog/accessory_files/2016_Series_100_RMST_Truck_7-16-2015.pdf