What to do for a fuse ?

[shankos]

I am not an electronics person so looking for some assistance.

I am running two pumps that are rated for a 25 amp fuse each.

I have one main power line that brings the power to the pumps from the battery. I then split this power line into two and connect it to each of the pumps.

I was told by a shop keeper to put a 50 amp fuse on the main electrical line as two pumps are running via this line.

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However I was unsure if this is correct. The reason being I may be running one pump at a time or I may be running two pumps. When I am running one pump then the 50 amp fuse will be higher then the single pump 25 amp rating.

So could i or should i put a 25 amp fuse on the power line after i split it into two to connect to the two pumps.

 

[Diver300]

If the pumps are rated to work with a 25 A fuse, then a larger one would probably not protect the pump if it jammed.

Running two pumps from one fuse could make the fuse blow if both pumps start at the same time.

So you should put a 25 A fuse feeding each pump.

That leaves the wire from the battery all the way to the fuses unprotected. If that shorts to ground, the wire will be damaged. So you should put a 50A fuse as close to the battery as possible.

 

[shankos]

**broken link removed**

Is this what you mean in the diagram it is showing just the positive line from the battery terminal two the pumps.

I run 8g wire before i split it into 12g wire to go to each pump.

I also have a switch which would be located just after the 25 amp fuse in the diagram to turn the pumps on/off individually.

Is it ok to split a power line with a 50amp fuse and the put a 25 amp fuse on each power line after the split ?

I am guessing if one pump is running only 25 amps will be drawn from the battery through the 50 amp fuse but if both are running 50 amps will be drawn through the 50 amp fuse. each pump will only draw 25amps via the 25 amp fuse after the split in the power line.

Is this correct ?

 

[RMMM]

That diagram and your theory of its operation, is correct.

 

[4pyros]

The 50 amp fuse is just to protect the 8 gage wire and must be as close to the battery as posible. The 8 gage wire must go all the way to the 25 amp fuses. You can not split the 8 gage wire into two 12 gage wires and then fuse them because the 12 gage wire could burn in an overload before the 8 gage wire, Get it ? Andy

 

[shankos]

4pyros: you seem to be saying not to run the 25 amp fuses on the 12 gauge wire ?

The others are recommending to do so to protect the individual pumps.

My aim is to protect the pumps and not so much the wire.

I ran 8 gage wire to keep high voltage untill it was split to the two pumps. It was 6 meters in distance from the battery. The 12 gage wire was then used to run to each of the pumps as it was split at this time into two. A switch goes just after the split. The 12 gage wire then runs another 5 meters to the pumps.

 

[Reloadron]

Typically AWG 12 wire is rated for 20 Amp service. This can be argued for low voltage applications but personally if I have a 25 amp circuit I would run AWG 10 (30 ampp service). Since the pumps are recommended to be fused at 25 amps it is likely that under normal conditions they draw maybe 20 amps. However, if a pump has a locked rotor condition the current will increase rapidly and the 25 amp fuse should blow well before the wire melts or gets hot and starts a fire (or some other evil side effect). However, I would likely still use AWG 10 for the pumps. Not that 5 meters (little over 15 feet) is a long run but depending on pump current I wouldn't want line loss. I would run like the attached image but substitute AWG 10 for the AWG 12. The cost difference isn't enough to amount to much.

Just My Take
Ron

 

[shankos]

ok the general consensus seems to be to run as in the diagram reloadron has drawn. So I will do that.

As for the wiring I have already purchased it so I cant change it. The shop advised me on the AWG ratings to use. So if they are off by a little I cant do much about it now.

The pumps where running when i tested it all with the specified wire ratings, I just need to put the fuses in the lines.

 

[Reloadron]

It will do just fine.

Ron

 

[4pyros]

4pyros: you seem to be saying not to run the 25 amp fuses on the 12 gauge wire ?

No I did not say that. I said you must run the 8 gage all the way to the 25 amp fuses.

If you look at Rons drawing; The 12 gage wires after the junshoin with the 8 gage wire and before the 25amp fuses are not proporly protected. If either of the 12 gage wires after the junshoin with the 8 gage wire shorts to ground 50 amps will flow and burn the 12 gage wire. The 8 gage must end at the fuses not two 12 gage wires for safty. It is vary easy to over look and burns up cars all the time when thay wire two amps in the back of the car off one 8 gage wire, thay run it to one amp and use 12 gage jumper to the other amp. and the 12 gage jumper is now fused at 50 amps and overheats if it shorts to ground.

In the end 12 gage wire can not be fused at 50 amps! Andy

 

[shankos]

ok. I will run 8 gauge split it into two and put 25 amp fuse in it. then change it to 12 gauge

 

[KeepItSimpleStupid]

Let's ask some details. Distances and battery voltage. I have my doubts the wire size is adequate: See Wiring Size Guide

Your feed may have to be higher than 50 A to avoid inrush.

Battery voltage and distance NEEDS to be known. I have no experiance guessing the inrush for DC motor loads.

 

[shankos]

12 volt car battery.

5 meters 8 gauge
8 guage split into two to go through switches.
5 meters 12 gauge to pumps

 

[4pyros]

Just use slow blow fuses and you will be good.

 

[Reloadron]

Uh Oh, my bad and thanks Andy. My 25 amp fuses should be right at the junction.

Thanks Again Andy
Ron

 

[4pyros]

Uh Oh, my bad and thanks Andy. My 25 amp fuses should be right at the junction

Yes the OP should be using something like this with a big buss bar that can handle 50 amps.

 

[Reloadron]

Yeah, that is similar to what the wife (audiophile) has on her Jeep for her sound system. Matter of fact, 50 Amps. They ran AWG 6 battery through fuse at battery to her amp. Nice image and example.

Ron

 

[260z]

Hi Guys

This posdt is probably a bit late but i thought i would chuck in my two bobs worth. There was no mention of voltage but if this is a 12V system 11 meters is a huge run.

There are other considerations to think about. What type of fuse holder and how are the wires attached. With too small a wire cross section you will drop voltage by the time you get to the pump.

Fuses are meant to be rated at 125% of the load but what are the pumps pumping? You could run the wires from the battery separate to keep the pumps automemous.

Any way heat is the big killer, so if the pumps run cool and the wire and fuse holders stay cool then there shouldnt be a problem.

Geof.