What fusing is correct here?

[Hcw 10+ year member]

To determine the approximate current draw in “amps” of one’s amplifiers you need to calculate the total power of each amp. Multiply total number of channels times the number of RMS watts per channel. In this particular example we will use the first amp at 4x 150 rms watts = 600w rms. The second amp 1x 280w rms = 280w rms. These total 880w rms. This total is than doubled and divided by 13.8 to give approximate “current draw. So our total 880w rms x 2 = 1760 divided by 13.8 = 127 amps.

Using this figure of 127 amps we can determine the proper wire gauge size from charts. In this case we need to run a length of wire 10-13 ft. According to the charts on the net Cable Gauge Chart this would require a 4 gauge power wire to be run between the battery and the amps capable of supporting up to a maximum of 150 amps.

Questions:

So from this information does it mean that the power lead should be fused with a 150 amp fuse at the battery?

This would include that this lead is going to a junction block and each power lead from the junction block going directly into each amp?

I ask this as there are articles stating that one should add the sum of all fuses in the amps which in my case as an example would be 2x70amps in the first amp = 140 amps for it. The second amp has a 40 amp fuse for a combined total of 180amps.

Question:

So what than doe’s one fuse for at the battery? The maximum amount the 4 gauge wire is capable of supporting which is 150 amps or this new Figure of 180 amps? (30 amp difference) or the figure we obtained at the top of this page for “approximate amp draw” that was figured at 127 amps?

To further confuse issues we are told that the amps are protected with their built in fuses and that we are only protecting the “power wire” lead between TWO POINTS in case of shorts. This brings up the question of fusing between the battery and a junction block and than running from the junction block directly into each amp. Unless these power leads of the same 4 gauge are fused at this point between each amp and the junction block they are relying on the fuse at the battery as well are they not?

So adding a fuse between the junction block and each amp would protect these leads in the event of them shorting? These would have 140 amps on the first amp and a 40 amp on the second amp to match to their fuse rating built in?

So the question is by adding these additional fuses between each amp and the junction block does it make any difference in the fuse size that one uses at the battery because they are individually fused as well? This pertaining to the three different amperage Numbers we have obtained:

-The approximate current draw of 127 amps at the start of all this.

-The 125-150 amp figure the 4 gauge wire is capable of carrying (between battery and Junction Block)

-The 180 amp figure the total sum of all built in fuses to the two amps?

In another artical it states that you can fuse this power lead at the battery with a 60-80 amp fuse on a 4 gauge it is all it will need???

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[ahole-ic]

To determine the approximate current draw in “amps” of one’s amplifiers you need to calculate the total power of each amp. Multiply total number of channels times the number of RMS watts per channel. In this particular example we will use the first amp at 4x 150 rms watts = 600w rms. The second amp 1x 280w rms = 280w rms. These total 880w rms. This total is than doubled and divided by 13.8 to give approximate “current draw. So our total 880w rms x 2 = 1760 divided by 13.8 = 127 amps.
Using this figure of 127 amps we can determine the proper wire gauge size from charts. In this case we need to run a length of wire 10-13 ft. According to the charts on the net Cable Gauge Chart this would require a 4 gauge power wire to be run between the battery and the amps capable of supporting up to a maximum of 150 amps.

Questions:

So from this information does it mean that the power lead should be fused with a 150 amp fuse at the battery?

This would include that this lead is going to a junction block and each power lead from the junction block going directly into each amp?

I ask this as there are articles stating that one should add the sum of all fuses in the amps which in my case as an example would be 2x70amps in the first amp = 140 amps for it. The second amp has a 40 amp fuse for a combined total of 180amps.

Question:

So what than doe’s one fuse for at the battery? The maximum amount the 4 gauge wire is capable of supporting which is 150 amps or this new Figure of 180 amps? (30 amp difference) or the figure we obtained at the top of this page for “approximate amp draw” that was figured at 127 amps?

To further confuse issues we are told that the amps are protected with their built in fuses and that we are only protecting the “power wire” lead between TWO POINTS in case of shorts. This brings up the question of fusing between the battery and a junction block and than running from the junction block directly into each amp. Unless these power leads of the same 4 gauge are fused at this point between each amp and the junction block they are relying on the fuse at the battery as well are they not?

So adding a fuse between the junction block and each amp would protect these leads in the event of them shorting? These would have 140 amps on the first amp and a 40 amp on the second amp to match to their fuse rating built in?

So the question is by adding these additional fuses between each amp and the junction block does it make any difference in the fuse size that one uses at the battery because they are individually fused as well? This pertaining to the three different amperage Numbers we have obtained:

-The approximate current draw of 127 amps at the start of all this.

-The 125-150 amp figure the 4 gauge wire is capable of carrying (between battery and Junction Block)

-The 180 amp figure the total sum of all built in fuses to the two amps?

In another artical it states that you can fuse this power lead at the battery with a 60-80 amp fuse on a 4 gauge it is all it will need???

You fuse for the weakest link. So if you ran 1/0 but your amp only draws 100 amps max, fusing for 100 amps is perfect. If your amp can draw 600 amps but you only have 1 run of 1/0, first of all you're an idiot but secondly, fuse for 225 amps or whatever the rating is for the length of 1/0 you have.

 

[Kangaroux 5,000+ posts]

You're fusing for the wire, but if your amp is only drawing 100A of current and your wire can handle 250, then you can really fuse either or. What you never want to do is fuse for more than what the wire is rated at. I.e., don't drop a 250A fuse in for a line of 4g that can only handle 150A.

 

[All_Logix 10+ year member]

I am a little confused as too why this application wants you to multiply the power draw by 2 before dividing by the volts...most amplifiers now days are better than 50% efficient....

 

[Hcw 10+ year member]

The reason they give is :" That's because the typical analog amplifier is about 50% efficient. That means about half of the power it generates is turned into audio output while the other half of the power is lost as heat. So if your amplifier is putting out 400 watts, it's actually using enough electrical power to generate about 800 watts of power, and the amp's wiring needs to be big enough to handle that draw."

 

[Hcw 10+ year member]

So the figure of 127 amps for approximate current draw is really the figure that matters when choosing the fuse size at the battery providing the power wire is of sufficient gauge to handle the fuse.

The 180 amp figure being the total sum of all fuses in the amps really does not play into the fuse equation at the amp? Where than does it play into the scheme of things?

In addition is it wise idea to fuse the leads comming off thejunction block to each amp in your opinions? Does this have any impact on the primary lead from the battery to the junction block or just protects the individual leads running to each amp incase of a short?

 

[duanebro 10+ year member]

You are protecting against shorts. Short your batt + to ground without and your car "could" burn up! If you change wire gauge you must fuse again due to the smaller wire not being able to handle as many amps. You must use the right fuse for the wire gauge - a smaller fuse is fine if you are not using that much current.

In your example I'd use a 150 amp fuse.

I have seen burnt wires because someone used a small whip to connect a stove where I worked. The breaker never tripped, but the wires were gone!

 

[Hcw 10+ year member]

Thank you all for your replies!