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Wire gauge?

B

btam13

NAXJA Forum User
Location
Des Moines, Iowa
Ok, quick question to ponder. If you don't have any 4 gauge wire to run from the distribution post to a fused distribution block, could one use 2 strands of 8 gauge and effectively double the load capacity equal to 1 strand of 4 gauge?
 
No, it's not the same thing, you will end up bottlenecking anything that needs a lot of amps. With electrical bigger is better.
 
That's what I figured but had never tried what I asked about. What gauge would be recommended to run from dist point to fused dist block. Block feeds relays for H4 headlight upgrade for now. There are extra outs for future upgrades.
 
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How long of a run is it? If it is less than a foot than I would say that 4 gauge is what I would use (the bigger the better I say) if it is longer then I would use 2 gauge.
 
btam13 said:
Ok, quick question to ponder. If you don't have any 4 gauge wire to run from the distribution post to a fused distribution block, could one use 2 strands of 8 gauge and effectively double the load capacity equal to 1 strand of 4 gauge?
Click to expand...

The rated ampacity for a single conductor copper wire at temps up to 167 degrees F is 125 amps for 4 gauge wire, and 70 amps for 8 gauge. Two #8 wires would give you more than enough capacity, and in fact "paralleling" is a common practice with larger wire sizes. Both wires should be close to the same length and routed closely to each other. Automotive wiring, the wire itself and the insulating jacket, doesn't always have the same quality control as building wire, but if it's UL listed wire you should be fine.
 
Thanks DWK. My original thought was that multiple wires bundled together would have the same effect of the multiple strands bundled together inside a single length of wire.
 
My 1994 XJ had a single 8AWG wire coming off the alternator that split into two smaller wires to feed two 60AMP fuses. I am not sure I ike that arraingement but, Who am I to question it?
 
techno1154 said:
My 1994 XJ had a single 8AWG wire coming off the alternator that split into two smaller wires to feed two 60AMP fuses. I am not sure I ike that arraingement but, Who am I to question it?
Click to expand...

I suspect the reason that it is set up that way is that 60 amp fuses are easier to come by than a 120 amp fuse, and someone figured 60+60=120 :shhh:
 
You need to be more concerned with surface area then with the thickness of the cable. two 8 gauge will provide more surface area per foot then a single 4 awg. it will look cleaner to have one cable then two but if thats what you got....it will work
 
Magus2727 said:
You need to be more concerned with surface area then with the thickness of the cable. two 8 gauge will provide more surface area per foot then a single 4 awg.
Click to expand...

What is your reasoning behind this? How is more surface area better? The fewer connections the better.
 
DWK said:
The rated ampacity for a single conductor copper wire at temps up to 167 degrees F is 125 amps for 4 gauge wire, and 70 amps for 8 gauge. Two #8 wires would give you more than enough capacity, and in fact "paralleling" is a common practice with larger wire sizes. Both wires should be close to the same length and routed closely to each other. Automotive wiring, the wire itself and the insulating jacket, doesn't always have the same quality control as building wire, but if it's UL listed wire you should be fine.
Click to expand...
I spy an electrical engineer or electrician! :cheers:

Magus2727 said:
You need to be more concerned with surface area then with the thickness of the cable. two 8 gauge will provide more surface area per foot then a single 4 awg. it will look cleaner to have one cable then two but if thats what you got....it will work
Click to expand...
Close. With DC you should be concerned about cross sectional area, not surface area. Above a certain frequency (which depends on the diameter of the wire in use) circumference becomes more important than cross sectional area as the alternating current does not fully penetrate the metal, but rather flows on the surface - the "skin effect". If you are feeling lazy, for all but very specific purposes you can look up a wire ampacity table from the national electric code and just use those values, since they are valid at 60Hz they will result in you using slightly thicker wire than you need to, but hey, extra safety margin never hurt anyone.

two 8 gauge will be fine instead of a 4 gauge in your case.
 
The electrons flow on the surface of a metal, if you have a 2" by 2" hunk of 8 foot long metal the electrons will all be flowing on the surface. I work on high power, power supplies used in government telecommunication systems a flat plane of copper on a Printed Circuit Board can carry a large amount of current even though it is very thin (depending on the width of the copper).

While there is a point of having huge currents the electrons have no where else to go but not on the surface (your wire will start heating up). Fewer connections are better is there is loss in the connection that is large enough to be considered. If your using good connections (any thing is better then the oxidated and exposed copper with steel fittings that the factory normally has) If your splitting the current equal then you would just be spliting the loss equal between the two assuming same quality of connection, if you have a better connection then your loss will go down.

Edit: I guess I am in the mode for higher frequencies since I work with the GHz range at work.......
 
#12 AWG Copper wire is 6,530 Circular Mills
#10 AWG Copper wire is 10,380 Circular Mills
#8 AWG Copper wire is 16,510 Circular Mills
#8 AWG Copper wire is 26,250 Circular Mills
#4 AWG Copper wire is 41,740 Circular Mills

I agree with everything posted above but
To play it safe I would use Three #8 Wires in place of one #4 Wire.
 
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^^ I think you have a type O....

You have 2 8Awg with different specs..
 
Magus2727 said:
^^ I think you have a type O....

You have 2 8Awg with different specs..
Click to expand...

Sorry for the TYPO, the bigger CM should read 6 AWG

garr said:
#12 AWG Copper wire is 6,530 Circular Mills
#10 AWG Copper wire is 10,380 Circular Mills
#8 AWG Copper wire is 16,510 Circular Mills
#6 AWG Copper wire is 26,250 Circular Mills
#4 AWG Copper wire is 41,740 Circular Mills
Click to expand...
 
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Magus2727 said:
The electrons flow on the surface of a metal, if you have a 2" by 2" hunk of 8 foot long metal the electrons will all be flowing on the surface. I work on high power, power supplies used in government telecommunication systems a flat plane of copper on a Printed Circuit Board can carry a large amount of current even though it is very thin (depending on the width of the copper).
Click to expand...

I've been an RF electrical engineer for over three decades. What you say only holds true at high frequencies, not DC. At DC the total cross sectional area is all that counts.
 
Magus2727 said:
You need to be more concerned with surface area then with the thickness of the cable. two 8 gauge will provide more surface area per foot then a single 4 awg. it will look cleaner to have one cable then two but if thats what you got....it will work
Click to expand...

Not quite. As I recall, it takes a difference of six AWG numbers to double the cross-sectional area of the wire - 2AWG is twice the area of 8AWG. 4AWG is not twice 8AWG - it's just a shade less.

(I know it's picking nits, but I'm cranky about electrics.)

If you're going to select a wire size and try to "future proof" it, it's important to know what you've got planned positively, what you've got planned possibly, and know what capacity you'll have left (which will probably be determined by the ratings of the fuse panel you plan to use or of the distro post, more than anything else. For instance, a Buss six-circuit fuse panel may allow up to 30A on an individual circuit, but only be rated for 100A in total! Check the spec sheets carefully...)

Hit me backchannel if you want design advice or want help finding parts, and I'll see what I can do for you.
 
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