I have a setup using 16 AWG SOOW cord (basic rubber cord like a grounded extension cord or a cord for an electric drill). Only with more wires, one with 5 wires and one with 7.
The cables are rated for 8 amps. a #16 conductor in free air is related at 13 amps. Does that mean each conductor can carry 8 amps, or the entire cable can only carry 8 amps, or the average of the cable has to be 8 amps (I could have 1 wire with 12 amps, 1 with 4, etc.) Does it matter that only the neutral and 4 other wires at any given time will carry current.
The rating of the sheathed bundle has to be tested by its ability to lose heat.
Start with the 2 active conductors, no earth, of your electric drill cord.
Now you want to fit 4 active conductors in to the same cable. (Two drills from one cable )
Now, to fit 4 conductors in , you need to double the area. So the Diameter only has to be 1.4 times larger. Now the surface area of the outer sheath is circumference * length, and circumference is only 1.4 times larger., length is the same.
Since heat loss is related to surface area, it is the surface area of the cable’s sheath that limits current through it !.
If you put 8 amps through each conductor of a 7 conductor sheath, that would be 3 .5 times the heat produced, but only 1.7 times the surface area !
My point is that the outside jacket of the cable is responsible for cooling, not the individual conductor within.
Like Douglas Adams said - Don’t Panic!
The heat dissipation capability of the cable is taken into account in the current rating. That’s why a bare wire is rated for 13A, but the same gauge wire in the bundle is only rated for 8A.
Is this a setup where the neutral might have 8 amps, and the other four wires might have a total of 8 amps between them? Or could each of the five wires have 8 amps at the same time?
But those pages do not list your particular cables (16/5 and 16/7).
So let’s look at NEC Tables 400.5(A) and 400.5. For multiconductor SOOW cables that use 16 AWG wires, Table 400.5(A) says three conductors (wires) can each carry 10 A, or two conductors can each carry 13 A, for an ambient temperature of 30 °C. Table 400.5 says you must apply an adjustment factor if four or more conductors carry current… 80% for your 16/5 cable and 70% for your 16/7 cable. I assume you apply these percentages to the current values listed under subheading A in 400.5(A).
So I think this is the bottom line:
For your 16/5 cable,
If two conductors carry current, each can carry up to 13 A.
If three conductors carry current, each can carry up to 10 A.
If four conductors carry current, each can carry up to 8 A.
If five conductors carry current, each can carry up to 8 A.
For your 16/7 cable,
If two conductors carry current, each can carry up to 13 A.
If three conductors carry current, each can carry up to 10 A.
If four conductors carry current, each can carry up to 7 A.
If five conductors carry current, each can carry up to 7 A.
If six conductors carry current, each can carry up to 7 A.
If seven conductors carry current, each can carry up to 7 A.
Oh, and when I say “carry current,” I mean the wire more-or-less carries *continuous *current. Not a fault or transient current.
One more thing: those values are for an ambient temperature of 30 °C or less. You must decrease the maximum allowable current per conductor if the ambient temperature is ever greater than 30 °C. I don’t know what the derating factors would be. Perhaps there’s an NEC table that lists them.
The sum of all four hot wires that will be active at any given time will equal the load of the neutral, and the load will be fairly evenly distributed between the four wires.
Only two (a hot and a neutral) will be active at any given time in the 5 conductor, and 3 hots in the 7 conductor, so it looks like I can go more than 8 amps per the table.
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