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# inductor thickness wire

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#### MrAl

##### Well-Known Member
Hi there,

600 circular mils per amp is a good starting point, but it also depends on the type
of covering to be used and how many turns are present and stuff like that.
It also depends on where the inductor is going to be physically placed on
the PC board and if there are any fans. You can get away with thinner
wire if there will be less total turns (like say 10 total) and if any thermal
potting compound is to be used, etc.

A good idea is if it is possible, to construct one unit and test it as much as
possible by letting it run overnight in the max expected temperature environment.

#### MrAl

##### Well-Known Member
Hi again,

Circular mils is a description of cross sectional area of a wire.

You can use this next formula to calculate the required wire number AWG for a
give current and cm/A rule of thumb:

N=8.6249*ln(5/sqrt(cmpa*I))+36

where
I is the current, and
cmpa is the circular mils per amp rule, and
ln is the natural log

For example, say we use the 600 cm per amp rule, and we have a current of
2 amps. What wire size do we need?

Using the forumla:
N=8.6249*ln(5/sqrt(cmpa*I))+36

we plug in the value 600 for cmpa, and the value 2 for I, and we get:
N=8.6249*ln(5/sqrt(600*2))+36

and after we do the math we get:
19.3056

and so we can round to AWG #19 gauge wire size.

Here is a short table for wire size (before rounding) with current from 1 to 20
amps using the 600cm/amp rule:

Code:
AMPS  AWG
1   22.3
2   19.3
3   17.6
4   16.3
5   15.4
6   14.6
7   13.9
8   13.3
9   12.8
10   12.4
11   12.0
12   11.6
13   11.2
14   10.9
15   10.6
16   10.3
17   10.1
18    9.8
19    9.6
20    9.4

Last edited:

#### kinarfi

##### Well-Known Member
Mr. Al, the table, 20 amps gets a #8 or #10 awg wire, in my opinion, that's way to heavy. National electrical code says #12 for 20 amps and 10 is good for 30 amps for building cods and on other table in the code book, they are good for much higher currents.
Thunderchild, On your inductor, how many henrys are you trying for and what formulas are you using and how are you building them? Sounds like an interesting endeavor!
Thanks,
Kinarfi
Here's a some tables from NEC

Last edited:

#### smanches

##### New Member
Mr. Al, the table, 20 amps gets a #8 or #10 awg wire, in my opinion, that's way to heavy. National electrical code says #12 for 20 amps and 10 is good for 30 amps for building cods and on other table in the code book, they are good for much higher currents.
Thunderchild, On your inductor, how many henrys are you trying for and what formulas are you using and how are you building them? Sounds like an interesting endeavor!
Thanks,
Kinarfi
Here's a some tables from NEC

It ALL depends on how long the wire is. I'm assuming code defines a max length of the line.

#### Thunderchild

##### New Member
It will be iron core and possibly up to 100 uH but most like 10, it all depends on how big it comes out at and its just for power filtering

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