In part 1, we learned how to find a circuit’s phase and insulation color using long division. Here are the tables from part 1, with the addition of the long division remainders:
120/208/240 Volts:
| Circuit #’s | Phase | Insulation Color | Remainder |
| 1 & 2 | A | Black | 1 & 2 |
| 3 & 4 | B | Red 1 | 3 & 4 |
| 5 & 6 | C | Blue | 5 & 0 |
277/480 Volts:
| Circuit #’s | Phase | Insulation Color | Remainder |
| 1 & 2 | A | Brown | 1 & 2 |
| 3 & 4 | B | Orange | 3 & 4 |
| 5 & 6 | C | Yellow | 5 & 0 |
As great as it is, long division is not something easily done by most people in their heads. It is much easier to stick with addition and/or subtraction. The next method of finding a circuit number’s phase uses the simpler tool of subtraction, although one has to be aware of a few of the multiples of six.
The idea is to subtract multiples of six from the circuit number until the number becomes small enough to allow its phase to be identified. The larger the number, the larger the multiple of six we can subtract at the start.
First we’ll cover multiples of six. A multiple is of six is any number times six: 1 * 6 = 6, 2 * 6 = 12, 3 * 6 = 18, 4 * 6 = 24, … Therefore, the smallest multiples of six are 6, 12, 18, and 24. Along with those four multiples of six, we will want to remember that 30, 60, 90, and 120 are also multiples of six. These bigger numbers will allow us to subtract larger amounts from our circuit number to quickly get down to the smaller numbers.
Here is a table of the multiples of six that we will be using to help us find the phase that corresponds to a specific circuit number:
| Smaller multiples of six: | 6, 12, 18, 24 |
| Larger multiples of six: | 30, 60, 90, 120 |
Keeping these eight numbers in mind will make circuit phase identification much faster. The whole idea behind this method is to continually subtract multiples of six from your circuit number, using the largest numbers available until your number is equal to or smaller than six. Let’s test it out.
Our circuit number is 38. We need to find its phase. First we subtract the largest multiple of six from our list of multiples of six. In this case, the largest multiple of six that we can subtract from 38 is 30.
38 – 30 = 8
Then, we once again subtract the largest multiple of six we can from 8, which is 6:
8 – 6 = 2
Because 2 is less than 6, we can no longer subtract a multiple of six from our number. Therefore, our answer is 2. If we look at the table:
| Circuit #’s | Phase | Remainder |
| 1 & 2 | A | 1 & 2 |
| 3 & 4 | B | 3 & 4 |
| 5 & 6 | C | 5 & 0 |
we match our number to the circuit # column. We now know that circuit 38 is on phase A. We can double-check our answer using long division:
Matching our reminder of 2 to the above table gives us the same answer. Let’s do another example, circuit 99. We start by subtracting the largest multiple of six in our list, 90:
99 – 90 = 9
Then we subtract the next largest multiple of six that fits into 9, which is 6:
9 – 6 = 3
3 is our answer, and using the above table we can see that that circuit 99 is on phase B.
One more example, circuit 28. The largest multiple of six that can be subtracted from 28 is 24:
28 – 24 = 4.
4 is our answer, and by that we can see that circuit 28 is on phase B.
To use this method successfully, all we have to do is remember the eight multiples of six and subtract the largest ones possible from our circuit number until our answer is 6 or less and that will tell us on which phase our circuit is.
Upcoming in part 3, we will learn about another method that I use which I think is easier because I only have to do very simple addition, and then add or subtract either the number 3 or the number 6 to find a circuit’s phase.
Table of Contents
- Part 1: Introduction and Long Division
- Part 2: Subtracting Multiples of Six (this article)
- Part 3: Trick Based on Multiples of Six
- Part 4: Original Method Based on Multiples of Six
