120/208/240 Volts:

277/480 Volts:

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 larger numbers will allow us to subtract larger amounts from our circuit 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:

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:

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:

²

Matching our reminder of 2 to the above table gives us the same answer.  Let’s do one more 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.

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 add or subtract either the number 3 or the number 6 to find a circuit’s phase.

Part 1

120/208/240 Volts:

277/480 Volts:

Non-veteran electricians often struggle with knowing which circuit number is on which phase and therefore which color the wire insulation should be.  They are familiar with the above table of circuits one through six, and can therefore do the math, but once the circuit numbers become higher, say 83 for example, a calculator or long division on a notepad is needed.  Example:

³

It is the remainder which tells us on which phase that circuit 83 is.  Because we are dividing by six, the possible remainders are 0, 1, 2, 3, 4, and 5.  If the remainder is 1, 2, 3, 4, or 5, then just look at the corresponding circuit number in the table above.  For this example, the remainder is 5, and circuit 5 is on phase C and is blue (or yellow).  This means that circuit 83 is on phase C and its insulation is blue (or yellow).

So what about remainder 0 when the the number is divided equally by 6?  This means that it is circuit 6.   In short, no remainder = circuit 6.

There are other ways to find on which phase a circuit number is which require no division.  These will be discussed in upcoming parts of this article.

Part 2

This weblog is a place for me to share my observations of the electrical trade as well as a place for me to track my journey through my time as an electrician.  It is my hope that the things which I share will be of use to other electricians and that I will learn from them in return via their comments.