scope:

This specification covers switchboard electrical indicating wattmeters including prefixes such as, kilo and mega.

The type designation of wattmeters shall be in the following form, and as specified (see 6.2).

Wattmeters are designated by the two-letter symbol "MR".

The style is designated by a three digit number which signifies the following characteristics:

The first digit designates the nominal size and shape of flange on switchboard wattmeters as follows:

4 - 4-½-inch, rectangular flange.

The second digit designates the type of mounting and the nominal scale length in angular degrees, as follows:

9 - Flush mounting 260 degrees nominal scale.

The third digit designates either single phase or polyphase as follows:

1 - single phase

2 - polyphase (with 2 current coils and 2 voltage coils).

The color scheme of the dial background, markings and pointer is designated by a single letter as follows:

B - Black dial background, white markings and pointer.

W - White dial background, black markings and pointer.

The full-scale value of single-range wattmeters is represented by three figures designating the maximum number of units indicated; when the full-scale value is less than three figures, zeros are inserted at the left to fill out the figures. Where the letter "R" is used in this group, between two figures, it represents a decimal point. Example: 1R5 represents 1.5.

The full-scale deflection of zero-center or offset zero wattmeters is indicated by two numbers designating the numerical value of the end-scale points, with a letter between them designating the decimal value of the numbers, as follows:

D - tenths Example: 5D5 represents 0.5-0-0.5.

U - units Example: 1U9 represents 1-0-9.

T - tens Example: 2T2 represents 20-0-20.

H - hundreds Example: 5H5 represents 500-0-500.

Two letters designate the kind of current for which the wattmeter is designated as follows:

AC - Alternating current (60 cycles per second, nominal frequency).

AD - Alternating current (60 cycles per second, nominal frequency), and direct current.

AE - Alternating current (800 cycles per second, nominal frequency).

AF - Alternating current (400 cycles per second, nominal frequency).

Two letters designate the electrical units indicated by the wattmeters, as follows:

WW - Watts.

KW - Kilowatts.

GW - Megawatts.

A single letter designates a special feature, as follows:

H - High-impact-shock resistant.

The four letters "SPEC" are used in place of the letters specified in 1.2.1.5 and 1.2.1.6 for wattmeters having special characteristics, such as adjusted resistance or special scale marks. These wattmeters are arbitrarily assigned serial numbers which are to be used in place of the three figures called for in 1.2.1.4.

The type designation MR491W300AC, KWH signifies:

(a) MR - Electrical-indicating wattmeter.

(b) 49 - 4-½-inch rectancgular flange. switchboard wattmeter, flush-mounting, 250 degrees nominal scale.

(c) 1 - Single phase.

(d) W - White dial background with black markings and black pointer.

(e) 300 - Zero left, full-scale value of 300.

(f) AC - Designed to be energized by 60 cycle alternating current.

(g) KW - Electrical units in kilowatts.

(h) H - High-impact-shock resistant.

intended Use: