0:12 Hello everyone and welcome to this
0:14 video. All electrical conductors include
0:17 a small amount of resistance. This
0:19 resistance increases if the length of
0:21 the conductor increases or the conductor
0:23 size decreases. Think of blowing air
0:26 through a hose. If the hose diameter
0:28 decreases and or the length increases,
0:30 it would be harder to blow through. You
0:32 can also think of freeway traffic as
0:34 resistance. The freeway is the
0:37 conductor. The wider the freeway, the
0:39 faster and smoother you travel. As
0:41 electrical current flows through the
0:43 conductor, it experiences a decrease in
0:46 voltage between the source, the starting
0:48 point, and various points along the
0:50 conductor. Another example to look at is
0:54 the voltage drop in a 1,00 ft run of 16
0:57 AWG wire would be greater than that of a
1:01 1,00 ft run of 12 AWG. This is simply
1:05 because a 16 AWG conductor is smaller in
1:08 diameter than a 12 American wire gauge
1:10 conductor. Fire alarm equipment listed
1:12 to the standards of the National Fire
1:14 Protection Association and Underwriters
1:17 Laboratories UL is tested to determine
1:20 if can operate properly at 85% of the
1:23 rated name plate voltage. This limit was
1:25 set in place to make sure the circuit
1:27 can deal with a brownout condition or a
1:30 possible voltage drop which might result
1:32 from excessive resistance in the system
1:34 wiring. Signaling line circuit voltage
1:36 drop calculation confirms that the
1:39 minimum required voltage reaches the
1:41 last device on the power loop even under
1:44 worst case load conditions as required
1:46 in the NFPA72.
1:48 Fire alarm designers are required to
1:50 prepare voltage drop calculations for
1:52 the notification appliance circuits. As
1:54 part of the design, you as a designer
1:56 can use several different methods to
1:58 calculate voltage drop on a fire alarm
2:01 circuit. One method calculates the
2:03 overall voltage drop and the other
2:05 calculates the actual voltage drop for
2:07 each length of cable and device within
2:09 the circuit. These voltage drop
2:11 calculations must be included in the
2:14 submittal plans and specifications. The
2:16 suggested maximum allowable voltage drop
2:19 on a fire alarm circuit is 10% or the
2:21 voltage drop included in the fire alarm
2:23 control panel installation guide,
2:33 >> Lump sum method. Step one, take the
2:35 total current of the circuit. You can
2:37 achieve this figure by adding up the
2:39 current draw of each device on the
2:42 circuit. This will represent a in the
2:45 formula. Step number two, measure out
2:47 the length of the circuit in feet. Do
2:49 not double the distance of the circuit
2:52 for two wire loops unless you want to
2:55 use a multiplying factor of 10.8 versus
2:59 21.6. 6 C step number three this will
3:02 represent L in the formula step number
3:05 three use a multiplying factor of 21.6
3:07 six. This number represents the
3:09 resistivity of copper conductors. This
3:12 is a constant used in the formula. Step
3:15 number four. Find the circular mills for
3:17 the particular gauge wire you are using.
3:19 This can be found in the National
3:23 Electrical Code NEC chapter 9 table 8.
3:27 14 AWG= 4,110
3:31 12 AWG= 6530.
3:34 This will represent CM in the formula.
3:35 This formula calculates the total
3:39 voltage drop VD by multiplying the total
3:41 current A by the circuit length L and
3:45 the copper resistivity constant 21.6
3:47 then dividing by the conductor's size in
3:51 circular mills CM. This example uses the
3:54 lump sum method to confirm that a 0.356
3:59 amp circuit running 450 ft of 12 AWG
4:03 wire will result in a 0.530
4:05 volt drop. This final step shows you how
4:07 to convert the voltage drop into a
4:10 percentage by dividing the lost voltage 0.530
4:12 0.530
4:14 volt by the circuit starting voltage
4:17 which is 24 volts and multiplying by
4:19 100. confirming this circuit has a safe
4:23 2.2% loss. Now remember, you can also
4:24 perform this calculation for each
4:26 individual segment of wire and each
4:29 device on the circuit. This is known as
4:31 the pointto-point method. It is a more
4:33 accurate approach because it allows you
4:36 to break down the circuit and identify
4:38 exactly where the circuit should end due
4:41 to voltage drop limitations. [music]
4:49 Next, let's explore the NSV cabling app,
4:51 a specialized tool for faster, more
4:53 accurate circuit design and voltage drop
4:56 calculations. Start the process by
4:58 clicking alarm cabling command. A
5:00 configuration form pops up, allowing you
5:03 to define the key circuit parameters.
5:05 Within this form, you gain full control
5:08 over the circuit setup. You can define
5:10 the circuit type such as loop, zone,
5:12 sounder, and power. Select your
5:14 preferred unit of measurement like feet
5:17 or meters and precisely define circuit
5:19 tags and all electrical parameters in
5:25 Cabling begins from the fire alarm
5:28 control panel. From there you will
5:30 connect all the devices in accordance
5:32 with the circuit class, the project
5:34 design and the site specific
5:36 requirements. As you connect each
5:38 device, the software automatically
5:41 assigns an address based on the device
5:43 tag you selected in the draw cable form.
5:45 In the lower left corner of the screen,
5:48 you can monitor live data, including
5:50 cable length, current, and voltage drop,
5:52 giving you instant feedback as you
5:55 design. The NSVC CAD cabling app uses
5:58 the point-to-point method for voltage
6:00 drop calculations. The main advantage of
6:02 the point-to-point method is that it
6:04 provides accurate segment by segment
6:07 voltage drop verification, ensuring that
6:09 every device in the circuit receives
6:12 adequate operating voltage, something
6:14 the lump sum method cannot reliably guarantee.
6:16 guarantee.
6:18 After finalizing your design, generate
6:22 the riser diagram by typing NHRD in the
6:24 command bar, then clicking on the fire
6:26 alarm control panel to open the riser
6:28 form. Configure the block count and
6:31 device spacing in the dialogue and then
6:47 With the NSV cabling app, you can move
6:49 beyond guesswork to achieve faster, more
6:51 accurate, and fully compliant circuit
6:54 designs. For detailed guides and product
