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November 18, 2001

                   Northwest NICET Newsletter 
================================================================
Volume 1 Issue 21                                     11-18-2001
================================================================

        News for Fire Protection Engineering Technicians
        ------------------------------------------------

Contents:
---------
- News
- Tech Stuff
- Test Dates
- Class Schedule
- Administrivia

================================================================
NEWS
================================================================

NFPA gives nod to Internet fire transmission.
http://www.securitysystemsnews.com/november2001/gn/top_story5.htm

----------------------------------------------------------------

I have received a flurry of email chain letters related to the attack on
Sept 11. Many of the messages sound true enough but in fact many are
modified versions of true events or simply out-and-out fabricated
stories. Before you pass along another urban legend email, take a look
at http://www.urbanlegends.com or http://www.snopes.com.

I received an unsolicited email recently regarding Jane Fonda's
activities during the Viet Nam war. I remember what she did and I passed
the reminder along to others lest we forget what she did.
http://www.snopes.com/inboxer/outrage/fonda.htm

================================================================
TECH STUFF
================================================================

Volt-drop calculation
---------------------

This is project 1 of 2 for those of you attending the seminars in
November. Read through the example then perform the problem that
follows, and then send it to me by 12/1/01
mailto:Michael.B.Baker@home.com.


What is the minimum 7-strand, uncoated copper wire size (in AWG)
permitted by NFPA 70-1999 in the following example:

    |<----------------- 500' ---------------->|

+---+      .-.  .-.    .-.  .-.    .-.  .-.   +-------+
| + +--.  /   /     /   /     /   /   `--+  +-+  |
|   |   /    /    /    /    /    /      |  | |  |
| - +---'   /     /   /     /   /     .-+  +-+  |
+---+     `-'    `-'  `-'    `-'  `-'    `-'  +-------+
NAC Power Supply                              (10) Horn/Strobes
Class 2 Power Limited                         @ .1A each = 1A
24Vdc nominal                                 20-28Vdc

Average ambient temperature = 75 degrees centigrade.


Step 1)
-------
With any word problem, determine what units the answer will be expressed
in. In this example we're asked what the minimum wire size is in AWG.


Step 2)
-------
Simplify the problem by reducing the drawing to its electrical
equivalents:

[Source ]<------------[ Circuit  ]------------>[ Load  ] or;
[Voltage]<------------[Resistance]------------>[Current] or;
[ Volts ]<------------[   Ohm    ]------------>[ Amps  ] or;
[   V   ]<------------[   Ohm    ]------------>[   A   ]


Step 2)
-------
The minimum wire size is dependent upon the maximum permitted voltage
drop:

a) NFPA 70-1999 210-19(a) FPN No. 4: Conductors for branch circuits as
defined in Article 100, sized to prevent a voltage drop exceeding 3
percent at the farthest outlet of power, heating, and lighting loads, or
combinations of such loads, and where the maximum total voltage drop on
both feeders and branch circuits to the farthest outlet does not exceed
5 percent, will provide reasonable efficiency of operation. See Section
215-2 for voltage drop on feeder conductors.

b) NFPA 70-1999 110-3(b) Installation and Use. Listed or labeled
equipment shall be installed and used in accordance with any
instructions included in the listing or labeling.


Step 3)
-------
Because our example is a power-limited circuit, we choose option b.
Looking at the drawing we see that the manufacturer specifies that the
horn/strobe will operate properly at a minimum of 20Vdc and at a maximum
of 28Vdc. Comparing the NAC power supply voltage with the minimum
voltage at which the horn strobe will work we can determine the maximum
voltage-drop permitted.

Additionally, the manufacturer specifies the current requirement of
.100Amp per horn/strobe times (10) horn/strobe gives us a total load of
1A:

[24-20Vdc]<-----------[    ?ohm  ]------------>[ 1A ]
[4Vdc    ]<-----------[    ?ohm  ]------------>[ 1A ]


Step 4)
-------
German mathematician Georg S. Ohm is credited with, among other things,
delineating the relationship that exists between voltage, current, and
resistance;

Ohm's Law
---------
E=IR or;
I=E/R or;
R=E/I

Applied to our example:
E (in volts) is the maximum volt-drop permitted, expressed as 'Ed'.
I (in amps) is given to us by the manufacturer as 1A.
R (in ohms) is unknown.

We want to solve for R which is the resistance represented by the
circuit:

R=Ed/I
R=(24v-20v)/1A
R=4v/1A
R=4ohm

Another way to look at this answer is; the maximum amount of resistance
permitted to be represented by the circuit conductors is 4ohm. The
example is a 500' 2-conductor circuit or;

a 1000' 1-conductor or;

The maximum amount of resistance permitted by the 1000' round-trip
circuit is 4ohm or;

4ohm/1000'


Step 5)
-------
NFPA 70-1999 Chapter 9, Table 8, page 567, Conductor Properties, is
where we find the smallest conductor size permitted, which will not
exceed 4ohm per 1000', which turns out to be 14AWG; 3.14ohm per 1000'.


----------------------------------------------------------------


Try this one on your own:

What is the minimum 7-strand, uncoated copper wire size in AWG permitted
by NFPA 70-1999 in the following example:

    |<---------------- 2000' ---------------->|

+---+      .-.  .-.    .-.  .-.    .-.  .-.   +-------+
| + +--.  /   /     /   /     /   /   `--+  +-+  |
|   |   /    /    /    /    /    /      |  | |  |
| - +---'   /     /   /     /   /     .-+  +-+  |
+---+     `-'    `-'  `-'    `-'  `-'    `-'  +-------+
NAC Power Supply                              (1) Horn
Class 2 Power Limited                         .050A
24Vdc nominal                                 21-28Vdc

Average ambient temperature = 75 degrees centigrade.

EXTRA CREDIT
------------

What if the average ambient temperature is 70 degrees Fahrenheit?

================================================================
TEST DATES 
================================================================

Oregon
------
PCC Sylvania, Portland;
Test 11/17/01. Postmark deadline 9/29/01.
Test TBA/02. Postmark deadline 12/1/01.

Clackamas Community College, Oregon City;
Test 11/26/01. Postmark deadline 9/29/01.
Test 1/19/02. Postmark deadline 12/1/01.

Washington
----------
Bates Technical College, Tacoma;
Test 11/17/01. Postmark deadline 9/29/01.
Test TBA/02. Postmark deadline 12/1/01.

Walla Walla Community College;
Test 12/14/01. Postmark deadline 10/27/01.
Test TBA/02. Postmark deadline 12/1/01.

Spokane Community College;
Test TBA/02. Postmark deadline 12/1/01.

Idaho
-----
Boise State University;
Test 11/17/01. Postmark deadline 9/29/01.
Test TBA/02. Postmark deadline 12/1/01.

Ricks College, Rexburg;
Test 12/15/01. Postmark deadline 10/27/01.
Test TBA/02. Postmark deadline 12/1/01.

Montana
-------
Rocky Mountain College, Billings;
Test TBA/02. Postmark deadline 12/1/01.

Montana Tech, University of Montana, Butte;
Test 11/17/01. Postmark deadline 9/29/01.
Test TBA/02. Postmark deadline 12/1/01.

MT State University, Bozeman;
Test 12/15/01. Postmark deadline 10/27/01.
Test TBA/02. Postmark deadline 12/1/01.

Flathead Valley Community College, Kalispell;
Test 11/17/01. Postmark deadline 9/29/01.
Test TBA/02. Postmark deadline 12/1/01.

For a complete list of all test centers and test dates, point your
favorite http client to -->http://www.nicet.org/tests.shtml

================================================================
CLASS SCHEDULE 
================================================================

Clackamas Community College is sponsoring a 16-hour Saturday
Seminar(r)in January 2002:

--> 1-12-2002 8am - 5pm NICET Certification application process and Fire
Alarm Systems Level I Element Review.

--> 1-19-2002 8am - 5pm Fire Alarm Systems Level II Element Review.

Visit http://www.lerc.org to register.

================================================================
ADMINISTRIVIA 
================================================================

Fire alarm dealers looking for a central station with the capability to
administer accounts via a web browser should check out our newest
service called MASweb at http://www.csmul.com.

Send your contributions, suggestions, comments, and questions to -->
mailto:TheBakerGroup@home.com

To unsubscribe, click the reply button and type 'unsubscribe' in the
subject line.

Have a happy Thanksgiving!

Mike  http://go.to./baker

================================================================
Copyright (c) 2001 Michael B. Baker all rights reserved.
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