Archives 2001
Issue No. 1
Issue No. 2
Issue No. 3
Issue No. 4
Issue No. 5
Issue No. 6
Issue No. 7
Issue No. 8
Issue No. 9
Issue No. 10
Issue No. 11
Issue No. 12
Issue No. 13
Issue No. 14
Issue No. 15
Issue No. 16
Issue No. 17
Issue No. 18
Issue No. 19
Issue No. 20
Issue No. 21
Issue No. 22
Issue No. 23
Issue No. 24
Issue No. 25
Issue No. 26
Issue No. 27

  Log In

 

August 19, 2001

                   Northwest NICET Newsletter
================================================================
Volume 1 Issue 8                                       8-19-2001
================================================================

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

Contents:
-----------
- News
- Tech Tip
- Class Schedule
- Administrivia

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

It's a slow news week and I don't want to deprive you of information, so go
visit Britney Spears guide to semiconductor physics -->
http://www.essex.ac.uk/ese/news/britney.htm

================================================================
TECH TIP
================================================================

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

/. two-birds-with-one-stone dept.

This is project 1 of 2 for you recent seminar attendees. Read through the
example then perform the problem that follows, send it to me by 9/2/01. If
you have questions, email me at TheBakerGroup@home.com or call me 8am-5pm
503-209-7345.


What is the minimum 7-strand, uncoated copper wire size 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)
---------
Simplify the problem by looking at the drawing and squinting just a bit to
see its electrical equivalents:

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


Step 2)
---------
Determine 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 ]

Squinting once again we see just a bit of algebra peeking back...


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

In our example:
E is the maximum volt-drop permitted, expressed as 'Ed'
I is given to us by the manufacturer as 1A
R is unknown (see the algebra now?)

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'.


As the center fielder said of the lazy fly ball, "It's a can o' corn!"

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

Try this one on your own:

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

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

+---+                                         +-------+
| + +-----------------------------------------+  +-+  |
|   |                   [R]                   |  | |  |
| - +-----------------------------------------+  +-+  |
+---+                                         +-------+
NAC Power Supply                              (1) Horn
Class 2 Power Limited                         .050A
24Vdc nominal                                 21-28vdc

Send me your answer --> TheBakerGroup@home.com

extra credit:
---------------
The NAC Power Supply is installed in a room separate of the fire alarm
control panel that is not continuously occupied. Is a smoke detector
required to be installed in the room with the NAC Power Supply? Why?

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

Clackamas Community College is sponsoring a 16-hour weekday evening seminar
in September:

--> 9-10-2001 6pm - 10pm NICET Certification application process

--> 9-12-2001 6pm - 10pm Fire Alarm Systems Level I Element Review

--> 9-17-2001 6pm - 10pm Fire Alarm Systems Level II Element Review part 1

--> 9-19-2001 6pm - 10pm Fire Alarm Systems Level II Element Review part 2

Call 503-657-0135 to register.

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

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

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

Good luck and have fun!

Mike  http://go.to/baker

================================================================
:::::::::::::::::::::::: ADVERTISEMENT :::::::::::::::::::::::::
================================================================

Purchase the book used in my seminars:

Fire Alarm Handbook
NICET Level I and II
Element Review
ISBN 0-9707229-0-7

It is available in the Portland metro area at:

Building Tech Bookstore http://www.buildingtechbooks.com/
8020 SW Cirrus Drive
Beaverton, OR 97008-5986
(503) 641-8020
(800) ASK-BOOK

In the Seattle metro area at:

CW Cable, Inc.
20422 87th Ave.
Kent, WA 98031
(253) 872-6590
(800) 444-4961

or nationwide through:

NAAA [National Alarm Association of America] http://www.naaa.org/nicet.htm
800-283-6285

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

Coming soon...
Fire Alarm Handbook
NICET Level III and IV
Element Review
ISBN 0-9707229-1-5

With seminars to follow...

================================================================
Copyright (c) 2001 Michael B. Baker all rights reserved
Send a link to a friend        
 

 

Home - Clients - Book Store - NICET Level I - NICET Level II - NICET Level III - NICET Level IV - Glossary - External Links - Licensing - Photographs - Employment - Disney Crud(SM) - Archives 2001 - Archives 2002 - Archives 2003 - Archives 2004 - Archives 2005 - Archives 2006 - Archives 2007 - Archives 2008 - Archives 2009 - Archives 2010 - Archives 2011 - Archives 2012 - Archives 2013 - Misc

ET NewsSM content copyright © 2017
by Michael B. Baker. All rights reserved.
ISSN 1554-074X

RSS Content
Some information may be found within this web site that is reprinted with permission from one or more of the following: NFPA 70 National Electrical Code®,NFPA 72® National Fire Alarm Code®, & NFPA 101® Life Safety Code®, Copyright© NFPA, Quincy, MA 02269.

This reprinted material is not the complete and official position of the NFPA on the referenced subject, which is represented only by the standard in its entirety.