Using a Multi Meter to Locate Reverse Polarity on a Circuit

Do you know how to Use a Multi Meter to Locate a Fire Alarm Device or Appliance that has been connected with reverse polarity?

If not this article will explain how to set the multi meter up as well as how to properly break down fire alarm circuits to locate an initiating device and or notification appliance that has been connected with reverse polarity.

Real quick we will start with the basics.  "What is polarity?"  Polarity in electrical circuits is known as "Positive" and "Negative".  In DC (Direct Current) circuits one pole is always positive (typically marked with a + or red) and the other is always negative (typically marked with - or black).  Note that electrons within a DC circuit only flow in one direction.

This is where a lot of people become confused.  There are two common notations of flow for DC circuits. See below:

#1 is the Conventional Flow Notation.  This notation is based on Benjamin Franklin's conjecture regarding the flow direction of charge.  This notation shows charge flow moving from the Positive Pole of a DC circuit to the Negative Pole.  This is the notation that is most commonly used my engineers and is technically incorrect.

#2 is the Electron Flow Notation.  This is the true notation of charge flow as it shows the actual motion of the electrons in a DC circuit.  Note that this notation shows the charge flow moving from the Negative Pole to the Positive Pole. 

Now that we have covered how a charge or current flows through a circuit, it is important to understand how a diode works and how it can allow or block this flow from occurring.

Definition of a DIODE: A semiconductor device with two terminals, typically allowing the flow of current in one direction only.  This direction of current flow moves from the ANODE side through the CATHODE side of the DIODE.  An easy way to remember this is a DIODE allows current to flow in the direction of the arrow within the symbol.

Here is the electrical symbol for a DIODE:

Below are two diagrams that depict the same image however they show the current flowing in opposite directions (conventional vs. electron flow notation).  Notice that even though they both have a diode facing in the same direction the lamp is still illuminated.  "Why is this?"  I thought that a diode only allows current to flow in one direction and that a DC circuit only flows in one direction.  "This would make it impossible to illuminate the lamp in both scenarios, right?"

Conventional Flow Notation with DIODE

Electron Flow Notation with DIODE

           
This is correct.  However the symbol for a DIODE has never been updated to match the Electron Flow Notation.  Therefor the DIODE is always shown with the "Line" or Cathode side pointing towards the positive flow based on the Conventional Flow Notation.  Note that if we were to update the DIODE symbol and show the arrow facing the opposite direction, the diagram based on the Electron Flow Notation would make more sense.

Now on to the point of this article.  "How do I use this information regarding current flow and diodes to locate a fire alarm device or notification appliance that has been connected with reverse polarity?"

A fire alarm initiating device or notification appliance that is polarity sensitive meaning it must be connected with the correct input (positive/negative) will have an internal DIODE to restrict the current flow in one direction as stated above.  We can use the diode setting on our Multi Meter to locate any section of a fire alarm circuit that has been connected backwards or with Reverse Polarity.

How it works:  When you select the DIODE setting your Multi Meter will force a small amount of current through the DIODE and measures the voltage drop across your Multi meter test leads.



Forward Bias Diodes:  If you have the Positive test lead connected to the Anode side and the Negative test lead connected to the Cathode side of the DIODE, your Multi Meter should display something close to 0.548 Volts.

Reverse Bias Diodes:  If you have the Positive test lead connected to the Cathode side and the Negative test lead connected to the Anode side of the DIODE, your Multi Meter should display OL (Open Line).

I suggest testing a single device/appliance on a specific circuit prior to searching for reverse polarity on a fire alarm run. This can be accomplished by using a spare or by taking down a device on a circuit you need to test.  Once you have the fire alarm device or notification appliance removed, place your positive (red) multi meter test lead on the positive terminal of the equipment and the negative (black) multi meter test lead on the negative terminal of the equipment.  If your multi meter displays 0.548 Volts then you have a circuit with Forward Bias Diodes.  If your multi meter displays OL then your circuits has Reverse Bias Diodes.

Here is the key to the puzzle.  If you test the wire in your circuit and your meter displays a dead short (0.000 and typically sounds a steady beep) then your circuit has one or more devices wired backwards.  This is known since diodes in Forward and Reverse bias positions would allow the current in your circuit to travel in both directions ultimately resulting in a dead short.

Now that you know which orientation your circuit's diodes face, you can start breaking down the circuit in halves.  Each time you cut the circuit in half, read the wires in both directions paying attention to multi meter's display looking for either 0.548 V, OL or a dead short.

This easy to use Multi Meter trick will help you eliminate very time consuming labor when troubleshooting fire alarm circuits.

UBC Requirements for UL 217 Smoke Alarms

310.9 Smoke Detectors and Sprinkler Systems.

310.9.1 Smoke detectors

310.9.1.1 General. Dwelling units, congregate residences and hotel or lodging house guest rooms that are used for sleeping purposes shall be provided with smoke detectors. Detectors shall be installed in accordance with the approved manufacturer’s instructions.

310.9.1.2 Additions, alterations or repairs to Group R Occupancies. When the valuation of an addition, alteration or repair to a Group R Occupancy exceeds $1,000 and a permit is required, or when one or more sleeping rooms are added or created in existing Group R Occupancies, smoke detectors shall be installed in accordance with Sections 310.9.1.3, 310.9.1.4 and 310.9.1.5 of this section.

Exception: Repairs to the exterior surfaces of a Group R Occupancy are exempt from the requirements of this section.

310.9.1.3 Power source. In new construction, required smoke detectors shall receive their primary power from the building wiring when such wiring is served from a commercial source and shall be equipped with a battery backup. 
The detector shall emit a signal when the batteries are low. Wiring shall be permanent and without a disconnecting switch other than those required for over current protection. Smoke detectors may be solely battery operated when
installed in existing buildings; or in buildings without commercial power; or in buildings which undergo alterations, repairs or additions regulated by Section 310.9.1.2.

310.9.1.4 Location within dwelling units. In dwelling units, a detector shall be installed in each sleeping room and at a point centrally located in the corridor or area giving access to each separate sleeping area. When the dwelling unit has more than one story and in dwellings with basements, a detector shall be installed on each story and in the basement. In dwelling units where a story or basement is split into two or more levels, the smoke detector shall be installed on the upper level, except that when the lower level contains a sleeping area, a detector shall be installed on each level. When sleeping rooms are on upper level, the detector shall be placed at the ceiling of the upper level in close proximity to the stairway. In dwelling units where the ceiling height of a room open to the hallway serving the bedrooms exceeds that of the hallway by 24 inches (610 mm) or more, smoke detectors shall be installed in the hallway and in the adjacent room. Detectors shall sound an alarm audible in all sleeping areas of the dwelling unit in which they are located.

310.9.1.5 Location in efficiency dwelling units, congregate residences and hotels. In efficiency dwelling units, hotel suites and in hotel and congregate residence sleeping rooms, detectors shall be located on the ceiling or wall of the main room or each sleeping room. When sleeping rooms within an efficiency dwelling unit or hotel suite are on an upper level, the detector shall be placed at the ceiling of the upper level in close proximity to the stairway.  When actuated, the detector shall sound an alarm audible within the sleeping area of the dwelling unit or congregate residence, hotel suite, or sleeping room in which it is located.

Conduit Bender Offset Reference Table

This is a chart to help you better understand the the shrink amount and the distance between conduit bends when performing a saddle with EMT, Rigid electrical conduit or any other type of electrical conduit. You will want to use the arrow mark on the conduit bender and refer to the degree markers along the side of the conduit bender head. Make sure the electrical conduit is always in line with the pipe bender to insure nice straight bends.

	22.5°	22.5°	30°	30°
OFFSET	DISTANCE BETWEEN BENDS	SHRINK	DISTANCE BETWEEN BENDS	SHRINK
2"	5-1/4"	3/8"
3"	7-3/4"	9/16"	6"	3/4"
4"	10-1/2"	3/4"	8"	1"
5"	13"	15/16"	10"	1-1/4"
6"	15-1/2"	1-1/8"	12"	1-1/2"
7"	18-1/4"	1-5/16"	14"	1-3/4"
8"	20-3/4"	1-1/2"	16"	2"
9"	23-1/2"	1-3/4"	18"	2-1/4"
10"	26"	1-7/8"	20"	2-1/2"
	45°	45°	60°	60°
OFFSET	DISTANCE BETWEEN BENDS	SHRINK	DISTANCE BETWEEN BENDS	SHRINK
2"
3"
4"
5"	7"	1-7/8"
6"	8-1/2"	2-1/4"	7-1-4"	3"
7"	9-3/4"	2-5/8"	8-3/8"	3-1/2"
8"	11-1/4"	3"	9-5/8"	4"
9"	12-1/2"	3-3/8"	10-7/8"	4-1/2"
10"	14"	3-3/4"	12"	5"

NFPA 72 2007 Mistake with Smoke Detector Spacing

After looking into the National Fire Protection Association NFPA 72 2007 edition, I came across what I consider a mistake.  Now this might be something that was intentional but I will explain my reasoning below.

NFPA 72 2007 section 5.7.3.2.3.5 states that for smooth ceilings, all points of the ceiling shall have a detector within 0.7 times the selected spacing.

Now this is no big surprise.  We know that smoke detector spacing is determined by the manufacturer's recommendations which is typically around 30'.  If we take 30' and multiply it by 0.7 we arrive at a new spacing for smoke detectors of 21'.  This is the reason, NFPA 72 clearly states that for corridors or rooms 10' in width or less, smoke detectors can be located 20.5' feet from the end wall and spaced 41' between detectors.

Knowing this information, "How many smoke detectors would be required to cover a room that measures 25' by 34'?".

To find the answer we need to use the Pythagorean Theorem of A squared + B squared = C squared.  This is the formula used to determine the distance of an unknown side of a triangle   For example or room measures 25' x 34' so we will need to solve for 25 squared + 34 square = C squared.  This equates to 625 + 1156 = The square root of 1781.  The square root of 1781 is 42.2019.  Now for someone who is new to this, it might seem kind of crazy to do all of this work to find out the quantity of smoke detectors required to cover a specific room size.  However, it is quite simple.  All we did by using the Pythagorean Theorem is determine the distance diagonally across the room measuring 25' x 34'.  We now know that the room measures 25' Long x 34' Wide x 42.2019' Across Diagonally.

Now using the 0.7 rule we know that all points in the room shall have a smoke detector within 21'.  Clearly out diagonal distance of 42.2019' split is half is greater than 21'.  With this information, we know that 2 smoke detectors are required to cover this space.

This is where it gets interesting:

NFPA 72 2007 section 5.7.3.2.4.2 deals with level ceilings of solid joist or beam construction.  Note #5 within this code section specifically states that if the room is 900 square feet or less, only one smoke detector is required.

If we take the manufacturer's recommended spacing of 30' for smoke detectors we can cover 900 square feet since 30' x 30' is 900'.  Keep in mind that this is not incorporating the 0.7 rule found in NFPA 72 2007 section 5.7.3.2.3.5.

This is where in my mind, the mistake is located.  According to NFPA 72 2007 edition, 2 smoke detectors are required to cover a room measuring 25' x 34' if the room has smooth ceilings.  However, if the room has solid joist or beam ceilings, you are only required to install one smoke detector.  Keep in mind both rooms are under 900 square feet as we are using the same measurements for both scenarios.  If anything  this rule should be reversed allowing only one smoke detector in rooms with smooth ceilings measuring 900 square feet or less.  Rooms with joists and beams will slow the movement of smoke across the ceiling to a point where additional smoke detectors may be required to achieve the same response time of the same room with smooth ceilings.  

The kicker is that NFPA must have caught this mistake as it has been corrected in the NFPA 72 2010 edition.  Now if you look at section 17.7.3.2.4.2(5) in the 2010 edition, it states that for rooms measuring 900 square feet or less, smooth ceiling spacing shall apply.

This takes us back to the smooth ceiling spacing section which requires a detector within 0.7 times the selected spacing to all points on the ceiling.

To recap, NFPA 72 2007 edition requires 2 smoke detectors for a room with smooth ceilings measuring 25' x 34' yet only requires 1 smoke detector if the room has solid joist or beam construction ceilings.  NFPA 72 2010 edition requires 2 smoke detectors in both scenarios.

If you would like to shed some light on this topic or just explain your thoughts, we encourage you to join our Facebook group.

Fire Safety for the Elderly

Fire safety for the elderly is extremely important. It is our job to both inform and help protect our elders.  This post is dedicated to some key points and topics regarding fire safety for the elderly.  Older persons have to take extra precautions to maintain safe conditions around the home when it comes to fire safety.  As we get older, we naturally become slower.  On top of this, our eyesight and hearing may not be what is used to be.

• With this in mind, we need to "Be Prepared".  Make sure you have an evacuation plan in place as well as the necessary item you would need in the event of a fire.  It doesn't matter what age you are, we naturally panic in the event of emergencies and often forget our training.  Make sure to have an emergency kit close at hand.

• Smoking is slowly becoming a thing of the past but for now it is still here and we need to be aware of the dangers that cigarettes can cause.  Aside for health related deaths, smoking in bed can be very dangerous.  Never smoke in bed!  Make sure you are using large over sized ashtrays and wet all cigarette and cigar butts before throwing them in the trash.

• Space heaters can cause household fires.  Keep in mind that space heaters can get hot enough to ignite drapes, paper an clothing.  Make sure to keep all combustible and flammable objects at least 3 feet away from space heaters.  Always turn off space heaters before going to bed.

• As with every home smoke alarms are very important   The elderly need as much warning opportunities as possible.  Install a smoke alarm inside and outside each sleeping unit, the basement, near the kitchen, the garage and on every level of the house.  Be sure to turn the audible alarm to the loudest selection possible (if applicable).  It is very important that you test these smoke alarms monthly and  replace the batteries twice a year.  Remember change the smoke alarm batteries when you change your clocks.  Kidde Night Hawk Combination Smoke/CO Alarm w/Voice/Alarm Warning (Google Affiliate Ad)

• The kitchen is one of the most dangerous areas for fires.  Never begin cooking a meal if you feel drowsy or intoxicated from medication or alcohol.  Always use loud timer buzzers to remind you when to turn off the oven or burners.  When cooking on the stove top, turn pot handles inward to avoid accidental spills and always use oven mitts to avoid burns.  NEVER leave cooking foods unattended.  Remember to smother grease fire DO NOT USE WATER!  

• Like we stated above, plan your escape.  Make sure you know at least two ways out of every room in the house.  Practice these escapes frequently as to avoid confusion in the event of a real fire emergency.  If one of your routes is blocked by flames or smoke, make sure you can escape by an unobstructed optional route.  First Alert EL52-2 Escape Ladder - 2 Story 14 Foot (Google Affiliate Ad)

• In a household for the elderly, it is important to have locks and safety latches that are easy to undo in the event of a fire emergency   Remember every second counts.  

• If you are living in an apartment or even a town home  it may be common that your front door is located in a corridor or even above the ground floor.  Make sure you can find your way out of the building in the dark.  When smoke builds it may become very dark almost as if the lights were completely out.  It is a good practice to count steps, doors, columns, etc.  This will help you find your way in the dark or in the event of a fire.

• In the event that you can not get out via one of your two escape routes, don't panic.  Use your phone to call for help.  It is recommended to keep your phone close at hand.  If for some reason you cannot locate your phone, use a red towel out of the window to signal someone.  Make sure you advise your neighbors to check on you during an emergency.

• Always check doors for heat.  There may be a fire on the other side of a door used in your evacuation.  Use the back of your hand to lightly feel for heat on the door or door handle.  If it is hot, do not open it.  Fire is always looking for oxygen and may engulf you if you open the door.

• If for some reason you are trapped in a room, block off the smoke and poisonous gases.  This can be accomplished by stuffing rags or clothes (preferably wet) under doors and around windows.  Once this is complete, signal for help.  

• In the event of a fire and you need to exit through a smokey area, crawl.  The lower you get, the cooler, safer and cleaner the air will be.  Try to stay below 2 feet if possible.

• Remember what we learned in elementary school.  If you catch fire, STOP, DROP and ROLL!  Do not run around as this will fan the flames.  Get down as quickly as you can, cover your face with your hands and roll around to smother the flames.

• Once you evacuate the building via your planned escape route, STAY OUT!

These steps should be followed for fire safety for the elderly.  Planning now can save a live tomorrow.

NUP Connector for Notifier ONYX Panels

If you are faced with the task of creating a NUP connector for your Notifier ONYX panels this follow this simple step process.

Take a standard DB9 cable and cut off the male end (end with the prongs sticking out).  Now strip back the cable and use a mutimeter to verify the following three pins (#2, #3, and #5).  Once you have these verified, mark them down on a paper with the wire color and the pin number.

Now on the NUP connector, pull off the red and black cables as these are used for power.  Simply pull them out of the NUP connector completely and discard.


You should be left with three cables on your NUP connector.  White, Green and Brown.  With a soldering iron splice the following pairs together.  The brown NUP cable to pin #2 on the DB9, the white NUP cable to the #3 pin on the DB9 and the green NUP cable to the #5 pin on the DB9.

Once you are done, make sure to separate each splice with tape or shrink wrap and finally shrink wrap the entire connection.

You should now have a functional DB9 to NUP cable for programming the Notifier ONYX panels and NCM Network Control Module boards.

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