Working of tester

A Neon screwdriver or tester is commonly used to check the live wires. If the circuit is live, the neon bulb glows. We can also name it as voltage testing device. However the terms Phase checker, Line tester, Live checker and Positive presence checker is also used to identify the instrument. Here is the full construction with all parts indicated.

Metal Rod:

It is a metallic rod. The lower tip of the rod is specially chamfered to a specific screw design. This end is connected with the live wire. The upper end of this rod is completely cylindrical and it joins with the resistor.

Resistor

Resistor reduces the amount of current in the circuit. This current reduction provides a safe limit for the neon bulb. Next to resistor, the neon bulb is connected.

Neon Bulb

The neon bulb is used as the current indicator. When connected to live circuit, this neon bulb glow and we can know that circuit is live. If there is no current the bulb will not glow.

Spring Elements

Next to neon bulb a metallic conductive spring element is connected. It serves as a bridge or junction between the bulb and cap.

Cap

Next to spring a cap connects. This cap serves two purposes. Its internal sides keep all the equipment tightly pressed within the plastic assembly. Whereas its external side in pressed by the finger. (Full working explained in the working section)

Clip

A clip is conventionally connected with the cap.

Plastic Assembly

The plastic assembly surrounds the whole arrangement and its purpose is to insulate the entire design from human body so as to prevent shock and hazardous conditions.

Working

During working the low end of the metallic rod is connected with the live wire whereas the upper end of the cap is pressed by the human finger. The internal resistance of tester connects in series with the human body. Remember that this internal resistance is very high typically it is the order 200 k. Now the circuit completes and limited current runs through the human body. This current also flows through the neon bulb and it lights up if the circuit is live.

There are a few precautions that should be employed while using the tester. However, two most important precautions are mentioned here:

• The tester should only be used when you are sure that voltage is within 500 V. Also make sure that proper resistor is connected. Never connect the instrument until you are 100% sure.
• Always use the good quality instrument, you can save a few bucks on low-quality material but it can harm your life.

Why don't birds get electrocuted sitting on power lines?

Current flows in a loop[ which means the circuit is closed]. A bird sitting on a transmission line does not complete the circuit. If the same bird keeps one leg on one line and another leg (or any part of its body) on another line(or the neutral points), then it will get roasted.

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Consider this circuit where a bird sits on the wire:

The values R1 and R2 are resistances of the line. Electricity takes the path of least resistance. The two legs of the bird which is perched on the same line does not complete the circuit. The R_Bird( resistance of the bird’s body) is much higher than that of the line, so the bird might not experience high current. The potential difference between the two legs of the bird is same( since the resistance of the line is the same throughout).The current flows on.The bird is safe.

Now consider this scenario:

A bird sitting on a line decides to fly away and raises the wings. With one wing touching the neighboring line and the leg on the first line, this creates a closed circuit. Thus electricity (following the path of least resistance) will detect a potential difference between the wing (which touches the other line) and the leg(which is placed on the first line). The current tries to take on that path creating a short-circuit. Eventually the bird gets zapped and falls off the line. Now the current will continue to flow on.

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The lesson we learn here is that when ever we play with electricity, make sure you (your body) does not close the circuit. When we poke our fingers into an electrical socket we get shocked because our body will offer a lower resistance . Thus a potential difference will be created between your finger and the feet( which is placed on the floor acting as a neutral point).

Is it bad to charge your phone over night?

As we know, our smartphone batteries are bad as they barely last a day. At the earlier days when we buy it, it’s the fault of smartphone manufacturers. But what about several days later? It’s to some extent your own fault for charging it wrong this whole time. For example, charging phone overnight.

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Firstly, let’s have a look at the following saying: charging phone overnight, or more specifically, charging phone when it’s already fully charged, will keep it in a high-stress, high-tension state, which will surely do wear down the battery with lasting damage at the same time.
So, is it true? Is charging phone overnight bad?
Well, you’d better ignore that. We couldn’t be more wrong.
And the truth is that Charging phone overnight will not harm your battery in the slightest. Any device with a Lithium Polymer battery must incorporate a charging circuit that will cut off charging power when the battery reaches 100%.
Besides, the smartphone battery is as smart as the phone itself. Apple, Samsung and all the top tech companies, almost of whose products use lithium-based batteries.

That aside, however, Lithium-ion batteries don’t need to be charged all the way to 100%. While your phone runs troughtout the night, it loses battery life. And this will cause the charging mechanism to kick in over and over again as amounts of battery drain occurs during standby when checking emails, receiving text messages, and updating various apps while you sleep.

Let’s take an example. If you head to bed at 11 p.m. with a battery percentage in the single digits, your phone will be fully charged by 2 a.m. If you wake up at 6 a.m., that’s 4 hours that your phone stays plugged in with a full battery.

So what is the optimal way to charge your phone? That is to keep them charged between 50 and 80 percent.

Additionally, we have to mention Charge Cycles, that is, your battery goes from empty or near-empty to full. Every phone battery has a limited number of charge cycles before the end of its life. An iPhone has about 500 charging cycles. When charged up from 90%, only 10% of a complete charge cycle used. Whereas, when charged up from zero, then a complete charge cycle done. Or you’ll actually shorten your battery life if you do so.

Surely, here is another good idea for charging, or portable charging. And that is to take a power bank in hand, in pocket.

Magnetic Starter - Control Stations

One of the advantages of magnetic starters is the ability to add control stations. These stations may be located at any convenient location and duplicated as required. The maximum number of stations and their location is unlimited for all practical purposes. Stations are built using Normally Closed (STOP) and Normally Open (START) momentary contact switches. These switches must be rated for the control circuit voltage at a minimum. Over-rated switches will work fine. Many manufacturers incorporate both Normally Open (NO) and Normally Closed (NC) contacts in a single switch body. By rewiring the switch you can change it from one to the other. Many manufacturers also provide interchangeable buttons in at least red and green.

The last station must always be provided to complete the circuit. The intermediate stations may be repeated as many times as required. Suitable 3 conductor control wiring is required from the starter to each of the control stations in turn (daisy chained).

Air Compressor or Float Pump/3ph Starter/1ph Motor

Line Voltage Control Magnetic Starter controlled by a air compressor pressure switch (NC). Includes Auto/Hand/Off control and low oil switch (NC). Both of these are optional and may not be present in all applications. In some cases, the switch will include only Auto/Off. The Auto/Hand/Off is sometimes an integral part of a factory pressure switch. Auto allows for unattended, automatic starting of the compressor when the air pressure in the tank falls below the preset limit. Hand (manual control) allows the pump to be turned on regardless of the position of the pressure switch. This may or may not be appropriate for all applications and is shown in the interest of completeness only. Hand should be used with caution and due consideration to what is happening in the circuit. Off is self explanatory. If no low oil switch is present, merely remove it from the circuit and continue the wires from the start switch back to the coil.

Incidentally, the same circuit can be used to power a sump pump. The float switch (NO) for the sump would be connected in place of the pressure switch. When the switch detects liquid, the contacts will close and the pump motor will start - assuming that the Start Switch is in the Auto position. Hand is obviously desirable in a sump pump application as it allows the pump to be activated even if the float switch is not functioning.

3ph Starter/3ph Motor/Reversible

Line Voltage Control - double contactor three phase motor starter controlling a reversible three phase motor (rev 08 Aug 2006) (Note: L1 becomes T3 and L3 becomes T1 when the reverse relay is actuated.) The motor must be STOPPED before REVERSING unless the contactor allows for on-the-fly reversing. The coils are locked out via the NC contacts (M1, M2) usually contained within the mechanical interlock. When Coil #M1 is engaged, Coil #M2 is locked out and vice-versa.

3ph Starter/1ph Motor

Line Voltage Control three phase (3ph) motor starter controlling a single phase motor (rev 08 Aug 2006) Some 3 phase Magnetic Motor Starters require current to be seen across each of the three overloads. This may be accomplished by directing the output of second circuit back into the input of the third (previously unused) circuit and feeding the motor off of the output of the third circuit (rather than the second). Wiring then becomes: Line 1 → L1 → T1 → Motor 1 (L1-hot 240v or neutral 120v) Line 2 → L2 → T2 → L3 → T3 → Motor 2 (L2-hot 120v or 240v)

Manual Starter? Merely ignore the control wiring in RED