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Generally speaking, you need to account for any variance in electrical output. There are a lot of factors that can cause a fluctuation in electrical amperage. You wouldn't want to set the fuse too low or it would blow needlessly, but you also don't want to set the fuse too high, or a dangerous short will not be interrupted.
A power source/device can produce/draw more amperage while damaged than in normal operation.
A 4.33 amp device might not run at 5 amp while working, but while damaged could exceed that dramatically.
When looking at the reason for having a fuse, it provides two things:
1) help protect a working device from having too much amperage forced into it from a damaged power source
2) help protect the power source from having too much amperage draw from it by a damaged device.
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What value of current in a 1W - 20V zener diode must be limited to a maximum?
ANSWER A reverse biased 20 V zener clamps the voltage across its terminals to 20 V. Since 50 mA x 20 V = 1 W, the current through the diode should be limited to a maximum of 50 mA. In practice, this current maximum would be derated for reliability reasons.
Why must the instantaneous current wave be exact 90 degree out-of phase with the applied voltage waveform across an ideal inductor?
Because the voltage induced is proportional to the rate of change of current, and the maximum rate of change of current occurs at the point where the current waveform is 'steepest' -i.e. as it passes through zero. So, as the current passes through zero, the corresponding value of induced voltage is maximum, which means the voltage and current waveforms are displaced by a quarter of the wavelength, or 90 degrees.
Maximum safe load limits of what must be posted within buildings and structurs?
floors
When grounding a metal box what must be done?
The grounding system of a distribution must be from zero ohms to a maximum of two ohms. This is usually obtained by bonding all metallic parts back to the distribution centre with a wire capable of handling the circuits fault current if the circuit should ground out. The ground wire in cable sets is used for this purpose.
What is the Maximum number of outlets on a 20 amp circuit?
If following the National Electric Code (NEC) - most commonly used in USA there is no distinct limit to the number of outlets. You must calculate load in accordance with Article 220 and you must determine the largest motor load anticipated.
Is there a fuse on a Wii?
All plugs, by law, must have a fuse. Unplug the wii and open up the plug with a screwdriver to get at the fuse if you think it has blown. Remember that if you replace it, make sure it is with a fuse of the same maximum voltage!
Why must a fuse always be connected in a non-earthed conductor?
It is the ungrounded conductor that carries the load current. It is that conductor that needs to be protected should a fault current occur. That is what the fuse in that circuit does.
Is it necessary to connect a fuse at the secondary side of a current transformer?
Definitely NOT! An open circuit (across a melted fuse for example) on the secondary side of a current transformer is subject to a dangerously-high voltage, so a fuse must not be fitted. The secondary side of a CT must never be open circuited.
Why is there a fuse in a plug?
All UK-style 13-A plugs are fitted with a fuse for the purpose of overcurrent protection. The fuse rating must be appropriate for the load supplied by the plug, up to a maximum of 13 A.
What Precautions must be taken when using fuses?
the fuse protection feature should be adapted to overload characteristics of protected objects, considering the possible short-circuit current, choose corresponding fuse breaking capacity;2, fuse to be adapted to line voltage level, the rated voltage of rated current of the fuse is greater than or equal to the rated current melt;3, line fuse melts at all levels in the rated current to the corresponding coordination, keeping the level of the melt must be greater than the rated current level of the melt under the rated electric current;4, fuse melts to use combination according to the requirement of the melt, not allowed to increase the melt or other conductor instead of the melt.
Can a 250V 2.5A fuse replace a 125V 2.5A fuse?
Yes, a 250V fuse can replace a 125V fuse if they have the same ampacity rating. The voltage rating is simply the maximum voltage that the fuse is capable of safely interrupting. You can go higher, but you can not go lower. Obviously, the form factor of the fuse must be the same, but that is often the case.
What value of current in a 1W - 20V zener diode must be limited to a maximum?
ANSWER A reverse biased 20 V zener clamps the voltage across its terminals to 20 V. Since 50 mA x 20 V = 1 W, the current through the diode should be limited to a maximum of 50 mA. In practice, this current maximum would be derated for reliability reasons.
What is a fuse used for?
A fuse is a safety device that lies in series in a circuit between an electrical source and its associated load(s). When the current, or flow of electricity, exceeds its designed threshold, the fuse is calibrated to permanently open the series circuit, thereby disconnecting the load(s) from the power source. Unlike circuit breakers, which can be reset to allow current to flow again, once a fuse disconnects, it must be discarded and replaced with a new fuse.
Why the transformer rating in kva why not in kw?
A transformer has separate ratings for maximum voltage and maximum current. Both limits must be observed. The maximum voltage is set by the magnetic flux density in the core, while the current limit is set by the size of the wire used in the primary and secondary windings. Multiplying the two together gives the VA or kVA rating.
What do circuit breakers and fuses have in common?
Both fuses and circuit breakers cut off a circuit from its power supply when the total current through the circuit exceeds the current rating of the fuse or circuit breaker, usually due to a short to ground or overloading of the circuit. Both use materials that respond to heat.
Why must the instantaneous current wave be exact 90 degree out-of phase with the applied voltage waveform across an ideal inductor?
Because the voltage induced is proportional to the rate of change of current, and the maximum rate of change of current occurs at the point where the current waveform is 'steepest' -i.e. as it passes through zero. So, as the current passes through zero, the corresponding value of induced voltage is maximum, which means the voltage and current waveforms are displaced by a quarter of the wavelength, or 90 degrees.
The fuse 13 A in a plug is intended to?
This is intended to protect the flex of a plug. A fuse is a little wire that all of the electricity coming into the appliance flows through. If something goes wrong and the current is higher than it should be, this fuse will overheat and burn out, thus breaking the wire and cutting the flow of electricity. If there was no fuse, the circuit would not be broken, this could overheat the plug and it could possibly catch fire. The 13A means that that fuse is set to 13 Amps of current, If it gets anything over that, the fuse will blow. Depending on the appliance the number will vary. 13A fuses are mostly used in the flexes of an appliance that have a high voltage, such as heating appliances like kettles fan heaters. When choosing a fuse for a plug you must choose a fuse that is higher than the current that the appliance has as current is higher when things are first switched on. If you choose a fuse that is too low for the appliance, the fuse will keep blowing out. Never choose a fuse that is too high for an appliance as this will not blow out if the current is too high.
