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MK 6 AMP TYPE 2 M6 MCB CIRCUIT BREAKER 240V LN 5906 BS 3871

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Now, imagine that I start delaying phase W more and more. As I do so, it gets more and more different from phase A. The sine wave that is the difference between phase A and phase W gets larger and larger. Eventually this resultant sine wave is actually _greater_ than phase A. This difference sine wave reaches its peak when phase W is exactly 1/2 cycle from phase A, meaning that the +peak of A corresponds to the -peak of W. At this point, the amplitude of the _difference_ between the two phases is twice the amplitude of each phase alone. This is to say that if phase A is 277V relative to neutral, and phase W is 277V relative to neutral, and 180degrees out of phase with phase A, then the voltage A to W is 534V. This is developed in Note 2 to regulation 536.4.203, which states that ‘ If an assembly deviates from its original manufacturer’s instructions, or includes components not included in the original verification, the person introducing the deviation becomes the original manufacturer with the corresponding obligations’. A Type 1 SPD is designed to provide protection against surges caused by direct lightning strikes. These often feature spark gap technology, which can handle very high voltages by creating a short to ground when a level of current is reached. Type 2 OC or 40 OC,the purpose of the latter value being to avoid the necessity of de-iating thermally sensitive circuit-

The reference calibration temperature for types B,Cor D shall be 30 'Cand for types 1, 2,3 and 4 shall be eitherMy only hope is now if someone has any brochures stored somewhere with let through tables/graphs. Otherwise I will be replacing them At time zero, phase A is zero, but phase W is negative, say by a couple of volts. Then at time 1/240 phase A is at its positive peak, but phase W is slightly below. A teensy bit later, phase A is on its way down, and phase W hits its peak. And so on through the cycle. Both phases have the same amplitude, but hit their peaks at different times. There is usually a slightly different voltage between the two, but since sometimes A is more positive and sometimes W is more positive, the two graphs _must_ cross. A Type 2 device offers protection against over-voltages from switching and indirect lightning strikes. This type more commonly uses a metal oxide varistor (MOV) to divert the current away. Type 3

Now imagine another point in the system, also connected to phase A. If we measure the voltage at this point, we will get the exact same curve. Finally, try to measure the voltage between these two locations. If you look at each instant in time, the voltage _difference_ will be zero. The average of zero is still zero. Net result is that if you measure the voltage between two points, both phase A, you will get zero volts, as expected. The 17th edition of the IET wiring regulations amendment 3 introduced the Cmin (0.95) factor which reduced the old maximum zs values to allow for the fluctuation of the voltage. Step 1 is to remember that voltage is _always_ measured between two points. So when you say that a particular circuit is 277/480V wye, you provide the following information: Measured phase to phase the voltage is 480V. Measured phase to neutral the voltage is 277V. The source is wye connected, eg. a transformer bank with 277V secondaries. Protection against transient over-voltages shall be provided where the consequence caused by over-voltage: So now consider phase A in our 277/480V wye system. We can plot the voltage relative to our earth reference as a function of time, and get a graph, ideally a nice sine curve. At time zero the voltage will be zero. At 1/240 of a second, the voltage will be +392V (277V * 1.414, the square root of 2). Then at 2/240 second the voltage will again be zero. At 3/240 of a second the voltage will be -392V, and at 4/240 second (1/60 second) the voltage will again be zero. This cycle will repeat.should be taken as soon as possible to improve the safety of the installation." would be appropriate but maybe your not talking about the LoadMaster WHY used square root 3 in calculation –> this is the answer,please read discussion on this forum : http://www.electrical-contractor.net/forums/ubbthreads.php/topics/129279/1_732_square_root_of_3_where_d.html For this reason, while fuses can be cascaded, and if the thin one blows, the fatter one behind it will not, for all values of fault currrent, for MCBs no such statement can be made. Indeed it is common to find a random selection of breakers open under fault, and for really high current faults the fuse at the origin fails instead. In summary, can you mix devices in distribution boards (including consumer units)? Yes, you can. But you need to seek assurance from the manufacturer of the original assembly that the devices will be compatible, or conduct your own study to ensure the requirements are met. In the words of BEAMA, ‘The installer has responsibility to act “with due care”. If this is not done then there is a probability that, in the event of death, injury, fire or other damage, the installer would be accountable under Health and Safety legislation.’ I don't for one moment think we need to use 3000 A for 0.1 seconds in this case but if you did then the 300 becomes more like 1000, and the minimum cable size is probably 10mmsq....

So I2t is actually a function of the prospective fault current, and is either depicted graphically, or listed as spot values . For mcbs made to the IEC standards since 1999 or so this is a spec parameter, and guaranteed by design. for earlier devices it isn't Let through energy is a bit problematic for breakers - a fuse gets faster as the fault current rises, and tends towards a constant let- through energy (I squared r times time, but the resistance r is a fixed parameter of the fuse, as is the weight of metal to be raised to melting point to start it breaking) So the Zs calculation formula for a 0.1s to 5s disconnection time for a BS EN 60898 MCB or BS 3871 to calculate the maximum Zs would be:The last bit is to ask ‘how do I calculate the voltage difference between two phases with some other phase angle?’ Clearly this is some function of the amplitude of the phases, and also a function of the phase angle between them. Simplify the question by stating that both phase A and phase W have the same phase to neutral RMS voltage V. Call the phase angle between these two phases T. The voltage between the phases is then given by V * 2 * sin(T/2). So for the 180 degree phase difference we get V * 2 * sin(180/2) = V *2 The values of earth loop impedance shown in these tables must compensate for conductor temperature rise, if the measurement of loop impedance is taken at ambient temperature. A useful rule of thumb is to allow for a temperature rise from 20 degrees to 70 degrees by multiplying the listed value by 0.8. The measured value can then be compared to the compensated value. Now I’ll set up a nifty little tool; a special transformer that lets me produce output of arbitrary phase angle. The output is still 277V RMS relative to our zero reference, but I can shift its phase relative to phase A. Lets call the output of this transformer ‘phase W’. I adjust phase W so that it is very slightly delayed from phase A, and graph the two phases. Make a graph of the difference between A and W, and you will find out that it is a sine wave with low amplitude. In fact, it is a law of mathematics that the sum or difference of two sine waves of the same frequency (but possibly different amplitudes or phases) is another sine wave of the same frequency, again with different frequency or phase.

If devices from different manufacturers are used together, the venting characteristics may not be coordinated which could result in significant further damage to adjacent devices or other parts of the distribution board. The Institution of Engineering and Technology (IET) Wiring Regulations (BS 7671) has updated its guidance on surge protection devices (SPD) in successive editions. Current 18 th Edition, released in July 2018 and applicable from January 2019, outlined revised guidance advice for contractors, and new criteria for where these devices should be installed. To see how AC voltages add up, we have to remember that the AC voltage is a form of average, and we have to look at the instantaneous values, get an instantaneous sum, and take the average of that.Type 3 SPDs provide local protection for sensitive equipment. As these have a relatively low discharge capacity, they should always be installed in addition to a Type 1 or 2 device. In other words, adding together CE marked products from one manufacturer with another’s CE marked products does not necessarily equal a CE marked assembly which is compliant with BS EN 61439. This may also be true when mixing product ranges from the same manufacturer. This is reinforced in Note 1 of regulation 536.4.203 which states that ‘ The use of individual components complying with their respective product standards does not indicate their compatibility when installed with other components in a low voltage switchgear and controlgear assembly.’ The regulation in question, 536.4.203, was introduced by BEAMA (the UK trade association for manufacturers of electrical equipment including switchgear) to warn designers and installers of the possible dangers of mixing devices from different product ranges or manufacturers in the same distribution board; mainly, but not exclusively, circuit-breakers. When installing a new final circuit for example, if there is spare space in a consumer unit and a circuit-breaker that appears to fit is to hand, it is tempting to use it. Another example is replacing a circuit-breaker with an RCBO to afford better protection for the user. K~ 145 for rubbers and 115 for PVC insulation , with certain assumptions about starting temperature. The 100% values should be recorded as the maximum permitted Zs value on the electrical test certificate and the temperature adjusted 80% values are used to compare against the actual readings obtained when testing the circuit. 60947-2 Max Zs Values

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