Capstone - Short CCT Temp Rise Flashcards
Thermoplastic V-75 & V-90 have a normal temperature limit of what?
75*C
XLPE X-90 has a normal temperature limit of what?
90*C
XLPE X-HF-110 has a normal temperature limit of what?
110*C
Which table of the AS/NZS 3008 is used to determine temperature limits
Table 53
What table of the AS/NZS 3008 is used to determine normal temperature of a conductor?
Table 1
Table 52 of the AS/NZS 3008 is used to determine what?
Constant K
What is the formula used to determine the time at which conductor insulation deteriorates during short circuit conditions?
I2 x t = K2 S2
In the formula I2 x t = K2 S2 describe the meaning of each value
I = short circuit current
t = time
K = constant K
S = cross sectional area of cable
Describe Clause 2.5.7.2.3 in the AS/NZS 3000
___
When considering two circuit breakers, if C2 is >=800A then discrimination will be determined by using what?
Manufacturer’s data
For most circuits, what is the discrimination between ratings?
C1 = 1.5 x C2
For overloads when using HRC fuses, what is the discrimination between ratings?
F1 = 1.6 x F2
For short circuits when using HRC fuses, what is the discrimination between ratings?
F1 = 2 x F2
How do you determine discrimination when using both a circuit breaker and fuse?
A fuse and circuit breaker combination where the fuse is upstream and the circuit breaker is downstream shall be selected such that the characteristics of the devices provide discrimination between the overload curve and the instantaneous setting or short delay setting of C2 and the time-current curve for F1.
What is the meaning of HRC for a fuse?
High rupturing capacity
HRC and Current Limiting are referring to the same thing, True or False?
True
The rated voltage for a fuse may be AC, DC, but not both. True or False?
False, it may be both
What is a fuse’s current rating?
The value the link will carry continuously without affecting its’ characteristics.
The minimum fusing current is the minimum current required for the fuse to conduct, True or False?
False - it is the minimum required to interrupt the circuit.
A curve showing pre-arcing before interruption of a fuse is called what?
Time-current characteristics
I1t is proportional to energy in what?
Amp-seconds
Maximum instantaneous value of current that a fuse will let through during operation is called what?
Cut off current
What are the three main regions of a trip curve for a Type C circuit breaker?
1 - Thermal region
2 - Electro-magnetic region
3 - Moving contacts region
What are the three main regions of a Type C circuit breaker?
1 - Thermal region
2 - Electro-magnetic region
3 - Moving contacts region
Which region of the trip curve for a Type C Circuit breaker has the shortest time?
Moving contacts region
What is the part of a Type C circuit breaker that detects current overload?
Bi-metal strip
What does an electromagnetic region of the trip curve for a Type C circuit breaker detect?
Short circuit
I 1 = ____ x I N and refers to what?
1.13 Thermal non-tripping
I 2 = ____ x I N and refers to what?
1.45 Thermal tripping
I 3 = ____ x I N and refers to what?
5 Magnetic non-tripping
I 4 = ____ x I N and refers to what?
10 Magnetic tripping
On a 10A Type C MCB, 20A will cause the breaker to trip in how long?
10 - 45 seconds
MCBs are designed to carry the nominal rated current at what temperature?
30*C
IN = _____
Nominal tripping current
Grouping factor K(g) is applied to what?
De-rating MCB thermal current
If you have an enclosure with 3 MCBs to each supply 22A loads, with a 40*C ambient temperature, would 25A be suitable?
No, required to use 32A due to temperature de-rating
Talk to assessor about what method of calculating cable impedence is preferred of the 1 options given.
1 - Using resistance only
2 - Using resistance and reactance only for cables bigger than 120mm2 and resistances only for cables 120mm2 or less. (b5.2.2)
3 - Using resistance and reactance only for cables bigger than 35mm2 and resistances only for cables 35mm2 or less. (b4.3)
4 - Using resistance and reactance for all components (transformer, mains, submains).
Prospective fault current on equipment is usually marked in what value?
kA
What is fault loop impedance?
A low enough circuit impedance that will draw a high enough current to operate the protective device within the required time
Final subcircuits with GPOs <63A must be interrupted during a fault within what time?
0.4 seconds
Portable equipment that can be moved during use and hand held Class 1 equipment must be connected to a final subcircuit which disconnects during a fault in how long?
0.4 seconds
Circuits supplying fixed or stationary equipment must trip during a fault in how long?
5 seconds
Impedance that is upstream of a protective device is considered to be what?
External
Impedance that is downstream of a protective device is considered to be what?
Internal
The fault path of an earth fault after the MEN link will be via what conductor? Why?
Neutral, PEN - because of larger cross-sectional area, meaning less resistance
Table 8.1 provides what values? What does it take into account?
Maximum impedance values for the size and type of circuit breaker. ZEXT + ZINT
If a calculated or measured value in a circuit exceeds that given for the device in Table 8.1, the circuit is compliant - True or False?
False it is non-compliant
