304 Flashcards
What is meant by initial verification and why is it carried out?
The first time that inspection, testing and certification of new work is carried out. This is to verify that all requirements of the design specification and regulations have been met.
During which 2 stages of an installation is inspection carried out?
During erection and on completion
What is the purpose of the inspection?
To verify that the correct equipment has been selected and erected and that it is not damaged or defective so as to impair safety
List 5 supply characteristics which must be recorded on the Electrical Installation Certificate
Any 5 from: Earthing arrangement, number of live conductors, type of live conductors, nominal voltage, nominal frequency, Ze, Ipf, Supply Protective Device and rating.
State the correct names of the 2 documents which must accompany an Electrical Installation Certificate.
Schedule of Circuit Details, and Schedule of Test Results
What do the letters IP stand for?
International Protection
State the 2 alternative IP codes for enclosures generally
IPXXB or IP2X
State the 2 alternative IP codes for horizontal top surfaces of enclosures
IPXXD or IP4X
In the code IP4X, what is the relevance of the X?
This means no protection specified.
What would an enclosure rated as IP56 be protected against?
Ingress of dust and jets of water
A new conduit system is to be inspected prior to the cables being installed. The conduit extends over some 30m of wall and supplies a number of socket-outlets.
Complete the table below, stating 5 items that should be checked before the cables are installed, what is being checked for and the human sense to be used in each case.
Item number -> What item is being checked -> What is the item being checked to confirm? -> Human sense used
1 -> Saddles -> Sufficient mechanical support and saddles appropriately spaced -> Sight
2 -> Saddle fixings -> Security of fixing -> Touch
3 -> Inspection bends/boxes -> Sufficient number of inspection boxes to allow ease of drawing in cables -> Sight
4 -> Correct size of conduit -> Sufficient capacity for number of conductors -> Sight
5 -> Joints -> Joints securely made -> Touch
Appropriate type of conduit to comply with specs and environment, no screw threads showing, galvanising spray used, deburring -if for steel conduit. and for either metal or plastic conduit checking that no damage was visible. See GN3 for a comprehensive list of other possibilities.
State the instrument used to carry out the following tests:
i) A continuity test on a main protective bonding conductor
ii) An earth electrode resistance test for a generator on a construction site
iii) An earth electrode resistance test on a TT installation protected by an RCD
i) Low resistance ohmeter
ii) Earth electrode resistance tester
iii) Earth fault loop impedance tester
An insulation resistance test is to be carried out on a low voltage lighting circuit
i) State the test voltage and minimum acceptable result, including the units
ii) What action should be taken with lamps and switches prior to test?
i) 500 VDC and 1 M Ohm
ii) Lamps out, switches on -operate 2-way switching if present.
Briefly describe the 3 steps of the ring final circuit test, with the reason for each step
1) End to end, confirm a ring exist in all 3 conductors
2) X-connect L-N and measure at each socket, verify that each point is connected to the ring and identify any spurs
3) As for 2 but with L and CPC, record highest measured value as (R1+R2)
The value of r1 in a ring final circuit wired in 2.5/1.5 mmˆ2 T&E cables is .45 ohms
i) What value would you expect for r2? -show your full working.
ii) For sockets on the ring, what would be the expected value of (R1+R2)
i) Multiplier = 2.5/1.5 = 1.67 so r2 = 1.67(r1) = 1.67(.45) = .75 ohms
ii) (R1+R2) = (r1 + r2) / 4 = (.45 + .75) / 4 = .3 ohms
State 3 reasons for carrying out a polarity test on a new electrical installation prior to it being energised.
See Reg 643.6:
- Single pole switching/protection in line conductor only
- Correct connection of Edison screw lampholders
- Correct connection of sockets and other accessories
An RCD providing additional protection is to be tested
i) State the maximum permitted value of IAn for this RCD
ii) List the 2 test currents to be applied
i) 30 mA
ii) 15 mA and 30 mA
State the 3 areas of responsibility which are designed for on an Electrical Installation Certificate
Design, construction, inspection & testing
Explain why the tests should be carried out in the order specified in BS7671
Each test makes it safe to continue to the next test (safety) and the sequence ensures testing is completed effectively (efficiency)
An earth electrode for a substation is to be tested
i) List the 3 connection points for the instrument to carry out this test
ii) If the earth electrode is 3m deep, what is the suggested distance between this and the furthest temporary electrode?
iii) What should be recorded as Ra if the values recorded are x, y and z ohms?
iv) What action should be taken if values of a, b and c ohms were obtained?
i) Electrode under test, current spike and potential spike
ii) 30 m (10 x depth)
iii) The average = [( x + y + z ) / 3] ohms
iv) More than 5% difference, repeat test with greater distances
What must be agreed with the client prior to periodic inspection and testing?
Extent and limitations
Describe how polarity could be confirmed for the lighting circuits without testing
By inspection of the connection at the terminations
Describe how polarity could be confirmed for the lighting circuits without testing
By inspection of the connection at the terminations
What insulation resistance test would you normally not carry out during periodic testing of existing circuits?
Live to live
State the 3 types of work that can be certified using an Electrical Installation Certificate
New builds, additions and alterations
Give an example of installation work which can be certified using a Minor Electrical Installation Works Certificate
Alteration of a single circuit, i.e; adding a socket to an existing ring circuit
A new single phase distribution board is to be added to feed power and lighting in a new conservatory extension in a public house. The installation forms part of a 230 V TN-S system with a Ze of .12 ohms and PFC of 2.3 kA.
The distribution board houses circuit breakers to BS EN 60898 and RCBOs to BS EN 61009.
The ring final circuit for sockets is wired using single core 70 degrees C insulated thermoplastic cables, with copper conductors in surface mounted PVC conduit and trunking. The live conductors have a cross-sectional area of 2.5 mm^2 and the CPC is 1.5 mm^2. The ring is approximately 40 m long. -the resistance of a 2.5 mm^2 conductor is 7.41 mohms/m.
All testing is to be carried out at an ambient temperature of 20 degrees C.
On completion of the new work, the rest of the pub is to be subjected to a periodic inspection and test.
