1. Article 450 of the NEC covers transformers. Which transformer(s) are(is) NOT covered by Article 450?
(a) Utility transformers.
(b) Transformers used for power-limited fire alarm circuits.
(c) Transformers for sign and outline lighting.
(d) Answers B & C
2. Marking required on a transformer nameplate must include _______.
(a) Phase
(b) Weight
(c) Required clearance for ventilation
(d) All the above.
3. The largest transformer permitted to be installed in hollow spaces of buildings not permanently closed in by structure, provided they meet the ventilation requirements is____ kVA.
(a) 75
(b) 37½
(c) 100
(d) 50
4. A transformer rated 1000 volts or less and equipped with coordinated thermal overload protection by the manufacturer and arranged to interrupt the primary current shall be permitted to have primary overcurrent protection rated or set at a current value that is not more than ______ times the rated current of the transformer.
(a) 5
(b) 4
(c) 6
(d) 2½
5. All transformers and transformer vaults shall be ____________qualified personnel for inspection and maintenance or shall meet the requirements of 450.13(A) or 450.13(B).
(a) Readily accessible to
(b) Accessible to
(c) Selectively accessible to
(d) secured except to
6. Where a transformer (other than class 2 or 3) is located in a remote location from a disconnecting means, the following is required: ______.
(a) The disconnect location shall be field marked on the transformer.
(b) The disconnecting means must be lockable in an open position.
(c) Answers A and B are correct.
(d) Voltage shall be marked on each transformer if more than one primary voltage is present.
7. For autotransformers rated 1000 volts or less, more than 9 amps, they shall be protected by an individual OCP installed in series with each ungrounded input conductor. This OCP may not be rated or set more than ______% of the autotransformer’s full load current. When this calculation does not result in a standard rating of a fuse or nonadjustable circuit breaker and the rated input current is 9 amperes or more, the next higher standard rating described in 240.6 shall be permitted.
(a) 125
(b) 140
(c) 167
(d) 200
8. To maintain safe temperature levels for transformers, which of the following tasks are required to meet this requirement?
(a) Transformer top surfaces that are horizontal and readily accessible shall be marked to prohibit storage.
(b) The required clearances shall be clearly marked on the transformer.
(c) Transformers with ventilating openings shall be installed so that the ventilating openings are not blocked by walls or other obstructions.
(d) All tasks are required.
9. Where separate equipment grounding conductors and supply side bonding jumpers are installed, _____.
(a) a terminal bar for all grounding and bonding conductor connections shall be secured inside the transformer enclosure.
(b) a terminal bar shall be bonded to the enclosure after all non-conductive material (paint) is removed from the contact surfaces.
(c) A terminal bar is not permitted to be installed over any vented portion of the transformer.
(d) All the above apply to the statement
10. When considering construction requirements for a transformer vault, the walls and roof material must have a minimum fire resistance rating of_____ hours.
(a) 2½
(b) 3
(c) 3½
(d) 2
ANSWERS
1. (d) Answer B & C Article 450.1(5)&(7)
2. (c) Required clearance for ventilation Article 450.11(6)
3. (d) 50 Article 450.13(B)
4. (c) 6 Table 450.3(B) Note 3
5. (a) Readily accessible to Article 450.13
6. (c) Answers A and B are correct Article 450.14
7. (a) 125 Article 450.4(A)
8. (d) All tasks are required. Article 450.9
9. (d) All the above apply to the statement Article 450.10(A)
10. (b) 3 Article 450.42