Conductors with _____ marked on the insulation are NOT approved for use in a wet location.
- ANSWER THHN
conductors with THHN insulation are approved for use in dry and damp locations only and
conductors with THWN, THHW, and THW insulation are recognized for use in dry and wet lo-
cations.
Given: A one-family dwelling unit with a demand load of 200 amperes is supplied with a
120/240 volt, single-phase, electrical system from the local utility company. What is the
MINIMUM size aluminum THW conductors required for use as service-entrance conductors
for this residence? - ANSWER 4/0 AWG
one-family dwelling 120/240 volt, single-phase, service-entrance conductors to be sized at
an ampacity of not less than 83% of the service rating. Therefore, 200 amperes x 83% = 166
amperes; size 4/0 AWG THW aluminum conductors with an allowable ampacity of 180 am-
peres should be selected for this dwelling.
Where a 150 kVA, single-phase transformer having a secondary voltage of 120/240 is in-
stalled at a multi-family dwelling, the full-load current rating, in amperes, of the secondary is
_____. - ANSWER 625 amperes
To find the full-load current rating of the single-phase transformer apply the single-phase
current formula as shown:I = (150 kVA x 1000) / 240 volts = 15,000/240 = 625 amperes
Which one of the following listed circuit breakers is NOT a standard ampere rating? - AN-
SWER 75 amperes
1
, the standard ampere ratings for fuses and circuit breakers. A circuit breaker with an ampere
rating of 75 amperes is not a standard ampere rating.
The MINIMUM length of free conductor to be left at each junction box for the purpose of
splicing conductors, or making connections to illuminares or devices shall be _____ . - AN-
SWER 6 inches
free conductor is to be left at each junction box for splices or the connection of luminaires or
devices. The intent of this rule is to ensure enough conductor slack for the terminal connec-
tions or splices to be made easily.
In general, overhead service-drop conductors shall NOT be smaller than _____. - AN-
SWER 8 AWG copper
overhead service-drop conductors to be not smaller than 8 AWG copper or 6 AWG alumi-
num or copper-clad aluminum. Do not get service-drop conductors, the overhead conduc-
tors between the utility electric supply system and the service point, confused with the ser-
vice-entrance conductors, the conductors from the service point from the utility company to
the service disconnecting means.
When a galvanized eye-bolt is to be used as the point of attachment for an electrical service,
the NEC requires the eye-bolt to be installed NOT less than _____ above finished grade. -
ANSWER 10 ft.
provide adequate vertical clearance of the conductors and prevent physical damage to the
conductors and prevent persons from making accidental contact with the conductors which
may create a shock hazard or electrocution. In no case shall the point of attachment of the
service-drop conductors to be less than 10 ft. above finished grade.
Why is electrical continuity required for metallic conduit? - ANSWER To establish an ef-
fective ground-fault path and facilitate the operation of the over-current protective device.
2
- ANSWER THHN
conductors with THHN insulation are approved for use in dry and damp locations only and
conductors with THWN, THHW, and THW insulation are recognized for use in dry and wet lo-
cations.
Given: A one-family dwelling unit with a demand load of 200 amperes is supplied with a
120/240 volt, single-phase, electrical system from the local utility company. What is the
MINIMUM size aluminum THW conductors required for use as service-entrance conductors
for this residence? - ANSWER 4/0 AWG
one-family dwelling 120/240 volt, single-phase, service-entrance conductors to be sized at
an ampacity of not less than 83% of the service rating. Therefore, 200 amperes x 83% = 166
amperes; size 4/0 AWG THW aluminum conductors with an allowable ampacity of 180 am-
peres should be selected for this dwelling.
Where a 150 kVA, single-phase transformer having a secondary voltage of 120/240 is in-
stalled at a multi-family dwelling, the full-load current rating, in amperes, of the secondary is
_____. - ANSWER 625 amperes
To find the full-load current rating of the single-phase transformer apply the single-phase
current formula as shown:I = (150 kVA x 1000) / 240 volts = 15,000/240 = 625 amperes
Which one of the following listed circuit breakers is NOT a standard ampere rating? - AN-
SWER 75 amperes
1
, the standard ampere ratings for fuses and circuit breakers. A circuit breaker with an ampere
rating of 75 amperes is not a standard ampere rating.
The MINIMUM length of free conductor to be left at each junction box for the purpose of
splicing conductors, or making connections to illuminares or devices shall be _____ . - AN-
SWER 6 inches
free conductor is to be left at each junction box for splices or the connection of luminaires or
devices. The intent of this rule is to ensure enough conductor slack for the terminal connec-
tions or splices to be made easily.
In general, overhead service-drop conductors shall NOT be smaller than _____. - AN-
SWER 8 AWG copper
overhead service-drop conductors to be not smaller than 8 AWG copper or 6 AWG alumi-
num or copper-clad aluminum. Do not get service-drop conductors, the overhead conduc-
tors between the utility electric supply system and the service point, confused with the ser-
vice-entrance conductors, the conductors from the service point from the utility company to
the service disconnecting means.
When a galvanized eye-bolt is to be used as the point of attachment for an electrical service,
the NEC requires the eye-bolt to be installed NOT less than _____ above finished grade. -
ANSWER 10 ft.
provide adequate vertical clearance of the conductors and prevent physical damage to the
conductors and prevent persons from making accidental contact with the conductors which
may create a shock hazard or electrocution. In no case shall the point of attachment of the
service-drop conductors to be less than 10 ft. above finished grade.
Why is electrical continuity required for metallic conduit? - ANSWER To establish an ef-
fective ground-fault path and facilitate the operation of the over-current protective device.
2
