Question 1
In a commercial building with many electronic loads on a 120/208 V, three-phase, four-wire system, neutral conductors are found to be running hotter than expected. Which is the MOST likely explanation?
Question 2
A commercial building has many non-linear loads such as computer power supplies on a 3-phase, 4-wire, 120/208 V system. What is a potential issue related to the neutral conductor in this situation?
Question 3
In a commercial installation with many nonlinear loads, what issue can occur in the neutral conductor of a 3-phase, 4-wire system?
Question 4
The nameplate of a dry-type transformer reads 600 V primary, 120/240 V secondary, 3 kVA. What is the maximum secondary current at 240 V?
Question 5
Which of the following describes 'Harmonics' in an electrical system?
Question 6
A facility experiences significant overheating in its neutral conductors and transformers, despite the 3-phase loads being seemingly balanced. Which phenomenon is most likely responsible?
Question 7
Which phenomenon is most likely to cause overheating in the neutral conductor of a 120/208V, 3-phase, 4-wire system serving significant non-linear loads like computer servers?
Question 8
What is the primary effect of triplen harmonics (3rd, 9th, 15th, etc.) on a balanced 4-wire, 3-phase Wye system neutral conductor?
Question 9
Which phenomenon is most likely to cause overheating in the neutral conductor of a balanced 3-phase wye system serving non-linear loads like VFDs and computer power supplies?
Question 10
A three-phase, 208 V, 15 kW heating load has a power factor of 1. Approximately what line current will each phase carry?
Question 11
In a 3-phase, 4-wire wye system serving nonlinear loads such as computer power supplies, what can happen to the neutral conductor current?
Question 12
An electrician measures unusually high neutral current on a feeder supplying several nonlinear electronic loads. What is the most likely explanation?
Question 13
A feeder in EMT contains three 2/0 AWG copper phase conductors and one 2/0 AWG copper neutral. The calculated load is non-linear with significant harmonic content. Which design adjustment may be necessary?
Question 14
A 3-phase panelboard has several single-pole breakers feeding nonlinear electronic loads on each phase. The neutral bus and neutral conductors feel unusually warm under normal operation. What is the most likely cause?
Question 15
A three-phase, 208/120 V panelboard is heavily loaded with nonlinear electronic loads on all three phases. What issue is most likely to appear in the neutral conductor?
Question 16
A commercial tenant fit-out adds nonlinear electronic loads on a 208/120 V wye system. Which conductor may experience higher than expected currents due to triplen harmonics?
Question 17
In a commercial office with many computers and electronic power supplies, the neutral conductor in a 120/208 V panelboard is found to be running unusually hot. Which is the MOST likely contributing factor?
Question 18
In a commercial installation with many non-linear loads on a 3-phase, 4-wire wye system, which issue can significantly increase neutral conductor current?
Question 19
During troubleshooting, you discover a neutral conductor carrying significant harmonic currents from multiple nonlinear loads on a 3-phase, 4-wire system. What mitigation strategy is most appropriate?
Question 20
A multiwire branch circuit uses two ungrounded conductors from opposite phases of a 120/240 V single-phase panel and a shared neutral. Each ungrounded conductor supplies a 10 A 120 V load. Assuming balanced loads and no harmonics, what current flows in the neutral conductor?
Question 21
A multiwire branch circuit shares a neutral between two ungrounded conductors on different phases of a 120/208 V system. Why is it important that the ungrounded conductors be on different phases?
Question 22
A facility has numerous nonlinear loads such as computer power supplies. The journeyperson notices that the neutral conductors in a 120/208 V system are running hotter than expected even though phase currents are balanced. What is the MOST likely cause?
Question 23
A commercial panelboard feeding office receptacle circuits has significant nonlinear loads such as computer power supplies. The neutral conductor is carrying high current even though the phase currents are balanced. What is a common solution?
Question 24
A 3-wire, single-phase 120/240 V feeder consists of two ungrounded (hot) conductors and a neutral. Under balanced conditions, what current flows on the neutral when equal 120 V loads are connected between each hot and neutral?
Question 25
A facility has frequent breaker trips on a 3-phase panel feeding nonlinear loads such as computers and electronic ballasts on a 4-wire wye system. The phase conductors are lightly loaded, but the neutral conductor is running very hot. What is the MOST likely cause?
Question 26
A 277/480 V lighting panel supplies multiple electronic lighting ballasts. Over time, several ballasts fail, and thermal imaging shows elevated neutral conductor temperature on the feeder. What is the most likely electrical cause?
Question 27
Which practice helps reduce harmonic distortion in a distribution system?
Question 28
Which harmonic order is known as a 'triplen' harmonic and can cause overheating of neutrals in a 3-phase wye system?
Question 29
What is the effect of harmonics on the neutral conductor in a 3-phase 4-wire system feeding non-linear loads?