Schneider Electric PM810, PM870, PM820 Section I Common Problems for 3-Wire and 4-Wire Systems

PowerLogicTM Series 800 Power Meter	63230-500-225A2
Appendix A—Instrument Transformer Wiring: Troubleshooting Tables	3/2011

Section I: Common Problems for 3-Wire and 4-Wire Systems

Section I—Case A

Symptoms: 3-Wire and 4-Wire	Possible Causes
	• CT secondaries shorted.
• Zero amps	• Less than 2% load on power meter based on CT ratio.
• Zero kW, kVAR, kVA	Example: with 100/5 CT's, at least 2A must flow through CT window for power
	meter to “wake up.”

Section I—Case B

Symptoms: 3-Wire and 4-Wire	Possible Causes
• Negative kW of expected magnitude	• All three CT polarities backwards; could be CTs are physically mounted
	with primary polarity mark toward the load instead of toward source or
• Positive kVAR	secondary leads swapped.
• Normal lagging power factor	• All three PT polarities backwards; again, could be on primary or secondary.
	NOTE: Experience shows CTs are usually the problem.

Section I—Case C

Symptoms: 3-Wire and 4-Wire	Possible Causes
	• PTs primary and/or secondary neutral common not grounded (values as
• Frequency is an abnormal value; may or may	high as 275 Hz and as low as 10 Hz have been seen).
not be a multiple of 50/60 Hz.	• System grounding problem at the power distribution transformer (such as
	utility transformer), though this is not likely.

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