Solar Lattice

FailureMode

DC string miswiring

ID
fm:dc-string-miswiring
IRI
https://solarlattice.org/kb/fm/dc-string-miswiring
Status
active
Also known as
cross connection between input A and B, swapped string connections, asymmetrical strings at input A, interchanged cables in DC string box, wiring error, wiring mistakes

DC string miswiring means strings are connected wrongly at the inverter: a string is reversed, or strings with different module counts share the inputs. Wiring mistakes are more likely in layouts with many long DC string cables. The inverter may raise a reverse-DC alarm or a string current reflux alarm. To confirm, measure each string with a meter to check polarity and open-circuit voltage, and count the panels in each string. A reversed string can cause severe damage and arcing, so never disconnect it under load or open the DC switches while current flows. Wait until string current is low, for example at night, then open the DC switches and fix the polarity or the module count.

<!-- review notes

Claims

caused_by

c1 drafted · lead Long DC string cables proposed

Designs with many long DC string cables make wiring mistakes more likely.

presents_as

c2 verified · fact Reverse polarity

The inverter Reve-DC alarm is raised when a string is connected the wrong way round, or when string inputs have different module counts.

verified by: review-workflowverified on: 2026-10-24

c3 drafted · lead String reverse current

The String Current Reflux alarm can come from a string that has fewer modules than the others, or from wrong module wiring or configuration.

review note: support check: partial - Reflux alarm is tied to fewer modules in a string and wiring/configuration checks, but 'wrong module wiring' as a cause is only implied by a check step, and shading/orientation are other causes.; review: partial - The String Current Reflux rows tell you to check for a string with fewer modules and to check module wiring and configuration, but they never say wrong wiring causes the alarm, so that causal link is only implied.

detected_by

c4 drafted · lead String polarity measurement

Use a voltmeter or multimeter to check the polarity of each string between positive and negative.

c5 drafted · lead Open-circuit voltage measurement

Measure the open-circuit voltage of each string and compare it with the expected module count.

review note: support check: partial - Passages mention measuring VOC and checking string voltage versus panel count, but the steps aren't given and comparison with expected module count is only loosely implied.

mitigated_by

c6 drafted · lead String polarity correction

Wait until string current falls below the safe level (for example at night), open the DC switches, then fix the polarity. Do not disconnect reversed strings while they carry load.

c7 drafted · lead String configuration correction

Change the system configuration so that all strings on the inputs have the same number of modules.

c8 drafted · lead DC wiring check

Make sure the DC connection in the inverter is correct and check the string cabling.

review note: support check: partial - Passages say to ensure the DC connection in the inverter is correct and check string cabling, but in a damage/fault context rather than specifically miswiring.

leads_to

c9 drafted · lead Arc fault

A reversed string can cause severe damage and an electric arc hazard.

Data