Support bolts within the common busbar section of an LV panel were becoming warm. Temperatures were not high but load on the panel was low in comparison to the design rating of the panel-less than 25%.

PROCESS
We carried out thermal imaging on the internal busbar to capture images of the bolts and to identify the cause of the heating. Thermal and digital images were recorded along with load and voltage readings.

REPORT
As the issue was not severe and not affecting the daily or prolonged use of the panel it was decided that the support bolts should remain in place and be monitored during our annual visits. The temperatures have remained stable over our subsequent visits.

REMEDIAL WORKS
We notified the panel manufacturer of our findings and they were considering using insulated or non-ferrous bolts in future panels to avoid the heating effects.

CONCLUSION
This was an interesting problem and we looked closely at the design of the panel and the materials used. The steel bolts supporting the busbars were affected by the circulating currents flowing in the panels and were causing the bolts to heat up. The bolts between the phase-phase conductors were affected and became warm while the bolts between the phase-neutral conductors were unaffected as the opposing current flow in the phase & neutral conductors cancelled the heating effects.