Fault records are the best starting point for choosing a conductor type. This chart lists the common causes of faults on medium voltage overhead feeders and shows, in qualitative terms, how each option responds. It does not give outage rates, because those depend on the network. Use it alongside your own feeder fault logs.
Fault cause by conductor option
| Fault cause | Bare overhead | Covered conductor (MVCC) | Aerial bunched cable | Underground cable |
|---|---|---|---|---|
| Tree branch or creeper contact | Phase-to-earth fault or flashover likely | Brief contact is tolerated by the covering | Insulated, contact tolerated | Not exposed |
| Phase-to-phase clashing in wind | Arcing and conductor damage possible | Covering limits direct metallic contact | Bundled, phases cannot clash | Not exposed |
| Bird or animal bridging | Fault likely across phases or to earth | Lower likelihood, bare fittings remain a risk | Insulated, lower likelihood | Not exposed |
| Pollution, salt and humidity on the line | Deposits build on conductor and insulators | Anti-tracking outer layer resists tracking | Insulated outer sheath | Not exposed |
| Lightning | Flashover at insulators | Covering is not a lightning protection device | Same limitation | Lower exposure when buried |
| Vehicle or crane impact on poles | Pole damage and conductor drop | Same limitation | Same limitation | Not exposed to poles |
| Third-party excavation | Not applicable | Not applicable | Not applicable | Main risk for buried routes |
How to read the chart
Covered conductor improves the causes that involve brief contact or surface contamination. It does not remove the causes that involve physical damage or lightning. Where a feeder fails mainly for those reasons, a different measure is needed, such as arresters, stronger poles or underground routing.
The covering is not shock protection. A covered conductor must always be treated as live.
Next steps
For the APAR covered conductor range, see the MVCC product page. For voltage class and conductor type, use the covered conductor selection guide. For fittings, see the accessories and installation guide.