Intermittent arcing fault on underground low-voltage cables

Arcing faults on 600/347-V underground cables can cause considerable damage, even explosions, despite the installed protection system. In fact, the protection sometimes appears to be quite slow to operate considering the prospective short circuit. Laboratory tests provided an opportunity to better characterize these arcing faults and prove that they can be intermittent. They can be quite random in nature, usually comprising periods of conduction lasting one half-cycle separated by periods of nonconduction lasting from a few cycles to several minutes. This type of fault can easily make fuse-type protection ineffective, as other tests proved. The fuse operating time can become even longer, to the extent that explosive gases will form.