Partially Blown Fuse

Discussion in 'General Electronics Chat' started by Loyd Heimbruch, Oct 12, 2005.

  1. Loyd Heimbruch

    Thread Starter New Member

    Oct 12, 2005
    I have a problem with the main electrical service overcurrent protection in my home. The service consists of an overhead service lateral from a pole mounted transformer, 240V. 1 Phase 60A. fused disconnect switch, with a #8 AWG CU grounding electrode conductor to a 1 1/4" water pipe at least 20' long straight down into the earth. Fuses are 250V. 60A. class K5 (Bussman).

    The problem is that one of the fuses will overheat and cause all of the lights on the affected phase to dim. The fuse continues to conduct current and does not completely interrupt the current flow. It seems to me that the fuse in a partially blown condition is behaving like a rheostat. The fuse looks normal, not blackened at all, but it will crumble at the line side fuse clip (top end of the fuse) when removed. I do not think this is a safe condition.

    This is the third time this has occurred within the past year. The first time phase A was affected, about a month later it was phase B, and several months later (today) phase A was again affected. This typically occurs at times when there is low demand on the electrical service and major appliances (range, water heater) are not in use.

    There is a small broken branch from a tree hanging on the high voltage utility primary, in contact with one of the phase conductors. The utility company needs to remove this. I was wondering if voltage to ground from this tree branch could cause this, but since either phase can be affected in my home I do not think this is the source of the problem.

    I do not see any grounding electrode connection to a driven ground rod, only the connection to the water pipe. I plan to test the resistance to ground to verify the integrity of this ground. If this is more than 25 ohms, could it be the problem? I plan to replace the grounding electrode conductor with a #6 AWG CU to a newer 2" water pipe at least 20' straight down into the earth. I do not want to do this and just assume that it may correct the problem, I want to find the source of the problem and correct it.

  2. thingmaker3

    Retired Moderator

    May 16, 2005
    Check your phases and neutrals for corrosion or loose connection. And, yes, a bad ground could indeed cause brownouts on one phase - accompanied by brighter lights on the other phase.