- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
I was called to troubleshoot a machine that was not working. I discovered a blown fuse. It was a "midget fuse" 250V 7A dual element, FNM-7. The only fuses available locally was a 6.25A so I replaced it with one of those. It was late and I told them there was probably something wrong to cause the fuse to blow and I didn't feel secure that I fixed anything.
Well, I was right. They called back and said it blew again. I went back when I had time and dug into it. The machine has several functions/operations. So I had them turn them on one at a time until the fuse blew. It was a circuit that operates a gas blower motor and igniter. After taking it apart I found a cut wire that was shorting to the motor housing. I repaired the wire and had them run the machine. Everything worked as it should and no blown fuse.
Now two days later they call and said the fuse blew again. They changed it and it ran for several hours and blew again. I know that I fixed that one wire and it doesn't appear that the fuse is blowing from a short this time. No, I didn't check the amp draw when I was there as it was late when I finished and everything was working. My question is, do you think it is blowing from overload since the original fuse was 7A and the replacements are 6.25A?
Well, I was right. They called back and said it blew again. I went back when I had time and dug into it. The machine has several functions/operations. So I had them turn them on one at a time until the fuse blew. It was a circuit that operates a gas blower motor and igniter. After taking it apart I found a cut wire that was shorting to the motor housing. I repaired the wire and had them run the machine. Everything worked as it should and no blown fuse.
Now two days later they call and said the fuse blew again. They changed it and it ran for several hours and blew again. I know that I fixed that one wire and it doesn't appear that the fuse is blowing from a short this time. No, I didn't check the amp draw when I was there as it was late when I finished and everything was working. My question is, do you think it is blowing from overload since the original fuse was 7A and the replacements are 6.25A?