Old wiring + PCB fuse - Page 1
Forum section: electronics / repair

author: JKKDev
author_rank: Regular Contributor
timestamp: February 14, 2021, 06:22:37 am
content: Hello,I have a modern wood furnace that is fully controlled by electronics. It is located in a house that has very old wiring (probably at least 50 years old). I also have a small workshop in this same building (I'm planning to redo the wiring just haven't gotten around to it yet). Whenever I run a higher power tool (angle grinder, router,...) in the workshop it blows a 100mA fuse on a PCB of the furnace.Do you think this is a result of the old wiring or could there be some other reason for it? I do feel that the most common things to blow the fuse are inductive loads. The only thing that's confusing is that it blows randomly and not always. Also I don't remember ever having this problem when running 3 phase motors.Thank you for any kind of insight (it's driving me up the wall as it has been going on for the last 5 years). Have a nice day.

author: S. Petrukhin
author_rank: Super Contributor
timestamp: February 14, 2021, 10:52:18 am
content: I can assume that when you turn on the tool, the voltage drops significantly, the PWM in the power supply unit of the oven indecently increases the duty cycle, which leads to an increase in current and a fuse burnout.

author: BrokenYugo
author_rank: Super Contributor
timestamp: February 15, 2021, 01:17:29 am
content: Were the 3 phase motors on soft starters/VFD?

author: JKKDev
author_rank: Regular Contributor
timestamp: February 15, 2021, 10:36:43 am
content: We have 3 phase 380v line coming in. No VFDs or soft start electronics used.On the answer about the line voltage drop. It's strange (it happens randomly). From time to time the lights do flicker when I turn one of the high power devices on and when that happened I did notice that the fuse burned. At this point I'd like to figure out why it's random. There are no machines that would cause additional line current draw randomly (like a fridge turning on or the sorts). It's basically only the furnace and the workshop.It's also not the case of subpar local distribution network. The other 3 phase coming in to the property doesn't have any voltage dipping (at least not noticable to the point of lights dimming).One cause I could see is turning a heavy load on at the peak of the AC cycle. Would that together with old wiring cause a severe line voltage drop? I could probably rig up line voltage logging and track when the fuse blows. Or just run a nice new cable from the fuse box to the furnace and call it a day (until a complete overhaul is done) :p

author: S. Petrukhin
author_rank: Super Contributor
timestamp: February 15, 2021, 10:55:49 am
content: Quote from: JKKDev on February 15, 2021, 10:36:43 amI think this is the best solution!The loss of voltage is the heating of the cable or even sparks in the commutation.It may well be in the old wiring of the times of Soviet Czechoslovakia. We know what the quality was then.

author: JKKDev
author_rank: Regular Contributor
timestamp: February 15, 2021, 11:11:46 am
content: Quote from: S. Petrukhin on February 15, 2021, 10:55:49 amSame sentiment just a different country here (ex Yugoslavia)A new wire for the furnace and another one for the outlets in the workshop and I'll sleep easier until the overhaul.

author: S. Petrukhin
author_rank: Super Contributor
timestamp: February 15, 2021, 11:29:42 am
content: Quote from: JKKDev on February 15, 2021, 11:11:46 amOh, sorry, I made a mistake - I didn't see the flag correctly.Actually, they were all the same in Soviet times.