Why does the 3A fuse in the 24V relay circuit inside the PLC cabinet keep blowing?
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As the title suggests, there are dozens of DC 24V relays inside the cabinet, organized into several circuits; each circuit is equipped with a 3A fuse. The instruments have just been installed, and the construction team is carrying out circuit tests. However, the fuse for the same circuit has blown twice already. The people from the construction team say they don’t know what’s going on; it’s not clear whether they really don’t know or are pretending not to know. But I really have no idea :( I’m asking everyone for advice: how should circuit tests be conducted so that fuses don’t blow so frequently? It’s 24V DC, DO circuit,,, Thank you all in advance
A blown fuse is usually caused by the current flowing through the circuit exceeding the fuse’s rated current. In the situation you described, possible causes include: 1. Short circuit: There may be a short circuit in the wiring or elsewhere inside the cabinet, which leads to a sharp increase in current and thus the fuse blowing. 2. Overload: The load connected to the circuit exceeds the fuse’s capacity; in other words, the total current demand from the relay and other devices is greater than 3A. 3. Wiring error: An error may have occurred during wiring, causing devices that should not be connected in series or parallel to be linked incorrectly. 4. Damaged relay: One or more relays may be damaged, causing an internal short circuit and increasing the current load. 5. Power supply issues: If the 24V power supply output is unstable or subject to high-voltage spikes, this can also lead to an increase in load current. During testing, all loads should be disconnected first, and then each relay along with its corresponding wiring should be checked one by one. A multimeter can be used to measure resistance in order to check for short circuits, or loads can be added one by one to monitor whether the current exceeds the rating of the fuse. Ensure that all connections are correct and that every component is functioning properly before gradually bringing it into operation. .
Physical knowledge: determine whether there is a short circuit, measure the loop current, and the resistance to ground.
It’s probably a short circuit. I’ve encountered this issue with clients recently as well – there’s a short circuit inside the meter, and every time power is supplied, the fuses in the client’s electrical panel blow
Actually, when fuses blow, it’s necessary to check the wiring to see if there are any short circuits or grounding issues. Loose connection terminals that cause poor contact can also lead to fuses blowing. The most common situation I encounter is where the 4A fuses in the control circuits of the distribution room control cabinets keep blowing. There was an operation panel on site to control the start and stop of the pump; upon checking the wiring, it was found that the terminal connections behind the control cabinet in the power distribution room were not loose, and there were no issues with the return circuits of the thermal relay and contactors. After powering off, it was discovered that one of the 8-core wires in the control circuit leading to the site was short-circuited, which caused the fuse to keep blowing. After replacing that wire, the fuse stopped having problems. Later, I went to the site to check the cables in the cable tray (it was really time-consuming), and found that the 4m2 cable used for workshop lighting had short-circuited and overheated earlier, which had caused the insulation of the control cable to burn off, leading to the short circuit and ground fault.
It’s probably a problem with the wiring on site or with the circuit
A 24VDC ground issue or a short circuit in the circuit requires detailed analysis; a multimeter can be used to check whether the load is short-circuited, and a megohmmeter can be used to inspect the cables.