breaker and RCD trips when turning UPS on - Page 1
Forum section: electronics / projects

author: mcinque
author_rank: Unknown
timestamp: July 07, 2022, 02:11:56 pm
content: Hello, I'm asking for an advice:when I turn on an UPS in the office (any one, not a specific one), at the specific and exact moment it turns on, sometimes the breaker (16A) of the line it is connected to blows. A few times even the main RCD (30mA) has blown.what can this phenomenon be due to? the circuit breaker will probably just blow because of too much peak/inrush current. but why the RCD? there is a ground fault evidently.I checked the differential with an rcd tester and it trips normally, with the correct current value (30mA and not at 20 or 10) and with correct timings, so the UPS are the problem?should I check the earth ground?perhaps with an isolation transformer I would be able to eliminate the problem? at that point, however, there would be no RCD protection being all pc's no longer referenced to ground.

author: tru3533
author_rank: Regular Contributor
timestamp: July 07, 2022, 04:01:23 pm
content: To much inductive load? Monitors/pc'sCheck that fuse type meets the requirement for the equipment connected. (slow blow / fast / IT )

author: BrokenYugo
author_rank: Super Contributor
timestamp: July 07, 2022, 04:27:14 pm
content: Try the UPS alone? PC plugged directly?One issue you can have with a whole house RCD is PCs and anything else with a 3 wire cord and a switching power supply normally leak a couple milliamps to earth, enough equipment can add up to a false trip.Circuit breakers are also known to fail occasionally, false trips are one sign.

author: themadhippy
author_rank: Super Contributor
timestamp: July 07, 2022, 05:11:43 pm
content: Are the mcb and rcd next to each other?Only seen it once,but it was put down to the magnetic field in the mcb affecting the rcd.

author: mcinque
author_rank: Unknown
timestamp: July 07, 2022, 05:50:20 pm
content: Quote from: tru3533 on July 07, 2022, 04:01:23 pmat the main UPS, there are 4 switching PC PSU, 1 monitor, 4 or 5 wall-mount PSUs and two network switches connected. When the morning it's turned on, SOMETIMES it trips the breaker and sometimes even the RCD, but not always.Quote from: BrokenYugo on July 07, 2022, 04:27:14 pmall equipment connected to the ups is switching. when the ups turns on, it connects all the devices toghether.at the secondary UPS, there are only 1 switching PC PSU, 1 wall-mount PSU and 1 monitor.I wonder if I should install class C breaker (delayed)Quote from: themadhippy on July 07, 2022, 05:11:43 pmno, they are far from each other.

author: TheMG
author_rank: Frequent Contributor
timestamp: July 07, 2022, 06:28:27 pm
content: What type of UPS? Model/manufacturer?It matters because if it's a standby or line-interactive type, it switches the load on to mains power quite suddenly utilizing relays. Line-interactive type would usually also contain an auto-transformer for the buck/boost function, which presents potentially even more inrush and inductance when that is initially energized. Some models of UPS will also run a self-test on power-on, which disconnects and reconnects the load to mains while it does so. This switching of the relays on and off mains can produce spikes/noise enough to false-trip an RCD in some cases.A double-conversion UPS on the other hand might have a slightly softer switch-on since its inverter turns on and starts powering the loads, rather than just whacking the load right onto the mains through a relay. The switching between mains and battery power is also seamless.Maybe it would help instead of turning the UPS on and off, to switch the connected equipment on and off through for example a switched power bar or PDU, and leave the UPS on at all times.

author: tru3533
author_rank: Regular Contributor
timestamp: July 09, 2022, 12:21:58 am
content: Class C breaker will most likely solve your problem

author: themadhippy
author_rank: Super Contributor
timestamp: July 09, 2022, 01:11:31 am
content: QuoteJust make sure your earth loop impedance is low enough.

author: jordannedev
author_rank: Contributor
timestamp: July 09, 2022, 06:44:30 am
content: https://www.electrical-installation.org/enwiki/Types_of_RCDsHere is also some information about the different types of RCDs. We should keep in mind what type of load we have and what type of RCD we are using. Maybe the problem is complex.

author: mcinque
author_rank: Unknown
timestamp: July 29, 2022, 08:17:23 am
content: Quote from: tru3533 on July 09, 2022, 12:21:58 amit is already a class C.Quote from: jordannedev on July 09, 2022, 06:44:30 amThanks, very useful infos

author: geggi1
author_rank: Frequent Contributor
timestamp: July 29, 2022, 08:50:04 am
content: In many cases the RCD can trip due to capacative loads.These loads can be things like inductive stow tops, directly electrical heated floors, RFI filters in electrical equipment and also just the size of the electrical installation. When adding all these capacative currents together this can be enought to trip the RCD.Here in Norway the recommendation now is to have breakers with integrated RCD so that any capacative leak current only will affect the one circuit and not the whole installation.