3 phase rcd wiring to single phase - Page 1
Forum section: electronics / general

author: kokodin
author_rank: Regular Contributor
timestamp: September 06, 2021, 11:21:18 am
content: Hello, i have rather iritating electrical problem in one of my work computer rooms.On a warm day everything works just fine, but whenever moisture in the air go up the silly classroom trips rdc like crazy when more than 3/4 of computerss are plugged in.Since those are all highly integrated all in one computers i can't replace power suplies that cause electrical fault and all i can do is either double the rcd trip current or put 2 of the rcd breakers nect to esch other.I do however have few of the 3 phases rcd's in my spare breakers box, and no single pgase ones.Each and every computer is alone fully ok, there is no difference which one i unplug, it is just that 17 anti interference capicitors banks in every computer carry some current to the ground, and when they synchronize rcd trips at it's intended current.The question is: would the trip fault still ocured with 3 phase rcd if i wire every 5 computers circuit to 3 separate phase outputs of that rcd, keeping neutrals together and spliting single phace to all 3 inputs of that breake?i assume each outpur on the rcd would still prorect users from being zaped, i am simply not sure how would it handle return currentsif all 3 outputs were used . would it still trip or would it remain latched.

author: themadhippy
author_rank: Super Contributor
timestamp: September 06, 2021, 12:25:41 pm
content: if the operating current of the 3 phase rcd is the same as your single phase device then its still going to trip.

author: kokodin
author_rank: Regular Contributor
timestamp: September 06, 2021, 01:06:05 pm
content: Thanks, that is what i thought but i wasn't sure if the rcd could even work like that.If i had more room in the enclosure i would probably just use it as a 2nd single phase leaving l2 and l3 unpopulated but i am 2 slots too short for that thus idea for swaping rcd's.My boss probably won't like it but i will have to buy another rcd.blessing in disguise there is no others rcd's in series with that room circuit, up untill main boards one, and that is much bigger trip current (0,3 instead of 0,03A)We had entire mains rebuild this spring because we had ghost shutdowns of entire building due to bad design of rcd staging, and we had every rcd and circuit tested for trip current, insolation and ground continuity, so i am sure that's not the power installation problem but rather cheap computers with self proclamed 80 plus bronze certification.

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 06, 2021, 01:52:49 pm
content: Theoretically, if you distribute the loads across 3 phases, the leakage currents should cancel out.

author: madires
author_rank: Super Contributor
timestamp: September 06, 2021, 02:27:05 pm
content: If you're forced by regulations to use RCDs with a trip current of 30 mA the best way is to protect each phase separately with a single phase RCD. And if necessary create groups of PCs each powered via a dedicated RCD to stay below the trip current. The typical leakage current to PE is around 1 - 2 mA per seat. Also note the a 30 mA RCD may trip starting at 15 mA.

author: madires
author_rank: Super Contributor
timestamp: September 06, 2021, 02:29:56 pm
content: Quote from: NiHaoMike on September 06, 2021, 01:52:49 pm... if you're able to enforce a specific order of turning on and off all seats.

author: ejeffrey
author_rank: Super Contributor
timestamp: September 06, 2021, 03:40:23 pm
content: If the faults are related to humidity it probably isn't just the EMI filter capacitors causing the problem. So you may have an actual leakage problem although it may be small enough on its own to ignore.

author: kokodin
author_rank: Regular Contributor
timestamp: September 07, 2021, 08:21:53 am
content: Quote from: NiHaoMike on September 06, 2021, 01:52:49 pmIn real 3 phases system yes, in one phase system splited over 3 phase outputs with shared neutral, they would most likely add up.I was more interested of how the rcd itself would react to that.Quote from: madires on September 06, 2021, 02:27:05 pmI am well aware of the actual trip current, because we tested it. 18mA for this particular 30mA breaker.But that classroom only get 1 phase 25A feed and there is no way to upgrade it to 3 phases at this moment, there is 3 more computer classrooms on this floor alone and they require more current and are in more frequent use so all of that floor power was already redirected to those.Quote from: ejeffrey on September 06, 2021, 03:40:23 pmThe problem is with the pc's though the same classroom had no problem with 24 older vista computers plus monitors (mostly fujitsu and dell) but those new ones are well.... assembled from off the rack parts by polish domestic oem builder, and the quality of the parts vary from model to model. That actually exactly the same problem as we had in another classrooms with other polish oem builder pc's, and that time swaping 12 computers to 17 refubed hp's actually solved the problem for us, and in that classroom rcd didn't trip once in 2 years.The problem is we can't exactly swap new computers with known working ones, we don't have that kind of budget.It was one thing swaping vista boxes to windows 10 ones, if there is no upgrade along the way i have to solve the problem with computers in some other way>>>read by tweaking the power grid in that classroom.

author: f4eru
author_rank: Super Contributor
timestamp: September 07, 2021, 02:13:23 pm
content: 1) get a measurement means for the leakage (an non-nice option is to use a mA-meter in series with the earth terminal. Use with caution!)2) find out the fault.3) repair or exchange.Seriously, if humidity does it, there is definitely a serious fault,and it will not go away with any amount of rewiring.it will become worse and worse due to electrolysis with the water.

author: EPAIII
author_rank: Super Contributor
timestamp: September 09, 2021, 06:25:31 am
content: Thinking a bit "outside the box", I see two possible solutions.1. Use 1::1 isolation transformers on each computer or on groups of two or three. That way the return current will always be the same as the supply and, therefore no trip. I do not know the electrical codes, if any, in your country so that should be consulted, but I would be sure to carry the safety ground through from the outlets, past the transformers, and to the computers. You would probably mount a transformer and one to three outlets on a common chassis so the wiring, including that ground would be internal. I also think that chassis should be connected to the safety ground for safety. And, yes transformers can be expensive.2. Sounds like a good reason for requesting a proper HVAC system in the classrooms. Or, at least, in that one. One with a humidity control specification that the supplier would be required to meet. And yes, I know it may be less expensive to buy new computers but then organizations often do things in strange ways. And for even stranger reasons.

author: kokodin
author_rank: Regular Contributor
timestamp: September 09, 2021, 11:32:20 am
content: Quote from: f4eru on September 07, 2021, 02:13:23 pm1 i would gladly do that but i don't have clamp meter with that small current scale and measuring it directly would add meter as a resistive load and mess all measurment, also when it does not matter wher and on which phase computers are connected , the number is the problem, i highly belive it is that those pc's are in fact the problemAs i stated before we had the same problem in different classroom with a different set of computers, where moving just few of them to different place messed up that place so we get rid of them all. not liking to badmouth brands but manufacturer was actina poland and power suplies were made by ibox and those drifted with time so first it was 17 with no problem later 8-10 could trip an rcd regardless of where they were installed, we talking 3 different buildings, 5 classrooms here.i presume polish assembler NTT who win public orders only by lowest price could again pick really crapy parts without thinking2 and 3the installation is practically new, with no faults i could detect 2 months ago when i took it all apart and reasembled like legoit is literally 5 double sockets on each breaker after rcd connected via wago push in 3 pin connectors, there is nothing i could find wrong with it (cables are in pvc ducts so i inspected them from end to end, even high vlotage insolation tested them)

author: themadhippy
author_rank: Super Contributor
timestamp: September 10, 2021, 09:26:08 pm
content: id be tempted to get rid of the rcd and replace the breakers with rcbo's