Which standard is for DC current in the mains? - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: May 07, 2023, 12:02:37 pm
content: Hi,Does any one know what EN regulation standard covers DC current in the mains?...eg from single phase rectified loads, or from loads that are pulsing on and off say 10ms/10ms (or 8.33ms/8.33ms).

author: Jeroen3
author_rank: Super Contributor
timestamp: May 07, 2023, 12:17:06 pm
content: Should be included in the harmonics requirements, IEC EN 61000-3-2Or do you mean something else?

author: Faringdon
author_rank: Super Contributor
timestamp: May 07, 2023, 12:45:25 pm
content: Thanks, but the following says nothing of DC in the mains...https://www.epsma.org/wp-content/uploads/2021/01/PFC-Guide_03032018-3-final-7-7.pdfAs well as half wave rectification, pulsed loads, even to PFC'd PSUs, can cause an average DC level in the mains...the attached is the mains input current to a 400W SMPS that is load pulsing on/off (400W/zero Watts) every mains half cycle...there is some 500mA average DC in the mains from this......this wouLD corrode all the pipes...it must be illegal(?)...but i cant find the EN standard that says it is illegal.Do you know?

author: Wolfram
author_rank: Frequent Contributor
timestamp: May 07, 2023, 04:26:13 pm
content: Quote from: Faringdon on May 07, 2023, 12:45:25 pmWhy would it corrode the pipes? As long as there are no DC leakage currents, there won't be any galvanic corrosion.QuoteI would suggest reading the actual standard, not some third party guide to it, because 61000-3-2 does address DC current. I don't want to do Andy's homework for him, but for anybody else curious, I found an open-access summary:http://rfemcdevelopment.eu/en/emc-emi-standards/en61000-3-2-2014This is the relevant part:Quote

author: Faringdon
author_rank: Super Contributor
timestamp: May 07, 2023, 06:13:35 pm
content: Thanks, the statement that asymetric loads are not allowed unless below 100W clinches it.....so if you have a pulsed load (even of PFC'd) with power overall >100w, and it is pulsing on and off every 10ms, in synchrony with the mains, then it is illegal....because it will be asymetric, pulling more current on one half cycle, then the next.Strange that the standard doesnt question how asymetirc it is...because the post on #2 above, is asymetric, but not by much......but the average power draw >100w , so by the letter of the standard, its illegal.(Putting to one side the bit about corrosion at the moment)

author: Gyro
author_rank: Super Contributor
timestamp: May 08, 2023, 12:56:34 pm
content: Much more relevant than any corrosion risk is that any significant DC current offset will blind most RCDs and RCBOs by saturating their current transformers.

author: marekm
author_rank: Contributor
timestamp: May 08, 2023, 02:22:22 pm
content: DC fault current would saturate them of course (that's why these expensive RCDs type B exist), but DC that returns normally (no earth fault) via the same RCD should not.More interesting - would it also blind some energy meters?

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 10, 2023, 03:33:31 am
content: Quote from: marekm on May 08, 2023, 02:22:22 pmI remember an "energy saver" gadget for a water heater which was just a huge high current diode in a box. If it caused the energy meter to read low, it could indeed "save" a lot of energy!

author: coppice
author_rank: Super Contributor
timestamp: May 10, 2023, 03:45:55 am
content: Quote from: NiHaoMike on May 10, 2023, 03:33:31 amThe IEC specs for energy meters are a bit weak in the area of asymmetric waveforms. If a meter uses a shunt or rogowski coil for current sensing it should be OK. If it uses a hall sensor or CT, then in most countries the utility requires the meters it buys to have a high DC tolerance. However, there are some pretty small CTs used in some places, which clearly don't have a lot of tolerance.