Earth to mains line clearance, and Aerospace clearances/regulations? - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: March 08, 2024, 06:47:44 pm
content: Hi,Earth to mains line clearance:I once did a PCB review on a PCB with offline 230VAC Flyback SMPS in it. The Earth connection came on to the input of the PCB with line and neutral. The earth was then tracked around the PCB, and was 0.6mm away from the mains line conductor. It then squirmed its way across the isolation barrier at the side of the PCB...and was 0.3mm away from secondary side traces (it was actually the secondary ground).It got soldered to the TO220F heatsinks on its way round the board.I complained of it, but was told "no, it doesnt matter that earth to mains line clearance is only 0.9mm overall, becauseEarth is the safety conductor". My response that Earth may not actually be connected up was ignored.So is there any leeway in the standards here?___----____PCB Clearances in Airliners:Also, considering clearances, usually at high altitude, the clearance distance increases, but in aeroplanes, it does not, presumably because they are pressurised to sea level atmospheric pressure?___---_____Mains transient protection in airlinersAlso, once i reviewed an offline 40W (LED lighting) flyback for 115v/400Hz (airline use)and the contractorhad used no MOV at the input. But he had used a diff mode mains LC filter which usedmassive inductors...they were rated for more than 10 times the current they would see.He wouldnt say why he had used these, but you can only imagine it was because he realisedthey wouldnt so readily saturate in the event of a mains transient, and so they were usedfor mains transient protection, instead of a MOV. Just downstream of the mains rectifier,he had put a SMC size TVS.What would you say are the normal mains transient protection measures in airliners?___---___Lightning and aircraft:Airliners get hit by lightning twice per 1000hrs flying.Does it ever cause electrical noise problems?Can it cause transients on the aeroplane electrical power distribution system?....like it does "on the ground"?_____------______Earthing in an aircraft?On earth, the earth itself is used as the earth conductor.In an aeroplane, the airframe and fuselage is the "earth".When AC 115V/400Hz is used, the Neutral is also at earth potential.However, there is no earth wire in the mains cables of an aircraft.(since it would make the cables too heavy for aircraft use)Due to this there is nowhere to connect Y capacitors to at the input ofAeroplane offline SMPS's. As such, they simply are not used.This makes them potentialy more noisy, and noise isntwanted on an aircraft.As such, do you agree that aircraft offline SMPS's often utilise two cascadedcommon mode chokes at the mains input? (instead of just one)Though a Y cap is used across the isolation barrier of aircraft offlineSMPS's.So , generally, how do they mitigate noise issues concerned with aircraft offlineSMPS's?Presumbaly the use of 115VAC means the switching nodes arent as violentas in 240VAC.Also, how many direct connections are there from airframe, to the aircraft'scircuitry/distribution ground?....and where are these connections? (how far apart)Also, are capacitive connections to the airframe commonly used?(eg like as in Y cap useage)

author: pqass
author_rank: Super Contributor
timestamp: March 08, 2024, 07:10:20 pm
content: This topic gives me the tingles.

author: Gyro
author_rank: Super Contributor
timestamp: March 08, 2024, 07:13:03 pm
content: Quote from: Faringdon on March 08, 2024, 06:47:44 pmTroll thread reported - please do likewise.Edit: OP post edited massively

author: tggzzz
author_rank: Super Contributor
timestamp: March 08, 2024, 08:05:01 pm
content: Quote from: Faringdon on March 08, 2024, 06:47:44 pmAsk a professional. Make sure they have adequate professional liability insurance.QuoteFalse presumption.Ask a professional. Make sure they have adequate professional liability insurance.QuoteAsk a professional. Make sure they have adequate professional liability insurance.Are you a professional with adequate professional liability insurance? If not, in what way will the answers here change your actions?

author: Simon
author_rank: Unknown
timestamp: March 08, 2024, 08:09:35 pm
content: Can't you just ask the question?

author: SeanB
author_rank: Super Contributor
timestamp: March 08, 2024, 08:17:58 pm
content: Quote from: Simon on March 08, 2024, 08:09:35 pmthink the ChatGPT interface has malfunctioned again today......

author: langwadt
author_rank: Super Contributor
timestamp: March 08, 2024, 08:21:54 pm
content: Quote from: SeanB on March 08, 2024, 08:17:58 pmI don't think AI has yet gotten to the point that it is capable of so consistently making such silly question

author: Faringdon
author_rank: Super Contributor
timestamp: March 08, 2024, 08:22:17 pm
content: QuoteThere's loads of questions, so i thought best to write it out...and if any kindred reader disagrees with any of it, they may perhaps chime in and give the correction or perhaps, just say "no thats wrong".(EDIT Where there are questions, they are now italicised...ENDofEDIT)

author: jpanhalt
author_rank: Super Contributor
timestamp: March 08, 2024, 08:23:54 pm
content: Now airplanes...Wouldn't something for "airplane" apply to any craft aloft, including lighter than air craft? Is this thread related to his two closed threads having to do with UAV's?Questions about grounding in craft aloft were addressed years ago.

author: Zero999
author_rank: Super Contributor
timestamp: March 08, 2024, 08:34:36 pm
content: Basic insulation is required between earth conductors and the mains. A quick Google for PCB creepage and clearances found the following inks to all the information required to design a mains PCB. Obviously one should obtain copies of the relevant standards, if it's to be used in a commercial application.https://www.eevblog.com/forum/projects/pcb-creepage-and-clearance-requirements-from-around-the-world/https://www.protoexpress.com/blog/importance-pcb-line-spacing-creepage-clearance/https://resources.altium.com/p/high-voltage-pcb-design-creepage-and-clearance-distance

author: tggzzz
author_rank: Super Contributor
timestamp: March 08, 2024, 09:49:33 pm
content: Quote from: SeanB on March 08, 2024, 08:17:58 pmQuestion, from at least 40 years ago: in the battle between Artificial Intelligence and Natural Stupidity, which will be triumphant?

author: langwadt
author_rank: Super Contributor
timestamp: March 08, 2024, 09:58:31 pm
content: Quote from: jpanhalt on March 08, 2024, 08:23:54 pmI think even Boeing would have concerns about letting OP anywhere near airliner electronics

author: jonpaul
author_rank: Super Contributor
timestamp: March 09, 2024, 09:31:43 am
content: FTTS: Consult a professional compliance firm: ETL, UL, TUV, VDE, Expect cost ~ 20k$ for ONE product initial .Buy $10M liability and E&O insurance policy.Buy and read appropriate regulatory standards, for electrical safety , medical electronics, avionics.These will differ depending the Countryeg DO-160 FAA for avionics in USA.Enjoy,JonPS: In 1980s,,1990,an avionics device cost 300K and took a JUST YEAR for FAA, DO-160.For a medical illuminator cost $1M and 1 YEARJUST for USA reg compliance and FDA.

author: Faringdon
author_rank: Super Contributor
timestamp: March 09, 2024, 12:22:49 pm
content: Thanks, and the question about1....whether you have Line/Neutral/Earth cables in an airplane?...or are they all just Line/Neutral?..and if so, how do you get over the extra noise problems that you get when you dont have the ability to connect Y caps from Line/Neutral to earth?(by "earth" i mean fuselage potential)You see, any offline SMPS in an airplane is going to be quite close to the airframe ....so it will radiate to it, and you will get massive common mode noise current loops......so how do you mitigate this in an airplane?Obviously you are going to go heavy on the common mode line chokes.....but any other measures?2....Lightning strikes an airliner twice every 1000hrs....does the lightning strike cause high spike voltage transients on the internal mains cables?And do they use a single big transient suppressor on the mains, or does each offline SMPS have a big internal transient suppressor?Is this why i saw a engineer do a 70W offline flyback with two mains input filter inductors which were each the size of half a bar of soap?

author: Psi
author_rank: Super Contributor
timestamp: March 09, 2024, 12:35:30 pm
content: ...and then you get into Paschen's curve when going up into actual space where 500V can jump almost 1 meter, given the right situation.

author: jpanhalt
author_rank: Super Contributor
timestamp: March 09, 2024, 12:38:48 pm
content: In case you missed it, this is the first hit on a Google search for "AC power supplies in modern airliners." You didn't state whether you meant civilian or military. I made a huge leap and assumed civilian, even though your prior posts suggest the use may be for military use.

author: Faringdon
author_rank: Super Contributor
timestamp: March 09, 2024, 01:04:00 pm
content: Thanks yes, 115VAC 400Hz is it...but do they have an earth cable in with the line and neutral when its single phase?And when its 3 phase, do they have P1,P2,P3,E,N ?I suspect no earth wire in with the cable, for reasons of lightness.For 3 phase transmission you suspect only P1/P2/P3 in the cable, but even having no neutral could cause problems.Military and civil i would have thought were the same.

author: nfmax
author_rank: Super Contributor
timestamp: March 09, 2024, 01:09:56 pm
content: Minimum allowed Earth clearance for civil aircraft in the UK is 500 feet except while taking off or landing

author: jpanhalt
author_rank: Super Contributor
timestamp: March 09, 2024, 01:24:04 pm
content: "L-N" means line + neutral. What advantage would be had by adding a third line connected to N somewhere else on the airplane?BTW, starting in 2017 or abouts, the NEC (USA) allows a GFCI to substitute for a ground (green) wire in rework. In contrast, in some locations, a GFCI is required even when there is a ground wire. That is for household wiring, not aircraft, but I found it interesting.

author: langwadt
author_rank: Super Contributor
timestamp: March 09, 2024, 01:54:09 pm
content: Quote from: Faringdon on March 09, 2024, 01:04:00 pmthey obviously have earth wires, all connected to an earth rod in a plant pot full of dirt

author: Zero999
author_rank: Super Contributor
timestamp: March 09, 2024, 04:42:20 pm
content: Quote from: jpanhalt on March 09, 2024, 01:24:04 pmI don't know about aviation but military vehicles which have an inverter or alternator, the neutral is normally connected vehicle's metal chassis, which serves as the earth connection. Boats and ships also have their electrical systems earthed to the metal hull. I suspect this is also true for aeroplanes. This is done for EMC purposes and to the electrical system with floating at a hazardous voltage, with respect to the chassis/hull/airframe.

author: mag_therm
author_rank: Frequent Contributor
timestamp: March 09, 2024, 04:54:00 pm
content: Quote from: jpanhalt on March 09, 2024, 01:24:04 pmYou can read about it and maybe edit this.

author: jpanhalt
author_rank: Super Contributor
timestamp: March 09, 2024, 05:07:40 pm
content: Quote from: mag_therm on March 09, 2024, 04:54:00 pmI am indeed flattered that you would attribute something from Zero999 to my humble self.

author: jc101
author_rank: Frequent Contributor
timestamp: March 09, 2024, 05:10:24 pm
content: You mention aviation, for which class of test do you refer? Each of these has limits for temperature, moisture, vibration, power, etc. plus well defined test procedures.Perhaps grab some of the standards for aviation? DO-160 is just one, ~550 pages or so.To be able to test to get aviation certification I think you have to be a Design Authority. To become a Design Authority, open your cheque book, generate lots of procedures and policies, and have plenty of time. Let us know how you get on...Equipment CategoriesThe following categories cover the wide range of environments known to exist in the majority ofaircraft types and installation locations. It should be recognized that not all possible combinationsof temperatures and altitude limits are covered in these equipment categories. Categories for inflightloss of cooling are defined in paragraph 4.5.5.Category A1Equipment intended for installation in a controlled temperature and pressurized location, on anaircraft within which pressures are normally no lower than the altitude equivalent of l5,000 ft(4,600 m) Mean Sea Level (MSL), is identified as Category A1. This category may also beapplicable to equipment installed in temperature controlled but unpressurized locations on anaircraft that operates at altitudes no higher than 15,000 ft (4,600 m) MSL.Category A2Equipment intended for installation in a partially controlled temperature but pressurized locationon an aircraft within which the pressures are normally no lower than the altitude equivalent of15,000 ft (4,600 m) MSL is identified as Category A2. This category may also be applicable toequipment installed in partially controlled temperature but unpressurized locations on an aircraftthat operates at altitudes no higher than 15,000 ft (4,600 m) MSL.Category A3Equipment intended for installation in a controlled or partially controlled temperature butpressurized location within an aircraft within which the pressures are normally no lower than thealtitude equivalent of 15,000 ft (4,600 m) MSL, where the temperatures will be more severe thanthose for categories A1 and A2, is identified as Category A3.Category A4Equipment intended for installation in a controlled temperature and pressurized location, on anaircraft within which pressures are normally no lower than the altitude equivalent of 15,000 ft.(4,600m) Mean Sea Level (MSL), for which temperature requirements differ from category A1 asdeclared by the equipment manufacturer. This category may also be applicable to equipmentinstalled in a temperature controlled but unpressurized locations on an aircraft that operates ataltitudes no higher than 15,000ft. (4,600m) MSL, for which temperature requirements differ fromcategory A1 as declared by the equipment manufacturer.Category B1Equipment intended for installation in a non-pressurized but controlled temperature location in anaircraft that is operated at altitudes up to 25,000 ft (7,620 m) MSL is identified as Category B1.Category B2Equipment intended for installation in non-pressurized and non-controlled temperature locationson an aircraft that is operated at altitudes up to 25,000 ft (7,620 m) MSL is identified as CategoryB2.Category B3Equipment intended for installation in the power plant compartment of an aircraft that is operatedat altitudes up to 25,000 ft (7,620 m) MSL is identified as Category B3.Category B4Equipment intended for installation in a non-pressurized location on an aircraft that is operated ataltitudes up to 25,000 ft (7,620 m) MSL, for which temperature requirements differ from B1andB2, is identified as Category B4.Category C1Equipment intended for installation in a non-pressurized but controlled temperature location in anaircraft that is operated at altitudes up to 35,000 ft (10,700 m) MSL is identified as Category C1.Category C2Equipment intended for installation in non-pressurized and non-controlled temperature locationswithin an aircraft that is operated at altitudes up to 35,000 ft (10,700 m) MSL is identified asCategory C2.Category C3Equipment intended for installation in the power plant compartment of an aircraft that is operatedat altitudes up to 35,000 ft (10,700 m) MSL is identified as Category C3.Category C4Equipment intended for installation on a non-pressurized aircraft that is operated at altitudes up to35,000 ft (10,700 m) MSL, for which temperature requirements differ from C1and C2, isidentified as Category C4.Category D1Equipment intended for installation in a non-pressurized but controlled temperature location onan aircraft that is operated at altitudes up to 50,000 ft (15,200 m) MSL is identified as CategoryD1.Category D2Equipment intended for installation in non-pressurized and non-controlled temperature locationson an aircraft that is operated at altitudes up to 50,000 ft (15,200 m) MSL is identified asCategory D2.Category D3Equipment intended for installation in the power plant compartment of an aircraft that is operatedat altitudes up to 50,000 ft (15,200 m) MSL is identified as Category D3.Category E1Equipment intended for installation in non-pressurized and non-controlled temperature locationson an aircraft that is operated at altitudes up to 70,000 ft (21,300 m) MSL is identified asCategory E1.Category E2Equipment intended for installation in the power plant compartment of an aircraft that is operatedat altitudes up to 70,000 ft (21,300 m) MSL is identified as Category E2.Category F1Equipment intended for installation in non-pressurized but controlled temperature locations on anaircraft that is operated at altitudes up to 55,000 ft (16,800 m) MSL is identified as Category F1.Category F2Equipment intended for installation in non-pressurized and non-controlled temperature locationson an aircraft that is operated at altitudes up to 55,000 ft (16,800 m) MSL is identified asCategory F2.etc.

author: Zero999
author_rank: Super Contributor
timestamp: March 09, 2024, 05:22:50 pm
content: Quote from: Zero999 on March 09, 2024, 04:42:20 pmIt's just been the case in my experience. No doubt unearthed i.e. IT electrical systems exist on ships, just as they do on land, but they seem to be the exception, rather than the norm and even then there's normally a deliberate, high impedance connection to earth, for the purposes of fault detection.

author: tggzzz
author_rank: Super Contributor
timestamp: March 09, 2024, 06:47:54 pm
content: Quote from: nfmax on March 09, 2024, 01:09:56 pmExcept when you are rock pollishing, eyeballing sheep as they whiz past at 70ktAnd then there are competition finishes

author: Zero999
author_rank: Super Contributor
timestamp: March 09, 2024, 07:00:32 pm
content: https://monroeaerospace.com/blog/how-are-airplanes-electrically-grounded/

author: mag_therm
author_rank: Frequent Contributor
timestamp: March 09, 2024, 09:13:53 pm
content: jpanhalt. Sorry I screwed up Zero's quote.Regards

author: jonpaul
author_rank: Super Contributor
timestamp: March 13, 2024, 01:56:04 pm
content: altitude affects transient creep and strike distance. We tested -15,000 to +50,000 ftTemp was -25C to +85 CDC bus 12/28V has at least 75V alt load dump transients ~ 100 mS.Jon