Earth to mains line clearance, and Aerospace clearances/regulations?

[Faringdon]

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, because
Earth 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 airliners
Also, once i reviewed an offline 40W (LED lighting) flyback for 115v/400Hz (airline use)
and the contractor
had used no MOV at the input. But he had used a diff mode mains LC filter which used
massive 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 realised
they wouldnt so readily saturate in the event of a mains transient, and so they were used
for 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 of
Aeroplane offline SMPS's. As such, they simply are not used.
This makes them potentialy more noisy, and noise isnt
wanted on an aircraft.
As such, do you agree that aircraft offline SMPS's often utilise two cascaded
common mode chokes at the mains input? (instead of just one)
Though a Y cap is used across the isolation barrier of aircraft offline
SMPS's.
So , generally, how do they mitigate noise issues concerned with aircraft offline
SMPS's?
Presumbaly the use of 115VAC means the switching nodes arent as violent
as in 240VAC.
Also, how many direct connections are there from airframe, to the aircraft's
circuitry/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)

[pqass]

This topic gives me the tingles.   

[Gyro]

...
So is there any leeway in the standards here?

Troll thread reported - please do likewise.


Edit: OP post edited massively

[tggzzz]

So is there any leeway in the standards here?

Ask a professional. Make sure they have adequate professional liability insurance.

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?

False presumption.

Ask a professional. Make sure they have adequate professional liability insurance.

What would you say are the normal mains transient protection measures in  airliners?

Ask 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?

[Simon]

Can't you just ask the question?

[SeanB]

Can't you just ask the question?

think the ChatGPT interface has malfunctioned again today......

[langwadt]

Can't you just ask the question?

think the ChatGPT interface has malfunctioned again today......

I don't think AI has yet gotten to the point that it is capable of so consistently making such silly question

[Faringdon]

Can't you just ask the question?

There'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)

[jpanhalt]

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.

[Zero999]

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

[tggzzz]

Can't you just ask the question?

think the ChatGPT interface has malfunctioned again today......

Question, from at least 40 years ago: in the battle between Artificial Intelligence and Natural Stupidity, which will be triumphant?

[langwadt]

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.

I think even Boeing would have concerns about letting OP anywhere near airliner electronics

[jonpaul]

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  Country
eg DO-160 FAA for avionics in USA.



Enjoy,

Jon

PS: 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.

[Faringdon]

Thanks, and the question about

1....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?

[Psi]

...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.

[jpanhalt]

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.

[Faringdon]

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.

[nfmax]

Minimum allowed Earth clearance for civil aircraft in the UK is 500 feet except while taking off or landing

[jpanhalt]

"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.

[langwadt]

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.

they obviously have earth wires, all connected to an earth rod in a plant pot full of dirt

[Zero999]

"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.

I 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.

[mag_therm]

Boats and ships also have their electrical systems earthed to the metal hull.

You can read about it and maybe edit this.

[jpanhalt]

Boats and ships also have their electrical systems earthed to the metal hull.

You can read about it and maybe edit this.

I am indeed flattered that you would attribute something from Zero999 to my humble self.

[jc101]

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 Categories
The following categories cover the wide range of environments known to exist in the majority of
aircraft types and installation locations. It should be recognized that not all possible combinations
of temperatures and altitude limits are covered in these equipment categories. Categories for inflight
loss of cooling are defined in paragraph 4.5.5.

Category A1
Equipment intended for installation in a controlled temperature and pressurized location, on an
aircraft 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 be
applicable to equipment installed in temperature controlled but unpressurized locations on an
aircraft that operates at altitudes no higher than 15,000 ft (4,600 m) MSL.

Category A2
Equipment intended for installation in a partially controlled temperature but pressurized location
on an aircraft within which the pressures are normally no lower than the altitude equivalent of
15,000 ft (4,600 m) MSL is identified as Category A2. This category may also be applicable to
equipment installed in partially controlled temperature but unpressurized locations on an aircraft
that operates at altitudes no higher than 15,000 ft (4,600 m) MSL.

Category A3
Equipment intended for installation in a controlled or partially controlled temperature but
pressurized location within an aircraft within which the pressures are normally no lower than the
altitude equivalent of 15,000 ft (4,600 m) MSL, where the temperatures will be more severe than
those for categories A1 and A2, is identified as Category A3.

Category A4
Equipment intended for installation in a controlled temperature and pressurized location, on an
aircraft 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 as
declared by the equipment manufacturer. This category may also be applicable to equipment
installed in a temperature controlled but unpressurized locations on an aircraft that operates at
altitudes no higher than 15,000ft. (4,600m) MSL, for which temperature requirements differ from
category A1 as declared by the equipment manufacturer.

Category B1
Equipment intended for installation in a non-pressurized but controlled temperature location in an
aircraft that is operated at altitudes up to 25,000 ft (7,620 m) MSL is identified as Category B1.

Category B2
Equipment intended for installation in non-pressurized and non-controlled temperature locations
on an aircraft that is operated at altitudes up to 25,000 ft (7,620 m) MSL is identified as Category
B2.

Category B3
Equipment intended for installation in the power plant compartment of an aircraft that is operated
at altitudes up to 25,000 ft (7,620 m) MSL is identified as Category B3.

Category B4
Equipment intended for installation in a non-pressurized location on an aircraft that is operated at
altitudes up to 25,000 ft (7,620 m) MSL, for which temperature requirements differ from B1and
B2, is identified as Category B4.

Category C1
Equipment intended for installation in a non-pressurized but controlled temperature location in an
aircraft that is operated at altitudes up to 35,000 ft (10,700 m) MSL is identified as Category C1.

Category C2
Equipment intended for installation in non-pressurized and non-controlled temperature locations
within an aircraft that is operated at altitudes up to 35,000 ft (10,700 m) MSL is identified as
Category C2.

Category C3
Equipment intended for installation in the power plant compartment of an aircraft that is operated
at altitudes up to 35,000 ft (10,700 m) MSL is identified as Category C3.

Category C4
Equipment intended for installation on a non-pressurized aircraft that is operated at altitudes up to
35,000 ft (10,700 m) MSL, for which temperature requirements differ from C1and C2, is
identified as Category C4.

Category D1
Equipment intended for installation in a non-pressurized but controlled temperature location on
an aircraft that is operated at altitudes up to 50,000 ft (15,200 m) MSL is identified as Category
D1.

Category D2
Equipment intended for installation in non-pressurized and non-controlled temperature locations
on an aircraft that is operated at altitudes up to 50,000 ft (15,200 m) MSL is identified as
Category D2.

Category D3
Equipment intended for installation in the power plant compartment of an aircraft that is operated
at altitudes up to 50,000 ft (15,200 m) MSL is identified as Category D3.

Category E1
Equipment intended for installation in non-pressurized and non-controlled temperature locations
on an aircraft that is operated at altitudes up to 70,000 ft (21,300 m) MSL is identified as
Category E1.

Category E2
Equipment intended for installation in the power plant compartment of an aircraft that is operated
at altitudes up to 70,000 ft (21,300 m) MSL is identified as Category E2.

Category F1
Equipment intended for installation in non-pressurized but controlled temperature locations on an
aircraft that is operated at altitudes up to 55,000 ft (16,800 m) MSL is identified as Category F1.

Category F2
Equipment intended for installation in non-pressurized and non-controlled temperature locations
on an aircraft that is operated at altitudes up to 55,000 ft (16,800 m) MSL is identified as
Category F2.

etc.

[Zero999]

Boats and ships also have their electrical systems earthed to the metal hull.

You can read about it and maybe edit this.

It'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.

[tggzzz]

Minimum allowed Earth clearance for civil aircraft in the UK is 500 feet except while taking off or landing

Except when you are rock pollishing, eyeballing sheep as they whiz past at  70kt



And then there are competition finishes

[Zero999]

https://monroeaerospace.com/blog/how-are-airplanes-electrically-grounded/

[mag_therm]

jpanhalt. Sorry I screwed up Zero's  quote.
Regards

[jonpaul]

altitude affects transient creep and strike distance. We tested -15,000 to +50,000 ft

Temp was -25C to +85 C



DC bus 12/28V has at least 75V alt load dump transients ~ 100 mS.

Jon