Basic insulation or Reinforced insulation for Creepage/Clearance Distance in PCB

[Bjtpower_magic]

Hi,

I have basic question here, I have designing 3 Phase system which includes L1/L2/L3, N and PE.
There is a requirement of Creepage and clearance requirement from IEC61010

What do we mean by Basic insulation? Is it the Distance between L to N or L to PE
How do we get to know?

Basic insulation shows 3mm Creepage and clearance while Reinforced insulation shows 6mm Creepage/Clearance distance.
I am confused about how much distance we need to maintain in PCB
1. Distance between N Track and PE Track
2. Distance between L1/L2/L3 Track and PE Track
3. Distance between N Track and L1/L2/L3 Track

 

[barry]

It's a little squishy. Basic Insulation protects against shock; if it breaks down, there's a hazard. Reinforced Insulation means there's a second (or more) layer of insulation such that if one layer breaks down, there's still protection. However, I'm not sure this applies to PCBs. The insulation on the PCB is air and soldermask. Can that be considered two layers, i.e., Reinforced Insulation? I don't know.

The real question is: What are YOUR requirements?

If you've got the room, just use 6mm and be done with it.

 

[cupoftea]

In an offline isolated output SMPS, The 6mm in PCBs is for distance from "any primary conductor" to the any secondary conductor.

Also, in an offline SMPS, you shoudl have 2mm clearance between the Line and Neutral conductors. After the mains diode bridge, people often have just 1mm between post rectifier positive and the post rectifier ground.

Often , in offline SMPS, downstream of the input fuse, you often see just 1mm between line and neutral.

As long as the earth conductor can conduct the fuse current without being destroyed, there is not usually a requirement for much clearance from line to earth, because if line touches earth, then the fuse blows and youre protected anyway.

If you are on inner layers of the PCB, then the distance requirement between line and neutral is well reduced.

Other things like the pollution environment and humidity of the environment affect the clearance/creepage.
Also, whether or not the pcb is conformal coated or not, or just solder resist, or even no solder resist.

Page 9 of this gives guidelines

https://alternatezone.com/electronics/files/PCBDesignTutorialRevA.pdf

 

[FvM]

Double or reinforced or reinforced insulation is generally required between "hazardous parts" (e.g. L and N conductors) and "accessible parts" (exposed metal parts, any circuit that can be directly or indirectly touched). Metal parts with "protective bonding", a secured low impedance connection to PE only need basic insulation.

IEC61010 explains the requirement details in paragraph 6.5 and Annex D.

Inside the mains circuit, e.g. the primary side of a SMPS, you usually find basic insulation, between primary and secondary side double or reinforced insulation.

The secondary circuit may be connected to PE and nevertheless require double insulation because it doesn't entirely provide low impedance and sufficient current withstand of the PE connection.

 

[Easy peasy]

The soldermask is ignored unless it is a special brew designed for insulation purposes

you are referring to C & C - creepage and clearance on a pcb - these are defined

for 230Vac ckts, 3.2mm is typical for P/N to earth - however the pollution degree must be taken into account.

For working insulation inside a power converter - this is up to the designer ( there are standards too ) - as long as a fault can't cause a fire - e.g. fuse protection.

For input to output shock hazard limitation - the standards are fairly clear ...

 

[Bjtpower_magic]

Double or reinforced or reinforced insulation is generally required between "hazardous parts" (e.g. L and N conductors) and "accessible parts" (exposed metal parts, any circuit that can be directly or indirectly touched). Metal parts with "protective bonding", a secured low impedance connection to PE only need basic insulation.

IEC61010 explains the requirement details in paragraph 6.5 and Annex D.

Inside the mains circuit, e.g. the primary side of a SMPS, you usually find basic insulation, between primary and secondary side double or reinforced insulation.

The secondary circuit may be connected to PE and nevertheless require double insulation because it doesn't entirely provide low impedance and sufficient current withstand of the PE connection.

Hi FvM,
Thanks for your reply.

In system- We have Enclosure which is connected to Earth (and Which is user accessible parts-Mean user can touch it)
So Reinforced insulation applies for L/N Conductors and Protective Earth (Enclosure body) as Reinforced insulation?

Note: Enclosure is spray painted

--- Updated Jul 28, 2022 ---

The real question is: What are YOUR requirements?

If you've got the room, just use 6mm and be done with it.

Hi Barry.. I have resistor dividers between Live to Earth and Neutral to Earth.
Basically i wanted to measure voltage wrt to Earth as well wrt Neutral.

This is 3 Phase system where i would like to measure voltages (L1/L2/L3) wrt Neutral and Earth.

 

[FvM]

In system- We have Enclosure which is connected to Earth (and Which is user accessible parts-Mean user can touch it)
So Reinforced insulation applies for L/N Conductors and Protective Earth (Enclosure body) as Reinforced insulation?

If the enclosure has suitable PE connection, basic insulation is sufficient. There's nothing against providing reinforced insulation as extra safety margin. You should also consider that measurement equipment installed in the power distribution may require overvoltage category III and respective higher isolation distances.

Painting and standard powder coating doesn't count as safe insulation.

 

[cupoftea]

for 230Vac ckts, 3.2mm is typical for P/N to earth

...thats interesting, i opened up one 70W offline 230vac flyback of a highly sold product, and they had tracked earth from the mains input connector, and to the primary fet heatsink (to which this earth connected to), and then continued this earth tracking across the isolation barrier, and connected it to the secondary ground.

The earth in the secondary side was just 0.3mm away from other secondary conductors.....in the primary side, this earth was just 0.5mm away from the Line conductor.......i brought this up, and was told it was fine because if Earth got shorted to Line, then the fuse would blow.....so clearance between earth and line didnt matter so they said...because " if earth shorts to line, then the fuse will blow"

This flyback PCB was stood on spacers inside a large earthed metal case, with no vent holes.

 

[cupoftea]

Reinforced insulation is from any conductor not isolated from mains L and N, to any isolated "secondary" conductor...and is 6mm.

When you speak of isolation between L to N.....the following makes an interesting read....and shows how the regs are very often flouted for reasons of cost.....eg, just 0.75mm clearance between Drain and source of TO220 FET in offline flyback.......there are very few incidences of problems from this.

PCB Trace Spacing Calculation for Voltage Levels

The circuit designer's guide and calculator of the spacing between PCB traces for various voltage levels based on UL60950-1 and IPC standards.

www.smps.us

https://www.edaboard.com/threads/offline-230vac-flyback-smps-with-to220-fet-and-legs-not-bent-too-close-to-each-other.374017/

The key number to remember is 6mm from primary to secondary (any conductor) in an offline SMPS.

For the bit of an offline SMPS where there is L and N upstream of the input mains fuse...it is said 2mm clearance.....but after the fuse and whatever other inline components (eg filter inductors)...it seems to be a free-for-all, and whatever you can get away with. (pollution degree/humidity etc to bear in mind though). When you speak of the conductors downstream of the mains diode bridge, for some reason, many say you can have less clearance between conductors, then you would have just upstream of the diode bridge, even though the voltage between them is practically the same....(and a cap just upstream of the diode bridge needs to be X2 rated, but just downstream of it, it doesnt need X2 rating).

--- Updated Jul 28, 2022 ---

3. Distance between N Track and L1/L2/L3 Track

You need to tell us pollution degree, and whether you rproduct has vent holes which can let in impurities?
L1 to L2 spacing would be more critical, as it can be higher voltage than L to N (apart from maybe L to N transients)

If you can assure you wont get transients, ....then remind that the flashover distance for 1000v in air is 0.13mm.

But mains can get transients, so you need to account for this. But as said, when you are on a PCB inside a power converter, its designer discretion thats used....as after all, the thing is fused, and has the regulatory MOV for transient protection, and presumably a cover which stops sparks from jumping out, and stops prying fingers from touching the innards.

--- Updated Jul 28, 2022 ---

Basically, when you are inside the case of a power converter, you use your engineering discretion, and you know that flyback drain to source is easily 500V....and offline TO220 fets usually only have 0.76mm clearance between drain and source pads......so for anything 500V and less, 0.76mm isnt going to flash over on a PCB with solder resist on it......the actual flashover distance in V/m is not to be found anywhere on the internet though (considering pollution free environment in totally enclosed case where humidity levels dont factor in)

--- Updated Jul 28, 2022 ---

Attached from

PCB Trace Spacing Calculation for Voltage Levels

The circuit designer's guide and calculator of the spacing between PCB traces for various voltage levels based on UL60950-1 and IPC standards.

www.smps.us

--- Updated Jul 28, 2022 ---

...so ask what voltage will be used for the HiPot test for your product, and go 40V/mil for that.

 

[Easy peasy]

also:

Transformer Guide

Engineering Competence in Transformers and Magnetics

www.zettlermagnetics.eu

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