Using FR4 with 240V AC Mains

[Mike Warren]

I have not had much luck searching for answers to the suitability
of 1oz, 1.6mm FR4 as a Mains PCB.

In particular; is it safe to run 200mil tracks carrying active and
neutral across each other on opposite sides of a 2 layer board?

Here's what I want to do

Circuit
http://web.aanet.com.au/pics/circuit.gif

PCB Layout (grid is 100mil)
http://web.aanet.com.au/pics/layout.gif

The other thing I'm concerned about is the likelihood of EMC
issues due to the long earth trace from the junction of C3 and C4

This device will have a SBC and 50Khz SMPS in it and the mains
current at 240V is about 1.1A.

-Mike

 

[Mike Harrison]

I have not had much luck searching for answers to the suitability
of 1oz, 1.6mm FR4 as a Mains PCB.

In particular; is it safe to run 200mil tracks carrying active and
neutral across each other on opposite sides of a 2 layer board?

Yes.

 

[Rene Tschaggelar]

I have not had much luck searching for answers to the suitability
of 1oz, 1.6mm FR4 as a Mains PCB.

In particular; is it safe to run 200mil tracks carrying active and
neutral across each other on opposite sides of a 2 layer board?

Here's what I want to do

Circuit
http://web.aanet.com.au/pics/circuit.gif

PCB Layout (grid is 100mil)
http://web.aanet.com.au/pics/layout.gif

The other thing I'm concerned about is the likelihood of EMC
issues due to the long earth trace from the junction of C3 and C4

This device will have a SBC and 50Khz SMPS in it and the mains
current at 240V is about 1.1A.

As far as I remember, UL specifies 8mm distance
between tracks on the same side. If the 8mm are
not achievable, then you can mill a through-groove
out of the material.

Rene

 

[Mike Warren]

As far as I remember, UL specifies 8mm distance
between tracks on the same side. If the 8mm are
not achievable, then you can mill a through-groove
out of the material.

Hi Rene,

Thanks for the reply.

That's going to be a problem. several of the components don't
have that sort of spacing. I've seen a lot of equipment such as
TVs etc where that hasn't been done.

Do you have any idea where I can get the UL spec?

-Mike

 

[Mike Warren]

Yes.

Thanks.

-Mike

 

[Pooh Bear]

Hi Rene,

Thanks for the reply.

That's going to be a problem. several of the components don't
have that sort of spacing. I've seen a lot of equipment such as
TVs etc where that hasn't been done.

Do you have any idea where I can get the UL spec?

If you're in Australia ( as it seems ) you'll actually want the IEC
spec. UL is for the USA only.

It's 6mm IIRC between live parts and *secondary* parts btw. You don't
need 6mm between live and neutral.

Graham

 

[Mike Warren]

If you're in Australia ( as it seems ) you'll actually want the IEC
spec. UL is for the USA only.

It's 6mm IIRC between live parts and *secondary* parts btw. You don't
need 6mm between live and neutral.

Hi Graham,

That makes sense. I purchased AS/NZS 3820:1998 that appeared to
be what I want but it was a waste of time. This just lists safety issues
that are common sense.

Do you know which standard I need, or how I can find it?

Also, this device may end up being used in the USA so I do need to
find the UL spec as well.

-Mike

 

[Pooh Bear]

Hi Graham,

That makes sense. I purchased AS/NZS 3820:1998 that appeared to
be what I want but it was a waste of time. This just lists safety issues
that are common sense.

Do you know which standard I need, or how I can find it?

Also, this device may end up being used in the USA so I do need to
find the UL spec as well.

The 2 IEC safety standards I'm familiar with are IEC 60065 ( consumer audio,
video and the like ) and IEC 60950 ( IT equipment ). UL's UL 1950 is now
very similar to IEC 60950 btw.

You'll need to consider EMC issues from the compliance aspect too of course.

Graham

 

[Mike Warren]

The 2 IEC safety standards I'm familiar with are IEC 60065 ( consumer
audio, video and the like ) and IEC 60950 ( IT equipment ). UL's UL
1950 is now very similar to IEC 60950 btw.

Thanks. Plugging those numbers into Google gave me some good
links.

You'll need to consider EMC issues from the compliance aspect too of
course.

I have a bit of experience with EMC. I'm concerned about the trace
length of the ground from the junction of C3 and C4 and was hoping
someone with experience with mains would know if it is worth a
prototype or I need to do the layout again.

Anyway, I'll get the specs and see what I need to change for safety
and go from there.

-Mike

 

[Pooh Bear]

Thanks. Plugging those numbers into Google gave me some good
links.


I have a bit of experience with EMC. I'm concerned about the trace
length of the ground from the junction of C3 and C4 and was hoping
someone with experience with mains would know if it is worth a
prototype or I need to do the layout again.

Anyway, I'll get the specs and see what I need to change for safety
and go from there.

I'd keep all the mains filtering close to the inlet personally.

C3 and C4 should be *Y* types ( not X ) btw.

Graham

 

[Mike Warren]

I'd keep all the mains filtering close to the inlet personally.

I don't want to change the size of the PCB or position of the
IEC sockets if I can help it. If it's ok to run actives over neutrals
and earths anywhere then I have more options.

C3 and C4 should be *Y* types ( not X ) btw.

Ah, yes. Copy & Paste error.

-Mike

 

[RHRRC]

I have not had much luck searching for answers to the suitability
of 1oz, 1.6mm FR4 as a Mains PCB.

In particular; is it safe to run 200mil tracks carrying active and
neutral across each other on opposite sides of a 2 layer board?

Here's what I want to do

Circuit
http://web.aanet.com.au/pics/circuit.gif

PCB Layout (grid is 100mil)
http://web.aanet.com.au/pics/layout.gif

The other thing I'm concerned about is the likelihood of EMC
issues due to the long earth trace from the junction of C3 and C4

This device will have a SBC and 50Khz SMPS in it and the mains
current at 240V is about 1.1A.

-Mike

As others have responded there is no problem in running 240V (presume
that is 339V) between top and bottom layers of (1.6mm) FR4.
However looking at your layout there are serious safety problems if
this is to be a commercial product for sale in Europe - dunno offhand
aout the USA.
There is a 'regulation' called the Low Voltage Directive (LVD) which
demands that products be electrically 'safe'.
The keywords you are looking for are and need to understand to start
with include 'creepage and clearance', 'basic', 'reinforced', and
'supplementary insulation', and 'proof tracking index'.

As it is your design would be considered unsafe.

 

[Pooh Bear]

As others have responded there is no problem in running 240V (presume
that is 339V) between top and bottom layers of (1.6mm) FR4.
However looking at your layout there are serious safety problems if
this is to be a commercial product for sale in Europe - dunno offhand
aout the USA.
There is a 'regulation' called the Low Voltage Directive (LVD) which
demands that products be electrically 'safe'.
The keywords you are looking for are and need to understand to start
with include 'creepage and clearance', 'basic', 'reinforced', and
'supplementary insulation', and 'proof tracking index'.

As it is your design would be considered unsafe.

Can you point to the bit you consider unsafe ?

I didn't spot anything iffy on a casual glance.

Graham

 

[Mike Warren]

As others have responded there is no problem in running 240V (presume
that is 339V) between top and bottom layers of (1.6mm) FR4.
However looking at your layout there are serious safety problems if
this is to be a commercial product for sale in Europe - dunno offhand
aout the USA.
There is a 'regulation' called the Low Voltage Directive (LVD) which
demands that products be electrically 'safe'.
The keywords you are looking for are and need to understand to start
with include 'creepage and clearance', 'basic', 'reinforced', and
'supplementary insulation', and 'proof tracking index'.

As it is your design would be considered unsafe.

Thanks for your reply. I'll do some searching on the keywords you
mentioned. Can you offer any suggestions as to where the problems
lie or how to fix them?

-Mike

 

[RHRRC]

Can you point to the bit you consider unsafe ?

I didn't spot anything iffy on a casual glance.

Graham

Which *bit* do I consider unsafe?

By a cursory glance

1.live to neutral creepage & clearances in many places

2.phase (live and/or neutral) to earth creepage & clearances almost
everywhere

3.X2 caps connected between phase (live and/or neutral) and earth (I
cannot read the circuit diag well enough to see their value but can
make out they are X2 rated)

I do of course assume that phase to phase to earth integrity is not to
be enhanced (slotting/routing, potting, conformal whatever for
wherever). Even were this so (and it came up to spec.) the X2 caps
would open the door to prosecution if there was a problem and at the
least a total product recall if no bodily harm had resulted.

 

[RHRRC]

Thanks for your reply. I'll do some searching on the keywords you
mentioned. Can you offer any suggestions as to where the problems
lie or how to fix them?

-Mike

Is this for europe or the USA or wherever?

 

[Pooh Bear]

Which *bit* do I consider unsafe?

By a cursory glance

1.live to neutral creepage & clearances in many places

2.phase (live and/or neutral) to earth creepage & clearances almost
everywhere

What distance do you reckon is required then ?

3.X2 caps connected between phase (live and/or neutral) and earth (I
cannot read the circuit diag well enough to see their value but can
make out they are X2 rated)

Previously covered. They should indeed be Y types. Not a pcb layout issue
though.

I do of course assume that phase to phase to earth integrity is not to
be enhanced (slotting/routing, potting, conformal whatever for
wherever). Even were this so (and it came up to spec.) the X2 caps
would open the door to prosecution if there was a problem and at the
least a total product recall if no bodily harm had resulted.

Graham

 

[Mike Warren]

Is this for europe or the USA or wherever?

At this stage it's for Australia. However, there is a chance we
could sell in the US and a small chance of sale in Europe.

This is the first time I have done mains design and would
like to do it right anyway.

I have not found any specific information so far using the
keywords you gave me, but I'm still following the links.

The LVD documents I downloaded only talk about documentation
requirements.

-Mike

 

[Pooh Bear]

At this stage it's for Australia. However, there is a chance we
could sell in the US and a small chance of sale in Europe.

This is the first time I have done mains design and would
like to do it right anyway.

I have not found any specific information so far using the
keywords you gave me, but I'm still following the links.

The LVD documents I downloaded only talk about documentation
requirements.

LVD is simply the 'law'. The standards required will be the IEC ones (
actually ENs in Europe but they are essentially the same thing ).

E.g. I refer to BSEN 60065 ( the 'British Standard' ) for products I
design - equivalent to IEC 60065.

In Australia you have your own standards but again these are derived
from IEC.

Only the USA is different ( as ever ) but even here the more recent UL
standards have adopted most of what's in the the IEC equivalent.

Graham

 

[RHRRC]

What distance do you reckon is required then ?



Previously covered. They should indeed be Y types. Not a pcb layout issue
though.

Graham

Yes the caps have been previously covered.

Basic insulation for 230V mains is a minimum 2.5mm creepage, 2.0mm
clearance but you must fully understand what is meant by 'basic
insulation' .
'Basic insulation' here does not mean the 'minimum acceptable
insulation'

Best to start with EN60950