PCB trace width for 220v AC mains operation

Thread Starter

SHARANYADAS

Joined Apr 13, 2017
60
Hi all
I have built an automation circuit where 5 relays will be controlled using Bluetooth & IR.Each relay will control a max load of 100w.The Voltage to be operated on is 220v AC.The switching will be done on the Live side.(All neutral common for the loads).So to do this,I have connected all the COM pins of the relay's & then connected to 220v Live.The NO pin is connected to each load.So,the Max power on the track connecting all the COM's,will be 5x100w=500w(If all the loads are on).I have used 100 mil trace width for this track.I used this calculator to calculate the pcb width.Is this trace width ok to handle 500w in 220v AC?I am attaching PCB pic for your ref.The track is marked with red.The tracks that connects the NO pin to load is 66 mil.Will that be adequate to handle 100w load in 220v?Please give your valuable feedback....I have already built 10 pcbs

Circuit.png
 

Hymie

Joined Mar 30, 2018
1,003
More of a concern is the lack of separation between mains and low voltage circuits on the PCB.

As a good rule of thumb, there should be at least 5mm separating these circuits, otherwise should the insulation fail for any reason, your low voltage circuit could become at mains potential.
 

dendad

Joined Feb 20, 2016
3,940
Add slots to the board between the 240V and the low voltage traces.
Here is a random example.

upload_2018-8-31_8-36-36.jpeg

Also, leaving the solder resist off the trace so added solder can increase the current capacity is another trick.
 

-live wire-

Joined Dec 22, 2017
927
Add slots to the board between the 240V and the low voltage traces.
Here is a random example.

View attachment 159002

Also, leaving the solder resist off the trace so added solder can increase the current capacity is another trick.
But you shouldn't count on solder increasing the current capacity. And another thing is that should there be a short, your wiring needs to have a low enough resistance to immediately trip the breaker.
 

panic mode

Joined Oct 10, 2011
1,919
Hymie is right... those traces are awfully close.

you can choose different relay type to get more space between relay coil and relay contacts or use two layer PCB to keep AC and DC circuits on separate layers. outer layers get better cooling and can handle larger currents.

also your trace width calculation has no mention on Cu thickness. and what about inrush current considerations? what kind of loads we are talking about?

1oz/sqft was the norm for long time. but todays fabs may use 0.5 oz /sqft. thinner Cu layer means less etching time, less etchant used, sharper edges allowing finer structures etc. and all of this works a treat for surface mount parts, lowering cost and saving environment. but when higher currents are needed, Cu thickness is added in extra step (and it increases cost).
 

RichardO

Joined May 4, 2013
2,271
Also, leaving the solder resist off the trace so added solder can increase the current capacity is another trick.
I don't think trace thickness will be a problem for each relay alone. 100 watts at 220 volts is less than 1/2 amp. Just remember that the traces that carry the current for all 5 loads have to be 5 times wider.

I like that you have a fuse on the PCB.
 

jacen17

Joined Mar 21, 2013
2
To add to the previous posts, high voltage and low voltage need to be in completely different areas of the board, and layer thickness as well as internal and external layer spacing all needs to be considered. IPC-2221A gives guidance here if you can get your hands on it. In my experience I double the spacing guidance in that spec.
 

Thread Starter

SHARANYADAS

Joined Apr 13, 2017
60
Unfortunately i can't change the pcb design right now.But as i can inderstand from the replies,if i can remove the masking from the Live track & tin it using solder,i can increase the current carrying capacity...right?
 

dendad

Joined Feb 20, 2016
3,940
Unfortunately i can't change the pcb design right now.But as i can inderstand from the replies,if i can remove the masking from the Live track & tin it using solder,i can increase the current carrying capacity...right?
Yes, that can help. But the big concern is the safety, or lack of it, having close spacing between the mains and the low volts.
If you can, even cutting slots with a Dremel toll will suffice.
Slots.png
This is the bare minimum I'd think. Cut slots where the thick red lines are. Otherwise I'd advise not using the board at all.
 

Thread Starter

SHARANYADAS

Joined Apr 13, 2017
60
I have also built a v2 of that circuit which uses smd components & has fan speed regulation.Please take a look if something to modify before pcb production.I also increased the trace width of the main live track to 150 mil.

ckt_v2.png
 

Janis59

Joined Aug 21, 2017
1,357
The absolute maximum ++ for pcb current carrying capability stays near to 33 A/mm2 if copper ckickness is 35 microns. For thiner larger, thicker smaller. However indeed safe is 10-15 A/mm2. The separation space between 220V is 2mm if lacked and 3 in without lack.
 
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