Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

UK requirements for mains and low voltage on same PCB

Status
Not open for further replies.

malc-c

New Member
Hi,

I'm developing a project that switches mains voltage via SSR's. Normally I tend to have one board for the SSR's, fuses and connectors, and a seperate main board for the logic / micro etc, but this project needs to have both on one PCB.

I normally copper pour my boards top and bottom, with the pour attached to the ground net. However with mains potential on the same board there is a potential problem having zero volats DC close to 240v AC. I can set the area up for the copper pour to cover just the area for LV components, but have been unable to find any guidelines as to the min legal clearances etc required (not that this will be a commercial product, but there is a chance that one or two mates might want one). I've included cut outs to prevent possible cross over where possible, but would welcome any constructive comments.

Here's a screen capture of the board layout
 
If I recall correctly the required minimum clearance between a mains-voltage conductor and any other conductor is 3mm.
 
hi malc,
Look at pages #8 and #9 on this PDF.

E
 

Attachments

  • PCBDesignTutorialRevA[2].pdf
    384.9 KB · Views: 437
Look at:

IPC2221A: Generic Standard on Printed Board Design.

UL61010-1: Electrical Equipment for Laboratory Use.

UL60950-1: Safety of Information Technology Equipment

Here is a opto isolator that I use to get information across from the power line. The top picture meats clearance and creepage but the pads on the PCB will not so I use the "spread lead" version. (bottom picture) Now the pads will meat power line to (safety low voltage ground) requirements. OR I use the top package and rout a slow under the part but that cost money.
The line to line distance is not as critical. A spark will pop the fuse.
The line to ground distance is critical. A spark will kill some one.
upload_2015-11-4_6-49-19.png

You could look at any UL, CSA, VDE power supply. Look at what they do for a barrier between the power line and output. I usually put down a 6mm side silkscreen trace to remind me to keep out.
I use "Reinforced insulation" for line to safety ground, 6mm.
I use 3mm "basic" from line to line, 3mm.
Clearance+Creepage+Table.JPG

You could use 1/2 of my distances if you don't have to fight with UL, VDE, CAS.
 
Thanks guys for the feedback. I've slightly increassed the distance of the live and earth tracks from the pads of the terminal blocks. I also have isolation slots in the board to keep the mains and low voltage apart. I might not bother with a ground plane, as it might look odd, and be of no real advantage.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top