Mains Voltage on Strip Board – Safety Guidelines


I need to prototype something quickly as a proof of concept. Is it safe to use mains (UK 230V) on stripboard? It will be going to a transformer so I can control some appliance. Or should I design a custom PCB to do this?

Best Answer

"Is it safe?" cannot be answered as you haven't provided enough information about the use and design of the circuit, nor to what level of safety you intend to respect.

So instead I'm going to answer the question:

How do I safely prototype a 230VAC circuit on stripboard?

By prototype, I'm assuming that the project will only be used for limited duration periods under observation strictly for testing and proof of concept, and is not intended, at this stage and in this state, to be provided to laypersons for use.

You want to protect:

  • The user(s)s
  • The equipment to which it's attached
  • The power line
  • The circuit itself

Some of the things you will want to protect against are:

  • Short circuits
  • Over current conditions
  • Shock hazards
  • Fire hazards
  • Damage to the circuit and other connected devices

You're already protected from most shorts, over current conditions, and fire hazards with the use of fusing built into the plugs you are likely to use in your location. If not, make sure you have appropriately rated fuses in your power supply. As you've given limited information about the circuit itself and what it connects to, I cannot offer much advice on protecting the circuit and device it's connected to. Further, none of these are affected by the use of stripboard or a custom PCB. They have more to do with the design and use of the circuit than the method of manufacture.

The main issue here seems to be whether the use of stripboard is safe for high voltages.

In short, yes, it's fine - particularly for prototyping purposes as described above.

In long:

The breakdown voltage for air is about 3 megavolts per meter. A 230VAC line is given in RMS voltage. The peak to peak voltage is actually about 325V. At 3MV/m breakdwn, 325V may bridge gaps of about 0.1mm. This means that under general operating conditions, the gap between adjacent strips in a stripboard is more than sufficient to maintain the potential without shorting or sparking.

If the prototype is meant to pass HI-POT testing, which CE and UL require, then you will need to guard against 3kV or 4kV power spikes as well. This means you'll need a 1mm to 1.4mm gap between adjacent strips - some stripboards have sufficient gap, some don't. You'll have to examine the board itself and its specifications to find out if it meets that requirement. Alternately, you can use insulating epoxies over the tracks and anywhere these lines come near each other as long as the epoxy is rate for greater breakdown voltages than air.

If the user is to come into contact with the circuit or any buttons, case, or attached parts, the user must be further insulated from the AC line. Most devices simply use plastic and never permit the user to come into contact with any metal parts. Any exposed metal parts are generally grounded, and depending on the requirements devices with exposed metal parts may be required to have a GFCI inline with the power cord.

So make sure the prototype is suitably enclosed, and any user interfacing or accessible parts are insulated from the power lines.

Lastly, if your circuit has an isolated low power section (for instance microcontroller control, etc) then you should have similar separation gaps between the isolated circuit and the power circuit. Again, 1mm may seem small, so it shouldn't be a problem, but I prefer even larger isolation in prototypes simply so testing and debugging is easier and safer.

If possible, use an isolation transformer during all testing - it will save you a lot of headaches, and a few hazards.