Mains Voltage on Strip Board

Question

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?

Answer 1

"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.

Answer 2

If you peel the strips off to provide a boundary between low voltage and high voltage circuits (and between live and neutral), reinforce the mains wiring, and use the correct fuse, it will probably be OK.

Use a relay that has the coil terminals at one end and all the switch contact terminals at the other end (for example, Panasonic JW1 series).

Answer 3

Simple answer is no. You should do a custom PCB and check the design criteria carefully.

There are minimum safe distances to be maintained between circuit board tracks for any particular voltage. Bear in mind that 230V has a Peak voltage of 325V peak to peak. If my memory serves, track distances should be 3mm or so. One should check that as that's an estimate. The minimum distance between tracks on stripboard is considerably less than 3mm! It's about 1/2mm.

(Knew someone would have done this already): Creepage distance for PCBs handling line voltage AC?

Answer 4

I have successfully used North American AC mains voltage (120 Vac) on stripboard (we call it "Veroboard"). I consider it safe to do so if you have at least one unused strip between each AC Mains strip and TWO OR MORE unused strips between either of the AC Mains strips and any other circuit.

Note that these conditions meet the minimum spacing specified for clearance. Applying conformal coat allows it to meet minimum creepage distance.

In practice, it seems to work out well. We use screw-type terminal blocks with 0.2" pin spacing. This automatically gives you an unused strip between the pins.

I'll often include Earth ground on the terminal block. Pin order then becomes: (closest to the edge of the board) Live, Neutral, Earth, other stuff, (now towards middle of board).

Do note that the copper strips on stripboard are NOT suitable for carrying significant amounts of current. It's okay for things like AC zero-cross sampling and voltage measurement but NOT okay for handling a 15A load.

Answer 5

As you're in the UK, if you don't want to etch a PCB you could try this product from good old Maplin:

http://www.maplin.co.uk/p/veroboard-copper-dil-stripboard-381x2146mm-fl17t

Slightly cheaper at RS, but remember to add VAT:

http://uk.rs-online.com/web/p/stripboards/1595420/

I believe the manufacturer calls it Verostrip (as opposed to the name Veroboard for their regular stripboard.)

It's basically a stripboard with a track length of just 15 holes, with every track broken in the middle, giving you pairs of tracks of just 7 holes each. The idea is that you can mount DIL IC's on it, or transfer a circuit direct from a breadboard.

The 2.54mm gap in the middle should give you a reasonable separation between live and neutral. Certainly easier than ripping out entire tracks from a regular stripboard as others have suggested.

The short track length reduces the risk of touching a live track, but as others have said, be careful to ensure they can't be touched when in use.

Answer 6

If it's just a quick hack and doesn't have many components, consider using terminal blocks. Less risky than having a stray bit of solder bridging the stripboard.

Answer 7

I wouldn't worry about gaps between tracks - if your board is dry and clean, as little as 1mm is a sufficient gap, so powering two tracks with 2-3 unused tracks between them would be OK.

The real danger here is to have 230V all across the board with no insulation. The probability of something conductive touching the wires increases with their length, make sure to select the shortest lines necessary for the 230V part. You'll have to solder very carefully, especially near the 230V region, and use insulated wires for long connections. Also, I wouldn't put my hands near this thing when it's powered.

PS. Oh, and don't forget to use a fuse just in case! (For best results, the fuse should come before the board, e.g. in a power chord).