Piface / Relay / Voltage and current limitation

Hi Damien,

I've not seen the board, but generally the PCB tracks and clearance may not be sufficient to switch larger loads. Basically, it could be hazardous to the user and cause damage to the board and attached hardware too.

When switching mains loads, there are many precautions (enough to write a book basically).

Hi,

Thank you for your answer.

The clearance between the tracks is about 16 mils (Voltage can be up to 250V, the board is varnished) and the tracks width is about 100 mils (Current can be up to 5A)...

And for the connector, the rated current is 6A and the rated Voltage is 250V... So I don't understand why 20V - 5A and not 250V - 5A ?

I control a Led Tower, like that :  https://www.google.be/search?q=Led+tower&hl=fr&source=lnms&tbm=isch&sa=X&ei=HThlUb3EOtHSsgbk_YCQDA&ved=0CAoQ_AUoAQ&biw=1920&bih=958#imgrc=TGol6GTzjRSBZM%3A%3BDrBBEHpWr6KbVM%3Bhttp%253A%252F%252Fimg.directindustry.com%252Fimages_di%252Fphoto-g%252Fled-tower-light-53616-2841149.jpg%3Bhttp%253A%252F%252Fwww.directindustry.com%252Fprod%252Fpatlite%252Fled-tower-lights-53616-356554.html%3B794%3B678 and the voltage is 240V (the current is pretty less than 5A) so I just need to know if it's OK ?

Many thanks.

Hi,

It's definitely not ok, 16mil is tiny. There are many other things to take care of, like when a wire breaks, can it touch anything else?

Screw terminals may have different precautions too, e.g. separation, size of barrier between terminals. There is also separation from the

board below to consider, and heating. The board may even move and touch the board below if it's just secured by a header.

There literally is a books-worth of things to check, including materials used. I wouldn't be comfortable to state that it is ok.

You could wire to a separate off-board SSR and thus keep mains off your existing board, and enclose in a box with IEC connector

with fuse and switch and thus begin to make it acceptable as one approach, or find a product that already controls mains and has a

safe interface (e.g. there are network-controlled mains switches, although they may be expensive; cheaper methods for home use

probably exist too, I seem to remember there was a home automation method called X10? I've never used it and am not really familiar with

it, but it may be worth investigating).

In summary, if you can find a way to keep mains off the board (e.g. a separately wired plugged-in relay mounted at a distance) then this

can help make it safer, or alternatively try to use an additional product such as the network-controlled switch or X10, etc.

If you go with the separate relay method, then do take care to take precautions like mount it in an enclosure, make sure no live parts

can be touched by fingers, make sure that even if the cable is tugged nothing can cause a short, and so on

The IEC connector with built-in fuse and switch is a great option to get your mains into the enclosure safely.

Just as a disclaimer legally you're still on your own with this method (I don't know the legislation in your area), but just as an opinion

it is safer than having the mains on the existing board.

I'm sorry, the terminal support 250V, I said the connector but it's the terminal.

About the clearance, i'm not agree with you, look at this : http://www.electronics-project-design.com/PCB-Design.html   in the "PCB Design Electrical Clearance" section. Any calculator, any books, etc, tells that it's ok with 16 mils (I speak about a coated PCB, not an uncoated one).

- There is no danger with the board below (the raspberry) and no heating.

- The board can not touch the raspberry, there is a support, not just a header.

I'm not a beginner in pcb design, but here I just not understand why the limitation is 20V. For me, everything is ok for 240V - 5A (not 10, I agree the width is too small).

Thank you for your help

The standard you should most likely be checking is 60065 (not free, and not easy to understand even if it was free, since it is several hundred pages long in terms of detail). So, it can not be possible to confirm the safety by the URL referred to. By the way, the green stuff on the PCB may not be considered insulation by some standards, for good reason.

I'm not sure what you mean by 'no heating'. How do you know what material the DIL header close to the relay is made of, and if it is flame retardent if some part of device got hot (doesn't have to be directly caused by your device). What if the electrolytic on the Rasp-pi board, near the relays went pop? Some of these things may seem unlikely, but it only takes one mistake to cause permanent damage to you or to someone else.

I trust you may play it safe since you have board experience to examine it more closely, but others reading this may think it is safe to connect mains but it isn't. For those, they should pursue at least an off-board relay method or an indirect method like X10 etc.

The off-board relay method isn't bad - not everything needs to be on a PCB. Just ensure you purchase a large enough enclosure, so that you've room to route your cabling from the mains supply or IEC connector to the relay, etc.

Edit:

Found this image of the reverse of the board, from this it is fairly clear why they rated it at 20V.

So, personally I would just wire directly from the board onto an off-board relay, because it would be hard to do it any other way with the existing board.