PiFace Home Timeswitch - turning a light on and off

I agree 100% with mark on this one.

Also, just because the relay can handle the 250V at 10A, does not mean that the board it is on can or should, it is all about how the board is designed, built and protected from other things, when dealing with Mains voltages there are very clear guidelines regarding PCB trace spacing. creapage allowances etc that MUST be followed for a module to be certified safe. This includes how it is boxed

in the case of a PIFace, it would never get a CSA or CA or UA etc approval sitting on top of the primary RPI board with nothing more than the connector preventing it from contacting the main board or a finger getting to the high voltage connectors

It is a low voltage design through and through. If there are no warnings on the board then perhaps there should be but there are warnings in the documentation

THERE IS.

This was the whole point of this comment made at the time an element14 staff member did this DANGEROUS project.

I see that despite the promises this has not been updated (Peter did remove the 230v references) and because it has been created by a staffer, you can't report it to the moderator.

Samuel

If I can offer this advice from many years experience.....

It always pays to check and research the subject if you are going to offer advice/comment.

The one thing you have during your career/life is your reputation and credibility.

Both of these are under your control, so treat them well since it's the one thing others can't take away from you.

They may question it, but if the evidence is on your side then its their credibility that gets questioned.

The operation of a light using a relay that is well underrated and used moderately is unlikely to create "    another point of failure.    "

In this particular application it is essential for safety.

Mark

The black catches out so many people here.

Green or Green/yellow is earth and but any other colour is allowed to be phase.

• Not sure about your plugs, but here the earth wire should be the longest, so it remains intact after the rest are pulled.
• The active and neutral wires should not cross over.
• Strain relief is correctly tensioned and not damaging the cable.
• Correct tension on the screw
• Correctly filling the terminal by twisting and then doubling back the wire
• No stray conductors hanging out

So there are 6 things to ensure a plug is correctly terminated ... and then you have the fuse.

there is a 110V on each terminal centered around gnd

Is it simply floating or can you actually pull current

Mark

Earth is longest simply because it is the furthest from where the lead enters the plug. In my school science class we spent more than an hour being taught how to wire a plug and select a fuse. This not including the time spent on the theory about why all this is done.

15Amps either side, used often to power cookers and dryers so effectively 220V at 15A vs 110V @15A, centered around GND so nothing is ever actually much above 110V from gnd

Earth is longest simply because it is the furthest from where the lead enters the plug

Same here, but it doesn't make it last to be pulled out.

It's great you have had instructions, they don't seem to worry here in NZ, which leads to some frightening discoveries.

Peter

That seems a strange system and I'd heard it was floating but obviously not like an isolation transformer floats the 230v.

Can you actually run an appliance at 110v.? Do they use the ground as the return in that situation ??

Mark

yup, there is a wiring technique where if you need 2 * 110V but at full current and uses one twin socket. The ones  here can be split by removing a jumper and then you connect one phase to the lower and one to the upper giving 110V on each but there actually separate phases centered around neutral

on some socket types you can split the bridge between the upper and lower socket

Peter, it would be best not to post such WRONG images. When the voltage is "120V AC" the RMS value of the sine wave is 120V. That means that the top of the sine wave is at around 170V. Pictures like yours perpetuate the falsehood that the peaks are at the rated voltage.

There seems to be lots of "incorrect" images out there.

Its also interesting that it shows the phases as 180 degrees apart.

Here our phases are 120 deg (meaning all three equal 360).

Obviously the load in the neutral (which is often a screen around the phase cores) should be zero, but at worst only carries the current of one phase.

Mark

Yes, the USA has 180 degree out-of-phase system (and 2 phases), while europe has a 120 degreen phase shift and three phases. I don't know what the rest of the world does.

If your wires can carry say 10A, at 200V(*), you can can carry 2kW using two wires. Upgrade to four wires and you can transport 4kW, right? Well, for USA and their system that's true. But with the 120 degree phase shift, you can transport 6kW with those same 4 wires!

That's the advantage of the three-phase system.

(*) I'm using nice round numbers, to ease manual calculations. No relationship with actual real-world voltages or currents implied.

Not my image , I borrowed it and without looking close enough (I saw what I was looking for, not what was correct) but now you mention it, yes I totally agree, when I get home I will create an image of my own and replace this one

Rodger

Very interesting ... thanks

NZ and Australia both use 120 deg and you're right about the power capability.

Most houses here are 60A/phase but are usually single phase at 230v.

Neutral and earth are the same potential (they derive the neutral from the earth at the transformer)

cheers

Mark

Rodger

Very interesting ... thanks

NZ and Australia both use 120 deg and you're right about the power capability.

Most houses here are 60A/phase but are usually single phase at 230v.

Neutral and earth are the same potential (they derive the neutral from the earth at the transformer)

cheers

Mark