Connecting FG on the PSU

I’m building a small skiff and got me a compact Tracopower PSU. These are apparently pretty good and smaller than then Meanwells. Reading through all the documentation it says that I have to connect the Earth wire (from the mains) the the FG (Frame Ground) point on the PSU, which totally makes sense… unfortunately there is no such thing as a FG point on the PSU.
The terminals are: 1&2 (L and N connectors) PE (earth connector) and then the output connectors (ground, +12V and -12V).
Anybody knows what I should do?

It’s either the Earth wire, or quite possible the leftmost screw on the case, thereby representing frame ground… I’m guessing that you could just solder it onto the case somewhere, but crimping a cable shoe onto the (split) earth wire, and connecting that to the bolt on the frame seems like a solid idea…

So basically you’d suggest that I split the earth wire and connect one end to PE and the other to the screw on the frame? Sound logic to me.

Yup, that’s what I would do :slight_smile:
Can’t find any reason not to, as long as stuff is sort of done properly, which I expect every member of this forum to do (Well, maybe except Frank :wink: ).

Hahaha! :smiley:

As you might have noticed i always chime in into a good joke, even if its about me.

My humor stops when it comes to Mains Voltage.

Dont split the “Schutzleiter” - the yellow-green cable. It must be connected to PE. The blue and brown go to the other 2 Terminals and it doesn’t matter which where as this would change if you plug in the jack 180°.

always very reassuring that other people know as little as i do, and still go and fiddle with AC mains wires. :wink:

Maybe two questions to clarify: Is the earth wire from mains (within the psu) connected to the ground wire for the +/-12V? Is this one and the same ground (I recall seeing a schematic somewhere where they are actually connected).

And, second, is it always necessary to use the mains ground wire. For example, my doepfer power supply (from the DIY kit) has no connection to mains earth (two wires only).
I was wondering whether also the MeanWell could be connected without mains earth? The reason i ask: there are a lot pre-configured cables available (for lamps), wired with switch and plug, and I thought about just putting a cable gland on a case and using on of these. It would minimize any interaction with the cable (the ends can be screwed into the Meanwell connectors very conveniently, nothing is exposed, and the cable gland protects the cables from being yanked out). It seems like a safe solution. BUT: these preconfigured cables are available with two wires only, no earth.

@fcd72: Ok then you suggest that I just ignore the whole FG thing? The rest is totally clear to me. The way I did it on the other case is exactly that. green cable to PE and the other two to the AC terminals. And yeah, I’ve always ignored polarity since in Europe we have connectors that fit in both ways…

@morcego: I’ve got the Doepfer DIY PSU too and that one is different afaik, since it has an external power brick that transforms the AC mains to 12VDC, the PSU in the case just creates the -12V I think. so the two cables going to the case are just+12V and GND
I would attach the earth connector, you can just use any PC PSU cable (with the 3 connectors) to power the modular, these are easy to find and usually you end up having spares (at least I have a bunch here).


yeah of course. Earth is not ground, that’s one thing I know :slight_smile:
In Italian it’s called “put to earth”, which explains pretty well what it does. In DC voltage current flows from the GND to the potsitive voltage (or was it the other way around) in AC is alternates between the two poles, but it does no flow to the mains ground as far as I know. well if did a normal connector without the earth tip (just to pins) would not work, but most table lamps have such a connector and they work fine :slight_smile:
So yeah I know the difference between the mains earth tip (how is it called properly?) and the DC ground.

but still the question here is what the FG connector is. FG stands for Frame Ground and is a security measure, should for some reason some current end up going to the metal frame of the PSU… but there is no FG connector…
The manual says “protective earth” (that’s the green-blue wire afaik) must be connected to FG".

But I’m starting to thing that FG and the PE (protective earth) connector are the same… though I’ve read somewhere that the FG connector usually is connected to the frame via a cap.

ok, i guess I will not connect them. never ever. (but I am pretty sure I have seen instruction where they recommend connected the mains ground to the case (as in frame ground above). However, also the low voltage ground is connected to the case (implicit, via pots and jacks), so they do seem to make contact sometimes.

@rumpelfilter: i meant that the doepfer psu has no connection to earth mains at all. Already the external power brick only uses a 2-pin mains plug. I wonder whether you can do the same with the MeanWell, just not connect to earth at all?

And yes, i could likewise use a 3-wire cable, of course, just take a spare PSU cable and cut off one end, but then I have to strip insulation and all that. These pre-configured cables come with everything ready and nice metal rods at the end that goes into the MeanWell PSU.

But no experiments with MeanWell yet, anyway, still using the doepfer kit and have build the synthrotek psu. Might not be the best, but at least i do not electrocute myself using it.

FG=PE it’s a safety feature

With any metal framed device, the metal case is connected to the earth in case of a catastrophic short so it will go to earth instead of you (along with some shielding benefits). With a non-conductive case, it’s a moot point.

The earth ground in a AC power grid is really there for safety, you dont really ever use it for a circuit since just about everything coverts to DC in the device itself where the ground potential is based on the AC waves, not the actual earth

It is sometimes suggested to connect the PE terminal (green-blue wire in EU) to the metal parts of the frame so any voltage that gets incidentally into the frame go down to the earth conductor, which is the main purpose of that wire afaik.

My Doepfer power brick has a German SuKo plug, i.e. is has a PE connector.

There is no advantage in not connecting PE, also the PSU will work normally, but if things go wrong you have one security measure less. means it’s more likely that you get an electrical shock and good bye.