PSU Earthing

[tflnemesis]

Hi All,

Need some advice please.

I have an old 12V 6A PSU that I am wanting to repurpose as a permanent supply for a small project.

The mains power lead on it is dual core and the unit is double insulated according to the legend on the front.
The mains lead is also 9 inches long, far too short for what I need so I am going to replace it, I have available dual and tri core mains cable.
My question: can I use the tri core and earth the case (full metal case) and if I can SHOULD I earth the case?
I am going to be drawing approximately 3.5-4A from the DC side.

Thanks in advance!

 

[EBME2]

If it’s a reputable make and designed as double insulated then it doesn’t need an earth. Personally if you are opening the case I would earth it, but if you are just joining onto the bit that sticks out because the unit is sealed I would leave the earth not connected.

 

[voipio]

If using a metal case, then the case should be earthed.

https://www.bbc.co.uk/bitesize/guides/zwwnb9q/revision/4

 

[WorkshopChris]

If the mains side is of double insulated construction the case should not need to be earthed.
It all depends on the design of the PSU.
If it's of reputable manufactures construction then I wouldn't, and if it's of doubtful origin then you probably shouldn't be using it anyway.

 

[tflnemesis]

It's a .Lab Craft model 1282 MKII

Thermally protected double insulated.
I have the case open atm so I can solder in the new cable and whilst I had it open I thought I would ask about the earthing.

I have previously used this PSU for electrolysis rust removal.

 

[brightspark]

It's a .Lab Craft model 1282 MKII

Thermally protected double insulated.
I have the case open atm so I can solder in the new cable and whilst I had it open I thought I would ask about the earthing.

I have previously used this PSU for electrolysis rust removal.

don't earth it if its double insulated no point. some folk have it in there heads it must be earthed. the silly season for bonding everything metal in sight stopped 10 years ago thank god

 

[voipio]

The question is then, is the power supply itself plastic cased and, if so, does the mains wire go into and terminate inside that plastic case? Furthermore, if a mains wire comes loose, can it touch the metal case?

 

[tflnemesis]

Its a steel case and comes apart much like a computer PSU, all wires inside are soldered into place.

 

[voipio]

That tells me the double insulated reference means the output is double insulated, but the mains input could not possibly be. It means the output doesn't have to be tied to earth in use.

But the input is a different kettle of fish. If something happens to displodge the mains cable, maybe an accidental something in the workshop falling on it, what then? The frayed end of the mains cable would likely touch the case. If the case is grounded, the circuit breaker trips or fuse blows, and it fails safe. If the case is not grounded.......

Put it this way, the UL (Underwriters Laboratory), or TUV, wouldn't allow a manufacturers product to be on their list if it wasn't earthed.

It would also fail PAT testing, and couldn't be used legally in the workplace.

See also: https://en.wikipedia.org/wiki/Electrical_safety_testing