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bench power supply not grounded

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Thread Starter

casulica

Joined Apr 17, 2013
5
Hi everyone,

Maybe its just a stupid question but, hey, I rather ask experienced guys like you than to risk getting a nasty shock!
I just bought my first power supply(ebay cheapo), and just wondering ... Is it safe to use it if its not grounded(it has only 2 prongs), or should I change it to a 3 wire cable with 3 prongs,with the ground wire connected to the metal case of the power supply?

And also the funny thing is that it has 3 output connections , + , ground, and -.
Why would it have the 3rd output connection(ground) when it's not even grounded that damn thing!!!

Thanks!
 
studiot

studiot

Joined Nov 9, 2007
4,998
Can you give us more details?

You say it has a metal case?

But you say the mains supply lead is only two core or has the earth core been truncated?

You say the supply terminals are marked + earth -

Is this correct or are they marked + 0 -?

If it has a metal case it would be illegal in the UK not to ground the that case for safety reasons which would still apply wherever you are.
 
crutschow

crutschow

Joined Mar 14, 2008
38,745
In general, yes you should use a three-wire power cable to ground the chassis.

The ground output pin connects to the chassis. Without a connection to the power line ground, it probably doesn't do much.
 
studiot

studiot

Joined Nov 9, 2007
4,998
Hey guys we don't know enough about this psu.

The actual power supply may be floating and the ground terminal (if it is one) may be to ground the case, perhaps in an equipment rack to the rack ground. It may not be to supply ground to anything!

Bear in mind this is an unknown, possibly second hand unit off Ebay.
 
Stuntman

Stuntman

Joined Mar 28, 2011
222
Few thoughts.

A.) Yes, that is silly that it has a ground terminal yet no ground to your outlet.

B.) A simple continuity tester will tell you if the ground terminal is at least tethered to the chassis. Find a bare piece of metal on the chassis to probe between it and the ground terminal.

C.) In a few minutes, a hacked computer cable could be rewired into the PSU to fix it. Often, the line power wires hook on with solder lugs or 1/4" quick disconnects.
 
MrChips

MrChips

Joined Oct 2, 2009
35,093
Just to reiterate what others have said.

1) Tell us what country you are in so we know what are the AC mains in that country, or show a photo of the AC mains outlet.

2) Tell us the make and model of the PSU and take pictures of the front, back and power cord.

3) Take and ohmmeter and measure the resistance between the GROUND terminal and the metal chassis.

4) Disconnect the 2-conductor power cord and install a 3-conductor power cord with the proper grounded power plug.
 
C

Thread Starter

casulica

Joined Apr 17, 2013
5
Hi guys, I have attached a few photos of the power supply, it clearly shows that it has only 2 wires which connects to the outlet.
A brown (hot) with a fuse in series and blue(neutral), and there is no ground wire.
Also thats why I was saying how funny this thing is because it has an output ground which is connected to the case(it can be seen in the picture) but the power supply itself is not grounded!!!

And btw, I live in Canada.
 

Attachments

MrChips

MrChips

Joined Oct 2, 2009
35,093
That PSU would not meet CSA approval.

The power switch is wired incorrectly.
Rip out the 2-conductor cable and install a 3-conductor cable:
BLACK - LIVE
WHITE - NEUTRAL
GREEN - GROUND

BLACK - FUSE - SWITCH - TRANSFORMER
WHITE - TRANSFORMER
GREEN - CHASSIS

Put some heat shrink tubing over the fuse connections.
 
MrChips

MrChips

Joined Oct 2, 2009
35,093
Yes. But just as important, you have to rewire the power switch.
The switch goes between the fuse and the transformer.

Also, put some heat shrink tubing over the switch connections.
 
studiot

studiot

Joined Nov 9, 2007
4,998
Put some heat shrink tubing over the fuse connections.
Click to expand...
Yes, Mr Chips is correct this unit dangerous, and his advice sound.

The above is an often missed point that it is part of the wiring regulations that any conductor at live potential (eg the end of the mains fuse as shown) must be covered so that it cannot be touched.
Don't only insulate the fuse terminal, make sure there are no other mains voltage bare conductors accessible inside the box.

From the photos there would appear to be adequate spacing between conductors for the potentials involved.

ok, so should I change it to a power cord with 3 wires and connect the ground to metal case?
Click to expand...
Yes

From what I can see there is a cable retainer at the entrance to the case. This must be maintained.
Also the earth wire must be the longest of the three so that if the cable is yanked then the earth will be the last wire to separate.

go well and safely
 
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