Swapped Live and Neutral in power cable

Thread Starter

MrChips

Joined Oct 2, 2009
30,467
I just received a 10A/30VDC bench power supply from China. The PSU works fine.
The power cord supplied with the unit, like the one shown in the picture below, has LIVE and NEUTRAL swapped. This means that if the power switch is OFF or the fuse is blown, the internal SMPS circuitry is still live. Seems to me that this contravenes IEC-60320 C13 code and is downright dangerous.

Has anyone encountered a power cord with this problem?

 

AlbertHall

Joined Jun 4, 2014
12,328
Our electricity board wired the supply to our house like that, bypassing all the fuses in the house. The only protection being back at the sub-station.
 

dendad

Joined Feb 20, 2016
4,426
Years ago, when PCs were new, a mate of mine was selling PCs, and had a new molded power cable that had the Neutral and Earth swapped. All would have worked well enough as the Neutral and Earth are connected together at the house power board anyway. But, he had a home made extension lead that the Active and Neutral were swapped! This put the Active on the monitor chassis.
Fortunately the result was just one blown up new monitor and PC. It is just as well it happened at his place and not at a customer's and someone could have been killed very easily. Oh, and this was before safety switches were the norm.
 

SLK001

Joined Nov 29, 2011
1,549
If your PSU is like a standard SMPS, then neither the hot nor neutral go to any place but the high side of the PS. Nothing is shared directly with the low side. This shouldn't be a problem if they are reversed.
 

WBahn

Joined Mar 31, 2012
29,857
If your PSU is like a standard SMPS, then neither the hot nor neutral go to any place but the high side of the PS. Nothing is shared directly with the low side. This shouldn't be a problem if they are reversed.
But it is a standard power cord that is used on lots of different types of equipment. Many of those, including most bench power supplies and oscilloscopes, have parts of the circuitry referenced to the safety ground wire. At the very least, swapping them invites ground loop currents.
 

DickCappels

Joined Aug 21, 2008
10,122
A few years ago I bought a powerstrip with the same problem. Since it was not a molded assembly it only took a few minutes to correct the error. Related: Most of the extension cords and powerstrips sold here with three prong sockets do not have ground connections. Normal for this part of the world.
 

Jony130

Joined Feb 17, 2009
5,485
But what difference does it make? Where is neutral and live wire? Do you have any standard on which side of the socket the live wire is?
 

cmartinez

Joined Jan 17, 2007
8,177
I just received a 10A/30VDC bench power supply from China. The PSU works fine.
The power cord supplied with the unit, like the one shown in the picture below, has LIVE and NEUTRAL swapped. This means that if the power switch is OFF or the fuse is blown, the internal SMPS circuitry is still live. Seems to me that this contravenes IEC-60320 C13 code and is downright dangerous.

Has anyone encountered a power cord with this problem?

I'm so glad you've pointed this out. I've never looked for this sort of anomaly, but now I definitely will.
This sort of thing could be very dangerous when working with isolation transformers
 

MaxHeadRoom

Joined Jul 18, 2013
28,513
I have seen a Chinese hobby CNC power unit displayed for sale that had output socket for the solenoids etc, the problem was they were made to take the same power end as the OP, but recessed MALE end, IOW the pins were potentially Live!
I see that after I reported it in the forum they were being used in they were withdrawn.
The other issue is that many Chinese origin machines come in without proper grounding or NEC/CEC code requirements.
Max.
 

Thread Starter

MrChips

Joined Oct 2, 2009
30,467
In case you are curious as to how I came upon this issue, I learned from past experience to be suspicious of imported electrical appliances.

A colleague had received some power supplies from Asia. On closer inspection I discovered that the ON/OFF switch was on the LIVE input while the fuse was on the NEUTRAL line. The danger here is that if the fuse blows the circuit is still live.

The fuse must be the first component encountered from the LIVE input (besides any mating C13 to C14 connector) followed by the ON/OFF switch.

With this PSU received yesterday, I opened it and was checking with an AC voltmeter to make sure it was wired correctly. The discovery was that the LIVE input was not live while the NEUTRAL input was the live wire. Thus, comparing with other power cords revealed that the cord connections were swapped. It is interesting to note that the C13 molded female end has L, N, E on the connector and L is not live while N is live.

There you have it.

Of course, many years ago, AC plugs were not polarized and you could reverse the connection by just turning the plug 180-degrees. If your radio or stereo hummed, sometimes turning the plug got rid of the hum. Plugs are now polarized for good reason.
 

WBahn

Joined Mar 31, 2012
29,857
But what difference does it make? Where is neutral and live wire? Do you have any standard on which side of the socket the live wire is?
The difference can literally be between life and death. Consider something as simple as a lamp -- nothing more than a switch in series with a (normal Edison) bulb. The switch is supposed to be between the LINE wire and the bulb so that when you switch it off to change the bulb, if you contact either of the terminals you are either touching a floating wire or a wire connected to the earth. Furthermore, even if the switch is on, the LINE wire is connected to the terminal in the bottom of the socket, making is a bit difficult to accidentally touch, while the NEUTRAL is connected to base, which is very easy to touch. If the two are reversed, you switch off the light but now the LINE is connected to the easily touched base just asking to find a path to ground through the poor shmuck changing the bulb.
 
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