Can a switching 12v power supply somehow malfunction and give me 120v it's plugged into?

Thread Starter

drbuck187

Joined Aug 15, 2019
10
I use a switching power supply, similar to this:

1608689966094.png
It is in my shower along the ceiling powering a, say 6' strip of LEDs. It was plugged in a GFI outlet in my bathroom, away enough from the shower. It did a good job lighting and I was happy with it! BUT my apartment was inspected and it I did not pass because it was said it could shock me with 120 somehow!! I don't think this is possible; is this possible? Thanks!!
 

dendad

Joined Feb 20, 2016
3,835
These 2 pin plug packs do not have a protective Earth connection and a lot are, shall we say, less than ideal in their design?

Using a power supply , particularly in a potential wet area, one needs to use a well designed and Earthed one.
Just as a test, if you have a multimeter, plug the power supply in, power it up and then measure the AC voltage from the output to a good Earth.
It may be quite high.
Then, this may be a good one. I'm not sure I would trust it.

Have a look at this...
http://dismantle-it.com/dangerous-chinese-travel-adaptor-4-2volt/
 
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Thread Starter

drbuck187

Joined Aug 15, 2019
10
Really? I would think that because it's in a GFI outlet and is a switching P/S it would be protected enough! What is the test you said going to prove either way? Thanks!!!
 

dendad

Joined Feb 20, 2016
3,835
Really? I would think that because it's in a GFI outlet and is a switching P/S it would be protected enough! What is the test you said going to prove either way? Thanks!!!
It SHOULD!.
But there are many cheap junk power supplies on the market (I've seen lots) that do not have enough separation, both physical and electrical, between the mains side and output side.
Good ones have no primary tracks near the secondary, and a slot cut in the PCB to "widen" the spacing, as well as very good insulation between the transformer windings. Cheap bad ones often have none of those.
A protective Earth connected to the 0V side of the output is a good safety measure as any leakage will go to Earth via the wires and not via you. And trip the Earth leakage relay that I hope your house has installed.
 

kaindub

Joined Oct 28, 2019
69
You need the inspector to be a bit more specific, assuming the inspector is someone with some sort of technical qualification.
The plugpack you show has the double square symbol, which means the plugpack is double insulated. Assuming it has actually Meets the requirements of double insulation, and there is nothing to suggest otherwise, then there is no chance of bridging between the mains supply and theoutput under any circumstances.
 

bassbindevil

Joined Jan 23, 2014
158
There are a some that have no isolation at all, according to a teardown on YouTube. It would be safest to use one that has really passed safety standards, meaning it came with a brand name product purchased locally, and is rated for damp locations.
Or just rig up a battery and recharge when necessary.
 

kaindub

Joined Oct 28, 2019
69
You can tell your inspector that the outlet location doesn't meet code.
This seems to be the reason for the fail. I am not familiar with USA electrical codes, but here is Australia all power outlets and light switches in a bathroom need to be a prescribed distance away from a wet source.
Looks like,e your going to need an electrician to fix it, and a contractor to patch the wall
 

anniel747

Joined Oct 18, 2020
1,059
This seems to be the reason for the fail. I am not familiar with USA electrical codes, but here is Australia all power outlets and light switches in a bathroom need to be a prescribed distance away from a wet source.
Looks like,e your going to need an electrician to fix it, and a contractor to patch the wall
I think it's a worldwide thing to put electricity far from your shower or bath.
 

djsfantasi

Joined Apr 11, 2010
7,693
Yeah, I can do that, bring me a 100' extension plus lots of tape and hotsnot glue.
Or install an outlet to code with a 10’ cord.

I’d be glad to bring that to you. But I think that’s not what you need. I think you need a few feet of zip cord, some heat shribk tubing and a plug from your local hardware store.

Railing against your local inspector isn’t going to help you. Working with him to agree on a simple solution (29’ of zip cord) I’d what you need to accept.
 
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anniel747

Joined Oct 18, 2020
1,059
Or install an outlet to code with a 10’ cord.

I’d be glad to bring that to you. But I think that’s not what you need. I think you need a few feet of zip cord, some heat shribk tubing and a plug from your local hardware store.

Railing against your local inspector isn’t going to help you. Working with him to agree on a simple solution (29’ of zip cord) I’d what you need to accept.
If my local inspector was incompetent as the one of the OP, I would make sure he gets expulsed within hours.
 

MisterBill2

Joined Jan 23, 2018
8,760
If the GFCI is working properly you can get a shock so small that you don't notice it. That has happened to me several times. A power tool would develop some leakage current that had to be passing through me because there was no other path ti ground, and the GFCI would trip and I would reset it and keep on working.
So a shock that is so weak that you do not notice it is not a danger.

I know that a bunch of folks chained to fear will jump all over me but that is how it is.

And the inspector actually delivered a big uinsult by asserting that the TS was so stupid as to grab a string of lights while standing in the shower. Really. If the string of LEDs is adequately mounted and above the water spray and you do not touch them how are you going to get a shock? And that is presuming that the switcher power supply is one of those non-isolated ones that some folks assert are all around us, but I have never come across.

Of course, being a government person the inspector would not think, but only recite a script. That is the government way.
 

dendad

Joined Feb 20, 2016
3,835
And that is presuming that the switcher power supply is one of those non-isolated ones that some folks assert are all around us, but I have never come across.
All the power supplies I've come across were isolated. But a lot of them have been cheep knockoffs, even with the "official" certifications printed on the label. And, here in Oz, we have 240V so the insulation is under more stress than for 110V.
Also, I would hope the LEDs were in a waterproof housing.

Recently, I purchased a couple of EBAY circular LED lights for replacement of the flouro tubes in our kitchen and dining room. When they arrived, I had a look at the 240V LED drivers included.
They are still in the boxes in my shed. They will not be installed until I get some new LED drivers that are really up to spec.
 

Thread Starter

drbuck187

Joined Aug 15, 2019
10
Thanks for all the replies! When installed (like I had it for 10 months or so but then had to take it down...), the light go along the ceiling, well out of waters way, so no real shock hazard UNLESS they somehow fall while I'm showering!! (there's always a chance!) I'M ASSUMING the inspector was thinking the shock hazard would be from 120, not the 12, but I dunno!! Yeah the outlet placement isn't the best (really at all...Just on the other side of my mirror would work...)...I now see the P/S is UL rated!! Lol It's been a while (like a month and a half?) so I don't think he cares. I got a letter saying it didn't pass and will be inspected again on like 12/9 but no one ever came or anything...Thanks for the replies again!!
 
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