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

Thread Starter

drbuck187

Joined Aug 15, 2019
14
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
4,110
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
14
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
4,110
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
93
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
373
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
93
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
 

djsfantasi

Joined Apr 11, 2010
8,256
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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MisterBill2

Joined Jan 23, 2018
11,588
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
4,110
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
14
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!!
 

K OBrien

Joined Nov 28, 2020
14
There is that case of the Navy Guy electrocuting himself with a 9 volt battery when trying to measure his own internal resistance. The muscles in a wet body might very well be triggered by a 12 volt potential. Even a fall due to a shock can cause injury. You say the lights could fall. I would call that dangerous since a bathroom is not really the kind of place where temporary lights like on a Christmas tree are usually used. The US electrical code allows for class two wiring (no need of boxes for splices) of under 24 volts and 100 VA like the doorbell or a low voltage thermostat. Your LED wiring would fall under that exception. I put a nice 12 volt LED fixture in my camp trailer bathroom for shaving. The trailer has 12 volt DC for lighting to begin with. Did the inspector put in a small device in the GFI receptacle to test your GFI? Even a properly wired GFI will shock you and if improperly wired will not operate properly. My advice is do a good workmanship like job that won't fail and you won't have a safety hazard.
 
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MisterBill2

Joined Jan 23, 2018
11,588
I am wondering about what is the specific complaint about the 240 volt drives for the circular kitchen lights that Dendad does not like. I know that there have been some that produce a whole lot of emitted RF radiation, and the noise is far above legal limits. So it will be educational to know the brand and the complaint.

AND, @kob, the TS did not say that the lights might fall, but rather that falling would be the only way contact was possible, since the were above normal reach. Many of those standards are intended to protect the dumbest 2% of the population, while getting in the way of the 98% who would never have a problem. It is a very diligent effort to thwart natural selection.
 
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dendad

Joined Feb 20, 2016
4,110
I am wondering about what is the specific complaint about the 240 volt drives for the circular kitchen lights that Dendad does not like.
Here are some photos of the LED driver I was referring to.

LED_Driver3.jpg
This case is about 68mm across. But the board inside is quite small...
LED_Driver1.jpg
It is 38 x 17mm.
LED_Driver2.jpg
This shows my main concern. The clearance between the 240VAC input and the output was my initial worry, but that is moot as this LED driver is not isolated!
Also, I'm not confident the LED ring insulation is up to it. The LEDs are on an Aluminum ring and as the original lamp fitting is earthed, I doubt it would stand the voltage to Ground with sufficient overhead.
LED_Ring.jpg
Although it may tecnically work ok, it is not going to be installed in my house without extensive mods to isolate and cover the parts for safety sake.
I should get my Megger out and test it but even if it has a sufficient insulation breakdown voltage, I do not like the idea of a non isolated power supply going into a lamp fitting that has a removable cover.
 

MisterBill2

Joined Jan 23, 2018
11,588
Ok, this power supply is probably not isolated, and it would not get the UL tag. It might not even meet code in rural Mexico. But there are parts of the world where it would be quite acceptable, and would not have any stgatistical effect on the rather short average lifespan. If it could be securely mounted in an adequate manner in an adequatly grounded steel enclosure, Then it might be OK, except that it does not appear to have any interference filter components.
 
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