I'm working on a thing in which I mount a few pounds of weight to one of those light-bulb-to-wall-socket adapters and I'm curious if there's a posted weight limit on hanging something from just the light bulb socket itself.
This is not really for a home improvement thing; it's a work project, but the application seems relevant to this stack's topic.
Not a great idea.
Electrical devices are designed and approved to be used unmodified. Adding parts or using them other than as intended voids the UL listing and, more importantly, poses risks of fire or electrocution.
Attaching something to a plug in device at or near the plug runs the specific risk of shorting out the spade terminals, risking the above noted fire or electrocution.
The weight that could be supported (but shouldn't be) would depend on whether the plug in socked was inserted horizontally or vertically (hanging down), the latter being much less reliable than the former, which is also not reliable.
The actual strength of the hold is a factor of the tension created by the contact points within the wall socket itself. This is variable across brands, types of outlets, and changes over time and usage. It is impossible to predict whether a socket will hold a regular plug, let alone extra weight attached to a device that already puts a downward strain on the grip. Another reason not to do it.
Finally, plug in lamps are varied in their quality and hence their strength, again making a load prediction nigh on impossible.
Don't do it.
The National Electrical Code is quite specific about the listing requirements and the weight of a luminaire attached to the screwshell of a lampholder. Which is what your question indicates.
Here are the pertinent sections:
410.6 Listing Required. All luminaires and lampholders shall be listed.
The definition of listed follows:
Listed. Equipment, materials, or services included in a list published by an organization that is acceptable to the authority having jurisdiction and concerned with evaluation of products or services, that maintains periodic inspection of production of listed equipment or materials or periodic evaluation of services, and whose listing states that either the equipment, material, or service meets appropriate des-ignated standards or has been tested and found suitable for a specified purpose.
UL (Underwiters Laboratories) and the CSA (Canadian Standards Association) are two examples of listing agencies that are normally acceptable to the AHJ. But they are not the only listing agencies in the world.
IV. Luminaire Supports
410.30 Supports.
(A) General. Luminaires and lampholders shall be securely supported. A luminaire that weighs more than 3 kg (6 lb) or exceeds 400 mm (16 in.) in any dimension shall not be supported by the screw shell of a lampholder.
So, field modified or home made luminaires would normally be considered a violation of the NEC.
You should find a different way to do this especially in a work environment that would expose the company to liability.
You are not allowed to use an electrical product in any way contrary with its labeling and instructions.
You are also not allowed to use any electrical equipment as a support structure for ”something" e.g. Anything else. The most common blunder is hanging phone, internet or thermostat cable off Romex or conduit. I just removed some of that from a brand new furnace installation. But it also applies to using a light socket or junction box to hang a mobile, pinata, model airplane, etc.
A luminaire (light fixture/assembly) is the exception. It is allowed to hang a luminaire off a junction box, if it weighs less than six pounds. This weight can also be hung off an Edison screw base in USA (NEC 410.30A), but that seems unlikely -- far more likely you would mount it to the junction box.
A heavier luminaire can be hung off a special junction box made for that purpose.
An even more special junction box is made for ceiling fans. A common violation is hanging a ceiling fan from a ceiling box which is not listed for ceiling fans. Aside from the unexpected weight, the problem is also vibration - I've never seen a fan that was balanced, and the vibration will eventually pry the nails out or crack the box.
The question of "leeeegal" gets super pedantic super fast due to the complexities of (especially US) law, and quickly devolves into "what do I think I can get away with" - this amounts to trying to make a simple thing complicated, with a motivation most foul: trying to cheat safety. So let us cleave this Gordian knot with a more basic question: Is there any competent regulatory agency in the world which on fair contemplation, chooses to explicitly authorize general use of electrical equipment contrary to its listing, labeling and instructions? I assert you will not.
This is crazy, don't do it. Don't even ask whether it may "work".
If I understand "light-bulb-to-wall-socket adapter" corrently, you are planning to screw something that isn't anything like a lightbulb into one of these and expect it to carry a weight. At work, to make things worse.
First, is it immediately obvious that this isn't the greatest idea ever. The adapter is neither meant/designed to be used that way, nor approved (on the contrary!), nor likely to function reliably as intended by you. Also, the mere mention of "high voltage" should raise a red flag in everybody's head, even without the explicit absence of proper grounding or safety breakers such as is necessary for anything that has a conductive surface and is connected to high voltage of sorts.
Second, even assuming that you don't care much about the previous paragraph because, hey, what can happen, and your boss said it's OK... you are (intentionally) violating workplace security. If nothing else, this can mean major trouble involving a big-$$$ fine for your employer (and you being fired) in case of an audit. It can also mean that the casualty insurance may refuse to pay in case someone gets hurt directly or indirectly by, or only just nearby your thingie. The workplace as such is not approved with such an unapproved construct at it or nearby. That's a huge thing.
Third, you are personally liable (civil action) in case someone gets injured or killed at your office, or in case the whole shit burns down. Do you really want to discuss about regress on a 2-digit million sum with a fire insurance?
