220v outlet with 110v extension cord

[n2ocharged]

Good Day, everyone, I came across this forum and thought this would be the place to ask my questions...

I am not an electrician but I have a decent knowledge base, my mother was a certified electrician most of my life but has been out of the game for many years now. What I am trying to accomplish is running a 220v 30 amp circuit to my garage but use it with 110v devices.

Scenario:
I would like to make an extension cord (10-2ga), and have a 125/250v plug (Leviton L14-30p) on one end to connect to the outlet and a receptacle (Leviton 5-20R, i'm only using the leviton name because that is what is at the big box store) on the other end to plug my tools into it. The wiring going from the panel to the plug would be 10-3 to support a 30 amp circuit. While I don't plan on pulling 30 amps, I want to have enough capacity to power multiple tools at once (IE: 110v welder/Plasma cutter and an air compressor at the same time). This would double as a 220v vehicle charger in the future (not while other stuff is plugged in)

My question is this: Would there be anything preventing me from "legally" making this cable/setup? I cannot find anything about it while doing an online search. I know there are "Generator Cables" (see image) that do, essentially, the same thing but I don't know if everything will fit together or if they are wired "correctly" if I got one of those. What I do know about them is that there is an electrical standard that has to be followed when wiring, so I am assuming the wiring will be correct. I also know there are many twist lock outlets on the market (125v, 125/250v, 440v-3 phase, etc...) and I will be purchasing all of the correct parts to make it work. I know there have been some "questionable" contraptions made, I do not want to be one of those questionable device owners.

I've attached some pictures so you have an idea of what I'm talking about.

Thank you in advance.

 

[Lucien Nunes]

The snag here is that the 5-20 outlet(s) will not be fully protected by the 30A breaker feeding the L14-30. Even if you use large enough wiring to be safe in the event of a fault, the cords and appliances that you plug into it with 5-15 and 5-20 plugs might not be. I don't know how common it is to find such adaptor cords in the US; here in the UK people do sometimes make them (e.g. 32 - 16A) but they don't meet code and are considered bad practice.

Perhaps you could put a small sub-panel in the garage to feed some 120V wall outlets?

 

[n2ocharged]

The snag here is that the 5-20 outlet(s) will not be fully protected by the 30A breaker feeding the L14-30. Even if you use large enough wiring to be safe in the event of a fault, the cords and appliances that you plug into it with 5-15 and 5-20 plugs might not be. I don't know how common it is to find such adaptor cords in the US; here in the UK people do sometimes make them (e.g. 32 - 16A) but they don't meet code and are considered bad practice.

Perhaps you could put a small sub-panel in the garage to feed some 120V wall outlets?

Seeing as you were the only one to reply, I appreciate the advise. After consideration, I have decided to go with a sub panel in the garage that will be able to hold 50 amps using a 6-3 (with ground) and a 50 amp breaker on my main panel. This way I'll be able to break off of the sub panel and run a couple of 20 amp circuits and a 30-amp 220 circuit (Smart/Hybrid/Electric car charger later?)

I may not be an expert but I'm not dumb and that's why I'm asking questions, but if someone tells me my idea is bad practice, I generally don't tend to go that route. However, I tend to go overboard with protection so my extension cords will all be 10awg wire so my breakers will give long before the wire gets hot. That being said, I know the breakers are meant to protect the wire, not necessarily the user.

I appreciate the input.