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This question reminded me that when we bought our house, I found the previous owner had taken the dryer's 220v circuit and continued half of it from the 220v outlet to make a 110v circuit for the rest of the garage.
The 220v outlet still powered the dryer.
Even as a new naive home owner this struck me as probably incorrect and had it fixed when we upgraded the panel.
Can you explain the specific reasons why this was bad - and what code it breaks?
Other than what @ArchonOSX has pointed out as code requirements. Adding receptacles added on to a dryer circuit is just not considered good electrical practice.
Consider how you started your question "previous owner had taken the dryer's 220v circuit". You called it the Dryer's circuit. That means the original circuit installed is a specific circuit designed to service a dryer, not a dryer and anything else we can stick on it. Depending on what you put on the circuit, it could create an imbalance (impedance) between the two phases and directly affect the life of both the circuit and piece of equipment. I also have a question about what your overcurrent protection looks like since most branch wire is protected by 15A and 20A breakers. To add devices that should be protected by these breakers to be attached to a 30A breaker would they have to meet a whole new set of requirements. By the way if you have a problem with your dryer and call for warranty repair and the service representative sees the attached receptacles. He would be in his right to void the warranty.
Some could make an argument that it might not affect the dryer but we don't design circuits around what they might do. We design circuits that we know work.
So best advice install dryer circuits for dryers and add general power circuits for general power.
Hope this helps and stay safe.
The Code problem here has nothing to do with voltages and everything to do with currents. First off, 210.21(B)(3) and the associated table prohibit putting a 20A receptacle on a 30A branch circuit. In addition to that, you can't run a receptacle off a tap conductor, as this is prohibited by 210.19(A)(2) (as well as being excluded by the list in 210.19(A)(4) exception 1):
(2) Branch Circuits with More than One Receptacle. Conductors of branch circuits supplying more than one receptacle for cord-and-plug-connected portable loads shall have an ampacity of not less than the rating of the branch circuit.
If you read my answer to that other question you cited and read the National Electrical Code carefully, you will see that your case was NOT necessarily a Code violation.
There is an exception that allows line to neutral loads and line to line loads on the same Multi-Wire Branch Circuit as long as the circuit breaker opens all ungrounded conductors. A double pole breaker satisfies this requirement.
210.4 (C) Line-to-Neutral Loads. Multiwire branch circuits shall supply only line-to-neutral loads.
Exception No. 1: A multiwire branch circuit that supplies only one utilization equipment.
Exception No. 2: Where all ungrounded conductors of the multiwire branch circuit are opened simultaneously by the branch-circuit overcurrent device.
However, single pole breakers with a handle tie do NOT satisfy this other section of the Code.
240.15 Ungrounded Conductors.
(B) Circuit Breaker as Overcurrent Device. Circuit breakers shall open all ungrounded conductors of the circuit both manually and automatically unless otherwise permitted in 240.15(B)(1), (B)(2), (B)(3), and (B)(4).
(1) Multiwire Branch Circuits. Individual single-pole circuit breakers, with identified handle ties, shall be permitted as the protection for each ungrounded conductor of multiwire branch circuits that serve only single-phase line-to-neutral loads.
Additionally, you stated the previous owner continued the 120 volt circuit
for the rest of the garage.
There is a Code requirement that prohibits the garage circuit from supplying outlets outside the garage. Since you stated the rest of the garage I concluded your dryer was installed in the garage. Therefore you could use the double-pole breaker exception cited above.
I would agree it is better form to have those circuits separated but the Code allows it if someone so chooses.
Hopefully, this post helps advance the understanding of this particular section of the Code.
