Code issue would be if 50A is too low for an ATS. With an ATS, powering the full load is required of the generator, or load shedding must drop the load to the rated output of the generator.
Perhaps the AHJ will be understanding. A hardline inspector will likely interpret the ATS (even one manually flipped), 50A inlet combination as a violation. What is the chance a permit will be pulled when the system is revised?
Look at 702.4(B). The issue is with the transfer switch being an ATS. Doesn't really matter whether a generator is hooked up or not when you have a 50A inlet connect to the standby side (I'm assuming the calculated load is greater than 50A). The fact is, the transfer switch is an ATS, which in Code speak is "automatic transfer equipment". Does the transfer switch being manually operated matter?
IMO, no.
You are allowed to shed loads manually. The fact that a portable generator with a temporary hook up is being used means that you have manual transfer equipment even though the transfer switch is automatic.
Code makes no allowance for nonautomated automatic transfer equipment... and I'm only saying this from the position of a hardline inspector.
I'm guessing the transfer switch in question is rated 100 or 200 amps, he just wants to connect a 50 amp (max) source to the "standby" side of the switch, and is perfectly fine if it is an ATS and it can't transfer to more then 50 amps of connected load, or if it is a MTS and the user manually sheds any excess load. No answer here so far to whether you can use an ATS as a MTS
That ATS is not going to transfer just because you connect voltage to the inlet, it still needs additional control wires and a signal from a genset designed to work with the ATS before it will automatically transfer, you won't get that out of a typical 4 wire inlet, you may however right or wrong, rig your own controls that would automatically give it a signal when the inlet is energized. One thing it still won't do is automatically start the generator when power fails, so that means even if you rig it to automatically transfer if inlet has power, you still need operator intervention before there is power to initiate the whole process, unlike a traditional ATS system where it will start the generator and then transfer even if there is no operator to witness anything.
Exactly what happens with a typical manual transfer setup, OP is going to manually connect the generator and manually operate the transfer switch.
702.4 Capacity and Rating.
A service-rated ATS is listed as such. Using it in a manual manner does not change what it is.
