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Considering that power to the pole is single phase and a center tap is used to split power to L1/L2/N 120V, would having a 1:1 center tap primary to standard wound secondary be capable of giving a 240 L1/N Euro style power but at 60Hz since it is sourced from US 60Hz?
Is there some reason in between that would cause such a setup to have issues or cause issues in the supply side of the circuit?
This depends on the equipment.
Setting aside synchronous machines like induction motors that are affected by line frequency, you have to consider the earthing + neutral arrangement in the appliance.
EU standards have the following classes:
Not safe on split-phase. Class O devices only have a single layer of insulation between exposed metal parts and line voltage. If there is a device fault and it's on a split-phase system, the exposed portion will be at 120V or 120V, vs. 240 or 0V if it were on its native EU system.
Even worse, devices that have exposed lamp socket bases that are supposed to be neutral (like the lamp bases of old-school Christmas lights) will always be live when connected to a North American split-phase feed.
These 3-wire appliances are safe on split-phase 120 if there are no exposed neutral points. Again, if it's a lamp with a screw base, nope - the base will be at 120V, not neutral.
Something to verify however: ensure there is no bond between the 240V appliance's neutral and protective earth before hooking it up. I can't vouch 100% for this not being a thing in the EU (I don't believe it is). A 240V appliance sourced from outside of the EU? I’d have no confidence of this unless I were to check it myself with a meter.
What makes me paranoid about this issue is the fact that some North American 120/240V appliances (e.g., clothes dryers) allow bonding neutral to protective ground in the appliance, to be able to use the old 3-wire L5-30R ‘dryer’ plug.
These 2-wire appliances are safe on split-phase, as there is no exposed line or neutral, and in addition have an extra layer of reinforced insulation to protect against faults. Most devices with plastic cases are like these, such as phone chargers.
These 2- or 3-wire appliances are safe on split-phase. SELV devices are powered by isolated supplies, that is, with no galvanic connection to the primary at all, and stringent limits on primary-to-secondary leakage.
Two things to be wary of in 240V land.
First, be suspicious of 240V appliances originating outside of the EU. Many lack a proper CE (let alone TüV) rating. Watch for the ones with the 'China Export' fake-CE marking. More here: https://www.cemarkingassociation.co.uk/ce-marking-and-the-chinese-export-logo/) If you're buying something off Alibaba or Temu, beware.
Second, when using North American split-phase, both 120V legs will have breakers, vs. only the 'hot' lead on a 240V EU-style plug. The 120V breakers are usually tandem but might be separate. In the unlikely event they are separate, it's possible that a device could fault line-ground on one leg, leaving the other leg still live with just the one breaker tripped. This wouldn't happen on an EU system, which would disconnect the 'live' leg, leaving only neutral connected.
A transformer may not be required.
The 240 V 50 Hz equipment is to be connected to L1 & L2 only.
A two-pole MCB is a must as both the lines are live.
It must be borne in mind that motor RPMs will be 20% higher on account of the 60 Hz source.
Caution!
As per IEC 60364, earthing systems (TT, IT & TN-S) require that the 'Neutral' and 'Protective Earth' conductors be kept separated whereas (TN-C and TN-C-S) require that they be combined.
Hence, before powering European 240 V equipment in the US, it should be ensured that its 'Neutral' and 'Protective Earth' conductors are indeed separate.
If that cannot be done, an isolation transformer is a must.
You can simply connect your European 240 V equipment to L1 and L2 - no transformer required.
If you do insist on an isolation transformer, you don't need a center tap on the primary - just connect the transformer to L1 and L2, ignoring the Neutral.
As the question is strictly about having a center-tapped primary for converting 120V-0-120V with L1/N/L2 connections, the center tap being connected to neutral is not a good idea.
The assumption is that L1 and L2 have equal voltages and the primary inputs are identical in regards to construction and number of turns compared to center tap.
But what if L1 and L2 already have some voltage imbalance due to more load on other line, or transformer primary windings not exactly equal in regard to center tap?
The two halves of the primary winding would waste some power as heat. Basically same problem as two imbalanced primary coils driven with live and neutral. The transformer has to be specifically made with tight enough tolerances that manufacturer guarantees proper operation.
Having a primary with center-tapped neutral can't guarantee other than the transformer itself being properly made with tolerances, but your L1 and L2 voltages can still be imbalanced.
Therefore if you have a center-tapped transformer, it would be best to not connect the center tap to neutral, and just use the L1 and L2 for the primary.
So you don't need center-tapped primary.
But in the end, you don't need an isolation transformer at all, as you can just use the equipment with L1/L2 connections directly, with also earth if the device needs it.
