As detailed in a previous post, I was planning to use the dryer circuit in my condo as a MWBC. A 120V/20A outlet between one of the two hot conductors and neutral would power my small washer and dryer and a 240V/20A outlet between the two hot conductors would allow me to power some European appliance without the need for an external transformer of questionable reliability.
This plan was based on the implicit assumption that all US residential electrical systems are split-phase, i.e., the two hots are out of phase by 180 degrees. As a reminder that failure is more often due to false certainties than to those critical issues that were identified and properly addressed, the measurements I did today showed 208V between the two hots. This indicates that the utility does not a feed me a split-phase signal but two of the three independent phases of the transformer.
A little reading seems to indicate that this is not too rare, even if uncommon. Since no much fuss gets made about it, I am led to think that all those US home appliances that need 240V (dryer, range) are designed to keep working with 208V.
However, I'm not sure the same can be said for 240V foreign home appliances. In general in Europe the specified working interval is 220V-240V. 208V is well below that. Considering a 1500W appliance, a decrease in supply voltage from 240V to 208V corresponds to an increase in current drawn of 1A, from 6.2A to 7.2A, which appears to be rather benign, well below the 20A nominal limit enforced by the breaker.
Is there any negative consequences from having 208V instead of 240V between the two hots?
Thanks for all the answers. I did not focus on the frequency mismatch because the appliance label indicates a working range from 50 to 60 Hz, which is confirmed by my current use of it via a 110V outlet and a 3000AV step-up transformer with no detectable performance hiccup.
The label also indicates a working voltage range from 220V to 240, but I believe Simon B might be correct in thinking of this as a nominal range and adding another 10% of tolerance with respect to its center point. I guess the worst can happen would be a slower heating element and a slower motor.