Not being there it’s a bit hard to speculate, but in the US it is characteristic for utilities to ground the midpoint of one transformer on a delta or open-delta service, even of the grounded conductor is not carried in to the building. If it is corner grounded, then one phase {typically Bø} must be marked white as a grounded circuit conductor. Grounding the midpoint of one transformer allows serving additional 1ø3w loads, even if only three conductors are brought to the 3ø servce.
Ungrounded 240V ∆3ø3w is more commonly found in larger induistrial buildings served from 480V-primary dry-type transformers for servce to localized machinery, and with the exception on drive-isolation transformers, a wye 240V source is not to prevalent, for it requires 139V coils on the transformer. In most cases locally served 240V 3ø ungrounded servce is immaterial if ∆ or Y.
To some extent it depends on the age of the installation, with 208Y and 480Y outpacing ∆ service for standardization and flexibility. It also depends on who owns the serving transformer.
[This message has been edited by Bjarney (edited 06-07-2002).]
