Common neutral and protective earth line in power outlets has been abandonded about 50 years ago, PE is required by safety rules, so if you have a 4 pin connector, it must be expected to expose 3 phases and protective earth, but no neutral. You can't connect a single phase load to this outlet, or need to use a transformer.
Situation is different for fixed machine connections with sufficient cable cross section, in this case a common neutral and protective earth line may be used, but separate neutral and PE is strongly recommended.
Can you show a picture of the connector you are talking about?