Too much Non-PhD-related work at research institute, unclear if contract requires it

Question

I am currently pursuing a PhD while being employed at a research institute as a doctoral candidate in Germany. I have a supervisor at the institution and a professor at university who I have meetings with.

In my day-to-day business at the institution, I feel heavily held back by the amount of non-PhD-related work I am given. There are two projects managed by coworkers of mine and I am expected to participate in weekly update meetings, where I am given tasks and associated deadlines to finish them. The amount of work is in the range of 20h/week, but sometimes higher (and also includes uncomfortable circumstances like working early and/or late). My research institution has a reputation of 'burning' PhD candidates, and apparently several people have quit over the amount of non-PhD-related work.

Currently, I have managed to get ahead in one of the projects, but for the other project I am supposedly months behind schedule despite putting in more than enough hours. This could of course be related to project management or my performance, but in my opinion should not hinder me in pursuing my PhD either way. Regardless, after finishing one task for a project I almost immediately get assigned a new, urgent task.

I am very unhappy with the situation. Both my PhD and my project work suffer from the lack of time or high amount of work. My PhD does not benefit from the project work in any way, although this was what I was promised when I was hired. Because of this, I am also wondering whether I am actually required to work this much on these projects.

My contract (names changed/omitted) states:

[Mister Schwarz] verpflichtet sich, seine gesamte Arbeitskraft für die Bearbeitung des wissenschaftlichen Vorhabens einzusetzen. Hierfür wird die betriebsübliche regelmäßige Arbeitszeit vereinbart. Als Arbeitszeit gelten auch die Teilnahme an Vorlesungen und Seminaren sowie Bibliotheksbesuche, soweit diese in unmittelbarem Zusammenhang mit der Erstellung der Doktorarbeit stehen.

Die Hälfte der für die Bearbeitung des wissenschaftlichen Vorhabens erbrachten Arbeitszeit gilt als Arbeitsleistung für [Research institute]. Hierfür wird eine monatliche Vergütung in Höhe von 50 v.H. der Entgeldgruppe 13 des TVöD gezahlt.

The english translation provided by them is

[Mr Schwarz] undertakes to devote his entire working capacity to processing the scientific project. The regular working time customary at the Institute is agreed for this purpose. Working time is defined as including the attendance of lectures and seminars as well as visiting libraries, insofar as these are directly related to the preparation of the doctoral thesis.

Half of the working time spent on processing the scientific project is considered work performed on behalf of the [Research institution]. Monthly remuneration of 50 percent of pay group 13 of the TVöD shall be paid for this purpose.

No clear definition of the 'scientific project' or 'wissenschaftliches Vorhaben' is given, although in previous sections the PhD is mentioned. From my understanding, the contract seems to specifically exclude non-PhD-related work in my working time. (I don't even have time to attend lectures or seminars).

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My questions are:

1. From the contract excerpt, am I required to perform 50% of working time corresponding to 20h/week of project work? Or am I required to work full-time on my PhD, which would have been my original interpretation?
2. Following this, how can I enforce a limitation of 50% or 0% project work? How do I communicate this to my institute supervisor and the project managers responsible for the meetings and so on?
3. Should I involve my university supervisor in the communication?
4. Should I talk to the HR department of the institute about the contract interpretation? Could they help me resolve the situation?

I realize this might also be relevant to workplace.SE, but I chose to post it here since similar related questions were already asked in this SE: a question about unrelated lab work at university instead of working on a PhD, lab promotion and student supervision at university and data analysis for coworker projects without gaining authorship. My situation differs in that I do not have a teaching responsibility or any other university employment and the contract seems to specifically exclude non-PhD-related work in my working time.

Answer 1

The 50% position is typically for work on a funded project that may or may not be related to your PhD project. It is reasonable for your employer to expect you to work on that project in return for the salary. It is not reasonable if you are spending substantially more than 50% on that project.

As is almost always true for conflicts with students or postdocs, the correct answer (regardless of question) is "Talk to your adviser". The HR department or any other component of your institution can not possibly come up with a solution to your problem that does not involve your adviser in some way. As a consequence, rather than going to the higher ups and then making them come tell your adviser about it, you might as well do as suggested: Talk to your adviser about the problem. They need to be part of the solution anyway, you might as well involve them right away and in a friendly context.