Electricity - From when is it allowed to install a meter cabinet

For us, it was sufficient that the room alone was lockable. At that time, we had neither a front door nor windows. The mason simply installed a lockable metal door in the basement room. That was sufficient.

Usually, the regional power suppliers have a builder's consultation. They will also tell you who among them is a licensed installer to connect the meter cabinet. Has your general contractor managed to leave "Fleischerhäuser"?

The electrician also didn't get any money from the general contractor and now wants the money from us. But since we have already significantly overpaid the general contractor, I cannot take over the invoices for the general contractor's service providers.

Where you yourself are not the client, the electrician will demand in vain from you.

Especially if the general contractor gets an insolvency administrator,

I believe I have already pointed out to the local OP that insolvency courts only act upon application. Classic external applicants are the health insurance funds. In the case of a mailbox general contractor, these may fall away, and the subcontractors often "prefer" to go bankrupt themselves rather than deal with their options in such cases. Without an application, there will be no expert, and consequently no expert for the administrator. By the time a public prosecutor even suspects delay tactics, the construction ruins have long since decayed. So first quickly to a lawyer and have them check the situation. If necessary, funds of the general contractor may first need to be seized. And the guy himself can still happily disappear if no proceedings are ongoing against him. With a bit of bad luck, the power supplier will say that the account must first be balanced – because the electrician will not have registered the construction power in his own name, and a frequently cash-strapped general contractor most likely under power of attorney on behalf of the builder. A head stuck in the sand falls under the guillotine faster than you think :-(

or whether it might be possible or allowed to install and register the meter cabinet in the basement now so that you are no longer dependent on construction power afterwards.

I don't know if you're doing yourself a favor with that. The utility operator needs a line to the house. And that is usually or often (because of the costs) handled at the same time for water and possibly gas or Telekom. So if you still need one or the other later, there will have to be digging twice. Just give them a call.

Without knowing the background that led to the construction stop

There was no construction stop. A construction stop is an official measure and not a standstill from the general contractor's or builder's side.

I don’t know if you’re doing yourself a favor with that. The utilities operator needs a line to the house. And that is usually or often (because of the costs) then arranged at the same time for water and possibly gas or Telekom. So if you need one or the other later, there has to be digging twice. Just give them a call.

It definitely makes sense to have all house connections installed in the basement at once, including Telekom. For us, that was about €4,500 for gas, electricity, and water and another €800 for Telekom.