The power box usually is the owners responsibility.
When you put on the power you pay for the fuses and the Box the power company simply connects you to the mains.
You should be talking to the other 4 shops and getting an independent electrical to give you a quote on the replacing of the junction box. If the electrician can give you a report that the damage to the box is because of the electricity company then you can see reimbursement from them.
But the mains box is owned by the property owner and the owners are liable to pay for its replacement.
So each shop that connects is liable for their share.
I hope this makes sense and is of assistance. If there is nothing further
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