electricalforum.nz

I have a client who wants a large oven installed at a commercial premises but the distribution board they want to connect to does not have the capacity.

Alternatively I have suggested that the best solution would be to run a new final subcircuit back to the main switchboard or to upgrade the submain to the DB.

They have said to me that the equipment they used is not all used at the same time and they are more than happy to have it connected to the DB despite the limitations and will deal with the consequences accordingly.

I'm just curious if it's actually compliant to do this? Although the clients are happy to deal with it, can I compliantly install something knowing that the installation is not suitable in design to handle such equipment? Do I simply apply max demand by limitation in my selection and design process? I've obviously used MD by limitation before but not usually in a situation such as this knowing that tripping is very likely

At then end of the day you need to ensure that the work you do will not lead to an electrically unsafe situation, buy fitting current limiting devices would be the way to go in lieu of bigger cables and DB's.
Let the customer know in writing what they can expect - nuisance tripping and what will be required to stop that from happening, this should stop any comeback from the customer "You didn't tell me that would happen".

I had the similar situation and current limiting device was my last source to avoid the electrically unsafe situations,

Because you can not trust customer saying that "we will not run all machine together" so making sure the rating of OCD will put you in safe zone.

The rule is that we must size conductors for the load to be carried, and then we protect them so they don't get overloaded.

The 2nd part of that is absolute; we can't allow any margin on over-current protection.
But for the 1st part we can allow for the fact that the entirety of the connected load won't be running at same time
- it's called diversity.