Panels

[Henry94606]

Hi forum.
I am new, and I am an architect working mostly residential.
I currently having a house with 200A main panel (with metter). We try to add another sub panel 125A for the house new addition (1000sf).

My knowledge of electrical work limits to fill out the panel schedule with amperage and VA in computer program. For this house the current 200A panel estimate connected load is 187A and the proposed 125A is 103A estimated load.
Q: do I need a 325A Disconnect (after the metter, and upstream from 200A and 125A panels) ?
Or will it just be ok if electrician can parallelly hot wired the subpanel feed to the 200A panel (if he chooses to) ?

The boldest wire inside this 200A are only #4 awg. My kindergarten electrical knowledge tells me I would need a #350 wire (after the metter) to make sure nothing blows up, but that thought can be seriously wrong
Let me know, please

 

[SWComposites]

a) why is this in the Student forum?
b) suggest deleting and reposting in an Electrical Engineering forum
c) but why not engage a competent electrical contractor or engineer?

 

[Henry94606]

A. It s a student level question.
C. It s irrelevant to the question.

 

[BridgeSmith]

A. It s a student level question.

Probably so, but it's not a question from an engineering student, so it doesn't belong here.

It's also something a competent electrical contractor should know, which is why you hire one to do the work.

 

[Henry94606]

I love this forum

 

[3DDave]

It's a licensed electrical contractor kind of question, one who has access to the local codes and knows what the power company wired the feeder to the house to handle. They can advise what panel design is required and if the feeder and meter requires an upgrade.

It seems reasonable to pay an electrical contractor to do the design work and then, if you select them for the installation, for them to discount what work they would have done that was already paid for.

 

[waross]

It looks as if the OP has done a demand study for the addition (I hope) and added it to the demand of the original house.
Suggestion.
Do a demand study of the complete site. That is the old and the new proposed addition as one unit.
If the resulting demand is over 200 Amps, the change out the main panel to a 225 Amp or 400 Amp panel and pay the utility for any upgrade that they require.
You may still use the original demand study to size the sub feed breaker.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[waross]

Connected load versus demand load.
Be sure that you know the difference.
The demand load is often less than the connected load.
Diversity factors are incorporated into demand studies.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!