Y code not allow

[hhsting]

If i have 1000A 208/120V service feeding building then why doesnt code allow 400A 208/120V service to the same building? Does anyone know? Is their any danger electrical engineering wise involved like some type of current circulating or not equal potential or any other reason?

 

[petersonra]

If i have 1000A 208/120V service feeding building then why doesnt code allow 400A 208/120V service to the same building? Does anyone know? Is their any danger electrical engineering wise involved like some type of current circulating or not equal potential or any other reason?

Read The rules carefully. It is allowed under certain cases such as exceeding the maximum service that utility will provide at a certain voltage.

 

[hillbilly1]

Also if a different voltage or type, say single phase, and a three phase service, or a 120/240 delta and a 277/480 three phase wye as an example.

 

[LarryFine]

Same occupancy/customer, or just same structure?

 

[tom baker]

I worked on a city hall building that had 4 services
120/208
120/240 single phase
120/240 wild leg
480/277. This was for main frame computers that were water cooled
It was challenging to turn off power as the schedules were obsolete.
so that’s why the NEC only allows one service, for safety

 

[hhsting]

Right if u please re read the post the situation is existing 1000A 208/120V 3 phase service and new 400A 208/120V 3 phase service. Y code dont allow it

 

[tom baker]

Don‘t know, likely a safety issue. Since it’s a code rule, accept and move on

 

[GoldDigger]

Right if u please re read the post the situation is existing 1000A 208/120V 3 phase service and new 400A 208/120V 3 phase service. Y code dont allow it

So far the only actual reason that has been suggested is the fairly significant one that is would make it more difficult to know which service to shut off to make safe work in a particular area. Especially if the two services end up interleaved throughout the building instead of being segregated in the form of an original building and a new addition.
An accidental cross-connection between circuits on the load sides of the two services, even if only in the form of a short circuit, could have unexpected consequences.
Yet another potential complication would come if the two services came from different vector group service transformers and so were out of phase with each other. I have not thought of an actual consequences, but it just does not feel right.

 

[electrofelon]

If i have 1000A 208/120V service feeding building then why doesnt code allow 400A 208/120V service to the same building? Does anyone know? Is their any danger electrical engineering wise involved like some type of current circulating or not equal potential or any other reason?

I'll bet most of the time what you describe would be ONE service with two sets of service entrance conductors and two service disconnects

 

[don_resqcapt19]

Right if u please re read the post the situation is existing 1000A 208/120V 3 phase service and new 400A 208/120V 3 phase service. Y code dont allow it

Need lot more details about the proposed installation. What you are calling a second service may really only be an additional service disconnect.

 

[flashlight]

What is the code section that does not allow it?

 

[electrofelon]

What is the code section that does not allow it?

What exactly? Lots of stuff being discussed here. 230.2 generally allows only one service but there are lots of exceptions. Then there is the question of whether it is indeed two services or just one service with two sets of service entrance conductors,. And the issue of if it is two services, whether they are both "supplying" the same building or structure, which is what 230.2 has the restrictions on.