NEC Calculations per 220.86

[Sparky2791]

Having a debate regarding these calculations.

If the final calculations for the school based on this section come to 208,550vA or 579A @ 120/208V 3Phase is a service disconnect of 600A permitted? Assuming you are sizing the buildings service for the smallest service NEC allows? Obviously the 600A service disconnect allows little room for additional loads.

Thanks for reading.

 

[wwhitney]

If the final calculations for the school based on this section come to 208,550vA or 579A @ 120/208V 3Phase is a service disconnect of 600A permitted?

The only issue I'm aware of would be continuous loads and 215.2(A)(1). See also 230.42.

Cheers, Wayne

 

[Sparky2791]

The only issue I'm aware of would be continuous loads and 215.2(A)(1). See also 230.42.

Cheers, Wayne

Hmmmm...... Yet 230.79 tells me the 600A would be sufficient.

 

[wwhitney]

Hmmmm...... Yet 230.79 tells me the 600A would be sufficient.

The service disconnecting means and the service OCPD may not be the same device. You could have an unfused disconnect with OCPD in a separate adjacent enclosure. 230.79 covers the disconnect, and 230.90 covers the OCPD.

Hypothetically, say you have a 580A load of which 200A is continuous. You could:

1) Use a single 600A 100% rated service OCPD. Your single downstream feeder could be 580A ampacity, your service entrance conductors (SECs) could be 580A, and your service conductors which aren't SECs (call them SCs) could be 580A.

2) Use a single 700A non-100% rated service OCPD. Your single downstream feeder could be 630A ampacity, your SECs could be 630A ampacity, and your SCs could be 601A ampacity.

3) Suppose your SCs supply two sets of SECs and the load is divided as (1) 380A of which 200A is continuous, and (2) 200A non-continuous. Then service OCPD 1 could be 450A, with 430A downstream feeder and SECs; service OCPD 2 could be 200A, with 200A downstream feeder and SECs; and the SCs could be 580A.

Cheers, Wayne

 

[Sparky2791]

The service disconnecting means and the service OCPD may not be the same device. You could have an unfused disconnect with OCPD in a separate adjacent enclosure. 230.79 covers the disconnect, and 230.90 covers the OCPD.

Hypothetically, say you have a 580A load of which 200A is continuous. You could:

1) Use a single 600A 100% rated service OCPD. Your single downstream feeder could be 580A ampacity, your service entrance conductors (SECs) could be 580A, and your service conductors which aren't SECs (call them SCs) could be 580A.

2) Use a single 700A non-100% rated service OCPD. Your single downstream feeder could be 630A ampacity, your SECs could be 630A ampacity, and your SCs could be 601A ampacity.

3) Suppose your SCs supply two sets of SECs and the load is divided as (1) 380A of which 200A is continuous, and (2) 200A non-continuous. Then service OCPD 1 could be 450A, with 430A downstream feeder and SECs; service OCPD 2 could be 200A, with 200A downstream feeder and SECs; and the SCs could be 580A.

Cheers, Wayne

OCPD and service disconnecting means not in the same enclosure seems odd, good point about the 100% rated. Scenario one would be the way I would go for the school this is being applied to. Has an existing 600A service they were hoping they did not have to upgrade as part of the complete renovation of the building. Need design to be done to see if the calcs make it possible.

 

[wwhitney]

OCPD and service disconnecting means not in the same enclosure seems odd.

Perhaps, but see figure 230.1. It illustrates the distinction between disconnecting means and OCPD, and that they are covered by different parts of Article 230.

Cheers, Wayne