Art. 230.42(B)

[seriouswatts]

When sizing service entrance conductors, do you size the SE conductors for the OCPD or the equipment it is mounted in?
Example: I have a 900Amp 3-phase 208V system, the OCPD is rated 900Amps, but the panel it is in 1200Amps. Are the SE conductors sized 900 for the OCPD or 1200A for the panelboard? Article 230.42(B) states "not less than the rating of the service disconnecting means..."

Thanks for the help.

 

[Dennis Alwon]

The se conductors need to be rated toe OCPD. Thus 900 amp se conductors

 

[augie47]

Welcome to the Forum.
I agree with Dennis. 240.4 states: Protection of Conductors.
Conductors, other than flexible cords, flexible cables, and fixture wires, shall be protected against overcurrent in accordance with their ampacities specified in 310.15, unless otherwise permitted or required in 240.4(A) through (G).
so if your 900 amp OCP protects the conductors, then they only need protection based on that OCP, not the panel rating.

 

[raider1]

Welcome to the forum.

You start with 230.42(A) which would require you to size the service entrance conductors based on 125% of the continious load plus 100% of the non-continious load.

230.42(B) would not apply to a 900 amp 3 phase 208 volt wye system.

Chris

 

[augie47]

Welcome to the forum.

You start with 230.42(A) which would require you to size the service entrance conductors based on 125% of the continious load plus 100% of the non-continious load.

230.42(B) would not apply to a 900 amp 3 phase 208 volt wye system.

Chris

Chris, my brain is "out to lunch" today. Would you expound on the 2nd sentance, please.

 

[seriouswatts]

Thanks for all the welcomes! Been here for a while and this is just my first post.

The OCPD doesn't specifically protect the SE conductors, since if there is a fault on the line side of the device the conductors would rely on the utility OCP.
I understand sizing the device per the facilty loads, but what makes up a "Specific Installation"?

 

[augie47]

Thanks for all the welcomes! Been here for a while and this is just my first post.

The OCPD doesn't specifically protect the SE conductors, since if there is a fault on the line side of the device the conductors would rely on the utility OCP.
I understand sizing the device per the facilty loads, but what makes up a "Specific Installation"?

I am awaiting Chris' answer to this, but in the meantime I will comment that in reagrd to services any OCP, being "downstream", can only protect against overcurrent and not "faults" (on the line side) which I guess is one of the reasons behind 230.70(A)(1)

 

[raider1]

I am awaiting Chris' answer to this, but in the meantime I will comment that in reagrd to services any OCP, being "downstream", can only protect against overcurrent and not "faults" (on the line side) which I guess is one of the reasons behind 230.70(A)(1)

What I mean by my comment that the 900 amp service does not fall under 230.42(B) is that a 900 amp service is far larger than any of the minimum size service disconnect sizes listed in 230.79(A) through (D).

All 230.42(B) does is require that the service entrance conductors be sized at a minimum to meet the minimum service disconnect sizes required in 230.79(A) through (D).

Chris

 

[raider1]

Thanks for all the welcomes! Been here for a while and this is just my first post.

The OCPD doesn't specifically protect the SE conductors, since if there is a fault on the line side of the device the conductors would rely on the utility OCP.
I understand sizing the device per the facilty loads, but what makes up a "Specific Installation"?

Take a look at the 4 specific required service disconnect sizes listed in 230.79(A) though (D).

Chris

 

[seriouswatts]

Thanks for the help guys, I think I got my brain wrapped around it this morning