I am designing an addition to an existing service. The MDP is a 3Ph, 120/208, 600A, MLO with 3-200Amp distributiion breakers installed existing. Each 200 Amp breaker in the panel serves a branch 225Amp MLO panel. The service feeder conductors are 500MCM to the CT cabinet which is directly on the back side (exterior) to the MDP. The utility has also pulled 500MCM approx 150 ft to the utility pole mounted transformers (between CT cabinet and pole). I want to make sure that this is a violation as I think it is before I require an up-size of the service conductors. Am I correct.
6 Disconnect Rule and NEC 230.80
- Thread starter derwood14
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charlie
Senior Member
- Location
- Indianapolis
Re: 6 Disconnect Rule and NEC 230.80
If 230.42 is met which basically permits the service entrance conductors to be size to carry "the sum of the noncontinuous loads plus 125 percent of continuous loads", then you installation is correct for the existing loads. Since you are adding to the service, you are required to recalculate the loads in accordance with Article 220. You must then be sure the service entrance conductors are sized correctly.
As far as the electric utility is concerned, they will size their conductors in accordance with industry standards as they see fit. They will also change out their undersized service conductors since they guarantee the installation forever.
If 230.42 is met which basically permits the service entrance conductors to be size to carry "the sum of the noncontinuous loads plus 125 percent of continuous loads", then you installation is correct for the existing loads. Since you are adding to the service, you are required to recalculate the loads in accordance with Article 220. You must then be sure the service entrance conductors are sized correctly.
As far as the electric utility is concerned, they will size their conductors in accordance with industry standards as they see fit. They will also change out their undersized service conductors since they guarantee the installation forever.
Re: 6 Disconnect Rule and NEC 230.80
Thanks Charlie, I also took an Amp reading on each phase (loaded as much as possible) readings on the three phases where fairly balanced around 70 Amps each. I know this does'nt comply with code for determining the load as i did not meter long enough, but it gave me a good idea. I will compute the existing and new loads and make sure we still comply. I would like to add a fourth 200 Amp breaker for the feed of the new addition, but will confirm that the load is under the capacity of the 500's. Thanks
Thanks Charlie, I also took an Amp reading on each phase (loaded as much as possible) readings on the three phases where fairly balanced around 70 Amps each. I know this does'nt comply with code for determining the load as i did not meter long enough, but it gave me a good idea. I will compute the existing and new loads and make sure we still comply. I would like to add a fourth 200 Amp breaker for the feed of the new addition, but will confirm that the load is under the capacity of the 500's. Thanks
Re: 6 Disconnect Rule and NEC 230.80
The utility is not required to use table 310.16 when sizing the conductor. As Charlie said they will install the conductor based on their estimate of the load. Sometimes they will install conductor to match the main capacity, but not always.
[ November 14, 2003, 11:46 PM: Message edited by: bob ]
The utility is not required to use table 310.16 when sizing the conductor. As Charlie said they will install the conductor based on their estimate of the load. Sometimes they will install conductor to match the main capacity, but not always.
[ November 14, 2003, 11:46 PM: Message edited by: bob ]
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Re: 6 Disconnect Rule and NEC 230.80
Also, if its an overhead service, the conductor ampacity is higher than it is in racway. For most applications the NEC service conductor size is conservative, and keep in mind the utility sizes conductors per the NESC.
Also, if its an overhead service, the conductor ampacity is higher than it is in racway. For most applications the NEC service conductor size is conservative, and keep in mind the utility sizes conductors per the NESC.
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