Parallel Service Lines

[Electriman]

Greetings,

I was wondering if that is OK for the utility to run two lines from different locations to provide me the service with adequate size. If so, do I need to have two meters or I can have one meter with two CT cabinets?
For example, I need a 2000A service and I am guessing utility can run a 800A line and 1200A line from another location to provide me the service.

 

[electrofelon]

Greetings,

I was wondering if that is OK for the utility to run two lines from different locations to provide me the service with adequate size. If so, do I need to have two meters or I can have one meter with two CT cabinets?
For example, I need a 2000A service and I am guessing utility can run a 800A line and 1200A line from another location to provide me the service.

Two separate utility feeds (that are not connected at the supply end) would only be allowed if you can meet one of 230.2 A thru D. In my experience, regardless of what the NEC says, utilities only want to supply a building with one service, unless they are different characteristics.

 

[steve66]

I am very doubtful a utility would ever do that. They would be basically paralleling transformer secondaries.

The only time I have ever seen that is with downtown network systems, where many transformer secondaries are paralleled together to provide more reliable power for multiple services.

 

[kwired]

Paralleling is much more efficient in many ways if the parallel segments are same size, type, etc.

If you were supplying separate 1200 and 800 amp distribution panels you could be more likely to see such setup, but if same voltage/number of phases they still would likely want to supply from the same source in most cases.

 

[electrofelon]

I am very doubtful a utility would ever do that. They would be basically paralleling transformer secondaries.

The only time I have ever seen that is with downtown network systems, where many transformer secondaries are paralleled together to provide more reliable power for multiple services.

It wouldnt be that bad if each supply fed separate enclosures, like one 1200 panelboard and the other feeding a 800 amp panelbaord. Not sure if that is what the OP was envisioning, but still doubt a POCO would even do that.

 

[Electriman]

It wouldnt be that bad if each supply fed separate enclosures, like one 1200 panelboard and the other feeding a 800 amp panelbaord. Not sure if that is what the OP was envisioning, but still doubt a POCO would even do that.

I just read NEC 230.2 and it seems that paralleling is only possible when the service size beyond 2000A unless other conditions apply which doesn't in my case. On the other hand also utilities don't like to provide parallel service. So I think those would kill my thought.

 

[electrofelon]

I just read NEC 230.2 and it seems that paralleling is only possible when the service size beyond 2000A unless other conditions apply which doesn't in my case. On the other hand also utilities don't like to provide parallel service. So I think those would kill my thought.

Just be careful with terminology: Parallel conductors are always allowed for 1/0 conductor sizes and over. Having multiple sets of service entrance conductors is allowed for a number of different situations (see 230.40 exceptions), which would be when they are joined at their supply end but not their load end. Multiple services are allowed in some situations (230.2).

 

[Electriman]

Just be careful with terminology: Parallel conductors are always allowed for 1/0 conductor sizes and over. Having multiple sets of service entrance conductors is allowed for a number of different situations (see 230.40 exceptions), which would be when they are joined at their supply end but not their load end. Multiple services are allowed in some situations (230.2).

Yes. Thanks for the heads up.

 

[kwired]

I just read NEC 230.2 and it seems that paralleling is only possible when the service size beyond 2000A unless other conditions apply which doesn't in my case. On the other hand also utilities don't like to provide parallel service. So I think those would kill my thought.

As mentioned parallel conductors must use 1/0 or larger conductors as the general rule - if you used just two 1/0 conductors in parallel that is well below 2000 amps ampacity wise.

The first major problem before even getting into issues with the sources is assuring you do not overload any of your individual conductors when paralleling them. If they are not same size, type, length, and in same type of raceway their impedance will vary and whichever one is lower will carry more of the load than the other.

What you have with 1200 amp and 800 amp supplies somehow connected "in parallel" is it will be difficult to assure neither set is pulling more than it's ampacity at any time during operation. Once the total load goes above 800 it is possible to overload the 800 amp portion of the setup.

 

[Electriman]

As mentioned parallel conductors must use 1/0 or larger conductors as the general rule - if you used just two 1/0 conductors in parallel that is well below 2000 amps ampacity wise.

The first major problem before even getting into issues with the sources is assuring you do not overload any of your individual conductors when paralleling them. If they are not same size, type, length, and in same type of raceway their impedance will vary and whichever one is lower will carry more of the load than the other.

What you have with 1200 amp and 800 amp supplies somehow connected "in parallel" is it will be difficult to assure neither set is pulling more than it's ampacity at any time during operation. Once the total load goes above 800 it is possible to overload the 800 amp portion of the setup.

Right. It might be one of the reasons that utilities don't favor parallel services.