Supply side tap

[Islandmon]

I am seeking input regarding a proposed 18 kW single phase system that I would like to tie in to an existing 200A single phase service.
I will start by saying that my experience with supply side connections is limited.
I will be approaching an electrical engineer with this scenario, but would like to have an understanding of the pros and cons.

The utility enters a Milbank meter mains enclosure with a 200A breaker on a pole roughly 50' from the building. From there, the conductors run to an interior 200A load center with 200A breaker.
The output of two inverters will be combined and have a continuous output of 75A and require 100A of overcurrent protection.
I understand that I have two options:
Run conduit to the outdoor meter mains and tap into the service between the meter and the main breaker. (Is the 1' of wire between meter and main breaker enough to make a tap?)
or
Upgrade the 200A meter mains to a 300A and make a load side connection between the meter mains main breaker and the interior load center.

Your input is appreciated.

 

[jaggedben]

First of all... Is there a space for an additional service disconnecting breaker in the meter main enclosure? Sometimes there is. If so, you're golden, just add your 100A breaker there.

If there isn't such a space, you could look for a replacement 200A meter/main that gives you that option.

As for other the options you mentioned...

Regarding tapping between the meter and main breaker: If it is a listed meter/main enclosure it is unlikely that the listing allows you to tap between the meter and the main, and it may further be impractical to do so. Unless it appears that the conductors between the meter and main are field installed and intended by the manufacturer to be so, I would not attempt this.

Regarding the load side tap: Upgrading the meter/main to 300A does not in itself help you here. What is critical is that the conductors you are tapping into (and those going to the solar) are all rated for 250A (300A divided by 120%). By code you could do this load side tap without upgrading the meter main if you are able to easily replace the conductors between the pole and the building.

You have (at least) two other options:

1) On the line side of the existing meter main, insert an new meter base on the pole, and a (probably separate) enclosure where you make your supply side tap. When done, put flats into the existing meter base. Aside from involving the utility in shutting down the service, this might be the most cost effective option.
2) Upgrade to a greater-than-416A load center on the pole that allows you to put your solar breaker there. Probably not the most cost effective.

 

[electrimate]

1 foot of wire should be plenty of room to make a supply side tap. I have used "couple taps" to make similar connections.
This is one brand of them: http://www.idealindustries.com/prodDetail.do?prodId=b-tap-insulation-piercing-tap-connectors
Check with your local supply house and see what they stock.

 

[BillK-AZ]

1) On the line side of the existing meter main, insert an new meter base on the pole, and a (probably separate) enclosure where you make your supply side tap. When done, put flats into the existing meter base. Aside from involving the utility in shutting down the service, this might be the most cost effective option.

I just saw an example of this in a presentation by John Wiles. The original service entrance was an all-in-one unit. A new meter socket was installed with a second simple enclosure containing a power distribution block located between the new meter and the old service. A meter by-pass kit was installed in the old service and the line side connection was made to the power distribution block. Utility shut down the power and removed cables from old service, suitable wire was used to connect the new meter/distribution block/old all-in-one and a new fused disconnect for the line side connection. Utility then connected the service to the new meter after inspection.