[RE-wrenches] Service rated tap devices

[Jeff Clearwater]

Hi Mac and All,

If you are about to do a Supply-side tap I'd encourage you to look into 
the many advantages of using a Feeder Tap instead - one of which is that 
since it's not on the load side of the Main the equipment need not be 
Service Rated. (not that you might not want it to be anyway.)

Be aware that Supply Side Taps make total sense when you are doing only 
grid-tie as you are always backfeeding and so the current produced by 
the solar is always cancelling the incoming utility current.  However as 
soon as you add battery charging to the equation from a large or 
multiple parallel multi-modal inverter, then you have the very real 
possibility of overloading the Service Entrance Conductors.  Basically 
if you have a 200A residential service whose Service Entrance Conductors 
were based on calcs that had close to maxed out the 160 Amp continuous 
capacity of a 200 A service, then adding 50 Amps of battery charging to 
that can push if over the edge.  Once you have bi-directional flow on 
your supply side tap you are basically adding loads to a service that 
may not be able to handle it in the case of large batteries with large 
charging capability.

Feeder Taps on the other hand force you to do 2 things 1) they limit the 
bi-directional current to your Main Breaker size (200 A) and 2) they 
then re-protect the main load panel downstream of the tap with another 
Feeder Tap Breaker (or larger conductor) according to NEC2020 705.12(B) 
- protecting it from the sum of the 200 A potential from the utililty 
combined with the sell-back current potential of the grid-tie inverters. 
(diagram attached).  With this configuration you can safely backfeed up 
to 160 Amps of solar into a 200 Amp service while still have a large 
battery bank on that system and not worry at all about overloading 
during heavy battery charging.

For new construction or any large install where I need to reconfigure 
the Service Entrance anyway we use Feeder Taps pretty much exclusively 
now - for sure so for anything with batteries.  It does require having a 
stand-alone Main Breaker and to do away with meter-main combo panels. 
But the safety and flexibility of what you now have to work with in 
terms of AC or DC coupled inverters and battery backup - including whole 
home backup are far superior in my book.

And for folks already having a Main Breaker that is tappable after the 
Main but before any busses, the Feeder Tap approach allows you to not 
require shut-down of the service during reconfiguration.

Hope that helps!

Best,

Jeff

> Mac Lewis via RE-wrenches <mailto:re-wrenches at lists.re-wrenches.org>
> July 19, 2023 at 10:01 PM
> Hello Wrenches,
>
> Is there any tap devices (piercing or other) that are UL Listed for 
> tapping on the utility side of a main breaker for a solar 
> interconnection?   Our AHJ won't allow anything that isn't service rated.
>
> Thanks in advance!
>
> -- 
>
>
>
> Mac Lewis
>
> *
>
> "Yo solo sé que no sé nada." -Sócrates
>
> *
>
>
> _______________________________________________
> List sponsored by Redwood Alliance
>
> Pay optional member dues here: http://re-wrenches.org
>
> List Address: RE-wrenches at lists.re-wrenches.org
>
> Change listserver email address & settings:
> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>
> There are two list archives for searching. When one doesn't work, try 
> the other:
> https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/
> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
>
> List rules & etiquette:
> http://www.re-wrenches.org/etiquette.htm
>
> Check out or update participant bios:
> http://www.members.re-wrenches.org
>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20230720/84e4ac1d/attachment.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Screen Shot 2023-07-20 at 4.36.07 PM.png
Type: image/png
Size: 66896 bytes
Desc: not available
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20230720/84e4ac1d/attachment.png>