Line and load taps

[ABoshant]

I have a solar back feed that we are tapping into on the load side that has a 400 amp main but the load side is in parallel (2x 2/0 per leg) the back feed will be protected with a 60 amp fuse disconnect. In order to tap it would I be tapping to one or both wires that are running parallel?
Second question. On a line side tap of a 600a would I need to match the wire size to pull to a new panel we are installing that has a main disconnect of 200a Or would I be allowed to tap onto it with wire that will be rated for 200a?
thanks

 

[pv_n00b]

1) Whenever connecting to parallel conductors you have to connect to all of them to maintain the parallel system balance. There is also the problem that you can't parallel conductors less than 1/0 and that's going to be much larger than you need for your PV system with a 60A disconnect. I would look for a different way to interconnect if it were me, tapping parallel conductors is not worth the trouble for small circuits.

2) You can size for the 200A panel. Size it as you would a 10' feeder tap, and of course keep the circuit under 10'.

 

[jaggedben]

Here's a thread that hashed out what could potentially happen if you tap only one set of parallel conductors.

http://forums.mikeholt.com/showthread.php?t=178235

EDIT: THIS thread is the original discussion as far as I remember.

http://forums.mikeholt.com/showthread.php?t=170330

 

[pv_n00b]

The 5 terminal tap seems reasonable and I had not thought of that.

If you tap one conductor and inject current that creates a voltage drop in the conductor that is not in the other conductor(s). Now when the existing circuit splits current between the parallel conductors it follows the equal voltage drop rule. Voltage will divide between the conductors so they all have an equal voltage drop between the terminals. If there is a voltage drop added by the PV interconnect to one of the conductors then the current from the existing circuit will split unequally. How the current splits depends on several factors but the fact that it now splits unevenly goes against the NEC concept of equal sharing of the current between the parallel conductors. So don't do it.

As always, because an AHJ does not flag something is not the golden ticket to do the same thing for the rest of your career. But you would not know that talking to some contractors.