What happens if there's a loop in the system?

[fandi]

If there's a configuration like this, I wonder what will happens:
pnl A feeds pnl B feeds pnl C feeds pnl A?

 

[LarryFine]

 

[Electricmo]

Everything is fine till you lose the feed to panelA. Hehe.

 

[charlie b]

Panel A will have two sources of power: the (unnamed) upstream source and panel C. Those two will not have the same voltage level, due to voltage drop from A to B to C to A. The greater the load on B and C, the worse the voltage difference will become. So as a minimum you will get high current resulting from the voltage difference between the two sources divided by the (very low) resistance of the conductors that connect them. At the worst, it will result in arcing and potential damage.

 

[fandi]

Is there any code section in NEC prevent this from happening?

 

[LarryFine]

Ah, you guys inserted an un-mentioned power source feeding Panel A.

Presuming phasing is kept constant, and you parallel Panel A's two sources, and presuming each feeder is supplied by a breaker, the entire group would behave as one large panel with inadequate OCP.

Basically a large ring circuit. No crazy currents would result. Sorry, Charlie.

 

[fandi]

I forgot to mention that panel A is fed from the grid. Sorry.

 

[LarryFine]

Draw it out. Just a loop. Over-current protection might be an issue with paralleled main breakers.

 

[fandi]

(5) 20A ckts from pnl C outside the house feeds back to main panel A in the house is a 225.30 violation. If panel C is labeled/treated with 'Optional standby system' (from the PV system feeds back the house when the grid is down), would that be an exception of 225.30 (A)(4)?

 

[LarryFine]

The system would behave the same with or without a loop, providing no over-current issues. Looping merely provides everything with a parallel, redundant current pathway.