[cruiser2000]

1) I have wired a subpanel feed with #2 ( or #3) wires protected with a 2 pole 100amp breaker. I am confused on why the code requres this. Doesn't each wire only carry half the load (50 A) max.

2) Does a subpanel on a second floor require a grounding rod (or water pipe) connection, or just the ground wire back to the main panel?

3) Is the bonding lug ( connected to grounding wire) sufficient to ground the sub-panel, or does the ground bar have to be bonded?

4) Will a 1-1/4 inch flex conduit be large enough for 3-#2 wires and a #8 ground wire

[tkrussell]

My answers follow your questions.


I have wired a subpanel feed with #2 ( or #3) wires protected with a 2 pole 100amp breaker. I am confused on why the code requres this. Doesn't each wire only carry half the load (50 A) max.

Each pole of a 100 amp breaker can handle 100 amps, so the wire feeding it must be rated to handle 100 amps.

2) Does a subpanel on a second floor require a grounding rod (or water pipe) connection, or just the ground wire back to the main panel?

Any panel that is remote from the Main Breaker must be supplied with a four wire feeder, which includes an equipment ground that you mention.

3) Is the bonding lug ( connected to grounding wire) sufficient to ground the sub-panel, or does the ground bar have to be bonded?

An equipment ground bar must be bolted directly to the metal box of a panel with machine thread screws. The Neutral bar in a panel that doens not contain the Main Service Disconnecting Means does not get bonded to equipment ground.

4) Will a 1-1/4 inch flex conduit be large enough for 3-#2 wires and a #8 ground wire

Assuming THHN or XHHW insulation on the #2, yes, it will fit.

[cruiser2000]

Thank you for your answer.. Sorry still confused.

If each pole can deliver 100 amps isn't that 200 amps, or 120v x 200amps = 2400Kva?

A double pole breaker is made up of 2-50 amp breakers physically connected with a common trip bar labeled 100 amps.

I know it may just be a naming convention but it's confusing to an old engineer like me.

[cruiser2000]

Sorry for calculation error 24 Kva or 24000 watts

[tkrussell]

If you were to cut a 2 pole 50 amp breaker in half, you would have two separate single pole breakers each rated 50 amps.

A 100 amp service is 240 volts, 100 x 240 = 24000 VA.