shared common?

[jdsac]

In order to not have to derate further the conductors in a run of pvc it was suggested that to get the 5 circuits required it could have 9 conductors, with one of the commons being shared.

This is residential 120v, there are 4 new 20 a circuits and 1 new 15 a circuit.

Would the best practice be to share the common from the circuit with the least load or?

A commercial electrician told me it's done all the time, just trying to be sure.

Thank You for the help.

 

[justsam]

Best would be two circuits with equal current.

You are describing an MWBC or Multiwire Branch Circuit. Review their application and make sure you use two breakers that are handle tied.

 

[sberry]

Share the common with the 2 that have the most load.
This is a place a little common sense is called for. The letter of the law is 9 conductors but does assume you might actually load them to some significant amount. 5 AC circuits is different than 5 general circuits in a house with one being lights, a fridge, a micro, a general or 2 etc.
I got a couple stuffed pipes a bud wired for me but in the end there is 5 A continuous, 10 more intermittent in a power tool between 4 circuits. Bundling and load count would be different in an industrial process with them all working at capacity.

But did I mention,, share the 2 with most load,,,, hahahaha

 

[Rookie2]

You can share a neutral with two legs L1 &L2 . L1 & L2 are 180 deg out of phase and can share the same neutral up to the conductor rating .
or L1 +L1 or L2 + L2 up to the wire or breaker rating

 

[Wirepuller]

Pick circuits that don't require an arc fault breaker. But yes. Sharing neutrals for conductors out of phase is common practice. More so in a commercial environment.