Can I run lower guage wire for a segment

[gbeichho]

I am planning on running some outdoor overhead wires to a shed, and I wanted to run 20-30 A 240 V. I may have access to some overhead cables used to feed the main power to some nearby houses. I'm assuming this would be rated at 100A.

Could I use this heavier than required cable just for the outdoor portion of the run? I would still use smaller cable running to the main panel, and I would put the lower 30A breaker there.

Thanks,

George

[Ron]

The wire must be sized to match the rating of the protection upstream.
Are you planning on tapping service feeders before they enter the main service disconnect?

[gbeichho]

I plan to run a subpanel in shed off of the main breaker panel.

[Homer]

Here's my read on what you are actually proposing to do, so correct me if I have misinterpreted you.

1) You intend to power a subpanel in your shed from a 30A double pole breaker in your main panel and do not intend to tap the service feeders as Ron was concerned about.

2) You intend to use conductors rated for 100A for the outdoor portion of the run.

3) You intend to connect to the 30A breaker in the main panel with 10 gauge copper conductors and splice to 100A rated conductors (copper or aluminum).

4) You intend to connect the 100A rated conductors directly to the subpanel in your shed.

If this is what you are proposing, then yes you can do it that way. Your 100A conductors are protected by a smaller OCPD (30A).

You will never have a problem with voltage drop concerns with this arrangement.

Be sure to use the proper split-bolt connectors to splice the conductors and don't forget the anti-oxidant if you're dealing with aluminum.

EDIT: I see you posted more info while I was typing.

Homer

[Wgoodrich]

In short answer attempting to limit confusion, you are allowed to install a larger wire in a feeder but the overcurrent device protecting that feeder must be sized not to exceed in amp rating of that protecting breaker or fuse the maximum ampacity rating of the smallest ampacity rated conductor in that circuit.

Short note. You could install 99% of a feeder or branch circuit any size you want but if you install 1% of that circuit with a smaller conductor then the protecting breaker must not exceed the ampacity rating of that smallest conductor in that circuit.

Good Luck

Wg

[gbeichho]

Thanks, that's what I thought. I'm going to try to pick up some of that wire.