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The main panel of the house already has a 50 amp breaker. There is 6-6-6 Awg wires and a bare copper ground coming from the breaker to the corner of the house that was used for a spa that is no longer there. I would like to run the 6-6-6 inside 1" conduit underground and run the 6 awg bare copper ground next to it for my RV service. Is this OK or do I need to install them all together in one larger conduit?

The 6-6-6 is shielded aluminum and twisted together.

The conduit is Sched. 40 PVC.

I'm using terminal blocks to connect the wires inside metal cabinets.

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    Can you give us a cable type on the 6-6-6? Are these 6-6-6 in a jacketed cable or are they 3 individual wires sorta stuck together? Is the neutral in the 6-6-6 insulated or bare (if insulated, how old is it?) Are they copper or aluminum? (aluminum is very OK here). Feb 4, 2022 at 20:47
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    ...what TYPE of conduit - what material is it made from? Is it metal or plastic???
    – Ecnerwal
    Feb 4, 2022 at 21:06

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You can't run ground (or any individual wire) outside conduit in the ground - it needs to be protected from damage.

But you really don't have a problem. Based on a quick look at some conduit fill tables, you can run a minimum of 5 x 6 AWG wires in a 1" conduit (Schedule 80 PVC), and even more in other types of conduit.

You also don't need a 6 AWG ground. See NEC 250.122. Based on a 50A circuit, 10 AWG is fine.

Just realized you are using copper. Unless local rules forbid it, you are much better off with Aluminum. 50A is actually OK on 6 AWG aluminum, though you need an 8 AWG aluminum ground instead of 10 AWG copper. But you can likely save a lot of money even if you go with much larger aluminum wires, which would give you increased capacity for the future if needed. If you have already bought the 6 AWG wire, you may want to consider returning it or selling it and buying aluminum to save a bunch. But if you do that, you need to make sure that all connections are done appropriately. Connections directly to breakers and panels are usually not an issue, but connections between wires (e.g., between the already installed 6 AWG copper in your house and new aluminum for the outside portion) need to be done properly - you can't just throw the usual wire nuts on.

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    Depending on the cable type, the ground wire may need a bump. When you use 65A wire for a 50A circuit, you gave the conductors a wire size bump, and you need to give ground a proportionate one. Feb 4, 2022 at 19:28

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