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The sub panel in my shed(about 75ft run from main panel)is very outdated and gfci breakers aren't available for it so I want to update the panel as gfci are required for pool equipment. The panel has 220v and currently has 2 tandem 15amp breakers powering 4 outlets and 3 lights and one double pole 20amp breaker powering the pool pump. Their used to be a pool heater but since has been removed. The supply from the main panel for this sub panel is on a 50 amp double pole breaker. Their is not a bare copper grounding wire ran to the sub panel either and I would like to add one

My questions: Will a 60 amp subpanel be sufficient? If so will the 50 amp double pole breaker in the main panel need to be changed? Would it be nearly impossible to run a bare 10ga ground wire through the existing pvc conduit that is run underground?

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You don't need to upgrade the supply breaker.

The sub-panel can be any size 50 amps or up. Sub-panel "size" is more about space than amperage, at any point past "at least as big as the supply" and space is a good thing to have which normally does not cost much.

It's often worth comparing the price of basic "main" panels that move in volume (100A, 200A) to the cost of a sub-panel which are sometimes MORE expensive, because they sell a lot less of them, or they cost a trivial amount less.

It's perfectly fine to feed a 100A(or whatever) main breaker from a 50 A breaker - the 100A breaker will be serving as a disconnect switch, and you will remove the bonding screw in that panel so it IS a sub-panel. Then you'll have plenty of space for anything.

In most cases the best way to add a wire in existing conduit (unless someone left you a pull string, and sometimes even then) is to pull out the wires in it now (and use them to pull in a pulling rope as you do), add the new wire, and pull all the wires back in together. Green insulated may be a better choice than bare for your grounding wire; Among other considerations, stranded pulls a lot easier than solid.

In the new sub-panel with a 4-wire feed, you'll keep the grounds and neutrals isolated (removal of the bond screw and using a separate bar for grounding connections) and you will either tie the grounds into the grounding electrode system the shed (as a separate structure) should already have had, or add that and bond it to your ground as well.

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  • Ok thank you very much for the information. Any tips on fishing an additional bare wire thru the underground conduit?
    – Zac
    May 7, 2019 at 12:55
  • As stated, pull out all the wires in there now, add the new wire, and pull them all back in, unless there is a pull-string in with the wires you have now. Ramming a fish-tape through there is going to be miserable and might damage your existing wires to boot.
    – Ecnerwal
    May 7, 2019 at 13:08
  • Ok thanks again. That was an idea I had just wasn't sure if it was the best way to go about it. The conduit is 1 inch and the current wires are 6 ga. It seems like it might be a tight fit to get them back in but other than digging it all up their isnt another way.
    – Zac
    May 7, 2019 at 13:16
  • You'll be 20-25% fill which is not bad, as pulls go. Max fill is 40% and I avoid that like the plague (i.e. I'll upsize conduit to stay at a lower fill percentage.) You can pick up a quart of pulling lube if you like, it might make things easier, but is often not needed, and it's messy.
    – Ecnerwal
    May 7, 2019 at 13:36
  • What size rope would you recommend? Also what is the best way to tie the 4 wires to the ropes while keeping the knots as small as possible?
    – Zac
    May 7, 2019 at 13:43

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