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I've got a 100 amp subpanel that the previous owners used for a hot tub. The new hot tub we're getting only needs 50 amps. Can I reuse the existing wiring, breakers and subpanel for the new tub, or do I need to change the subpanel and the main breaker to 60 amps?

Image of the subpanel: I've got a 100 amp subpanel that the previous owners used for a hot tub. The new hot tub we're getting only needs 50 amps. Can I reuse the existing wiring, breakers and subpanel for the new tub, or do I need to change the subpanel and the main breaker to 60 amps?

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Image: https://imgur.com/LZ10pqR

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    What gauge are the existing wires, and what's the diameter of the existing conduit? Aug 17 at 1:29
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How many Amps?

I think we have a bit of confusion here about 50 Amps vs. 100 Amps.

You appear to have a double-pole 50 Amp GFCI breaker. That means a few things:

  • It provides 240V at up to 50 Amps.
  • It can also provide 2 x 120V at up to 50 Amps.
  • It provides protection against ground faults, which is critical, and required by code, for hot tubs (and most other outdoor and/or water-related electrical connections).

It is not 100 Amps. If it were, the wires would be a lot thicker, among other differences.

The subpanel may actually be rated for much more. A small subpanel is typically rated for 60 Amps, but sometimes more. That allows for a 50 Amp double breaker for a hot tub (or an RV) as well as another circuit or two for other stuff - e.g., 120V lights, 120V convenience receptacles.

This subpanel appears (I am not an expert) to have incoming power on lugs (i.e., no master disconnect here - so to do any work on the subpanel you would turn it off at the matching breaker in the main panel) and 4 breaker spaces. Each breaker space can be a 120V breaker or 1/2 of a 240V double-breaker. You currently have a 50 Amp double-breaker and 2 empty spaces above it.

Neutral vs. Ground

Neutral and ground are supposed to be kept separate except in the main panel. It looks to me like all the grounds and neutrals are together in the lower left. I actually don't see the neutral coming from the main panel feed, but there are some hidden wires so it may be in there somewhere. The neutral gets extra confusing because for a GFCI it goes to the breaker (for monitoring) as well as to the neutral bar on the panel. But the grounds and neutrals should be on separate bars and the neutral bar not grounded to the case of the subpanel.

The good news is that if you indeed are missing a neutral, your wires are in conduit so you can add an appropriately sized white wire as neutral.

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    I don't see any neutrals in that box at all. Looks like all hot and ground with the GFCI wired for line-to-line current. Aug 17 at 4:56
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    There is a neutral from gfci to ground bar. Don't see neutral from either conduit. Aug 17 at 5:02
  • Looks like they are using the ground back to the main panel as the neutral path for the GFCI. Tisk, tisk, tisk...
    – tnknepp
    Aug 17 at 16:53
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I was cleaning my car's tires and I notice they say "130 MPH rating". Oh no! I only drive 70 mph! Do I need to get the tires changed? Where do I even buy 70 mph tires?

That's what you're talking about there. You have a subpanel that is rated 100 amps maximum. You are actually sending 50 amps through it. That is allowable and safe, because 50 < 100.


The THHN wire is #6, because the installer was a dummy. But you can take advantage of that. #6 THHN is actually good for 65A. Back at the main panel, this can be fed by a breaker as large as 70A (65A, rounding up to the next existing breaker size).

Inside this panel are several things.

First, there's a 50A GFCI breaker already in it. That's designed to feed 50A to a hot tub. And by wild coincidence, YOUR hot tub is 50A, and it needs a GFCI breaker! So yeah. You can reuse this GFCI breaker. And since they're $100 normally nevermind COVID shortages, that's a good idea.

Second, there are 2 empty spaces in this subpanel. Each space has 15 amps to spare. You can install 240V-only loads: continuous loads up to 12 amps, or non-continuous loads up to 15A. So for instance a well pump could go there.

Third, it really looks like the dummy who wired this chose to cut off strands of the wire to make them fit on the bars. That neutral bar ought to be able to take #6 wire just fine. So clean that up.

Fourth, this panel doesn't have neutral brought from the main panel. Nothing here uses neutral except the GFCI (to power itself), and that is bootlegging neutral from ground. That's not how I would've done it, but I'm not going to tell you it's unsafe. If you want anything in this panel that uses neutral, you will need to pull a neutral wire from the main. To make space in the conduit, change out that #8 ground (amateur!!!) to a bare #10 ground. Also, remove the neutral-ground strap and install an accessory ground bar, so grounds are separate from neutrals.

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The existing panel and breaker should be fine.

The panel is rated for up to 100A, the maximum current it is configured for based on wire size and matching breaker feeding the panel is 50A. You could use a 200A panel out there being fed by #8 thwn, and you could still only feed it with a 50A breaker due to wire size.

You need to separate the grounds and neutrals. it appears (though I can't be certain) that the bus you have is a neutral bus and should be isolated from ground. The panel cover should list a part number for a ground bus, some inspectors will insist that specific UL/CSA/ETL "Listed" part be used, but not always.

Also because of the warm ambient temperature in a hot tub the instructions may say to feed the tub from the disconnect with a specified minimum wire size that would normally be considered oversized. The instructions are part of the "Listing" and they must be followed.

Finally note if you have to change the wire to the tub from the disconnect install an insulated ground wire like before, the code doesn't allow bare grounds for hot tubs.

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  • I may have judged wire size incorrectly, pretty sure it is at least #8 so 50A is good, but it is possible you could use a larger breaker as noted by Harper. Aug 17 at 16:56
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As long as the panel is not undersized, then you can use almost any size panel you want.

Can have a 200 amp panel that only has a 15 amp circuit in it. The breaker size is what is important.

Wire gauge must be large enough for amps the breaker protects. If the wire gauge is correct for a 50 amp breaker, you are good to go.

For a subpanel do think you need to separate ground and neutral wires coming in. Wait for an expert to confirm.

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  • Yes, I have 4 wires coming into the subpanel. Two hot (black wires), a neutral white, and a green ground. The panel then only has 3 wires leaving, 2 hot, and 1 ground. I'm checking to see if the hot tub will work with 3 wires or if I need to add a fourth neutral wire going out.
    – Anks329
    Aug 16 at 23:47
  • It is that neutral and ground should only be connected/bonded together at main panel only. For sub panels they need to be separated, not bonded together.
    – crip659
    Aug 16 at 23:52
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So you have a 100 Amp sub panel but in it is a 50 Amp GFCI breaker so you should be OK. The only glitch would be if your new tub instructions stated that a 60 Amp breaker is needed. What size breaker in your main panel feeds this sub panel?

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  • There are two 50 amp breakers connected together in the subpanel, and the main panel has two 50 amp breakers connected together. So, since I'll only be pulling 50amp of load from the hot tub, I should be fine.
    – Anks329
    Aug 16 at 23:45
  • @Anks329 It's a double pole GFCI breaker with handle ties. 120/240 volt, 50 Amp
    – JACK
    Aug 17 at 0:40

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