Splicing 8 gauge wire to a 6 gauge?

Question

From the hot tub I have 4 6 Gauge insulated wires leading 20 ft to a sub panel with a 2 pole 50 amp gfci. I then have indoors into the basement a 6/3 w ground leading 30 ft to a junction box. The issue is the green looks a little thinner after being guaranteed it was a 6 as well. From there I have 15 more feet of 4 color 6 gauge leading to the breaker box w another 50 amp 2 pole connection. I've contacted the company that sold it to get double verification it is a 6 and not an 8 in the 30' NM but I believe my eyes here.

Do I have a problem?

Answer 1

Actually, that ground wire likely is smaller, but it is perfectly OK. While in an emergency the ground wire may need to carry the full load of the circuit (or more - when that happens it is often a short-circuit/overload situation), it gets to be sized smaller because the determination of size for wires is based on (over)heating, and that is just not as much of an issue when only used for a short period of time.

See the 250.122 chart (and more details) in How do I know what size grounding conductor is required?

but basically, once you get to copper wire bigger than 10 AWG, the ground wire gets to be a size (or more as it gets bigger) smaller than the hot & neutral wires. And in fact the Southwire cable information shows that's how they make the cables, with 10 AWG ground for cables that have 10 AWG, 8 AWG or 6 AWG conductors for hot/neutral.

These are the general rules. Another answer noted some rules specific to hot tubs. Rules for specific equipment and manufacturer instructions override any general rules.

Answer 2

Two probable issues here, NEC and Listing (UL/CSA/ETL/other).

If the Instructions (which are part of the Listing) for the tub specify #6 or #8 sized copper ground then most versions of NM won't be adequate because #6 NM-B normally has a #10 ground. The NEC requires complying with Listing.

The bigger NEC issue is that in the section for hot tubs 680.42 specifies equipotential bonding/grounding in accordance with 680.25, which specifies #8 minimum size, so using the #10 ground wire from NM-B would be inadequate for conditions that normally exist requiring bonding.

Answer 3

To answer the title question, ILSCO's "Mac Block Connector" can connect any Cu or Al wires up to #6 at affordable prices.

The conductors need to be big enough.

For 50A, you need any of the following:

• Copper NM or UF cable: 6 AWG CU (55A actually)
• Copper (any other type of) cable or wire with 75C terminations: 8 AWG CU
• Aluminum (any other type) with 75C terminations: 6 AWG AL

For feeder of this size, aluminum is not a problem as long as the terminations are rated for it. (that last was the crux of the problem you might have heard about. It also helps to set screw torques correctly, but that's true on any connection.)

For 50A circuits, ground must be #10. Unless...

A 30-60A circuit needs a safety ground wire of #10 copper or #8 aluminum. Any competent wire manufacturer will make cable with a ground of appropriate size.

The only exception is if you choose conductors larger than are required. If so, the ground must get a proportional "size bump" as well. This is a problem you will never have in multi-conductor cable, since not only do they bump ground sizes in proportion, but they are typically overkill anyway.