Wire gauge question for hot tub

We are getting ready to move our hot tub, and I’m going to need to run electrical service to the new location. This will be the third time I’ve done this, so I’m familiar with the procedure, no need to panic.

We have always used 6 gauge wire for these installations, without problem. The hot tub is 50 amp–a 50 amp breaker goes in the main box, and then on the outside box it splits to a 20 and a 30 amp breaker. The 6 gauge appears, googling around, to be the standard for hot tubs. But not according to the actual wire charts.

Our run is 43’. Looking atthis and other tables, we should be using either a 2 or a 1 gauge wire, but that’s huge! Nobody uses wires that big for service to a hot tub. What am I missing here?

That table says it’s for 12v circuits. 6 gauge is correct for this application.

Take a look at http://www.houwire.com/products/technical/article310_16.html

Ah! Thank you!

I don’t know anything about the electrical code, but I know that 6 gauge is about 0.4 ohms/kft. At 50 amps, the voltage drop across 1 ft of wire is 0.02 V, and the power 1 W. Over the 43 ft run, the voltage drop is 0.86 V.

The hot tub certainly won’t notice a <1 V voltage drop, and the wire will have no problem getting rid of 1 W/ft of heat. Seems safe enough in a basic physics sense.

The reason for different standards for 12 V is that the voltage drop is independent of the overall system voltage. 0.86 V is a much larger fraction of 12 V than it is of 120 or 240 V, so you need a thicker wire to achieve the same percentage tolerance.

Thanks, that is interesting. I’ve wired two houses in the past few years, and I know quite a bit about the NEC, but not much about the science of it. I’ve never worked with 12v systems. I should really go back and learn the nuts and bolts.

I just had my spa moved and the run from the 50 amp breaker is now approx 120 ft. We used 6 gauge wire the entire way and it is run through metal conduit. The spa was working fine prior to moving (10 ft from breaker) and now the problem is that it will run for about 10 seconds before it trips the 50 amp breaker. My electrician says it is the spa but I am thinking it is a voltage drop due to the length of the wiring. Before I get a third party out to investigate I would like some qualified opinions on if I am barking up the wrong tree here. If it is the length of the run what is the solution, 4 gauge wire?

Is there an outside box? Standard instalation is a 50 amp breaker in your main panel, going to a sub panel outside near the tub. Is that the setup you have? If so, which breaker is tripping?

I would’ve sworn the first word in the title was WINE. Hmmm… Might’ve made a more lively discussion? :smack:

Look at the name plate data on the spa. what is the amp draw?

The wire acts as a series resistor to the hot tub. I’m curious how additional resistance would trip the breaker. Anyways, according to calculator.net you are getting a 3V drop at 50A. Assuming 120V source.

Is the wiring warm to the touch when the tub is running? Should be cold.

Anyway look at the voltage and amperage on the hot tub name plate.
Also read the hot tube installation manual.

For longer wire runs, you need a larger gauge wire due to “voltage drop”. Size will be different if aluminum or copper wire.

Search google.com for the words…
Voltage Drop Calculator

Use single phase.