A colleague of mine posed this question to me today. He is doing a side job for a friend. He has to hook-up a 40A 240V single phase spa. He is running (2)#6's but found out that he had to up the neutral size to #4 (per manufacture - owners manual). Not sure why he had to. Is there any reason to have the neutral larger than the other ungrounded conductors? I told him I have not run across any situation where the neutral had to larger in any circumstance. He told me he ran a "high" harmonics xfmr which needed a larger neutral? Any responses appreciated.

I've seen a few circumstances that require a larger neutral, but I can't see why for a hot tub, if you find out let us know.

I'll bet it's because the spa manufacturer can demand it in the instructions and that won't preclude getting UL labeling. It's no skin off their backs.

most of the load is the heater, the motors are small....there's really no harmonica in the tub.....

My question is why the need to oversize the neutral, 240 volt residential, the neutral will the 'difference ' of the two legs, ie 20 on A and 25 on B then the total on the nutral will be 5 amps.
The heaters are generally 240 volts on both and the neutral is not involved, balance.
What am I missing here, it doesnt make sense to oversize the neutral in this case.
Right ???!!

-Mark-

The high harmonics xfmr was just another instance where he had to up the neutral. The hot tub is another situation. ( i don't see the reason to up the neutral (secondary) in the xfmr situation either!!

are U sure it wasn't the G-wire to said tub?

I don't think it was the ground that would've been oversized. Also if i recall somewhere in the codebook that the equipment ground was never supposed to be larger than the grounded conductor.

menegt Some of these hot tubs have two heating elements that use the neutral and if one of them opens then all of the load is thrown on the neutral most of these self contained hot tubs are set up to be connected to 110v by changing the hookup cord and not useing both heating elements and the motors also are 110v

The term "High Harmonics Transformer", was this something that was quoted in the book?

Sounds like a mistake in printing or something.

Just curious...

Scott S.E.T.