Steam Shower Unit Wire Size

[hixir]

Steam Shower Installation – Attic Access & Wiring Dilemma

Good afternoon everyone,


I have a bit of a dilemma and could use some advice.


I’m installing a steam shower unit in a second-floor single-family home, with the attic access being the intended installation location. However, the main panel is on the first floor, and due to the layout, running conduit or smurf tube directly to the unit would exceed the NEC’s 360-degree bend limitation.


The steam shower requires 55A at 240V.


I originally considered running 6/4 Romex, but I’m aware that the ampacity of NM-B cable is not the same as individual conductors rated per Table 310.15(B)(16). Since Romex is limited to the 75°C column, it wouldn't meet the ampacity requirement for this load.


Given the conduit restrictions, would it be permissible to run SER cable for this branch circuit to feed the 55A two-pole steam shower unit? If so, what size would be appropriate?


I appreciate any guidance on this. Thanks in advance for your help!

 

[infinity]

The steam shower requires 55A at 240V.


I originally considered running 6/4 Romex, but I’m aware that the ampacity of NM-B cable is not the same as individual conductors rated per Table 310.15(B)(16). Since Romex is limited to the 75°C column, it wouldn't meet the ampacity requirement for this load.

NM cable is actually limited to 60° C not 75° C however #6 AWG @ 60° C= 55 amps so looks like you're good to go.

Welcome to the Forum.

 

[Elect117]

It is 360° bends to the attic or to the unit? You could install pull box in the attic.

Are there install instructions for the unit? Sometimes they specify the wire / if it requires GFCI protection. The install instructions can be pretty specific for these things. I looked up two of them from Home Depots website. One required GFCI, the other did not. One said to only use copper.

 

[hixir]

NM cable is actually limited to 60° C not 75° C however #6 AWG @ 60° C= 55 amps so looks like you're good to go.

Welcome to the Forum.

Thank you for your warm welcome Rob,
You are right about the #6AWG @60 is 55amp. Please correct me if I am wrong, I thought that when installing NM-type cable in this case 6/4 Romex the ampacity would not be the same comparing the individual #6AWG ampacity. I thought it would drop the ampacity, the same as the MC-type wire.

please advise.

 

[hixir]

It is 360° bends to the attic or to the unit? You could install pull box in the attic.

Are there install instructions for the unit? Sometimes they specify the wire / if it requires GFCI protection. The install instructions can be pretty specific for these things. I looked up two of them from Home Depots website. One required GFCI, the other did not. One said to only use copper.

Thank you, I thought about that but, unfortunately, it will be over 4 bends, and installing a pull box would be really hard since the house will be a high-end custom home and there are not lots of places to install an accessible pull box

Still waiting the exact specs from the design team for those units.

 

[infinity]

Thank you for your warm welcome Rob,
You are right about the #6AWG @60 is 55amp. Please correct me if I am wrong, I thought that when installing NM-type cable in this case 6/4 Romex the ampacity would not be the same comparing the individual #6AWG ampacity. I thought it would drop the ampacity, the same as the MC-type wire.

please advise.

You look up the 60° C ampacity for NM cable and use that number (55 amps). If you had individual conductors in a raceway you can use the 75 ° C ampacity.

 

[suemarkp]

Does the steam shower need a neutral? If so, that is customarily called 6-3 with ground. If you are worried about derating, the neutral and ground don't count as current carrying conductors if this a 120/240 service. If the attic is hot, you can use the 90C rating of NM-B as a starting point for thermal derating.

 

[wwhitney]

You are right about the #6AWG @60 is 55amp. Please correct me if I am wrong, I thought that when installing NM-type cable in this case 6/4 Romex the ampacity would not be the same comparing the individual #6AWG ampacity.

First, I don't believe that NM cable is manufactured in 6/4 (4 circuit conductors plus EGC). And if the steam generator needs only a single 240V circuit at 55A, you'd just need 6/2 NM cable (not sure if that's made, or if you can only get 6/3).

But if you did have such a 6/4 cable, and all 4 circuit conductors are CCCs (say two separate 2-wire circuits), you are correct that you would have to consider the 80% ampacity adjustment factor for 4 CCCs. However, when derating a wiring method with 90C insulation (which includes NM-B, despite the overall limit to the 60C ampacity) you can start at the 90C ampacity, which is 75A for #6 Cu.

That means the ampacity (assuming no temperature correction) would be the lesser of (a) the 60C ampacity of 55A and (b) the adjusted 90C ampacity: 80% * 75A = 60A. So the ampacity is unchanged at 55A.

Cheers, Wayne