I've got a 200amp main panel in my basement that only has a single pole free slot. However, I have a 100amp sub panel in the garage that has only a couple of circuits on it (20 amps). I need to add an electric hot water heater to my home. I think most of the new one's require 30amp, so I can't use the single free slot on the main panel. My question is whether I'm ok to run the hot water heater directly to the sub panel in the garage? I'm guessing its ok as where the sub panel is located shouldn't matter, its just a further run I need for cable (50 feet maybe). Just wanted to check before I proceed. thanks

 

Is the sub panel fed with 100 amps? What size is the breaker in the main panel feeding the sub panel?

It might be easier to just install a sub panel next to the main panel for future. Just connect a short nipple between the two panels and move some circuits for the water heater and sub panel breaker(s).

Your panel might also be able to accept tandem breakers. Look at the label inside the panel door.

 

it's a 100amp circuit breaker over to the sub panel. So I'm hoping I can just use that rather than have to add another sub panel.

 

Unless there is currently a lot of load on the sub, I see no reason you cannot feed the new water heater off that.

 

thanks. one more question. do I need to use armored cable, and if so, does it need to be armored the whole length from the sub panel right to the water heater? Or could I run regular 10/3 from the sub panel to a junction box in the ceiling joist above the water heater, and then run a small section of armored cable from the junction box , down a wall conduit, and over to the tank? if it matters, the path from the sub panel would take it up a wall, across ceiling joists the width of the garage (28 feet), down the wall, through the wall and down into the utility room where the hot water heater would be located.

 

You use 10-2 not 10-3 for water heaters. NM-b can be used so long as it is not exposed to damage. Generally above 7'6" is considered protected. From the panel you could protect it with PVC conduit to that height then sleeve it in flexible conduit at the heater.

 

Adding to Ray's comment it is your LOCAL code that you need to satisfy and that may require armored cable or at least a "whip" of armored cable from the heater itself to a J-box on the wall. Also, if the circuit breaker for the heater is not less than fifty feet AND in a direct line-of-sight from the heater you may be required to have a local disconnect at the heater.

 

If the water heater has a smart thermostat and/or a circulator pump, 10-3 is needed, because the pump motor runs on 120 V, as do the electronics.