is using dryer plug acceptable?

I'm installing a new water heater.. 240V, 4500W, so that is 18.75 amps..so I need a double 20 amp circuit? I guess using the existing double 30A would be to much..(.Hmm just answered that question by looking at the other blog..150% over 18.75A is 28.125A and the next higher breaker is 30A so I'm good)....
I would also like to wire the heater to the existing dryer plug for ease of moving the tank, is it OK to use a dryer plug and wires of the correct gauge or should I really use metal conduit?

stay with a 30 or 25 amp breaker. Since a heater is not defined as portable, its probably "illegal" though I see no safety issues. Dryers only get moved every 10 years anyway.

In this area, the heater MUST be connected to the wall with a wire enclosed in a metal sheath, i.e., NO bare Romex or "line cord".

A 3 pole dryer receptacle would NOT be at all acceptable for a water heater. It has 2 hots and a neutral..no ground. It is completely unacceptable to use the neutral to ground the water heater. Back in the day, that was OK for a dryer, but not a good idea and no longer allowed on new circuits.
A 4 prong dryer receptacle would in theory work...2 hots , neutral, ground. But that is not the correct receptacle for a water heater circuit. You would really want to use a regular NEMA 6-30, IF your inspector allows a plug at all.

I wonder about the advisability of using a plug a the disconect means for a water heater, since you could easily indavertantly pull the plug under load....not a good idea.


A 20 amp circuit is probably not correct for 4500 watts. But 25 amps would be. Since 25 amp breakers are not common, a 30 amp is usually used.

The water heater should be on a 30-amp circuit with #10 wires, all the way to the unit.

Where you come out of the wall, you should have a disconnect switch. One of the $12 disconnects they sell for use with air conditioners will work fine.

Unless the heater is small (5 gallon or less), it's not allowed to have a cord & plug connection in the latest electric code. I may not like this, but that's the rule. So, your connection between the disconnect and the heater will probably use "MC," which has wires wrapped in a metal sheath. The length you use should have four wires in it. You'll need the black, the red, and the green. The white will not be used. The 'home stores" either will cut it to length, or sell you a 25-ft. roll.