Electrical Water Heater w/ Only 2 Wires

I purchased a A.O. Smith 30 gal electric water heater as a supplemental heater to my main heater (the reason is due to location of bathrooms and the main water heater). It is a 240 V, max 4500 watt unit. Anyway, when I opened the face plate to locate the wire connections, there are only two wires, one red and one black. There is also a grounding screw on the top of the unit near the face plate. Where is the white neutral wire for the electrical current to return to the panel box? Assuming this is correct, do I just connect the red and black wire to a 240 V, 20 amp breaker and the ground, and not connect the neutral?

 

Electric water heaters generally don't use a neutral wire. All you'll need is a 2 wire with ground feeder. No need for a neutral. You may be able to tape the white cable with red tape and have it used as a hot feeder. A 12-2 w/ground should be enough, although I would use a 10/2 for future "upgradability".

 

Thanks

 

10/2 is the standard cable for a water heater. Connect white to red. 12/2 would be insufficient for almost all water heaters.

 

I agree with the use of #10 wire. You wouldn't want a 30 amp breaker on #12. This is a 240 volt circuit and therefore a phase to phase voltage. A neutral isn't required because the "return" is the other phase wire (either black or white in this case - electricity is shade-insensitive). In your panel, you'll have the black wire (of your #10, 2 wire with ground cable) on one pole of the 240 volt breaker and the white wire on the other. At the heater, connect black to black and white to red (although it really doesn't matter - you could just as easily (and safely) connect black to white and red to black). The bare wire is an equipment ground which goes under the grounding screw on the heater and should be connected to the grounding bus at the electrical panel.

 

You need to use 10-2 on a 25A DP breaker. If you use 12-2 on a 20A DP breaker you will have to change the 4500 watt (4500 / 240) x 1.25 = 23.4 amps) elements to 3500 watt (3500 / 240) x 1.25 = 18.2 amps.

 

I don't think you're going to find a 25-amp breaker. Use a 30-amp breaker.

 

25A DP breakers are readily available. For some reason I changed from 30A to 25A breakers for 4500 watt water heaters years ago. I don't know if it was because of a code change that has since been ammended or possibly a local code. 422.11(E)(3) states that you can't exceed 150% of the rated current. In the case of a 4500 watt heater 4500 / 250 = 18 x 1.5 = 27 amps. The section allows you to go up to the next breaker size which would be 30A. It appears 30A is fine - just wish I could remember why I switched to 25A, which BTW I have never had a problem with. Is it possible that the nameplate tells you to use 25A breakers?

 

Thanks for the info mcjunk. I learn something new every day. Do you know which brand breakers come in the 25 amp size?

 

All breakers. For instance last time I looked, Lowe's carried Siemens, Murray, SqD Homeline, SqD QO, Cutler Hammer BR & CH, and they sell a DP 25 for all of them. If Lowe's sells them then they have to be available at any supply house. Often times an air conditioning compressor needs to have 25A OCP and a 25A breaker will allow you to install a non-fused disconnect as opposed to a 30A breaker with a fused 25A disconnect.

For the longest time I didn't know they made 30A SP breakers. I couldn't figure out why anybody would ever need one until I had to wire a 120V 30A outlet for a travel trailer. Since then I've even seen 50A SP and a few other oddities that I can't remember right now.

 

Do water heaters need to use the1.25 rule? I can't see why. A water heater will not normally run for more than 3 hours which is what I thought the requirement was for uping the current. If it is required what is the code section?
Thanks

 

422.13 Storage Type Water Heaters. A branch circuit supplying a fixed storage type water heater that has a capacity of 120 gallons or less shall have a rating not less than 125 percent of the nameplate rating of the water heater.

Water heaters don't normally run for more than 3 hours but it is certainly conceivable. A house full of people taking long showers on Saturday morning would do it.

 

mcjunk,
Thanks.... I found the rule last night after I logged off. Learn something new everyday.

Also, since I'm too lazy to reply to my other question about the 6' rule on service entrance cables, thanks for that as well. I suspected that it was something of a local rule.