240V water heater running on 120V. Should I change elements to 120V?

[Win E]

I have a rental property where a new tenant told me the hot water was running out. Previous tenants never complained. It is a 30 gallon Rheem rated for 240V. I tested the thermostats and elements (240V, 4500 Watts) and everything checked out.

Then I checked the voltage on the electrical supply and it was only 120V. I looked at the electrical panel and saw that the breaker was only a single pole 20 amp breaker. Makes sense that the hot water runs out since the elements would only get 1/4 of the watts it should.

There is no room in the panel to put a double pole. What I would like to know is if I change the elements to 120V, 2000 watts, will this improve the time to heat the water? If I understand this correctly, this would be the max wattage to keep the amps low enough to work with the current 20 amp breaker.

 

[Reach4]

There is no room in the panel to put a double pole. What I would like to know is if I change the elements to 120V, 2000 watts, will this improve the time to heat the water? If I understand this correctly, this would be the max wattage to keep the amps low enough to work with the current 20 amp breaker.

Yes, BUT...

You can often replace a pair of single pole 120 vac breakers with tandem breakers. This take one slot, and has connections for two different 120 volt circuits.

Some panels will support these in all some slots, some will support these in some slots. It will depend on your panel.
The point is to free up two adjacent slots to accept a 2-pole breaker.

There are more possible breakers available.

This one has a 2-pole breaker (for the WH) and two single pole breakers for other circuits. Two slots.

 

[Sponsor]

 

[Win E]

Yes, BUT...

You can often replace a pair of single pole 120 vac breakers with tandem breakers. This take one slot, and has connections for two different 120 volt circuits.

Some panels will support these in all some slots, some will support these in some slots. It will depend on your panel.
The point is to free up two adjacent slots to accept a 2-pole breaker.

There are more possible breakers available.

This one has a 2-pole breaker (for the WH) and two single pole breakers for other circuits. Two slots.

Thanks for the suggestion on breakers. I will have to look again to see if there is enough space. If I recall, the panel already had some of the tandem breakers in use. Wouldn't this suggestion also require me to run another hot wire from the panel to the outlet?

Since you said I can use the 120V 2000 watt elements, I assume that my heating time improvement would be directly proportional to the increase in watts (1125 to 2000 which is about 44%)?

 

[Fitter30]

Need #12 wire for 20 amp breaker. 4500 watt element @ 240 volts 18.75 amps most heater wired with #10 and 30 amp breaker

 

[wwhitney]

What size is the wiring from the panel to the water heater? What type of wiring is it (e.g. NM cable, aka Romex)? Modern yellow NM is 12 awg.

I'm confused by the existence of 120V 2000W elements. That would appear to imply a load current of 16.7A, and the NEC requires storage water heaters to be treated as a continuous load. Which would require a breaker of at least 125% * 16.7A = 20.8A. That is, a 25A breaker minimum, and #10 awg, which isn't a very economical choice. A 1920W element would be 16A @ 120V and would max out the available power on a 20A circuit that can be run with 12 awg Cu.

So is it a marketing thing, the 2000W rating is at 125V, so it's really 16A @ 125V, or 1840W @ 120V?

Cheers, Wayne

 

[Win E]

Thanks for the info. I hope that I can avoid running any new wire and just improve the heat time enough with new 120V, 2000 watt elements.

 

[wwhitney]

A water heater is a single voltage load, so it needs only 2 wires, whether it's 120V or 240V. So if you are able to add a double pole breaker (or use tandems), that's all you need to get 240V, you don't need a third conductor.

Do tell us the details of the existing wire, though.

Cheers, Wayne

 

[Win E]

A water heater is a single voltage load, so it needs only 2 wires, whether it's 120V or 240V. So if you are able to add a double pole breaker (or use tandems), that's all you need to get 240V, you don't need a third conductor.

Do tell us the details of the existing wire, though.

Cheers, Wayne

Not sure what the wire size is from the panel to the outlet, but I assume that since it is a 20amp circuit the wire size is #12. I would need to check it to verify but I have no reason to think otherwise.

I am not an electrician, as you can probable tell, so excuse any stupid questions I have. I was confused by your comment about needing only 2 wires. Wouldn't I need to have a hot wire from each side of the double pole breaker to get 240V (120V from each)?

 

[wwhitney]

Yes, but you would no longer need a neutral, as there would be no 120V loads that require a connection between hot and neutral. So if the wiring method is NM cable, you can lift the white wire off the neutral bar, reidentify it red, and land it on the the other pole of your two pole breaker. Or your electrician can.

Cheers, Wayne

 

[Win E]

Yes, but you would no longer need a neutral, as there would be no 120V loads that require a connection between hot and neutral. So if the wiring method is NM cable, you can lift the white wire off the neutral bar, reidentify it red, and land it on the the other pole of your two pole breaker. Or your electrician can.

Cheers, Wayne

To my surprise, this makes sense. The outlet is a 240v 3 prong dryer outlet (see below). I understand that you don't need a neutral or ground since each of the two 120V wires come from the panel from different phases.

I believe that I will need 30 amp double pole breaker and #10 wire. If the wire is #12, I should probably stick with the current configuration using the 20 amp single pole breaker and operating the water heater with the 120V 2000 watt elements. Is there an issue with using this outlet in this scenario?I think it is a 30 amp? Do you see any other issues?

 

[wwhitney]

OK, you really need to verify what the current wiring method is to know what your options are.

On the receptacle you posted, I'm not sure what the middle triangle is. If that's absent, it's a NEMA 10-30 receptacle, which is an ungrounded 120/240V 30A receptacle. It is not appropriate for any new installation, and if you are touching an existing one, you should replace it with the proper receptacle. If your current circuit is feeding that receptacle, there's some chance it's #10 copper, which matches the 30A rating of that receptacle. Or it may be #12 copper, which matches the 20A breaker you mentioned. [Are you 100% sure you've got the right breaker?]

A water heater could be cord and plug connected (if the option is permitted by the manufacturer's instructions), or it could be hard wired. Obviously you only need a receptacle if cord and plug connected. The receptacle and plug used would depend on the element installed. If it's a 120V/15A element (1800W), then you could use a regular 5-15 receptacle. If it's 120V/16A (1920W), then you'd need a 5-20 receptacle. And as per my previous posting, to my understanding a 120V/2000W element is not appropriate for a 20A circuit, you'd need at least a 25A circuit and a very rare NEMA 5-30 receptacle.

If you go with a 240V element, it looks like various sizes are available. A 3800W element would be just under 16A, and so it would work with a 20A 240V circuit with #12 copper conductors, and you could use a NEMA 6-20 receptacle if it's cord and plug connected (with the manufacturer's allowance). Or if you have #10 copper conductors, you could use a 30A circuit and use a 4500W element, as would be standard for a new install. That would require a NEMA 6-30 receptacle if cord and plug connected.

Cheers, Wayne

 

[Win E]

Wayne, you are a wealth of information and I appreciate your willingness to share it.

You are correct about the type of receptacle in the picture. The triangle is just the screw hole for the plate. This is an older home and the receptacles in it are not grounded. There are no ground wires at any outlet. The water heater has a cord and plug, which is common in my area.

I assume that a "proper receptacle" is one that has a ground? Given the non-grounded wiring I am not sure if I can legally use a receptacle designed for use with a ground unless I actually have a ground. Are you suggesting I run a ground wire from the panel and install an new receptacle?

The previous owner had a new breaker panel installed shortly before I bought it. Your suspicion that the wire is #10 makes sense since it would have been originally wired for 240V 30A. He was pretty cheap and would not have pulled new wire.

Right now it seems that my options are dependent on whether I can make room for a double pole 30A breaker and the size of the wire (#10 or #12).

Option 1
If the wires are #10 and the panel has room I will replace the existing breaker with a 2-pole 30A breaker and leave the existing 240V 4500W elements in the water heater. Don't really know what to do with the receptacle except leave it as is since the rating matches the breaker.

Option 2
If the panel has no room for 2-pole breaker and wire size is #10, I will replace the 1- pole 20A breaker with a 30A and install 120V 2000W elements. No change to the receptacle and plug.

Option 3
If the panel has no room for 2-pole breaker and wire size is #12, I will leave the existing 1- pole 20A breaker and install 120V 1650W elements. I will change the receptacle and plug to one that is properly rated or just hard wire.

Thanks again for all of your help.

Win

 

[wwhitney]

The receptacle would suggest the wiring feeding it would be 3 conductors--two hots and a neutral. The neutral might be insulated or it might be bare. As long as you can repurpose that neutral as an EGC, reusing it would be fine. [And if the wiring originates at the service panel, that repurposing may not involve actually changing the termination in the service panel, as there may be a combined neutral/ground bar.] The water heater needs to be grounded.

Option 1 should properly be a 6-30 receptacle and plug, or else hard wired. But leaving it as a NEMA 10-30 is understandable, particularly if the wiring originates in a service panel with a combined neutral/ground bar. As in that case the meaning of the 3rd conductor (neutral or ground) is somewhat ambiguous.

Option 2 needs to be a 5-30 receptacle. Providing a 10-30 with only 120V would be improper.

Option 3 could use a 5-20 receptacle, those are commonly available. I would suggest a simplex, to make it clear that nothing else should be plugged into the circuit. E.g.

https://www.homedepot.com/p/Leviton...t-Single-Outlet-White-R52-T5020-0WS/202066676

Cheers, Wayne