120v Tank Connected to 30A Dbl Brk

[wwhitney]

I reviewed all your posts in this thread, the details have changed a bit over time. And taking a voltage measurement between the black and red is the way to confirm that you have 240V at the water heater, vs say some wiring error that puts both the black and the red on one leg of the supply, providing 0V between them.

So how about a diagram that shows all the details as you currently understand them: the panel, the switch box, the water heater junction box, the size and type of cable between each of those, and how the wires are connected at each location.

But as a basic comment, certainly if you have 120/240V at your water heater (which would require 10/3, not 10/2), and your 3800W 240V heater is currently operating at 120V (so 950W), you can switch it to operate at 240V and get ~4 times the heating power.

And a 20A breaker is fine for a 3800W heater: the limit for a tank water heater on a 20A/240V circuit is 80% * 20A * 240V = 3840W. So 3800W elements are made for precisely this application.

Lastly, a single pole switch is fine as a _controller_ for a 2-wire 240V load, but not as a _disconnect_. A controller is just for turning the appliance on or off, which breaking a single conductor will do. While a disconnect is to remove all power downstream to make it safe to work on, which requires breaking both conductors. So the 20A double breaker would be your disconnect.

Cheers, Wayne

 

[Reach4]

took reading at panel, and at element and both legs have 124v + or - coming thru; 20 amp dbl breaker is a 20amp dbl breaker, pic will not change that fact

For a 240 volt circuit troubleshooting, do not put either meter probe on neutral or ground.

Suppose for the moment that you had a 240 volt circuit, but there was a break in the middle of the red wire. With one probe on ground/neutral, you would measure 120 volts at any point on either wire or the heating element terminals. That is because at one side of the red-wire break you would get voltage from one leg of the 2-pole breaker. On the other side of the red-wire break, you would get voltage from the other leg via the unbroken black wire, and via the element.

 

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[Bruce Dew]

I reviewed all your posts in this thread, the details have changed a bit over time. And taking a voltage measurement between the black and red is the way to confirm that you have 240V at the water heater, vs say some wiring error that puts both the black and the red on one leg of the supply, providing 0V between them.

So how about a diagram that shows all the details as you currently understand them: the panel, the switch box, the water heater junction box, the size and type of cable between each of those, and how the wires are connected at each location.

But as a basic comment, certainly if you have 120/240V at your water heater (which would require 10/3, not 10/2), and your 3800W 240V heater is currently operating at 120V (so 950W), you can switch it to operate at 240V and get ~4 times the heating power.

And a 20A breaker is fine for a 3800W heater: the limit for a tank water heater on a 20A/240V circuit is 80% * 20A * 240V = 3840W. So 3800W elements are made for precisely this application.

Lastly, a single pole switch is fine as a _controller_ for a 2-wire 240V load, but not as a _disconnect_. A controller is just for turning the appliance on or off, which breaking a single conductor will do. While a disconnect is to remove all power downstream to make it safe to work on, which requires breaking both conductors. So the 20A double breaker would be your disconnect.

Cheers, Wayne

The NEC recommends using a Gauge 10 non-metallic or metal-clad electric cable with two conductors (10/2) for 4500-watt water heaters.

 

[wwhitney]

The NEC recommends using a Gauge 10 non-metallic or metal-clad electric cable with two conductors (10/2) for 4500-watt water heaters.

The NEC doesn't have recommendations, it has minimum requirements. For a 4500-watt 240V tank water heater, the current is 18.75A, but the NEC requires that the branch circuit be treated as a continuous load, so the minimum ampacity conductor and OCPD is 1.25 * 18.75 = 23.4A. So the typical solution is #10 AWG copper conductors and a 30A double pole breaker. If the circuit length were unusually long, or if the conductors were in conduit with other circuits, there might be a reason or requirement to upsize the conductors to #8 AWG copper.

Cheers, Wayne

 

[Bruce Dew]

For a 240 volt circuit troubleshooting, do not put either meter probe on neutral or ground.

Suppose for the moment that you had a 240 volt circuit, but there was a break in the middle of the red wire. With one probe on ground/neutral, you would measure 120 volts at any point on either wire or the heating element terminals. That is because at one side of the red-wire break you would get voltage from one leg of the 2-pole breaker. On the other side of the red-wire break, you would get voltage from the other leg via the unbroken black wire, and via the element.

Then how would I read the wiring; at breaker there are 2 legs, white/black wire and grd, at top of wtr heater is white/blk wire and ground. dbl pole 20 breaker. Htr element say 240v 3500 watt. Each leg say 120, so would I just touch both the blk/white at same time with probes, no grd to get 240 reading, thanks.

 

[wwhitney]

so would I just touch both the blk/white at same time with probes ,no grd to get 240 reading, thanks.

Yes, that is how you measure the voltage between any two wires. When one of those wires is the ground (EGC), then you are measuring the voltage to ground, but you can measure between any two wires. Voltage is a relative measurement, not an absolute; ground is just an often convenient base point to choose.

Then how would I read the wiring; at breaker there are 2 legs, white/black wire and grd, at top of wtr heater is white/blk wire and ground. dbl pole 20 breaker. Htr element say 240v 3500 watt. Each leg say 120,

Based on the above description, sounds like your water heater is already 240V. But a complete circuit diagram would allow a more definite determination.

Cheers, Wayne

 

[Bruce Dew]

The NEC doesn't have recommendations, it has minimum requirements. For a 4500-watt 240V tank water heater, the current is 18.75A, but the NEC requires that the branch circuit be treated as a continuous load, so the minimum ampacity conductor and OCPD is 1.25 * 18.75 = 23.4A. So the typical solution is #10 AWG copper conductors and a 30A double pole breaker. If the circuit length were unusually long, or if the conductors were in conduit with other circuits, there might be a reason or requirement to upsize the conductors to #8 AWG copper.

Cheers, Wayne

That sentence came from web search showing that 10/2 and not 10/3 is used on water heater. I know my breaker is too small for 4500 elements but the replacement unit has a 4500 and I need replace it or the breaker.

 

[Reach4]

Then how would I read the wiring; at breaker there are 2 legs, white/black wire and grd, at top of wtr heater is white/blk wire and ground. dbl pole 20 breaker. Htr element say 240v 3500 watt. Each leg say 120, so would I just touch both the blk/white at same time with probes, no grd to get 240 reading, thanks.

At the breaker box, you have a 2-pole breaker. Each output has a hot wire. You would measure between the two hots. It is good to start there in that you will know the meter works. The problem could be the breaker, but that seems less likely. Still, since it is easy to identify, it is good to make sure you get the 240 volts thru the breaker.

Sometimes a white wire is used as a hot. In this case, the wire should be marked at each end. I am not sure of the rules, but one method some have used is to color the end with a black Sharpie.

At the other end of the line, you should have 240 volts also. If you have a problem to that point, you will not.

At the WH, if the top element has 240 volts across its terminals, but you don't get hot water, that element is bad. If you don't get 240, the problem is before that.

Why the top element? The thermostat should give priority to the top. If that is already hot, then it can feed the power to the lower element. Since you don't have hot water at all, the top element tells the story.

A failed thermostat can be what is blocking the voltage from reaching the element.

 

[wwhitney]

That sentence came from web search showing that 10/2 and not 10/3 is used on water heater.

That's right, so I was surprised when you mentioned 10/3 earlier in the thread (post #16).

I know my breaker is too small for 4500 elements but the replacement unit has a 4500 and I need replace it or the breaker.

So if you have a working 240V 2-wire circuit (not 120/240V 3-wire circuit) run in #10 Cu, which is currently on a 20A breaker, and a water heater with a 3800W element, that was all good. #10 was larger than required, #12 would have sufficed.

Now you want to replace the water heater and use a 4500W unit, which requires a 25A or 30A breaker. [It might actually run fine on your 20A breaker, but there's a good chance the 20A breaker would nuisance trip, so the larger size is required. Nuisance tripping is the only downside to the smaller breaker.]

Since the wire is the correct size already for the larger circuit, the only question to ask is whether there is a reason the smaller circuit was previously used. Does the supplying panel for the circuit, and the electrical service, have sufficient capacity for the larger circuit? A load calculation is used to determine that. Is the 10/2 cable running to the water heater passing through an unusually hot location (how hot?) and/or bundled with multiple other cables (how many cables, and how many conductors in each?).

Absent those two issues, you could upsize the breaker for your existing 10/2 cable to 25A or 30A. You would need a torque screwdriver to make the connections at the breaker to the torque specified on the breaker case.

Cheers, Wayne

 

[Bruce Dew]

Yes, that is how you measure the voltage between any two wires. When one of those wires is the ground (EGC), then you are measuring the voltage to ground, but you can measure between any two wires. Voltage is a relative measurement, not an absolute; ground is just an often convenient base point to choose.


Based on the above description, sounds like your water heater is already 240V. But a complete circuit diagram would allow a more definite determination.

Cheers, Wayne

I thought it was 120 originally and the receipt from 2004 says 120/240 purchased but now it appears more than likely it's 240v. Dia in manual says if unit has blk/red wire out top for connection then its 240. I don't know, and getting more confused daily.

At the breaker box, you have a 2-pole breaker. Each output has a hot wire. You would measure between the two hots. It is good to start there in that you will know the meter works. The problem could be the breaker, but that seems less likely. Still, since it is easy to identify, it is good to make sure you get the 240 volts thru the breaker.

Sometimes a white wire is used as a hot. In this case, the wire should be marked at each end. I am not sure of the rules, but one method some have used is to color the end with a black Sharpie.

At the other end of the line, you should have 240 volts also. If you have a problem to that point, you will not.

At the WH, if the top element has 240 volts across its terminals, but you don't get hot water, that element is bad. If you don't get 240, the problem is before that.

Why the top element? The thermostat should give priority to the top. If that is already hot, then it can feed the power to the lower element. Since you don't have hot water at all, the top element tells the story.

A failed thermostat can be what is blocking the voltage from reaching the element.

u say between the 2, do u mean placing probe on each wire connection and nothing to a grd. Mtr has 2 probes, so red probe to one wire and blk probe to other wire at same time.

 

[Bruce Dew]

That's right, so I was surprised when you mentioned 10/3 earlier in the thread (post #16).


So if you have a working 240V 2-wire circuit (not 120/240V 3-wire circuit) run in #10 Cu, which is currently on a 20A breaker, and a water heater with a 3800W element, that was all good. #10 was larger than required, #12 would have sufficed.

Now you want to replace the water heater and use a 4500W unit, which requires a 25A or 30A breaker. [It might actually run fine on your 20A breaker, but there's a good chance the 20A breaker would nuisance trip, so the larger size is required. Nuisance tripping is the only downside to the smaller breaker.]

Since the wire is the correct size already for the larger circuit, the only question to ask is whether there is a reason the smaller circuit was previously used. Does the supplying panel for the circuit, and the electrical service, have sufficient capacity for the larger circuit? A load calculation is used to determine that. Is the 10/2 cable running to the water heater passing through an unusually hot location (how hot?) and/or bundled with multiple other cables (how many cables, and how many conductors in each?).

Absent those two issues, you could upsize the breaker for your existing 10/2 cable to 25A or 30A. You would need a torque screwdriver to make the connections at the breaker to the torque specified on the breaker case.

Cheers, Wayne

Box has capacity, even more so than originally because I removed some items and placed in subpanel at main breaker box. Also I rebalanced the load yrs ago.

 

[Fitter30]

3800 watts is 16 amps at 240 vac
17 at 230 vac
Your fine just wire up take black electric tape wrap a inches over white wire. Change thermostat and limit if its not labeled 240vac. Mark the heater and breaker.

 

[Bruce Dew]

3800 watts is 16 amps at 240 vac
17 at 230 vac
Your fine just wire up take black electric tape wrap a inches over white wire.

I don't have anything 3800 watt, curent mdl is 3500watt and replacement is 4500. Have to replace breaker or element.

 

[Bruce Dew]

I don't have anything 3800 watt, curent mdl is 3500watt and replacement is 4500. Have to replace breaker or element.

I just came from heater and if I connect probe to blk and red at element I get 0/-1 reading but ea leg separately using grd on meter I get 120. How can I find out what is going to this unit, hire an electrician?

 

[wwhitney]

I just came from heater and if I connect probe to blk and red at element I get 0/-1 reading but ea leg separately using grd on meter I get 120. How can I find out what is going to this unit, hire an electrician?

Either hire an electrician, or post detailed pictures of every box with every end of every cable that you understand to be part of the circuit. Sounds like that would be the panel with the breaker, the switch box you mentioned, and the water heater junction box.

Cheers, Wayne

 

[Reach4]

I just came from heater and if I connect probe to blk and red at element I get 0/-1 reading but ea leg separately using grd on meter I get 120. How can I find out what is going to this unit, hire an electrician?

Depends on how motivated and able you are to troubleshoot yourself. Also, troubleshooting may take time. Electrician will be one and done. I had made some suggestions for troubleshooting. Did those make sense to you?

I would at least try to measure voltage across the input to the thermostat. If that does not show 240, you could call an electrician. If it does show 240, call a plumber. The electrician might just have to flip the lever on the breaker or replace the breaker. Or the electrician might have to track down where you lose continuity on the way to the WH.

You say you get about zero VAC across the element. Most WHs have two elements.

 

[Bruce Dew]

Either hire an electrician, or post detailed pictures of every box with every end of every cable that you understand to be part of the circuit. Sounds like that would be the panel with the breaker, the switch box you mentioned, and the water heater junction box.

Cheers, Wayne

Will the 240 only show when the heating element kicks on?

Depends on how motivated and able you are to troubleshoot yourself. Also, troubleshooting may take time. Electrician will be one and done. I had made some suggestions for troubleshooting. Did those make sense to you?

I would at least try to measure voltage across the input to the thermostat. If that does not show 240, you could call an electrician. If it does show 240, call a plumber. The electrician might just have to flip the lever on the breaker or replace the breaker. Or the electrician might have to track down where you lose continuity on the way to the WH.

You say you get about zero VAC across the element. Most WHs have two elements.

Just 1

 

[Reach4]

The 240 would show only when the heating element kicks on. But I am presuming your water is cold, so the thermostat should be sending power. This presumes the control is no turned to off.

Got it. Most have two elements, but I can see a smaller WH could have just the one..

 

[Fitter30]

Both legs of the breaker are on the leg of the panel not both legs. Can u move the breaker one slot up or down or move a breaker so the double pole fits? They make 3500 watt 240vac elements check how long the old element is or meausure diameter of heater subtracked 2" for the insulation.

 

[Reach4]

THe L1 bus in the panel zig-zags. THe L2 bus in the panel zig-zags but in the opposite pattern to the L1 bus.

The normal residential power breaker panel has alternating legs for slots one above the other. A 2-pole breaker outputs power from both legs. Those legs are out of phase with respect to ground/neutral.

First step should be to turn the 2-pole breaker off, and back on.

My suggestion for a next step is to see if you have 240 VAC across the two outputs of the 2-pole breaker. This will require removing the cover. Put the cover back on after completing the troubleshooting.