Voltage at elements & other questions

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JohnEdgewater

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I installed new heating elements in my 12yo AO Smith 40 gal. water heater today. I got the elements at Home D. The elements I removed were: top, 3500w 208v shorter; bottom, 4500w 240v, longer. The new elements were both the same length and both 4500w, 240v.

Quest. 1: Is it okay that I installed 2 of the same type elements?

Quest 2: Is it okay that the new element I installed in the top differs in watts and voltage than the element removed?

Quest 3: When I put a multimeter on the two screws that connect the power wires to the element in the top, the meter registers 240v. When I touch the probes of the meter to the screws on the bottom element, nothing. If I touch the meter probes to one of the screws connecting power to the bottom element and touch the other probe to the tank, I get 115v reading on the meter. Is everything okay here? Why no 240 at the screws on the bottom element? Why no reading at all at the bottom element when I touch the probes to both screws?

Quest. 4: do I need to do anything to the expansion tank on top after I've drained and refilled the water from the water heater tank?

Thx in advance for any help
 

Jimbo

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1. Your old elements were the same watts. A given element, which would be approx. 12.5 ohms, would produce 3800 watts on 208 volts, and 4500 watts on 240 volts. Many water heaters are rated at 3800/4500, and that is the deal.

2. NEVER trouble shoot a water heater by measuring from one terminal to ground.....that will lead you on a wild goose chase every time. The only measurement that matters is directly across the two terminals of the element. Either it has 240 or zero. Note that on a residential water heater, the two elements are never energized at the same time. That would pop the breaker, and the thermostats prevent that from happening.
 

JerryR

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Answer to quest 3:

Your readings are normal for a tank that is heating up.

One terminal on each element will always have 120 vac as measured to ground.

Upper element runs first. (240vac across both screws)

Once the top of the tank is hot the upper thermostat redirects one leg to the lower thermostat. If the lower portion of the tank is not up to temp at that time the lower themostat will connect the second leg to the lower element snd you should read ~240vac across both terminals on the lower element.

Once the tank is completely at temp you will read 0 across the 2 terminals on either element and you still should read 120 vac from one terminal to ground on either element.

FYI, One terminal on each element always has one of the 120 vac legs connected at all times. The thermostats switch the other 120 v leg as needed

Jerry
 
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Tessie

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"One terminal on each element will always have 120 vac as measured to ground."

On mine each terminal on each element reads 120 vac. Is something wrong and should I replace the thermostats? My electric bill is double what it unusually is so i'm checking the water heater. Thanks for any help.
 

Jadnashua

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"One terminal on each element will always have 120 vac as measured to ground."

On mine each terminal on each element reads 120 vac. Is something wrong and should I replace the thermostats? My electric bill is double what it unusually is so i'm checking the water heater. Thanks for any help.
WHen measuring from one terminal (either one) when the tank is hot and neither element is heating, to ground, it's normal to see 120vac. When measuring to ground, both ends of the element are essentially at the same electrical point because the internal resistance of the meter is WAY bigger than the resistance through the element...the element with no current going through it 'looks' like a straight piece of wire, so you can measure anywhere and get the same thing. Now, if your meter read out in millivolts, you might see a difference.

As was said, you really need to measure from one terminal to the other...it will read 240 volts or so when it is powered. If you have a clamp-on ammeter, you could check to see if they are drawing power. Basically, your 240vac WH does not have a neutral wire, so measuring to ground is not telling you much.
 

Tessie

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WHen measuring from one terminal (either one) when the tank is hot and neither element is heating, to ground, it's normal to see 120vac. When measuring to ground, both ends of the element are essentially at the same electrical point because the internal resistance of the meter is WAY bigger than the resistance through the element...the element with no current going through it 'looks' like a straight piece of wire, so you can measure anywhere and get the same thing. Now, if your meter read out in millivolts, you might see a difference.

As was said, you really need to measure from one terminal to the other...it will read 240 volts or so when it is powered. If you have a clamp-on ammeter, you could check to see if they are drawing power. Basically, your 240vac WH does not have a neutral wire, so measuring to ground is not telling you much.
Thanks very much for the reply. I was thinking one terminal would have 120 vac then the thermostat kicked on sending 120 to the other terminal. I ran hot water until it cam out cold then checked both elements for 240vac. Neither one shows 240. Next I adjusted the thermoset up by hand until I heard it click on then tested and the element shows 240. It's like the thermostat doesn't work on its own but I do have hot water. I'm trying to figure out why my electric bill has been double what it normally is. Thanks again.
 

Phog

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Hi Tessie, if the extra energy were being consumed by the water heater, it would ultimately have to end up as extra heat. One of the following would be the case:

-- Incoming cold water temperature has changed compared to previous years, requiring more energy to heat it up
-- Insulation on water heater removed, causing extra standby heat loss
-- Hot water leak somewhere in the plumbing causing increased hot water usage
-- Hot water much hotter than normal, likely also causing T&P valve to open
-- Unintended heating of the outside chassis of the water heater and/or the wiring, caused by ground short, very likely to show up as scorching or melting

If you can't detect any of those conditions, then it is not possible for this appliance to be the source of the higher bills.

Hope this helps.
 

Reach4

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It's like the thermostat doesn't work on its own but I do have hot water. I'm trying to figure out why my electric bill has been double what it normally is.
You could turn off stuff, including the WH. Then check the electric meter to see what the consumption is, if you can figure out how to read that. The meters vary. There could be something like a hole in your well drop pipe making the pump run a lot more, or your AC has degraded and is not as efficient as it used to be.
 

Jadnashua

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In residential WH, only one element turns on at a time. When the top is cold, the top one turns on. Once that is up to the set point, it enables the lower one to come on. But, since the thermostat only has a single pole switch, that means that there's always 120vac applied...you need to close that switch to apply the other 120vac and then 120+120 on a closed circuit allows current to flow.

One thing to look at is how often the WH is running. WHen you haven't used hot water for a long time, say in the morning before anyone takes a shower or after you come home from work with nobody home during the day, check the outgoing hot pipe from the WH. Convection might have it hot right at the WH, but a ways away, it should be cooler, and maybe cold , depending on how far away you can go. If it's hot, there could be a hot water leak. If you have pets, they'll gavitate to warmth. If this is on a slab, that might be the location of a leak, if it exists.
 
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