Water heater or electrical?

Hello everyone, I'm new to this forum and going into my 3rd yr as an apprentice plumber but I haven't really gotten any experience with water heaters and now that I am having problems with mine I don't know what to do. To start, I have been in this house for about 2 1/2 hrs, the water heater was already in there when I moved in. It worked perfect the whole time until last week, went in for a shower after work and found out I had no hot water. The breaker had tripped turned it back on and it worked for enough to heat up for a shower but after about 30 mins of it working it tripped again. I decided to try and diagnose the problem myself , but not before doing some homework on this stuff because like stated before I don't have much experience with water heaters and I also don't know much about electrical except for the fact that it is not something that you want to play with after researching these things I discovered that my water heater is on it own Independent breaker so I figured I could rule out an overload caused by anything else, I also crawled under the house and inspected the wiring running from the breaker to the water heater for any sign of damage that could cause a short but after checking it out everything looks like it should, I also put my voltmeter on the breaker and read 122 volts I also put my voltmeter on some of the other Breakers that I wasn't having a problem with just to compare the results and they were pretty much the same so I'm beginning to doubt that it is an electrical issue. I then turn to the water heater and put the ohm meter on the thermostats and the heating elements, I don't remember the exact results as it's been a week since I did that but I do remember that each individual part seem to test out fine the way that I researched it and had nearly the same results as all the examples that I looked up, while I was doing that also check for any loose connections to the water heater everything looked good, another thing I forgot to mention earlier that I discovered while I was tracing the electrical line to the water heater under the house is that water seeps through my t&p valve even when there is no hot water could this somehow be causing the breaker to trip? I don't see how it would as my understanding of a t&p valve is to relieve pressure caused by extreme temperatures to prevent a tank explosion. Does a water heater tank somehow go bad and prevent the whole system to not work correctly regardless of the condition of thermostats and elements or am I missing something here? I'm not sure what else to do all the research that I found has led me to inspecting my electrical and testing my water heater but again everything seems fine so I'm at a dead end has anybody had any similar issues like this that can help me out? I don't want to just buy a new one and replace it and hope it works and not ever know the source of my problem but I figured if I can fix it I would save a little money plus being a plumbing Apprentice I should learn how to do these things so that I will know what to do if I run into these issues again whether it be at home or on a job site any help at all would be appreciated thanks in advance and sorry about this huge post

Take the elements out and inspect them, then do your continuity test. More than once I've metered them out inside the tank, and I've gotten continuity but they still pop breakers because there's a split down the element.

Without being on site I'd say you may find a problem with the bottom element. If it runs for a half hour then pops, that's enough time for the top of the tank to heat up, then it pops once the bottom element is energized.

Also, you said you were getting 120V. Have you confirmed that the tank is rated for 120V? Most electric tanks are 240v

Where is your apprenticeship out of

Ok now that it was mentioned, I looked on the water heater label and it Is rated at 240v so would that Indicate that I have a bad breaker? My Apprenticeship Is in Texas, the company I work for does New Construction and remodels for hospitals

Something is fishy there. Is it a 20A breaker? Single pole or double pole?

which one of these looks like your breaker?

It's a single pole breaker but has a clip that holds the switch for 2 of them together.one has a white wire that comes out of it the other one has a black one and they both come out of the same insulation jacket and leads to the water heater

That makes it a double pole breaker. Either wire to ground will be 120 volts, but the voltage between the wires is 240 volts. The wires should be black and red, not black and white. Is the white one at least wrapped with black (or red) tape at the end?

you should have 10/2 with a ground and a 30 amp double pole breaker

More than likely you have a thermostat sticking on and not shutting off and causing the water heater to over heat and
shut off. On the top thermostat is the red button tripping?? That is probably why your pressure relief valve
is leaking.

Any evidence the tank is leaking ?

How many gallon tank ?

Just guessing , long distance , I would say you have a defective heating element . Normally they are not too expensive .

https://www.homedepot.com/s/water%20heater%20element?NCNI-5

The first item contains both elements and both Tstats .

https://www.homedepot.com/b/Plumbin...eater+element?Ntx=mode+matchpartialmax&NCNI-5

Single elements for around $ 10 + - .

Best of luck ,
Wyr
God bless

How old is the tank. What brand and could it be in warranty. They would probably send you new elements
and thermostats. Your problem would be over by changing these.