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gb77 07-05-2014 05:39 AM

6EM40-2 Richmond 240V electric WH stopped heating
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i have a 6EM-40-2 Richmond 240V electric WH installed 2-3 yrs ago at lake home (an hour drive away) which worked fine until now. water is not heating, reset switch is not tripped - flush to unit & no idea if i can force it to trip to reset it. house has well water which didnt lose pressure - water flows freely out any hot tap. moving temp setting from 105 to 125 changed nothing. looks like power for the WH & some baseboard heating runs thru a 2nd utility controlled meter outside. the wiring is similar to first pic. 2nd pic is identical to upper thermostat unit.

with power off: (1) checked 4500W elements & both read ~12.5 ohms (didnt disconnect any wires when checking) compared to 12.4 spec for comperable AOSmith elements & (2) high temp cutoff (T2) to power lead (L1) shows 0.3 ohms.

power on @ 30A breaker has 2 stranded copper wires @ 124V each going to WH using a flexible metal electrical conduit for ground (used this ground for all measurements). 124V @ all contacts - thermostats & elements.

not sure which (if not all) should read 240V (or 248 = 124+124). i checked the wiring @ the top of the WH with the incoming wires @ 124V & the green ground wire coming from inside the WH had 0 ohms to the flexible conduit ground. so i'm left with some failure i can't see in the wiring or the thermostats. i can pick up spare parts on the way to the lake. should i get both thermostats & an element or 2 (anything else) to swap out or is there enough info here for anyone to point to a likely culprit? what other tests could i do, and what would they indicate?

thanks for your attention & help

denman 07-07-2014 04:06 AM

I cannot say what is blown if anything.

You have to check for 240 volts (supply voltage) at the upper thermostat (black to red)
Using the white Neutral or ground (the conduit) will not tell you if you are getting the correct voltage.
Note that Neutral and ground are the same thing.
Neutral is not part of the heating element circuit.

One side of the elements is probably always connected to one side of the line so you will see it on both sides of the element as long as the thermostat contacts are closed.

Have you tride flipping the breaker off/on slowly a couple times.
Sometimes you can loose half the line without actually tripping the breaker.

FYI. I am do not know how much electrical knowledge you have so below is a blurb on how it works.
Your house wiring is actually 2 supplies (L1 and L2) which share a common Neutral.
Each supply is 120 volts but they are 190 degrees out of phase.
Therefore when one is at positive 120 volts, the other is at negative 120 volts.
If you measure between them you get 240 volts and this is what runs your heating elements.
The Neutral/ground is just connected as a safety. If one side of the line (element) shorts to the water heater then it will blow the circuit breaker instead of putting 120 volts onto the water heater case.

gb77 07-07-2014 04:37 AM

thanks for the reply. when i measure across L1 & L2 the voltage goes from 1v to 0 to -1v. from what i've read this happens if they are in the same phase cancelling themselves. i'll have to test from the breaker to see if it's happening there too next time i'm at the lake.

denman 07-07-2014 04:49 AM

Yes it looks like you have lost half the line at the water heater.

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