230 volt heating elements wired in series at 480 volt

[GlennH]

why not just get 480 volt elements? I've put several in water heaters over the years that were installed in industrial locations.

 

[kwired]

It's what he didn't say that I'm addressing. "The elements failed in a rupture type manor (split down the length) Said unit is built with this from the factory but seems a little odd to me."
This leads me to believe that the 230v heater failed and that there was 480v applied across the failure which resulted in the failure ending up to be a failure in a rupture type manor.
I you had one 230v heater fail where the element opened you will have 480v across that failure and not 230v which would result in significant more damage.

The failing point does not have 480 volts across it until it becomes fully open circuited. If you have any arcing going on you still have the resistance of the remaining good portion of element in series with the failing part which will drop voltage accordingly. Once it is completely open it is just like opening switch contacts. Oil is a good electrical insulator so there is likely almost no current faulting to ground via the oil either.

 

[Jraef]

That is understandable at the initial installation, but OP says they have been replaced more than once, is it safe to assume there may be design issues? Simple oil level switch would help with preventing from running dry. I did suggest earlier that if these indeed a water heater element by design that maybe they would not perform as well for heating oil, nobody has replied with any thoughts on that.

I had missed his statement that this has happened before, so you might be right about that.

And as I think about it, heating element mfrs usually recommend steel sheathed heating elements for oil immersion. If it ruptured along it's length, that to me indicates it's likely a ceramic sheathed element, so you have an excellent point there.