I have attached a diagram for a power circuit that I'd like to get some opinions on. The diagram only shows the power components. The rest of the components that aren't shown would be wired per Kal's Electric Brewery.
This design uses only two main contactors vs. Kal's three. Instead of a main power relay and one relay for each heating element, it uses one double throw relay to select an element, and one to switch power to whichever element is selected.
This has a couple advantages. There's one less contactor which means more space in the enclosure, or a smaller enclosure. It also makes it impossible for both elements to fire at once. Even if one or both relays fail you won't get more than one element powered. And when the control panel is turned on only the 120V buses are powered. None of the 240V wiring is energized until an element is actually on.
In order to do this I had to switch the neutral on one of the relay coils. What I'm wondering is whether that's kosher, and whether the advantages I've outlined above are actually compelling.
EDIT: the image looks lousy in the attachment so I posted it here as well: http://www.flickr.com/photos/jasongetsdown/7315929586/