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Single element, switch instead of relay/coil?

 
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tehjrow




Joined: 20 Sep 2015
Posts: 11
PostLink    Posted: Tue Oct 06, 2015 9:55 pm    Post subject: Single element, switch instead of relay/coil? Reply with quote

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In the walk-through it uses a 3 position switch to switch relay/coils for one leg to swap between elements. If I've only got 1 240v element, can I just use a switch for one leg and a PID/SSR for the other? Instead of using the switch to control a relay/coil?
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kal
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Joined: 12 Dec 2010
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Location: Ottawa, Canada

Drinking: Pub Ale, Electric Creamsicle, Mild, Pliny the Younger, Belgian Dark Strong, Weizen, Russian Imperial Stout, Black Butte Porter
PostLink    Posted: Tue Oct 06, 2015 10:34 pm    Post subject: Reply with quote
The number of elements doesn't matter.

A relay/coil isn't needed at all but is safer because it cuts both HOT legs physically. For more info, read the "How it works" section here: http://www.theelectricbrewery.com/control-panel-part-2?page=13

SSRs, when they fail, tend to fail closed so in your setup one of the two HOT legs would be live if the SSR failed.

As designed in the instructions, it's the safest way. The choice is up to you - you may choose to follow or simplify to save the cost of a relay, and possibly a switch (the switch isn't needed either technically - you can use the SSR to switch/cut the power).

Kal
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Vesteroid




Joined: 02 Sep 2015
Posts: 57
PostLink    Posted: Wed Oct 07, 2015 7:26 pm    Post subject: Reply with quote
not just safer, but required by any code I know of. any component used as a disconnect must de-energize completely....ie on a 120 circuit you could switch the neutral and therefore turn on and off a component, but there is still 120 volts to that component...same with 240 breaking one leg makes it not work, but still unsafe.
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tehjrow




Joined: 20 Sep 2015
Posts: 11
PostLink    Posted: Wed Oct 07, 2015 7:35 pm    Post subject: Reply with quote
What I'm really asking is can I just use a switch to control the second hot leg instead of a switch that then goes to a relay/coil?
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kal
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Location: Ottawa, Canada

Drinking: Pub Ale, Electric Creamsicle, Mild, Pliny the Younger, Belgian Dark Strong, Weizen, Russian Imperial Stout, Black Butte Porter
PostLink    Posted: Wed Oct 07, 2015 7:42 pm    Post subject: Reply with quote
tehjrow wrote:
What I'm really asking is can I just use a switch to control the second hot leg instead of a switch that then goes to a relay/coil?

I don't understand. Can you provide a diagram?

Or wait - are you saying you want to use a switch only instead of a switch and a relay? If that's what you mean, then no, generally speaking you can't. From the instructions here:

Quote:
Most small switches such as this one cannot handle the large amounts of current required by our system so current does not actually flow through the key operated power switch. Instead, the power switch is simply used to control a large relay which is capable of handling up to 30 amps. A relay is simply an electrically operated switch. Turning the power switch to the on position activates a coil in the relay which closes contacts able to handle up to the 30 amps of current we require. Current is then able to flow into the rest of the control panel to power the other devices including the high power devices like the heating elements.

Generally speaking, high power switching such as this is always controlled remotely in electrical panels where a smaller 'control' switch on the door is used to activate a larger switch (such as a high power relay or a definite purpose contactor) that is permanently installed on the back plate. This is done for ergonomic reasons (smaller switches are easier to operate) and for safety reasons (high power wires are not required to move or bend when the door is opened/closed).


Kal
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