SSR and element contactor position in control circuit

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stfinder

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I was poking around on Auber's website and found this image of the guts of one of their BIAB panels.

In this circuit, there's main power in -> main power contactor -> 30A breaker -> SSR -> element contactor -> element power out.

In the panel schematic that I'm using, the SSR comes between the element contactor and element power out and there's no breaker in the element power circuit. Is there any reason that one order is superior to the other? I'm fairly certain the 30A breaker is unnecessary if you're plugging into an outlet with 30A GFCI protection.

Any feedback on this question is appreciated!
 

doug293cz

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In my designs, I prefer the element power enable contactor closer to the input power feed, and the element power SSR closer to the element power out. This order removes power, both voltage and current, from more of the circuitry when the contactor is open. The closer the disconnect is to the incoming power, the more possible points of failure are isolated by the disconnect. Electrically, it works either way.

You are correct, if the unit is plugged into a circuit with a 30A breaker, then you don't need a 30A breaker inside the panel. An internal 30A breaker is needed if the unit is plugged into a circuit protected with a breaker rated for more than 30A. In any case, you need a GFCI somewhere before the control panel.

Brew on :mug:
 
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stfinder

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In my designs, I prefer the element power enable contactor closer to the input power feed, and the element power SSR closer to the element power out. This order removes power, both voltage and current, from more of the circuitry when the contactor is open. The closer the disconnect is to the incoming power, the more possible points of failure are isolated by the disconnect. Electrically, it works either way.
Thanks for your response. That makes sense. At this point I’m working out the most efficient way to run wires throughout my panel and how to orient the different components.

For contactors/switch blocks, does it matter which side is input and which side is output or are they engineering in a symmetrical manner? If they are symmetrical, that would help me wire everything more efficiently. Perhaps it’s best practice to be consistent with how everything is wired though? I can see that being helpful when troubleshooting.
 

doug293cz

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Thanks for your response. That makes sense. At this point I’m working out the most efficient way to run wires throughout my panel and how to orient the different components.

For contactors/switch blocks, does it matter which side is input and which side is output or are they engineering in a symmetrical manner? If they are symmetrical, that would help me wire everything more efficiently. Perhaps it’s best practice to be consistent with how everything is wired though? I can see that being helpful when troubleshooting.
For switches/contactors it usually doesn't matter which sides are input and which are output. The one case I can think of where it does is when using a double throw switch with a common. In this case the function that the switch is performing dictates whether the common is the input or the output, and reversing things would cause the circuit not to function.

GFCI circuit breakers can only be installed one way, or the leakage trip function won't work.

Brew on :mug:
 

sicktght311

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Just as long as the contactor is there to cut the power to an element in the event of a bad SSR stuck in the on position, thats all that matters. No contactor means no way to cut power if things go wrong other than shutting off the entire panel
 

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