SSR vs Contactor vs 30A industrial 2 Pole Switch

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Abyssal

Abyssal

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I'm sure this has been discussed a bunch somewhere but I am unable to find it so if someone can point me in the right direction that would be great!
I'm building my first control panel I'm just trying to wrap my head around the pluses and minuses of using a SSR, a contactor, or a 30A industrial switch in a 240V system (specifically one of P-J's diagrams, single vessel 240v 30A BIAB w/ a pump.

In most of P-J's diagrams the SSR is controlled by the PID and the contactor is controlled by a switch. So is the purpose of the contactor another saftey measure to ensure the element has to be manually turned on before the PID can kick it on?

And one more question, would the contactor be able to be replaced this: http://www.homedepot.com/p/Leviton-30-Amp-Industrial-Double-Pole-Switch-White-R62-03032-2WS/100356941 because I can get these from where I work. So a way for me to be cheap and save $10!

Single Element BIAB 30A PID.jpg
 
If you don't have the contactor there, one of your hot lines will be always connected to your element.
 
From www.theelectricbrewery.com
http://www.theelectricbrewery.com/control-panel-part-2?page=13
SSRs have a small amount of leakage current that flows through at all times, even when the SSR is off. SSRs are also known to fail from time to time and when they do, they tend to fail "closed" meaning that the heating element stays on. The mechanical relays provide us with the peace of mind that when we've turned the element off, there is no possibility of it coming on by accident nor is any side of it energized.
 
Ah okay thanks! That makes sense! I thought I had read something about the current but couldn't remember where!

So then if the contactor is just meant to stop the flow of current then the 30A switch should work fine then?
 
Abyssal said:
Ah okay thanks! That makes sense! I thought I had read something about the current but couldn't remember where!

So then if the contactor is just meant to stop the flow of current then the 30A switch should work fine then?
Click to expand...

Yes if ita rated correctly... just keep wet hands away from the switch... contactors are safer for that scenario and they are more reliable than most direct 2 pole switches.
 
Abyssal said:
Ah okay thanks! That makes sense! I thought I had read something about the current but couldn't remember where!

So then if the contactor is just meant to stop the flow of current then the 30A switch should work fine then?
Click to expand...

Yes, but for the same reason as using contactors over SSR's, using Contactors with switches gives you an added benefit.

IMHO you dont want to be pumping current through your switches, even if it supports it. Your actively grabbing them, if one is energized your ****ed.

In a typical setup your using the switch to control the on/off coil pins for the contactor, which only takes milli(micro?) amps and is not dangerous at all. Thats what the LED switch is doing in the image you posted.
 
FuzzeWuzze said:
Yes, but for the same reason as using contactors over SSR's, using Contactors with switches gives you an added benefit.

IMHO you dont want to be pumping current through your switches, even if it supports it. Your actively grabbing them, if one is energized your ****ed.

In a typical setup your using the switch to control the on/off coil pins for the contactor, which only takes milli(micro?) amps and is not dangerous at all. Thats what the LED switch is doing in the image you posted.
Click to expand...

Whether you use a direct action switch, or a switch and contactor combo, the voltage on the switch is still enough to kill you, although there may be a little less risk if the contactor controlling switch only has 120V on it vs. 240V on a direct switch. It's the voltage on the switch that is the main determinant of how much current could flow thru you (unless there is a current limit on the circuit.) The fact that the contactor coil only takes about 10 mA is irrelevant since it only takes on the order of 10 mA to to give you a nasty shock (more than a tickle), and on the order of 100 mA to kill you (https://www.physics.ohio-state.edu/~p616/safety/fatal_current.html.) That's why you have a GFCI on the power feed as they will trip at about 5 mA.

SSR's for rapid switching of high voltage/current loads. Mechanical switches or contactors for low cycle switching. A 30A two pole mechanical switch can replace a 30A two pole contactor plus control switch. It's more a mater of aesthetics than anything else. If you really want to go maximum safety, you use a contactor with a 24V or less coil. Then the control switch has no more than 24V on it.

Brew on :mug:
 
Yeah, the main advantage of SSRs in my experience is they aren't subject to fatigue failure. For something switched as infrequently as a homebrew system, should be fine.
 
doug293cz said:
Whether you use a direct action switch, or a switch and contactor combo, the voltage on the switch is still enough to kill you, although there may be a little less risk if the contactor controlling switch only has 120V on it vs. 240V on a direct switch. It's the voltage on the switch that is the main determinant of how much current could flow thru you (unless there is a current limit on the circuit.) The fact that the contactor coil only takes about 10 mA is irrelevant since it only takes on the order of 10 mA to to give you a nasty shock (more than a tickle), and on the order of 100 mA to kill you (https://www.physics.ohio-state.edu/~p616/safety/fatal_current.html.) That's why you have a GFCI on the power feed as they will trip at about 5 mA.

SSR's for rapid switching of high voltage/current loads. Mechanical switches or contactors for low cycle switching. A 30A two pole mechanical switch can replace a 30A two pole contactor plus control switch. It's more a mater of aesthetics than anything else. If you really want to go maximum safety, you use a contactor with a 24V or less coil. Then the control switch has no more than 24V on it.

Brew on :mug:
Click to expand...
This is one of the reasons all my pumps and relays use 24v dc in my panel although I must admit in reality, my hands are always dry when brewing
 
SSRs can handle the rapid switching of PID Control, the Mechanical Contractor is better suited for Hysteresis Control. That being said, the fact that you can have both legs of 240 OFF to the element is better for safety. I use a BCS to control an SSR which turns a 24 vac Transformer that actuates the Mechanical Contractor (https://www.amazon.com/dp/B003U7W3SM/?tag=skimlinks_replacement-20). I have a Hot Water Timer (http://www.homedepot.com/p/Intermat...gclid=CK2GmM6hx9ACFYVlfgodH8oKcQ&gclsrc=aw.ds) that I use as a switch when I want the power supply “Off”. I leave it on while Brewing but it and all other Power (Via Mechanical Switches) to my brewery is switched Off when I am not brewing. My Supply switches are away from anything that could get wet and about 20 foot from any vessel.
 
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