SSR then Contactor or Contactor then SSR?

Should you wire an SSR first in series followed by a contactor or a contactor first followed by an SSR? -WHY?

If you wire an "on" indicator light in between your SSR and your element and you're using PWM will the light visibly flicker?


Trying to understand a small part of these wiring diagrams at a time...



Thanks!
Adam

I usually wire the contractor before the SSR. But have seen it both ways. There isn't anything in the NFPA book that I have found. I look at the contractor as a e-Stop disconnect.

As for the light. You could always wire it in series with your SSR coil.

BrewGeek_Ohio said:

As for the light. You could always wire it in series with your SSR coil.

Click to expand...

Good call! -So obvious; embarrassed I didn't think of that.


Adam

You would want to wire the indicator light in parallel.

SSR then contactor then heating element (allows you to ensure the element is off with the switch that opens the contactor). For a 240V element, wire a 240V light in parallel with the element (from the contactor load).

meadmazer said:

You would want to wire the indicator light in parallel.

Click to expand...

Series or parallel is fine.

So figured I would investigate a little more now that I am at work and could look over my NEC 2011 book. There really isn't anything I can find thats a clear cut answer to this. I am going to call my rep at Tempco to day and ask the question. As I said in my earlier post. I have seen both ways, I have a system sitting here with SSR, Contactor, OverLoad. I have one here thats Contactor then SSR.
The light question is really a dozen ways to skin a cat.

wired to ssr coil:
Series - Light bulb blown, SSR coil does not get power. pros and cons? yes
Parallel - Light blown, SSR still fire but with no visual indication.

After looking at a few of my electrical drawings; I usually do the lamps in parallel as I will know if the heater isnt working due to an alarm that will be annoying me!

wired to element:
parallel - higher voltage lamp.

where do you even buy a 240v lamp?

here is a 120v LED http://www.automationdirect.com/adc/Shopping/Catalog/Pushbuttons_-z-_Switches_-z-_Indicators/22mm_Plastic/Plastic_Monoblock_Indicators/LED/ECX2052-127L

This is just my 2 cents. Everyone has there opinion and most likely have good reasons for their opinion.

jeffmeh said:

SSR then contactor then heating element (allows you to ensure the element is off with the switch that opens the contactor). For a 240V element, wire a 240V light in parallel with the element (from the contactor load).

Click to expand...

I have the feeling that this is a dumb question but I'm not quite sure why: in the SSR -> Contactor -> heating element configuration: in this configuration is the SSR consuming power even though the switch to the contactor is closed?


Adam

I wired mine Contactor -> SSR -> Element. My contactor breaks both legs of the 240 VAC line to the element and the SSR breaks just one leg. You don't need a 240 VAC light if you have a 4-pole GFCI by bringing the one leg to the neutral line (120 VAC potential). You do have to look up the proper way to wire the indicator lights though, mine are still incorrect but I haven't gotten around to correcting them. I intended to have one light as the "On" light to indicate power is being supplied to the SSR and then the other to indicate when the SSR leg was "On" to show when the element was being fired. The SSR is a current regulating device and will ALWAYS should voltage across the controlled lets. The indicator light will illuminate even though the element is not being fired. There is a way to correct this so the light works with the element but I haven't gotten around to it yet.

biertourist said:

I have the feeling that this is a dumb question but I'm not quite sure why: in the SSR -> Contactor -> heating element configuration: in this configuration is the SSR consuming power even though the switch to the contactor is closed?


Adam

Click to expand...

When the contactor is open (off - I think that is what you mean), the element will not draw any power, so the SSR is not really consuming any power. Similarly, you have power running up to your wall outlets, but unless you plug something in to draw power the outlet is not consuming any power.

You can put the contactor before the SSR, but it does not really matter. In both cases, both hot legs run through the contactor, only one runs through the SSR, and the SSR is potentially being switched by the PID even when the contactor is open (off).

Thanks Jeff.

I was just thinking that if the PID is sending the PWM signal to the SSR and the SSR has power to it that the SSR would still be switching the power output on and off rapidly and this would still use power. -I "get it" with a simple circuit but with the switching mechanism of an SSR I think the added complexity just made me second guess this.


Adam

The 110v and 220v LED panel mount indicators are about $3 each from ebay and other sources.
Personally, I would want to know if there is 220v (or 110v) at the output connector, regardless of the control signal input. For example, if the SSR fails shorted, the element light will be ON.

jCOSbrew said:

The 110v and 220v LED panel mount indicators are about $3 each from ebay and other sources.
Personally, I would want to know if there is 220v (or 110v) at the output connector, regardless of the control signal input. For example, if the SSR fails shorted, the element light will be ON.

Click to expand...

I agree. I think that's the smartest thing especially for me since my system will not have a liquid level safety mechanism and that would mean that I'm dry-firing the element...


Adam

biertourist said:

I agree. I think that's the smartest thing especially for me since my system will not have a liquid level safety mechanism and that would mean that I'm dry-firing the element...


Adam

Click to expand...

Why would you be dry-firing the element if you have a switch to a contactor that cuts both hot legs to the element? Don't turn the switch on unless the element is submerged.

jeffmeh said:

Why would you be dry-firing the element if you have a switch to a contactor that cuts both hot legs to the element? Don't turn the switch on unless the element is submerged.

Click to expand...

I just like safeties for my safeties. The contactor is definitely a safety feature against an SSR failing open and dry firing your element, an appropriately placed light is a visual indicator that such a thing is happening.
-To put this in Risk Management terms: the contactor is a Preventative Control and the LED indicator is a Detective Control -both have their place in Risk Management and both together help to mitigate risk. -It just depends upon what your own personal risk tolerance is. But now you're making me talk about my day job on a brewing forum and that's just not ok. ; )


Adam

biertourist said:

I just like safeties for my safeties. The contactor is definitely a safety feature against an SSR failing open and dry firing your element, an appropriately placed light is a visual indicator that such a thing is happening.

Click to expand...

LOL you'll be able to see and smell that your element just smoked.

I found what I was looking for.

Walker said:

If you tap a 120V lamp off the switched SSR hot line and neutral and have no element plugged in, it will light up due to leakage.

If you tap a 120V lamp off the switched SSR hot line and neutral and have the element plugged in, it will light up due to the path from the OTHER hot line, through the element, through the light, and then to neutral. Doesn't matter whether the SSR is or is not firing. It will light up all the time.

If you tap a 240V lamp off the switched SSR hot line and the other hot line and have no element plugged in, it will light up due to leakage.

If you tap a 240V lamp off the switched SSR hot line and the other hot line, and have the element plugged in, it will only light up when the element is actually firing (leakage current will almost all go through the element since it is MUCH lower resistance than the light).

Click to expand...

You will need a 240 VAC light for the "Element On" indicator.

mateomtb said:

LOL you'll be able to see and smell that your element just smoked.

Click to expand...

The light allows you to see at a distance whether there's power applied to an element or not-regardless of whether the element was "just smoked".

-I thought the ULWD elements can fire dry for quite a little while before destroying themselves, too but I have no experience with this yet. (*knock on wood*)


Adam

pvtschultz said:

I found what I was looking for.



You will need a 240 VAC light for the "Element On" indicator.

Click to expand...

Thanks for that reminder! -I've been assuming that all the lights so far are 120 VAC -hopefully I would've stopped to think about it but I could definitely see my self making the assumption that it was 120 VAC and then frying it.


Adam