Question about fuses used in control panel

Attached is one of P-J's wiring diagrams.

My question is about the fuse on Line 1. Or maybe my question is about how the PID receives power...not sure.

Why do you only need a 1A fuse. Isn't Line 1 sending 120v to the PID power terminal? I understand the fuse is there to protect the PID. Is it that the PID pulls a low number of amps so that is all that should be running through that line to the PID, even though it is a 120v line connected to a 30A breaker?

 

It's called supplementary protection. Even though you have 30A circuit, all the devices behind it don't likely use 30A rated conductors. The fuse doesn't protect the device, it protects the wiring.

Example, if you had a 30A main circuit breaker, and a buss bar feeding multiple devices, and all devices behind it were 22gauge power wires, if there was an overload on the PID controller, or other device, lets say 20A, the 30A breaker wouldn't trip, the 22gauge wire would melt (not rated for 20A), and you'd have a potential fire in your cabinet. All devices behind the main breaker should have supplementary protection.

As to why he doesn't show one on the power feed to the SSR, I don't know. Not how I would do it.


I have a breaker on my 24V power supply (feeds PLC and PID controllers), a breaker on each of my SSR's feeding the heating elements, a breaker on each of my pumps.

 

Yes. It probably draws half an amp or less under normal conditions but you still want to protect the wiring to it and, to some extent, it itself in the case of a fault to the wiring (hot conductive wort splashes and forms a bridge between PID hot input and grounds) or internal to the device (electrolytic across rectifier bridge in unit is not formed and shorts at first energization). If over an amp is drawn by the controller circuit something is wrong you want to open that circuit quickly, even though it is only a small fraction of the overall load, to prevent the small wires used in it from overheating and a potential fire hazzard or, if the failure was in the device, from further damage to it.

 

Gotcha!

I have a 40A GFCI going to my control panel, each of my elements could be on, so they each get their own 2 pole breaker. Different application for the OP. For his setup, yeah, don't really need another 2 pole breaker for the element IF the wire gauge is large enough.

 

Thanks for the replies. I understand. I watched a few videos about the relationship of Volts, Amps, and current and it makes sense.
Would someone take a look at the wire gauges I have labeled and let me know if I got it right?

 

Current in = current out, so for the E-Stop trip, 18Gauge for both is fine. Also, this assumes you have a GFCI breaker installed where you plug this control panel into. If you don't, that fuse will just blow and nothing will happen.

 

Just remove that GFCI fault altogether, as it never should have existed in the first place.

 

I don't think so. The 'short' will draw 120/2000 = 0.060 A, way blow the fuse's rating and each resistor will dissipate 1000*0.06^2 = 3.6 watts. After they stop burning, the circuit will open. Same thing happens if the GFCI doesn't trip. So if you are going to use this kluge as an emergency stop be sure to only tap the button or quickly close and then open the switch.

Why not use a proper E-stop?

 

A 1W resistor will probably hang on at 4W.

 

What I mean is this: If the Breaker isn't GFCI, the breaker is not going to trip if he does hit that E-stop. Basically that circuit won't work for crap unless he uses a GFCI. Sure it might blow those resistors, that wasn't what I was trying to convey. The E-stop in that circuit diagram only works on the assumption that a proper GFCI is used at the source.

That being said: I agree with you completely. I dislike the fuse/resistor tripping of the GFCI and think it's a huge kludge. I actually use an e-stop going to the PLC relay common. If I hit the E-stop, the power to those relay outputs drops and contactors open. Same can be used if you use a main contactor. Interrupt the power to the coils and the contactor drops out and you remove power from the panel.

 

You are correct in that assumption. P-J explained this E-stop was used to create a voltage leak and throw the GFCI at the main breaker box.

 

I'm all for modifying the design if there is a better/more cost effective/simpler design out there. I would need a diagram to look at though.

 

So when you are designing something and you have a dissipation of 3.6W you use a 1 W resistor? That's not the way I was taught. Now you can argue that if things are working properly that the circuit is going to open in milliseconds and the resistor will never see more than millijoules but supposing the current sense in the GFCI isn't working. They do fail and that's why you are supposed to test them monthly.

 

Like this...
http://www.amazon.com/dp/B002MPPTBQ/?tag=skimlinks_replacement-20

 

How do you define better?

Does more cost effective include expectational loss from a fire?

We can answer to simpler: No.

In the traditional scheme the equipment is fed by a contactor. The contactor's coil is fed by a series connection of a NO push button (START) and a NC pushbutton (STOP). An auxilliary contact on the contactor is wired across the START button contacts so that when you push the START button and the contactor picks up the circuit latches ON. When you push the STOP button, being in series, it interrupts flow to the coil and the contactor opens and stays open until START is pushed again. The advantages to this are several. Anything in that series chain will shut things down. You can, for example, have multiple STOP stations dispersed throughout the brewery. You could have a button thermostat on the kettle set for say 225 °F which would dump power should the kettle boil (or leak) dry etc.

 

Obviously burning the house down isn't part of brew day. I'm not modifying my set up out of necessity so I'm not trying to do it on the cheap. My main concerns are that the design is safe, logical, and works. I don't want to install component into this control panel that won't work as intended because of reasons unknown to me or are unsafe.

Lets just stick with the original diagram then. There seemed to be allot of positive feedback when this diagram was originally posted. It was simple and I had most of the components used in the design.

All I want to be able to do is set a temp for my HLT and be able to hold that temp without a hastle. Everything else is going to be old school.

 

I get what you're saying. I think i am going to eliminate the E-stop all together for now. I mean, what's the point of it if the GFCI breaker doesn't do it's job?? In what circumstance would I be using it? Maybe I'm missing something but it seems like it's a safety feature that is dependent on another safety feature that can fail.

 

Then you wouldn't use the kluge E-stop

Yes, there was but there was also a small group ardently opposed to it. That group was made up of people who had done or were still doing professional design of equipment control circuits. It is very clever (that is what Kluge means in German) but it is indeed a kluge. There were some pretty intense arguments about it. Does it work? Should unless the GFCI fails. GFCI's fail but contactors weld shut too. Does it work less well than a contactor? Who has done a test on such a question? Does the NEC have anything to say about it? Not AFAIK.

Interestingly enough I stumbled upon a very similar and equally heated debate on a professional electricians forum where someone had proposed saving a few bucks in a Halon installation by using this method instead of the accepted (IIRC) shunt trip breaker and associated wiring.

You'll do what seems best for you. If there is a fire for whatever reason (and I'm not suggesting that there will be one) just be sure to remove your panel from the ashes before the insurance adjuster gets there.

 

The emergency stop is if there's some reason for you to turn things off (fire, something overflowed, you've finished brewing, etc). GFCI is to protect from something you can't see, like a short to ground or neutral.

Controls engineers with UL 508 training would never use resistors inline to cause a GFCI to trip. This would never be done in the automation world and a UL inspector would immediately reject the panel. Some argue it's just fine, but it's not safe, and it uses the GFCI as a disconnect, not as it should be used (as an overload protection/ground fault detector).

As an Automation/controls engineer with 15 years of experience, I highly recommend that an E-Stop be connected to a contactor inside your control panel. The way the original drawing is using the GFCI is using the GFCI as a means for turning power on and off. Breakers are meant to clear a fault, not to be a means of turning on and off the panel.

Do yourself a favor, Use a GFCI. Also, use a main contactor and an E-stop. This allows you to turn power on and off as well as have a means to disconnect power inside the cabinet in case of emergency.

Here's some info:
http://learn.ebrewsupply.com/guide/wiring-your-contactors/
and here:
http://www.homebrewtalk.com/showthread.php?t=224250

 

This topic seems (to me anyway) to be coming up much more often. Possibly due to the better availability of low-cost components from overseas. It seems like we could put together a sticky on the topic of advantages and weaknesses of the approach.

One advantage that I perceived was that the GFCI approach will disconnect power all the way back to breaker with a single button press. Also, you don't have to buy more contactors (shrug).

After that I'm not really sure what would go in the (+) column. I did not use the approach because I couldn't identify a situation where that GFCI E-Stop would be more functional than a DPDT switch. In the event that the GFCI failed and someone was being electrocuted, it seems like GFCI E-Stop would actually be less effective.

 

Of course not, don't be ridiculous. My point was that the resistor may not burn up.

Anyway, lighten up. Not every post is an invitation for correction.

 

True but that is hardly relevant. It may. The point was that this is another way in which this design violates good practice and it appears you missed that. Therefore...

...it seemed prudent to point it out again in an even clearer way. More than that it is almost a duty. You are implying to a person with a level of understanding of these things telegraphed by "I watched a few videos about the relationship of Volts, Amps, and current and it makes sense." that perhaps it is OK after all to use a circuit like this because the resistors might not burn up. I'd be afraid to post a comment like that because some day some one of these guys who is studying the relationship between amps and current for the first time in his life is going to misconstrue some comment like that and have a fire or electrocution episode. Unlikely, yes, but possible. I promised myself I would not post to this topic any more because of fear of something like that but have clearly broken my own rule. Having done so I am going to be hard over in the conservative direction.

 

Why don't you keep that promise to yourself. You have been little to no help in this discussion. We all get it bro, you've got all the answers and i'm some clown plugging in a toaster for the first time while throwing a few back in my bath tub. I don't even know how you can visit these forums. If I was as gifted as you I wouldn't be able to sleep at night, knowing that there are people like me out there teaching themselves new concepts. I would have an overwhelming need to post a disclaimer in every thread. Maybe even send some bubble wrap to their house. You've really contributed to this whole thread going off topic and taking a giant dump.

I thank those of you that selflessly took the time to answer a question or offer advice. With that, I think it's time we put this thread out of it's misery.

Now, remember your promise to yourself. Remember it.

 

I shall.

Well as they say you can lead a horse to water....

As I said I try not to but if I see something over on the right side of the page and I think maybe someone can benefit from my experience I sometimes jump in.

As the intention is really to help you despite your appalling attitude I would suggest you learn the fundamentals of electricity with an Arduino kit or something like that rather than tackle a project involving 240V and 30 - 50 amps to start.

I don't consider myself particularly gifted. I just have many years experience with various aspects of electrical engineering. But if you were as gifted as I, limited though that may be, you would know where the subjunctive is required in an English sentence.

The disclaimers are required by fear of litigation. As I said in a previous post someday someone with your attitude and experience level is going to grab on to one of the poor practices often advocated here and get hurt. I don't want to be responsible for that and I particularly don't want some tort lawyer to be able to conjure up a scheme for making me appear to be so.

Well let's see. You asked about the fuse in a circuit that does not represent good practice and several people including me pointed out that it is not good practice and why. Several alternative schemes that do represent good practice were offered. This is off topic?

You need to make clear that the people that agree with me are not being thanked because they contributed nothing and took the thread off topic. You left that out.

And yes, I admit my motives in contributing here are purely selfish. Most people don't know this but I am being paid handsomely under the table for each post.

Promise.