Electrical Diagram feedback for a 50A HERMS Build

After months of research and pondering, I've finally finalized plans, and started ordering components. With that said, I've drawn up what I believe to be a fairly standard 50A, 2 PID, 2 5500W Burner, 2 Pump setup. Before I go ahead and finish speccing out and ordering my electrical components I just wanted to post the diagram, in case I'm missing something obvious.

Thanks!

Edit: The part that I'm still uncertain about are fuses for the various components, I'm thinking I should be fine with the single 5A fuse shown, but kept debating individual fuses for the various components.

 

Fuse your pid's per manufacturer recommendations. Auber has internal protection but I don't recognize your part numbers.

Are you aware of leakage through the ssr? You may get a dim light with the ssr off.

Any reason you chose the gfi shunt estop over your main contactor. I would kill the contactor since you have one there anyway.

Otherwise, it looks real nice.

 

Question-

It looks like you have a main power relay. Why wouldn't you use your e-stop to cut power to the coil of that relay, rather than trying to trip the GFI by leaking current onto the ground?

 

I was aware of the leakage, hadn't really contemplated the repercussions on the two element heating lights as they were a very last minute addition which I still might remove.

I was thinking about shunting to ground to trip the GFI so that there's no power whatsoever in my panel, instead of disengaging my main contactor coil and still having power present. If my thinking is off, I'm more than happy to hear it.

 

The proper way to do that is with a shunt trip breaker in the panel. Problem is that I can't find a GFCI shunt trip breaker (doesn't mean they don't exist - just that I haven't found one). Of course you can gin up your own GF detection circuit (TI has a chip) to trigger the breaker but that may be more than you want to undertake.

 

I've modified my diagram to have my E-Stop kill the coil to my main contactor as well as trip my GFI.

I know this isn't necessarily the 'proper' way to trip a GF(C)I, but I believe it to be a safe and effective way of doing so. Am I wrong in this?

 

I like the idea of e-stop killing the contactor coil and tripping the GFCI. May have to rewire mine like that. Feels like a good backstop incase either the contactor fails closed, or the GFCI fails to trip.

 

Besides the additional cost for a DPST (1-NO, 1-NC) e-stop, I love the idea. Grateful for this thread for inspiring me to go this route. I like saving money where I can, but if there's an emergency I'm trying to stop with this button, I want to do all I can to ensure that at least the electrical portion of it is stopped.

 

Should work nicely. I feel the contactor is a more reliable device for an e-stop. Throwing in the gfci shunt is extra insurance. Redundancy is a good thing in this circuit.

 

Once your question made me stop and think about it, I realized that I was idiotic not to have it trigger the coil, far more reliable a way to kill the power in the panel, even if it by itself doesn't accomplish my goal of killing power to the panel.

I'm very happy with the improved redundancy.

 

I went back and forth on the EPO method and opted for the GFCI trip. I looked into proper shunt trip beakers but they're damn costly so opted against. Tripping the GFCI is the next best thing in my opinion. Having the coil power run through the NC block on the EPO is a nice backup plan if for some reason the GFCI doesn't trip, but I think it should be the backup and not your primary option.

 

Agreed. The way I'm looking at it is this: Unless, I'm an idiot and have blown the fuse on my GFCI shunt, and my GFCI has not failed I kill all power to my panel. Unless something has seriously gone wrong with my contactor (or my e-stop switch) I've killed all power past my main relay. If both those have failed simultaneously, I should just expect the incoming meteor impact as I win the lottery.

 

An OH - By the way - The 1 amp fuse I placed in the diagrams is only there to insure that the wiring is done in a proper way. Once completed and tested, it is no longer needed. (It is a initial don't fail on me plan - once done? Not needed.!)

P-J

 

Sorry but I must disagree. Unless your control panel falls into your boil kettle, what is the reason for killing the feed? If it did fall into the BK, the gfci would take care of that anyway. Killing the main contactor will kill all power leaving the CP and that is where the issue would be. I think using both methods is smart. If I had to chose one, my e-stop would kill my main contactor and it does.

 

Come on PJ. It's there in case you push the big red button without the feed being connected to a gfi breaker. The resistor fries or the fuse blows...what's the difference? I will convince you someday...

 

Go about your mission.

Get over it. You do not stand a chance.!

Good luck.!

(Be carefull here! I'm very old and easily ticked off. I can shut down all of)
Never mind..

Never mind, do what you gotta do. I'll do what I gotta do.

 

PJ, I love you. I love arguing with you. This place is not the same without you. Cheers!

 

You came damn close to me shutting down all of my diagrams. (Because of your close affiliations with a significant moderator.)

Do what you gotta do...

 

I have no knowledge of that. It was certainly not my intent. I'm just here offering my opinions with an open mind in case I may learn something (and I definitely have). We disagree on some issues. So be it. No hard feelings on my end.

 

If something happens and a lot of liquid falls on my panel - maybe I have a carboy shatter on me, who knows... I want to secure all power.

Really, we're arguing whether it's necessary to kill power in a few feet of supply line. I figure if I'm going to do it, may as well do it all. If shunt trip breakers weren't $400 I'd kill power all the way to the main panel. At least with the leak current I kill power back to the spa panel.

 

For what it's worth, if I was only going to do one it would definitely be to cut the main contactor. The GFCI shunt is there as secondary to this, and stemming from some of my formal training to over-engineer everything.

Thanks P-J, I understand this, at the same time I'd rather keep it inline as redundancy. It's not harming anything being there, and in all likelihood will never blow but if I needed it to, I'd enjoy having it stop more than an amp going across that line.

 

But, if the 1A fuse is blown, your E-Stop is just a nice plastic red button that does nothing.

 

I agree with lschiavo.

Using a safety device as a control is a poor practice. Doesn't seem to be much different than jamming needle nose pliers into an outlet to trip a breaker so you can work safely on the circuit.

Also (and I am not a licensed electrician so my interpretation may be wrong) the NEC seems to prohibit intentionally using the ground as a current carrying conductor.

 

I suggest that you read the code that applies to the building wiring when it was installed. You might learn something.

 

I'll do that.

I'm always willing to improve my understanding.

Here's something to improve yours.

I am an Industrial Controls Tech. I maintain, repair and upgrade control systems like these every day. I showed your E-stop circuit to our Electrical Design Engineering group. Degreed Engineers with collectively over a century experience. Every one of them said it was a bad design.

Will it work? Probably.

Is it a good way to implement an E-stop? No.

Is an E-stop needed? No. Electrical failures happen too quickly and the E-stop button is located next to whatever disconnect you have anyway.

Don't get me wrong. The schematics you have provided are otherwise fine and I appreciate the free service you have provided to members of this forum.

If you want a detailed explanation of why the engineers didn't like your circuit I will be happy to have one of them contact you.

 

I'm an engineer (but I haven't worked on circuits like this for many years) and my objection is that such a system fails 'on'. You want a safety system to fail 'off'. Using the E-stop button to unlatch a contactor fails off and is the way that such controls are usually set up.

One way to do things is have the key switch send line AC to the controllers and a 24 V transformer. The secondary (24V) of the transformer would be connected to a series chain of push buttons, terminal blocks (with jumpers) and the contactor coil. The first push button (START) is NO has an auxiliary contact on the contactor wired across it. The other push button is NC. When you push the START button the contactor is energized thus closing the auxiliary contact and latching the contactor on. It stays on until you push the NC button which is the STOP button or one of the links on a terminal block is removed. Remote STOP (NC) buttons can be attached to the terminal blocks and daisy chained all over the place e.g. if your setup is in the basement and you smell smoke in the kitchen you can mash a STOP button at the top of the basement stairs. Other normally closed safety switches (e.g. liquid level switch or ground fault/N-G fault detection circuit) can be connected to another terminal block. Any thing which fails disables the system. It can't be turned on until the fault is cleared. And after the fault is cleared the system can only be turned on by pushing 'START'. An added benefit here is that the safety loop is low voltage - same as your doorbell and furnace thermostat.

The code does prohibit use of the ground conductor as a current carrying conductor. It does allow the use of the neutral as a grounding conductor in grandfathered installations. Not sure I see the relevance of that to this discussion here unless it refers to the fact that the ground carries the faux fault current in the 'fool the GFCI' arrangement.

With START/STOP push buttons and a contactor I don't see the need for the other two contactors.