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Old 05-23-2011, 05:41 PM   #11
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Hmmm.... I'll check when I go home, but I was under the impression that there is NO path the threaded base from the hot connections on an element. I 'll be getting my multimeter out tonight for sure.

That aside, the GFCIs we use trip at 5mA. To get 5mA of current from 240V, you would need a relatively low resistance path from to ground. Less than 50kOhm...

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Old 05-23-2011, 05:44 PM   #12
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Class A GFCI's are set to break at a current no greater than 3 mA. Class A is what is supposed to be used for house hold GFCI in bathrooms, etc.

The GFCI I have is a class A but exceeds the requirement, I've measured its breakage current at 0.8 mA.

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Old 05-23-2011, 05:50 PM   #13
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OK. I am seeing just tons of references to 5mA via google for a class A GFCIs, but that's a secondary thing at this point and not what I was most curious about. I'm more interested in the fact that there is an electrically conductive path between the hot connections and the threaded base of the element. That's news to me and I was totally unaware of it.

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Old 05-23-2011, 05:58 PM   #14
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Yea, I was very weirded out when I would get scorch smell and the GFCI poping, haha. So I measured and sure enough...

I'm just regurgitating what I've been told about class A GFCI's here on the forums, so who knows what is right.

I did measure what it takes to pop mine just out of curiosity though after this whole thing was going down and sure enough, it only took 0.8 amps RMS, even though it's rated for either 3 or 5 mA. I guess in this case I'm glad its that way because I'd rather have it be that far off in that direction than the other, its much safer.

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Old 05-23-2011, 06:26 PM   #15
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yeah, I think the GFCI requirements are stated that it must trip in X amount of time with Y mA or more, so as long as that is true, then the device qualifies. So... tripping at 0.8mA makes is in the class A range... WELL in it.

But, I think you're still off on something. If you have found the trip current to be 0.8mA on your 240V service, then it means you have a 300kOhm path or less (not 3MOhm) on your element. That seems wrong to me.

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Old 05-23-2011, 07:31 PM   #16
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Yea, but also remember that the resistance might be changing with voltage. If there is a dielectric in the element that is the insulator to ground and it melted away due to over heating during the scorching event it's possible that there is an air gap of some kind. A very small air gap at a volt meters voltage could (like a few microns or something) look like 2 megaohm, but at 240 volt you could arc and make it much less, or if you say ionized the insulator so now you have a highly ionic gas in the gap that conducts much better once you arc but then doesnt at low voltage (like how air works).

What I know for sure is that if I take the whole RIMS tube apart after a scorch but leave the element hooked up to the hots and ground the GFCI pops the second I turn it back on, if I remove only one hot line the GFCI still pops, if I remove both it does not. If I put a new element in it does not. I also know that a new element measured over 200 megaohm (beyond the multimeters range to measure), but after the scorch event it would measure (on 5 different elements I've scorched in the process of figuring this out) between 1.2 and 2 megaohm on the elements, the measurement was consistent for each element on re-measure, but each one varied between that range.

So something in the resistance of the element to earth ground changed during the scorching event. I wish I had an O-scope at home so I could hook it up and watch what happens as the GFCI pops so I knew more, haha, but knowing for sure that the element is the issue and the thing that caused it is the scorching is enough for me. The goal is just to replace the element and stop the scorching.

It's also possible, depending on the design, that the GFCI may work on peak current and not RMS current... which would make a small difference as well.

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Old 05-23-2011, 07:39 PM   #17
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I wonder if you actually dry fired your element? That would leave a horrible burnt smell as well as cause the inner workings of the element to heat up excessively (no liquid to carry the immense heat away.)

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Old 05-23-2011, 08:02 PM   #18
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it doesnt appear that way. Looking at the element the entire thing is covered in black burnt material that I can scrub off, and the element its self smells very strongly of burnt grain, as if you put dry grain in a pot and put it on your stove too long.

I've dry fired elements in the past and everyone I've done that to they crack and open a small hole in which water gets into and then causes the GFCI to pop. If I let the element air out and turn the GFCI on then it doesnt pop on those guys, so it seems like the water getting in the hole is the issue on the dry fired ones in my experience, and they didnt have the black material that I could scrub off on them, and the smell was more of a brazed metal than a burnt grain.

On all the dry fired elements I've had if I over heat them the GFCI pops, but then if I turn it back on right away it doesnt pop. Put it in water and it pops right away. The scorched ones pop right away no matter how long I let them dry out, in water or out of water, etc, they always pop the GFCI.

I suppose I should state that I only turn off 1 leg of hot on my heating elements so when the GFCI is turned on there is always 1 hot side, the other side is shut off with a SSR.

The elements I buy for the RIMS are camco ones and on the boxing it says they can survive dry firing, so to me the evidence points to the scorching and not dry firing.

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Old 05-23-2011, 08:06 PM   #19
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Beats me. Just thinking outloud.

I dry fired a 5500W camco element after a brew session. One of the black "incoloy" ones. ULWD, capable of withstanding a dry firing. It still had wort residue on it from the session (had not cleaned it yet). The garage instantly smelled like burnt organic matter and the element ended up with black crust on it that I was able to scrub off with a nylon scrubber.

The element did indeed survive and continued to work, but the plastic part on the back where the screw terminals are partially melted and I ended up replacing the element anyway.

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Old 05-23-2011, 08:17 PM   #20
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Hmm...


Well, if it was dry firing you'd think that only one part of the element would end up burnt I suppose... Of the latest elements that have poped the GFCI from "scorching" there was actually a decent flow rate (over 1gpm) when it poped.

Though, I suppose that after removing the output restrictions on the RIMS tube it might have flushed air bubbles out better. I guess the only real way to tell would be to mount the RIMS tube vertically instead of horizontally like I have it now.

I'll also add that the last time it blew there was the high flow rate like I said, however it was a grain bill with a fair amount of flaked wheat, and when we took the RIMS tube apart there was a LARGE build up of what I'll call "slop" inside the tube that got stuck in there built up around the heating element, and that was very burnt. The slop near the end of the tube was still slop, but the slop that was on the heating element was burned black and the surrounding slop was decreasingly black leading away from the element.

It makes me wonder if in wheat grain bills the extra crap that gets past the false bottom makes that slop build up in the RIMS tube if you dont have a good clean consistent flow (the last one blew with the flow switch on the output of the RIMS tube, and then on the same batch, 2 hours later after I cleaned the tube and put a new element in to continue the brew day and removed the flow switch, it never scorched again and we finished the brew) the turbidity of the flow in the tube causes it to drop out the "wheat" particles in the RIMS tube and as they build up you reach a point where you scorch and/or technically dry fire as if the element was in stagnant "slop" as the rest of the flow goes over the "sand barge" of slop that lays to rest at the bottom of the RIMS tube.

If the above is the cause of the problem turning the tube vertical to get rid of air bubbles would exacerbate the problem as the slop would built up starting at the base of the element rather than where the temperature sensor is.

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