Hooked up a shop built heater for a pull tester today. I’m using an inkbird temp controller with a solid state relay. One of the 8 heater cartridges burnt off a lead as soon as it was plugged in. (Maybe I should have the wire end of the heater slightly proud of the Al block they are in?). Any way it fried as soon as it was pluged in. The ssr is only switching the hot (black wire) on a 110v circuit. Found out the outlet that it was plugged into is wired backwards. Not a big deal for most things. I’m going to correct this, but should I go crazy and check every outlet in the shop?
How bad is it??
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I have no idea what most of what you wrote means.
You built some homemade 120v heater and burned an element?
You know at least one outlet was wired backwards? Yes, check the rest. Should take a half hour (if that) with a tester.
You built some homemade 120v heater and burned an element?
You know at least one outlet was wired backwards? Yes, check the rest. Should take a half hour (if that) with a tester.
Wrench97
Well-known member
Whats a pull tester?
Wrench97
Well-known member
Yes it's a concern but easily tested with a plug in tester.
Black wire to the gold screw, white wire to the silver.
Black wire to the gold screw, white wire to the silver.
Sorry, I should have been clearer. A tensile load tester. For applying a linear load to a mechanical part to determine its holding capacity. In this case it’s a crimped fitting on to a cable. We are also using this rig to measure that force at an elevated temperature (350c).
Absolutely. It's a quick thing to check for and while most modern electronics are fairly safe there are old electronics out there expecting a polarized plug as part of the safety of the device.
Not to mention if someone messed this up you don't know what else you'll find.
I’ll check them all over time. This is the first time it’s been an issue, as my heating unit only switches the hot leg. I might go back and install some inserts around the heater terminals. Not sure what might be available. Or just pull out the cartridges to be slightly proud of the Al block.
Make up your mind, earlier you said:
You need to check the outlets sooner then later, this isn't a big, involved task. Spend $15 on a tester and do the whole shop in a half hour.
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My favorite is finding the old All American Five radios that pre-dated polarized plugs. Some of them the screws on the rear make contact with the interior chassis which is tied to either the hot or neutral depending on how you plug it in.
You usually can tell somebody figured out the right polarity by the nail polish or Sharpie marking on the plug.
Ya, that’s what I’m afraid of! It’s a pretty old (tor Tempe) rental unit. I’ve been thru most af the 220 circuits and all of the 3phase stuff. This was the first incident that made me question the 110 stuff.
Didn’t really hurt anything but my inturn was a little freaked out. It was kinda worth it just for the look on his face. But that should not have been hot on just plugging it in.
This is a brand new rig. I have built very similar things before. The leads on these heaters are very close to the od of the holes. I’m going to back them all out a smige.
I don’t think this is a huge deal. But I too was surprised when one of the heater leads blew up when no power should have been there.
Is there anything that I could have built into my unit to correct/check for the h/n being reversed? Guess I will at a minimum add a fuse.
Is there anything that I could have built into my unit to correct/check for the h/n being reversed? Guess I will at a minimum add a fuse.
Simple solution is a polarized plug. A mis-wired receptacle is always a safety hazard. Expectation is you're plugging your thing into something correctly wired.
whateg01
Well-known member
How does the heater get power if the neutral is switched instead of the hot? If either leg is disconnected, there shouldn't be a path, right?
Post a picture of your rig, and the burned wire.
Sounds to me like you shorted the lead during assembly.
Lots of parts of Tempe pre-date the NEC requiring grounded receptacles. Best to pull them (or a sample) and check for bootlegged grounds while you're in there.
I saw one home in Tempe that had a junction box constructed from a can of Apache beer.
walta
Well-known member
I have some concerns Solid State Relays SSR are great until they are not. They almost always fail to the ON condition. Your circuit must have thermal fuses that will shut down the heaters before something starts a fire.
Note the fastest way to short an SSR is the failure you just had. If your failure had made excessive current flow thru the SSR it would almost certainty would have been destroyed.
Please make sure every metal part anyone could possibly touch is grounded before you test this thing.
Walta
Note the fastest way to short an SSR is the failure you just had. If your failure had made excessive current flow thru the SSR it would almost certainty would have been destroyed.
Please make sure every metal part anyone could possibly touch is grounded before you test this thing.
Walta
Great add.
I used to build heaters and controls as a side business. Not hard to setup a safe, redundant system but also super easy to build a fire/shock hazard with the abundance of cheap material available online.
Lots of good points. Rig is using a replacement plug. Not polierised but has a ground terminal so it kinda is. Everything is grounded. I’ll get some pics tomorrow. I have it wired to be switching the hot leg, but if the plug is backwards than that’s the neutral i suppose.
Thanks for all the support. I’m definitely looking to make this as safe as possible. Still very much in the testing phase., and debugging. Not sure if there is a way to avoid the input being backwards if the building plug is miss wired?
SMH
Buildings don't have plugs, the have receptacles or outlets.
There's no way to correct an improperly wired receptacle on the device side.
You need to check building receptacles! In the time you've spent making this thread you could have finished.
whateg01
Well-known member
Maybe you mentioned it before, but what is the reason for not fixing the receptacle? I suppose if you absolutely can't fix the receptacle, and you want the heater to be wired correctly, you could make a pigtail that swaps the legs, but that introduces the possibility of all kinds of other issues especially if somebody gets shocked
He could just wire the device backwards, but either way once he finds a correctly wired receptacle...
whateg01
Well-known member
That's why I suggested a pigtail. It could be removed when the receptacle is corrected or if it gets plugged into a receptacle that is wired correctly.
Idk, 2 minutes to fix the outlet vs. making a pigtail?
whateg01
Well-known member
I agree with that!
wyliesdiesels
Well-known member
same issue comes up with old antique lamps with non-polarized plugs. the metallic lamp holder is bonded to neutral so if you plug it in backwards, you can get a jolt touching the lamp holder and a bonded metal object or even by standing barefoot on concrete.
wyliesdiesels
Well-known member
thats because the fridge was wired or plugged in backwards, causing the chassis to be energized. touching the grounded/metal chassis of the range completed the circuit thru your body. The chassis on the range was bonded to neutral.
this is why polarized plugs and 4-wire dryer and stove/range circuits became required. it was to prevent a potential for shock. 3-wire dryer & stove circuits have a bonded neutral at the chassis terminal strip.
The hot leg was not switched so it shorted to the grounded Al block.
rlitman
Well-known member
Still not acceptable for a neutral connection to short to ground, even if the results are less dramatic. You need proper isolation. Maybe some kapton tape or a fiberglass sleeve?
Also, as walta correctly pointed out, we don't see any sort of high limit control there. You absolutely must not rely on the thermocouple input to the PID controller to be your high limit. That WILL fail with even more dramatic results. Either when the SSR fails closed, or simply when you lose connection to the thermocouple. Loss of thermocouple input to the PID will cause it to think it is way too cold and keep the SSR closed.
All very good points. I have pulled the carriages out of the block about 1/8”. What would you suggest for a limit control? This unit will only be powered on for about 5min shots under continuous operator supervision. Also being used with a secondary thermocouple to monitor the specimen temperature. This round of tests is at 350c but I expect that might change.