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RE: Circuit protection for small health & beauty product (for mass-production) similar to a foot spa whereby a portion of the user's body will come into direct contact with 1.5 gallons of water within the vessel. See original question link here: Do I still need a fuse if I'm using a GFCI?

Main components of vessel:

IP65 silicone heat pad: 500 watts @ 120VAC = 4.17a Note: adhered to stainless steel bottom; does not come into contact with the water. Air pump: 17 watts @ 12VDC = 1.42a LED: 70 pixels @ 0.3w per pixel/5vdc = 4.2a Total: 9.79A + 1 amp (auxiliary parts) = 10.79a total

Main components of PCBA: OLED display, two Pots, power button and AC/DC converters

Safety measures implemented to-date:

  1. Silicone heat pad in lieu of heating element

  2. 14/3 or 16/3 (TBD) GFCI cord similar to this one: https://www.amazon.com/dp/B000HEKUJA Note: Power cords with GFCI do not come with overcurrent protection. We will require overcurrent protection for the following reasons: A. we will seek UL, CE and other certifications in the future; B. "The Penny in the Fuse Box" https://www.schererelectric.com/blog/electrical/the-penny-in-the-fuse-box-and-other-diy-electrical-panel-nightmares/ Note: One of our stakeholders owns a large mechanical contractor company. He was the first one to alert me to "The penny in the fuse box" scenario. He says, "it happens more than you would believe. So, YES, you need overcurrent protection!"

Our options as we see them:

  1. GFCI cord + auto reset thermal circuit breaker like these: https://www.kuo-yuh.com/97-series-auto-reset-circuit-breaker.html https://www.alibaba.com/product-detail/Kuoyuh-97-series-10A-single-pole_1600651596086.html

Notes: This would have been the ideal solution for us had it not been for the potential major negatives as pointed out by these two EE's: see @PStechPaul comments on my previous question Stack Exchange link above. Also, see LEX@REDARC #1331 comment (second from top) here: https://www.redarc.com.au/forum/discussion/255/circuit-breaker-vs-fuse

Question: Is this still a problem with "thermal" auto reset circuit breakers today? One would think they have perfected this technology by now.

  1. GFCI cord + PCB (on-board) fuse: this still may be an option, although we still have reservations about this. Our initial concern was if the fuse blows, they will need to take it for repair. However, our PCB designer said: "if a major fault occurs they will need to take it to the repair shop anyway." Note: (added 6/12/23) a few engineers brought up that in some cases, overloads are temporary for one reason or another and that all it takes is a flip of the circuit breaker to be back up and running again. A PCB fuse cannot be replaced by a layman. Hence, should a temporary overload blow the fuse, the user would be required to take it to the shop for no other reason but to replace the PCB fuse if the problem for the temporary overload could not be determined.

  2. GFCI cord + manual reset circuit breaker (off-board). This seems to be LEX@REDARC preferred option although his comments were made nine years ago before advancements in auto reset fuses occurred, assuming advancements in auto reset fuse technology have occurred and I don't know that they have.

  3. Have someone make a custom GFCI cord with overcurrent protection. Note: if you are interested PM me. We will be needing 5,000 (+/-) per month starting Q3, 2024.

Our conclusions to-date based on what we've learned to-date:

  1. if auto reset fuses no longer exhibit the potential problems as noted by @PStechPaul and LEX@REDARC above, then we would probably choose this option. If the potential problems with auto reset fuses still exist, we will most likely rule this option out; even if there is a work-around because we prefer following the KISS method.

  2. still a possibility, but have reservations

  3. still a possibility, highest probability Note: the question with this option now becomes...do we use a GFCI circuit breaker in a distribution box or use #4 with a push button circuit breaker mounted separately in the product's compartment.

  4. still a possibility, but have reservations

Your comments and suggestions will be very much appreciated.

Thank you in advance,

Notes: That link to the cord is for example purposes only. We won't be buying any parts for this mass production product off of Amazon. We are an OEM and will be dealing in volumes where we will be able to bypass all distributors and only deal with the manufacturers of any parts we utilize. We will be required to get three bids and probably accept the middle bid, which is typical.

We've already considered fuse inlets for the main power cord. The product has another inlet with a conventional shape on the vessel (the vessel and power tower are not integral; the tower plugs into the vessel) so we had to change the main power cord and inlet thereof to an unconventional shape to force the user to use our GFCI cord which will be supplied with the product and also to prevent the user from plugging the main power cord into the inlet on the vessel. Because of the unconventional shape of the main power inlet, we have been unable to find a fuse/inlet combo so we have ruled using a inlet/fuse combo out for the time being.

The GFCI cord can not be attached to the power tower because of packaging related problems and assembly related costs. Also, there are two types of GFCI cords 120vac or 230vac; one for EU/UK and the other for US. Hence, less cost to just change the cord out in lieu of attaching two different cords 120vac or 230vac to the tower. Also, if GFCI goes out, the user just buys an other GFCI power cord from us.

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2 Answers 2

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Looks like I may have found the answer:

I found a 2 Pole 16A GFCI: https://www.sourceasi.com/product/ndb1l-32c-16-120v-16-amp-gfci-circuit-breaker/

It's DIN rail mounted which is also standard in EU/UK as I understand it. I can cut an access hole in the aluminum control tower sidewall. Then, I can mount a distribution 2 Pole switch DIN rail protection box, like the one in the link below, via the box face plate to the the inside of the control compartment tower and forget the idea of a GFCI power cord and fuse. Then, for product shipped to EU/UK we can just change out the breaker to the 240vac version. Also, in case the the GFCI breaker goes out, we can just sell our customers a replacement breaker instead of a replacement GFCI cord.

If I'm understanding all this correctly by now, we can also eliminate the on-board fuse option as well.

https://www.amazon.com/gp/product/B09P7Z2C77/ Note: For example purposes only. They may make a face plate mount box. If not, we can use this type of box and use the two screw holes in front to mount it via screws through the aluminum tower sidewall.

This idea is still in it's infancy but on the surface it sounds logical enough to warrant further investigation and to present to my team on Monday.

Also, in regards to the prices shown here, I consider those good prices for the retail market. Therefore, I'm very encourage I can get much lower pricing on a mass-production scale.

Also, since the power/control tower compartment is made with aluminum extrusion, I can design extruded snap lock fins on the interior whereby the distribution box can just snap into place thereby making assembly process that much easier.

If any of you have any additional thoughts on this path, it would be much appreciated.

Edited 6/13/2023 to include my further thinking on the GFCI circuit breaker mounted in a distribution box within the spa's compartment:

The potential problem with this is...I think that the power cord from the wall outlet to the portable spa will not be protected. Hence, what happens if the user reaches over and grabs the cord while they're using the spa.

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    \$\begingroup\$ My main concern with that GFCI breaker is that it trips at 30 mA, which I think is too high. Most residential GFCI outlets have a trip point of about 6-10 mA. The threshold of perception is around 5-15 mA, and 30 mA is rather painful, although usually not dangerous. I'm sure you can have a device like this manufactured with whatever threshold you require, and there are probably specifications for this. \$\endgroup\$
    – PStechPaul
    Jun 11, 2023 at 7:54
  • \$\begingroup\$ @PStechPaul Good observation, I missed that. 30mA is ground fault for equipment, I need ground fault for people which is 4-6mA I think. I'll research some more this coming week to see if I can find a residential 15A GFCI breaker. If not, I'll contact the manufacturer of this brand and ask them if they make such a GFCI breaker. Like you said, I don't think it will be a problem, or at least I hope not. Thanks for the head's up. \$\endgroup\$
    – tayglo
    Jun 11, 2023 at 8:14
  • \$\begingroup\$ After doing a little more research, it looks like the operating threshold is an easy adjustment if it's made for the North American market because we use electronic technology which is easy to operate at the 6mA level whereas the standard for Europe and the rest of the world is 30mA because they use electromechanical technology which is "extremely difficult" to operate at 6mA. So as long as I find a company that manufactures for the North American market, I should be good to go. \$\endgroup\$
    – tayglo
    Jun 11, 2023 at 8:54
  • \$\begingroup\$ Also, it's worth mentioning, that once I complete the general design, we will have one of the automation companies confirm and/or improve on my design to make sure it meets or exceeds UL standards before we go to market; such as this company: www.westernautomation.com \$\endgroup\$
    – tayglo
    Jun 11, 2023 at 8:58
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For safety measure #2, the GFCI cord is basically an extension cord which will also need to have the device's power cord plugged into it. I think it would be too easy for the customer to bypass, and it is also very expensive ($37!). The ideal location for the GFCI module is at the outlet, but I think the power cord should be permanently attached. Perhaps it would be good to have the GFCI device as a part of this cable, as it is on my pressure washer.

GFCI adapter

Image from Amazon

It may be more convenient to have a GFCI with a short pigtail to a standard plug, and then add a cord with a female IEC connector that would be inserted in a male inlet on the device. You can get power inlets with built-in fuses for about $2.

Power inlet

You could add a deliberate 6 mA ground fault by connecting a 5k resistor from hot line to GND and make it so the user must clear the fault before allowing the device to power up.

(edit) It might be something like this, where the 5k resistor causes the GFCI to trip. The user would press the button, which disconnects the fault and latches the relay ON. The GFCI will still trip if a real ground fault occurs. I need to make another edit.

schematic

simulate this circuit – Schematic created using CircuitLab

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    \$\begingroup\$ Thank you for your continued interest in helping out. I've addressed your suggestions in the main body of my question and explained why the things you're recommending are not possible for our circumstance. You may or may not want to delete this answer, I'll leave that up to you. Thanks again. \$\endgroup\$
    – tayglo
    Jun 11, 2023 at 3:05
  • \$\begingroup\$ I think I'll keep it open for now. Some of the information might be useful to others. And there may be further discussion of protection for the PC board. I also looked for DIY GFCI circuits, but I didn't find any - there are probably a lot of liability issues. \$\endgroup\$
    – PStechPaul
    Jun 11, 2023 at 3:41
  • \$\begingroup\$ We are hopeful when we reach out to the GFCI manufacturers they will be willing to make a GFCI with overcurrent circuit breaker for cord installation which will probably be our best bet when all is said and done. It's unbelievable that in the 21st Century there doesn't seem to be any on the market. Or, maybe there is and we just haven't found one yet. \$\endgroup\$
    – tayglo
    Jun 11, 2023 at 3:51
  • \$\begingroup\$ @tayglo In the majority of the world (at least as far as I'm aware), GFCIs are installed routinely on all residential circuits, so they can just be assumed to be present. No need to put an extra one on a cord when it would make the cord cost $20 or $30 instead of $5 or $10. \$\endgroup\$
    – Hearth
    Jun 14, 2023 at 5:29
  • \$\begingroup\$ I asked an EE friend to look at this entire chat (both questions) and give me his thoughts. He said the most likely reason I'm not getting more responses on my two questions is because @manassehkatz-Moving 2 Codidact already answered my question. So I went back and read his answer again on question #1 and sure enough he not only says to put the GFCI at the end of the power cord but gives the reason why it needs it "because some outlets don't have GFCI protection and are grandfathered in": manassehkatz-Moving 2 Codidact . Does that change your mind? If so, I can do that and focus on the fuse. \$\endgroup\$
    – tayglo
    Jun 14, 2023 at 12:24

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