Need help!

[Max SImons]

Hi guys/gals,

I've been struggling to come up with a solution to my problem on my own and have decided to consult with the internet for help.

My name is Max and I am an electrician in Calgary, Alberta. I am currently working on a prototype tool for use in electrical construction. I dont have a very strong "electronics" background as most of my experience is with 120VAC and up with very large circuits. So i need help with the small stuff!

The tool is simply a device with a switch, when flipped, trips the circuit breaker that powers that particular circuit. For years I have just used a switch, and wire it up to cause a dead short when flipped, however, i have some interest in making a prototype that can be sold in wholesale stores and the current method isn't exactly safe. Because of that, I have to design a circuit that will limit the current in the circuit to 25A in order to not blow up the contacts in the switch, and not exceed the maximum ampacity of #14AWG.

What I need help with is this, if i go with the power resistor route, i run into two issues:
1 - a resistor big enough to handle the current is outrageously expensive.
2 - the resistor gets incredibly hot (obviously)

The solution needs to be relatively inexpensive, small in size, and not melt in your hand.

Any insight you can provide would be great. The nominal system voltage here is 120VAC and the current needs to be limited to no more than 25 Amps.

Thanks so much!

Max

 

[Harald Kapp]

The solution needs to be relatively inexpensive, small in size, and not melt in your hand.

Whatever device you use: if the circuit breaker doesn't trip (or doesn't trip fast enough), this device will dissipate 25A*120V=3000VA (3000W is resistive).
I can't imagine any device that fulfills your idea of size and thermal behavior while being able to dissipate 3000VA at the same time.

I think it will be more practical to have a device that creates a short circuit with an integrated fuse that blows (or a resettable circuit breaker) that triggers with a small delay if the circuit breaker under test doesn't trigger as expected.

Whether such a device can be sold at all, not even speaking of sales in wholesales stores to laypeople is another story. I doubt that very much. In my opinion laypeople shouldn't be given such a tool.

As our terms of use state:

We consider some topics to be dangerous in less experienced hands (for example, mains powered circuits, high voltage/current, repairs to switching power supplies, etc...). We try to tailor our responses and advice to your perceived or demonstrated level of experience, but in some cases it may be that we feel we cannot give advice if we consider it is unsafe. If you think we've made a poor judgement call, tell us - this applies both to us assuming you know less than you do, or the reverse. By the same token, don't assume that advice offered to others is applicable to you. If in doubt, ask.

I consider this idea to fall under these terms and will therefore close this thread. Send a private message to me or my fellow moderators if you feel this is not justified.