Backyard Aquaponics
A place to discuss aquaponics

yeh, but what size motors?

i still find it highly unlikely that even a contactor closing on a shorted motor on a domestic 16 amp breaker is going to fuse.............

Motors varied in size. The problem was the arcing at the contactor ,, these motors are turn on and off , or forward and backward thousands of times a day , slowly the surfaces of the contact tips ( usually silver coated) begin to pit , causes more arcing etc etc . Hot joint appears / lots of carbon , melted metals around and sometimes just sometimes , welded.

so getting back to an AP application, specifically for change over of mains to inverter, you'd think that the chances are negligible, true?

Absolutely true ,, I'd say a single contact arrangement for back-up power would be good for several thousand years. If wired and arranged properly.
May need a bit of dust blown out every 50 or so years

Kuda,
I didn't mean the initial outage/brownout/overvoltage/surge, I meant when the apprentice does the on/off/on/off thing at the substation afterwards; the UPS waits for the mains to be stable for some time before re-connecting.
I only twigged to how 'evil' brown reconnects were when I replaced the THIRD electronic pressure control for the domestic pump at our place, or more accurately when I thought about the bore pump out the front in all weather with a bigger load and more earth leakage. That is, the bore pump had ye olde on/off pressure switch and had no problems!
No prizes for guessing what type is on the house now.

Jaymie,
Thanks for the vote of confidence. Your brother should be able to get contactors at any electrical engineering outlet like Atkins Carlyle, Lawrence & Hanson, RS Components & Farnell will also have them.

One thing to remember if switching the DC supply to your inverter;
Have several contacts of the contactor in series to reduce the DC arc when the contacts open. AC does not arc as long as DC, so DC needs to have a faster contact opening than AC. Be having 2 contacts in series, the contact opens twice as fast as a single contact. 3 in series open 3 times as fast as a single contact.
This will reduce the burning, pitting and possibly welding of the contacts.

Another thing to consider is the rating of the operating coil. Some coils are made for intermittent operation and may overheat, causing the coil former to distort and jam the contactor closed.

Have fun,
Tony

and factory roller doors

also known as electrical wholesalers lol...engineering makes em sound too clever .............would give Laurel & Hardy aka Looser & Hopeless a wide berth......also RS and Farnell............they would want your first born as well as an arm n a leg for their stuff.................you'll also have the choice of Ideal and Rexel up there

Agreed, 'Lousy and Hard up' as my electrician will milk you dry.
Farnell are great, and will have it on your doorstep the following AM, but then they would want the title to your property in exchange.
RS Simmilarly... These things should cost less than $30 imho, and if your lucky, as little as $15.

The stores mentioned above, might charge a heap, but they will have what you want, and they are easy to find. for the sake of a $15-$30 saving it's probably not worth your time finding a cheap supplier...

my $0.02