What switch type do I need?

A standard pair of start/stop push buttons, in conjunction with a two-pole normally open motor-duty relay, can handle this. Searching on "motor start-stop control" may turn up some sample diagrams.

On the button Tornado! Simple, straight forward and the logical way to go! GA from me!

Eaton makes some. You need to check out their website: Eaton

Maybe someone else like SqD , Furnas, Siemens make specific single phase ones also.

A302 Manual Starter and Protector

The A302 Manual Starter and Protector is a 3-phase manual motor starter and protector with an adjustable bimetallic overload and instantaneous magnetic short circuit trip mechanism. A302 starters are UL listed and CSA certified for group installations of motors and single motor installations up to 25 FLA. These manual starters can be field wired for single-phase motor applications by connecting the 3 poles in series.

Features:

• Compact 45 mm design — saves panel space
• Meets UL, CSA and international standards
• CE Mark
• Class 10 bimetallic thermal overload trip
• Single-phase fault sensitivity
• Snap-on DIN rail mount capability or can be panel mounted with screws
• Open starters can be padlocked in OFF (STOP) position
• Terminals are "fingerproof," located in the vertical plane, easily accessible from the front with screwdriver guide holes provided for ease of wiring
• Wide range of accessories, including auxiliary contacts, undervoltage release module and shunt trip can be added to the starter without tools

120 volt latching relay!

i do belive a latching relay is exactly what he does not want

The opposite in fact, like Tornado says, a simple electromagnetic motor starter which drops off when the supply fails, and requires manual re-start action. A latching relay will not drop off will it?

Ready-to-use single phase starters must be available ex-stock most places?

YES, its called a latching relay. A latching relay need a input, from a "push to make " button. The wirning on the relay itself allows the latch. A stop button need to be pressed or the power must fall away, or a high level switch break the latch.

Wha i meant was, the latching relay will stay ON whether there is incoming power or not. If you see the original post, he wants a switch which becomes OFF when power fails. And it should be switched on manually. A simple electromagnetic starter/relay with On and OFF buttons, as Tornado says. The magnetically held starter WILL drop off when power fails.

My post explained that the the relay get wired to latch ( electrically), loss of power will lose the latch. You can only remake the latch after pressing a button again. A level switch can be wired to automatically latch, unlatch, but this is not what the op wanted. Unless a magnet is magnetified by electricity, you must unlatch it by hand, also not what the OP wanted. All electric switchgear make use of electro magnetism, it need to be applied correctly.

I understood the reply to the OP. It is the way the relay or contacter gets hardwired that will latch or otherwise.

The following materials are required:

1.A manually operated push button.

2.An auxillary contactor of ,say,5 amps rating with 120 volts coil voltage.

3.Flexible copper wires for wiring works.

Wiring can be done in the following method:

Apiece of wire is to be connected at one end to the 120 v supply.This 120 v supply is to be taken to the coil terminal of the to auxillary via the manually operated push-button station.

The NORMALLY OPEN contact of the auxillary contactor is to be connected in paralell to the manually operated push-button contacts.

On pushing the manual button,120 v supply will reach the contactor coil and the contactor will close making the motor to run.If the supply fails,the supply to the contactor will fail and the conactor will be deenergised and the motor will stop.

On resumption of power supply,the motor can be started only by manually operating the push-button.

Both the push-button and the auxillary contactor can be housed in a small pvc box-type enclosure.

Hope this will meet your requirements.

Bye.

I am going to focus on a control (simple) circuit. You mentioned a circuit that is held by current flow. The examples that you wanted to prevent were (power company error, backhoe hits cable, etc.). Install a GFCI, and then in SERIES add a Voltage Controlled Relay. This simple relay requires a minimum voltage to operate of 100 volts A.C. (power company provides 240/120, 60hz in dwellings.)

These two items in series will provide the protection you point out from the Power Company going to LOW volts and the GFCI provides good sensitivity for the case where the circuit gets slammed with a backhoe or similar trauma. This post will draw some interest. If Voltage goes LOW the relay opens, if the circuit experiences leakage or unusual trauma it will open. Let's see how this goes over.....In either case YOU need to reset the device that opened (tripped).

A simple relay wired to latch will do the job perfectly. Anything happens to the cable anywhere before the switch, no power can get to switch and the latch will let go. Only if power is restored and a hand presses a button, will the latch work again.

This latching relay would only have trouble responding to 'LOW' voltage from the power supply (power company). It would have to be latching relay that drops out on 'LOW' voltage to meet the original post conditions! The orignal post did not specify how sensitive he needed the circuit, so a backhoe slamming the cable would certainly cause the latching relay to drop out!

Tripus is one of many companies that makes a low-voltage release switch. www.tripus.de/ Here's a link that should work, or just type low voltage release switch into your browser and go do some shopping.

Hey Dajo :Go to any electrity shop and before you tell a half you are telling us here, you will get what you need right on the table.-

"I want a switch that is push (toggle, whatever) to close and which is held closed by current flow, so that if the power drops (power company error, backhoe hits cable, etc.) the switch will open and stay open, requiring human activation for re-start. That's it"

Electromagnetic motor starters do just that. Any standard single-phase electromagnetic motor starter will do this job.

Your example of a backhoe hitting the cable triggered off thoughts in many that you require ground-fault protection too, which means some additional stuff like GFCI. i believed that this was just one example of how voltage can fail, and responded accordingly. Now you choose. You have many opinions.

Since i haven't seen any responses from you at all, you may have already found the right solution.

First and foremost: thank you everyone for the replies and advice; it is all
very helpful, and surprisingly entertaining! It is very pleasant to receive
help, especially since help is not always forthcoming in life.

Although the suggestions concerning *what* needs to be done (the theory,
circuitry, etc.) are interesting, and I have pursued them, my request really was
about *how* to do it. I just did not know what to search for. Furthermore, the
pump motor is rated at 150w and it is plugged into a standard household
receptacle. So the suggestions involving using proper industrial equipment are
out-of-scale for the application. Another thing that I should note is that the
back-hoe problem was a wild invention of mine; really I expect only to see very
ordinary power-failure. Also, the pump already is plugged into a GFCI.

Thus, at the moment, the most interesting thing is the search string "low
voltage release"; and I gather, through reading, that my request is for a Low
Voltage Protection (LVP) device. This has made my quest a little more
intriguing: I still have the feeling that someone makes *exactly* what I need,
all I have to do is find them and it. The absolutely ideal device would be a
standard American household size switched outlet, with LVP, that I can swap with
the two-outlet receptacle that I am using at the moment just by using a
screwdriver. And if you can point me to one of those, then please do. I am
still searching without success; Leviton, for example, appears not to make them.
And searching leads to much browser-fuzz: "low voltage" means something
completely different to Leviton, and leads to elegant light dimmers with LEDs.

The closest hardware to date is made by Tripus (thank you Oregoon) at
http://www.tripus.de/Recessed-switches-with-low-voltage-release-2967-90.html.
The problem with these European switches is the mechanical interfaces; if I use
one of these I shall need to make an in-line water-resistant box. However, I
may need to that in any event.

I have realized as a result of this posting that I had not considered reaction
time for the LVP. Someone comments that I had not mentioned sensitivity in the
original posting; I wonder if that is what I am calling reaction time. The
application (water system) can withstand a outage of many seconds; in fact the
excess water takes a few minutes to be lost through the overflow. So a magnetic
reaction time of longer than a few microseconds is desirable; having the lights
flicker implying pump stoppage would be a nuisance.

Dajo

If you aproach an electrical supply company they should be able to assist you in supplying an over and under current relay, which has been designed specifically for pump application. The current is measured via a control transformer and fed to the relay which in turn can clamp the upper and lower limits of the motor. The lower limit must be set slightly higher to the known no load current of the motor, (which is best to physically measure with a clamp meter), and the upper limit should be set to the maximum full load current of the motor which can be found on the name plate.

The relay has a potential free contact which can be connected normally closed in series with the stop part of the latching circuit of the contactor. Once the limits are realised the relay will change state and take the contactor out.

Hello dajo,

Dayton supplies the type of switches you are looking for. They are simple and offer protection from both under and over voltage and also high and low current draw.

A simple stop start circuit utilizing an 8 or 11 pin cube relay wired in series will complete the circuit protection you are looking for.

All the componants can be wired into a small junction box. And for added convenience you can install a line cord primary end and install a receptacle to the outside of the junction box to plug in the motor you want to protect. A simple neat little package.

You can obtain all the componants from Grainger Industrial Supply.

The voltage sensing relays are part numbers 1EJF1 for 80 to 150 volt and 1EJF2 for 160 to 270 volt

The AC current sensors depend on your current draw. First one in the line up is part number 1EJF3 and so on.

The current sensors are switch selectable from 0.1 amps to 10 amps.

Hope this is helpful.

Jerry D.

Thank you, this information was particularly helpful. It is quite likely that I shall follow your suggestion of an in-line box using the 1EJF1 except that I shall not install a stop button, pulling the plug will suffice. I have not started purchase and manufacture yet, I am somewhat preoccupied; I am writing to acknowledge your informative post without too much delay.
dajo