40 Amp 24VDC Reed Switch.

Use the reed switch to operate a contactor

This switch will interrupt a "ground check" circuit used in mines to monitor the integrity of the equipment grounding circuit, and these requirements are what MSHA (Mine Safety and Health Administration) specifies for any switch in this circuit.

http://www.gai-tronics.com/literature/mining/gtc070502.pdf

Try this

If you use a contactor then it will be with in the circuit not the reed switch. If this switch needs to be directly in the circuit some other device will need to be use. I do not think that you will find a 40 amp reed switch. What will activate the switch?

The reed switch needs to act directly on the circuit and be activated magnetically.

Boy, there are a lot of "No Sub" requirements here.

Like you, I know of none rated for more than about 4 amp. These guys will custom manufacture, and that seems to be their limit.

Must it really be a reed switch? Mechanical limit switch is out?

I am going to "spill the beans" here, or suffer harsh criticism for failure to provide detail

This is an explosion-proof enclosure of limited space that has only enough room left for a snickers bar (mmmmm) sized component. I found that a rare earth magnet is strong enough to penetrate the 3/4" thick aluminum enclosure wall to activate a standard reed switch. I asked MSHA about the ground check system and the requirements are what they gave me. This magnetic coupling would eliminate the expense of having to penetrate the enclosure wall with a mechanical rod or linkage. The direct action would eliminate extra components for which there is no room.

Well, try using the magnet to act directly on the relay. it is after all a magnetic solenoid operated switch is it not? maybe attach another magnet to the pole piece to help it out....

You mention of "another magnet" gives me an Idea. Suppose a pair of contacts held closed by a magnet attracted to a thin plate against the interior sidewall of the enclosure, now, if a another strong magnet (like pole) were brought up to this plate from the exterior, would this counter the attraction of the internal magnet to the plate?

yes, or you could use a spring to engage the contacts and have a relatively weak magnet (or even a steel plate for that matter) for the external magnet to act upon to overcome the spring force.

Now the question is, can you get something like this "off the shelf" and UL approved? probably not.

Acting directly on the circuit and being in it are not the same. Magnetically operated by what?

Thanks redfred, I knew there must be an explanation for the limited capacity.

I almost thought it was a con fancy calling it a Murphy Switch

Engine Protection Products » Murphy Shutdown Products » Murphy Switches, Solenoids, Fuel Valves
	117 TATTLETALE® Magnetic Switch View Details
	(117) Used to shutdown 12V through 32V distributor ignition or diesel engines. Breaks circuit when tripped. Opens distributor coil circuit to diesel run device (NC contacts). Automatically disconnects from battery after trip. Contacts 10 Amps 32V DC, 14 Amp fuse. Comes with reset button and is used on the WD300 Series shutdown panel.
	Price: $59.95
14 Amp AGC Fuse View Details
Replacement 14 Amp fuse for the Murphy magnetic switches.
Price: $4.95
	518APH Magnetic Switch, 12V View Details
	(518APH-12V) This magnetic switch allows for SWICHGAGE® and/or NC contacts to be wired "closed loop" (in series). Any contact open or SWICHGAGE® contact closed in the circuit shunt trips the 518APH. 12V DC. Contacts 10 Amp 24V, 14 Amp fuse.
	Price: $77.95

Engine Protection Products » Murphy Shutdown Products » Murphy Switches, Solenoids, Fuel Valves
	117 TATTLETALE® Magnetic Switch View Details
	(117) Used to shutdown 12V through 32V distributor ignition or diesel engines. Breaks circuit when tripped. Opens distributor coil circuit to diesel run device (NC contacts). Automatically disconnects from battery after trip. Contacts 10 Amps 32V DC, 14 Amp fuse. Comes with reset button and is used on the WD300 Series shutdown panel.
	Price: $59.95
14 Amp AGC Fuse View Details
Replacement 14 Amp fuse for the Murphy magnetic switches.
Price: $4.95
	518APH Magnetic Switch, 12V View Details
	(518APH-12V) This magnetic switch allows for SWICHGAGE® and/or NC contacts to be wired "closed loop" (in series). Any contact open or SWICHGAGE® contact closed in the circuit shunt trips the 518APH. 12V DC. Contacts 10 Amp 24V, 14 Amp fuse.
	Price: $77.95

now if it was me replacing a safety critical protection device, if i was allowed to replace it, i would use a 24 volt 50 amp rated normaly open relay so if magnetic switch fails the circuit goes open. same if wires to relay are cut etc.

in fact i think i would wire the switch to act both ways ie made one circuit open one circuit closed then a change over this would ensure safe operation even if the wire was trapped as the relay would need both a live circuit and an open circuit to be safe.

so it would be doulbe safe, if wires are cut = fail if wires are trapped or crushed =fail.

if wires short out =fail.

This ground check circuit continuously monitors the ground path (ground wire) from the main panel to the equipment and trips a circuit breaker in the main panel if this circuit opens. In our application there is a small manually operated control/circuit breaker box inline on the cable, through which this circuit passes. To test this function the mine inspectors must open this box (twelve 9/16 cap screws), and lift the ground check conductor from its terminal. For the benefit of these inspectors, I proposed this magnetically activated switch. If it won't work, it is not a problem for me.

Thanks for the help.

Aw heck, why didn't you SAY so! =b

Dude, Killark and others make switch actuators that will mount through o-ring/grommeted holes drilled in cast explosion proof boxes, we use them all the time.

Or you could mount a momentary test switch in the panel with a spring loaded guard to prevent accidental actuation. Not unlike the "test" switch built into residential GFCI outlets.

1. The reed switch drives a relay.
2. The relay drives a contactor.
3. The contactor switches 40A.

What you need is a 24v DC relay you dont need a reed switch at all & you can get 40 amp relays off the shelf.

The situation here is that the control is simply a manually operated motor control/circuit breaker with just enough room for the 4 pole shunt-trip breaker, a terminal strip, a trip capacitor and the wiring. Ther is no room to step down the line voltage (480 and 575v) for a control circuit. The ground and ground conductors pass through a feed-through terminal strip on their way to the equipment. The ground check circuit is effectively a loop comprised of the ground and ground check conductor. if this circuit is opened, the monitoring equipment disconnects the power source.The additional cost of another opening in the ex enclosure for a mechanical switch ( aside from the one for the existing on/off lever) would have to be born by the customer and unless it were mandatory, would not be acceptable.

I still think a momentary NC pushbutton in the ground circuit with a guard to prevent accidental actuation is the answer my friend. like perhaps this one. Square-D I am told has a pretty wide selection as well, wider than Curlee.

I completely agree, in fact, in the distant past, MSHA permissible controls had this, (called a "Funka" button after the Guy that developed it) and the vendor for our enclosures will incorporate it for an additional cost.

The problem is, the mines are on extremely tight budget now and because this test button is not mandatory, the mines don't want it.

My idea was to wave a "wand" carried by the inspectors, over a designated spot on the control and trip the ground check.

The enclosure would only need an additional drilled hole and an off the shelf push button switch. That can't be any more expensive than your custom reed switch. After all, you'd have to drill and tap at least one hole to mount the reed switch. So cost-wise I think the two are a wash at worst.

That terminal strip does not look like it can handle 40A. are you sure that that is the value you need?

It is a Buchanan brand rated 50 amps @ 600v.

The 40A rating is for "Any interrupting device in the ground check circuit" As mandated by 30CFR (Code of Federal Regulations). In reality, there is never amperage at this level on this circuit, we are talking about laws that were created years ago.

Use your reed switch to activate on of these Solid State Relays.

Crydom makes a good one.

They are totally encapsulated,only thing exposed is the terminals.

http://www.mouser.com/Electromechanical/Relays/Solid-State-Relays/_/N-ay0ti?P=1z0x15d