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Old 02-10-2007, 00:08   #31
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Gord, in the 70's mercury capsule light switches (wall mounted switches) were commonly sold in the US as "silent" switches, i.e. so you wouldn't wake someone with the "snap" of a switch.

I don't know if they are on the market here any more, with everyone trying to get mercury out of products and the environment.
I haven't been out to the Westport WA lighthouse since I was a kid, but at the time the huge glass Fresnel lens was supported by linkage floating in a huge pool of mercury. The tank which held the mercury was about 5 feet across and a couple of feet deep!
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Old 02-10-2007, 02:25   #32
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As hello’ suggested, mercury switches are no longer available. They weren’t considered “explosion-proof”.

National Vehicle Mercury Switch Recovery Program (NVMSRP)
On August 11, 2006, EPA announced a national program that will help cut mercury air emissions by up to 75 tons over the next 15 years. The National Vehicle Mercury Switch Recovery Program is designed to remove mercury-containing light switches from scrap vehicles before the vehicles are flattened, shredded, and melted to make new steel.

Limiting future use of mercury switches — In June 2006, EPA proposed a rule that would impose requirements on any future use of these types of mercury-containing switches in passenger vehicles.

Goto: National Vehicle Mercury Switch Recovery Program | Mercury | US EPA
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Old 02-10-2007, 12:29   #33
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Gord, I'm not sure how mercury switches have ever been used in vehicles--except as "tilt" sensors for alarm systems.

But those pictures of GE switches are indeed the ones once commonly sold in the stores. Those were sold for the home market--they were AFAIK never concerned with explosafe status, that's something no one bothers with unless they are applying to the BOM for special approvals.

In general, using any part of the word "explosion" on any consumer product packaging in the US is considered a terribly dumb move. People just don't want to see or hear it, they put it down and walk away. Unless you're selling fireworks.<G>
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Old 02-10-2007, 13:59   #34
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“Explosion-Proof is an imprecise vernacular term, that requires further definition. There are several ways to protect electrical equipment so that arcing or hot components will not be an ignition source causing an explosion.

The Electrical Codes of the U.S.A. & Canada deal with hazardous locations thus. (I don’t know how the US BOM (Mines) deals with them)

Explosion-proof or flameproof
protection requires an enclosure that can withstand an internal explosion without rupture, and prevents flame or an explosion inside the enclosure from causing an explosion in the surrounding atmosphere outside the enclosure

Intrinsic safety
involves limiting the electrical energy at potential sources of ignition in electrical circuits (hot components and spark sources) to such low levels that-even under abnormal (fault) conditions-there is no possibility of the electrical energy igniting an explosive atmosphere. This method of protection may be used for a wide range of low power equipment, including pagers, process control tank level transmitters, and portable gas detectors.

Non-incendive equipment
also limit energy at potential sources of ignition in electrical circuits (hot components and spark sources). But unlike the intrinsic safety method described above, non-incendive equipment is designed to provide protection only under normal operating conditions, which may include opening, shorting or grounding of field wiring. This method of protection may be used for a wide range of equipment, including pagers, process control tank transmitters, and portable gas detectors.

Encapsulation
involves molding the parts that could cause an explosion in a compound to exclude the external atmosphere. It is usually applied to components, such as valve solenoids.

A ClassI1hazard is one which is created by the presence of flammable Gases or Vapours in the air. (Class II is combustible Dust, Class III is easily-ignitable Fibers or Flyings)

The Codes also specify that hazardous material may exist in several different kinds of conditions, which, for simplicity, can be described as, first, normal conditions (Division I), and, second, abnormal* conditions (Division II).

(Div. II) When the hazardous material is expected to be confined within closed containers or closed systems, and will be present only through accidental rupture, breakage or unusual faulty operation.

The gases and vapours of Class I locations are broken into four groups, by the Code: A, B, C, and D. These materials are grouped according to the ignition temperature of the substance, its explosion pressure, and other flammable characteristics. Propane falls into Group D (Zone 11A).

For the exact definitions, see the NEC Articles 500 through 504, and 510 through 517, and/or the Canadian Electrical Code.
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Old 02-10-2007, 16:15   #35
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Not to start a flamewar. (Pun intended.) But, I think I'll just use kerosene.
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Old 02-10-2007, 19:32   #36
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Guinea pigs sound tasty... but what about that odd squirrel or skunk I find squished in the middle of the road? ha ha When in Rome... (or driving around in an RV...)
You don't know how long it has been there getting rotten, so you better not eat it unless you run it down yourself.

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Coot: Good ideas about the solenoids (or even a valve) upstream of each appliance. It would be good to have individual controls for LPG right next to each - even a manually turned valve. BUT... I also see a downside. That's 4 more flare fittings inside the vehicle (to install 2 valves or solenoids).
On a boat, you would put all the solenoid valves inside the propane locker, then run a separate low pressure hose from the propane locker to each appliance. It means more low pressure hose and more wire, but that seems a reasonable tradeoff to avoid having more joints inside the enclosed area.
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Old 04-10-2007, 08:10   #37
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On a boat, you would put all the solenoid valves inside the propane locker, then run a separate low pressure hose from the propane locker to each appliance. It means more low pressure hose and more wire, but that seems a reasonable tradeoff to avoid having more joints inside the enclosed area.

Sean can do the same on his RV. Build a manifold after the regulator at the tank with solenoids for each branch.

You can even put a small vent in the floor of an RV to allow propane that might leak to exhaust to the outside.
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Old 04-10-2007, 10:51   #38
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Sean, while we are entertaining you with the values of an explosive fuel onboard [g] perhaps I should also mention some 8-10 years ago that there was an incident at a Spanish campground. As I recall, a large LPG tank leaked and the gas rolled down a mountain road. Eventually something lit it off, tremendous consequences. The length of the fire was described as something like part of a kilometer long, not your usual "one or two buildings" event.

Putting a drain in the floor? Dunno, your woodburning stove might not be such a bad idea.[g]
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Old 04-10-2007, 11:05   #39
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My insurance is lower because I don't use propane or any explosive fuel as a main cooking source. Insurance companies know how to cover their asses. Too many incidences of fuel explosion. The improved detection and control technology has supposedly made it safer. Do you trust the boat next to you in a marina that may or may not have a properly maintained system. I would consider LNG as a cooking fuel source but it has not yet reached world wide distribution. It is coming however.so far it is only available as CNG.
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Old 04-10-2007, 11:48   #40
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It is now Zone 0 (explosive vapour always present) then Zone 1, etc.

We typically use Tech cable with the proper sealing glands for most outdoor, or indoor uses. It is certified for Zone 0 use, and outdoor use above or underground, or in water.

It consists of a tough elastomeric outer sheath around a spiral metal tube, inside of that the wire bundle is surrounded by another elastomeric sheath. Then a thin conductive shielding sheath, then the insulated wire.

It is available in many sizes for example 24 X 16, 24 counductors 16 guage, or say 4 X 10, (3 phase 10 guage wire with ground)

The terminations are gas/and water tight.

Surprisingly the cost is not really all that much (on a $200,000) boat.

If I was building or rebuilding a marine electrical system I would strongly consider this type of wiring cw spares for some of the main wiring.
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Old 04-10-2007, 11:59   #41
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I treat propane the same way I treat through hulls. If it's not being used at this very second it is shutoff.. No surprises...
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Old 04-10-2007, 16:08   #42
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And when the sniffer, located in a pool of LPG vapour, switches - what then?
Exactly, Gord. Seems there is no perfect solution other than to start using a wood cook stove. (joking)
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Old 04-10-2007, 16:13   #43
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Luckily, I have only 2 low pressure lines coming into the living area. One goes to an enclosure that is required for the lpg fired fridge. Part of that enclosure is a big hole in the floor (not a boat! ha ha), so I guess the gas could roll out under the vehicle that way.

The second line is about 3 feet long and attaches to the stove. We have cooked with the "devil gas" and boy did we like it.

I suppose a solenoid for each low pressure line is good, except in our case, the refer (which is lpg powered) is on 24/7/365... making a solenoid on that side a little bit useless.
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Old 04-10-2007, 16:50   #44
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Maybe the following will help.

First - LPG will only burn within quite a limited air/gas mixture ratio so to start with you have to be fairly unlucky for it to "explode" - of course, you are even unluckier if it does . I put "explode" in "" because LPG does not explode in the commonly understood sense unless there has been alot of mixing of the air/gas - check it out on the internet if you disagree. This means for it to "explode" unless there has been mixing, the point of ignition has to be at the critical air/gas mixture front.

The LPG solenoid is electrically a passive device (electrically it is just a coil) so there is no arcing switching danger from the solenoid's own operation should it be immersed in a gas/air mixture. In any event immersion in an explosive mix should be unlikely as the main solenoid valve should be in the gas locker (at around top of gas cylinder level one would expect).

The solenoid valve in our case has an Ingress Protection rating for dust/water suitable for its semi exposed location in the gas locker and is mounted directly on the regulator ie the regulator/solenoid valve are in one single assembly connected directly to the cylinder's own manual valve assembly.

In our own case the solenoid switching is via a manually operated switch or alarm all integral in the gas detector control panel - all switching whether for solenoid operation, sensor operation or alarming is solid state, there are NO switch contacts to spark. I would have thought this to be normal apart from in uninformed amateur hash up self built switch panels or very, very old ones

The gas detector sensors are passive devices - there are NO contacts at them to spark. They do heat up as part of the natural course of their operation though.

Of course, there is plenty of other switching equipment on most boats including in the bilge. In our own case, when first arriving at the boat I always open the sea cocks in the bilge first before turning the main battery and shore breakers on - hopefully, by putting my head in the bilge to open the sea cocks, if there has been a gas leak I would smell it before any chance of ignition.
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