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When to use a fusible safety switch versus a non-fusible saftey switch?

When to use a fusible safety switch versus a non-fusible saftey switch?

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Old 03-12-12, 03:46 PM
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When to use a fusible safety switch versus a non-fusible safety switch?

My current electric (240v 30amp) hot water heater does not have a safety switch (disconnect) and I would like to add one. Should I get a fusible or non-fusible saftey switch for the hot water heater? There is a 30amp double pole breaker in the panel. Hot water heater is not in line of sight of the panel.

Also what type of safety switch should be used on a well pump (240v 30amp)? fusible of non-fusible?
 
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Old 03-12-12, 04:56 PM
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If the water heater circuit is properly protected in the main panel with the proper size breaker (it sounds like it is), all you need is a non-fusible disconnect switch. A disconnect on a well pump might be a bit different. Is there a building built over the well with electric being fed through the building to the pump? I have seen many installations where the pump wiring is buried from the house to the well casing and not visible at all. In those cases, there is no disconnect at the well at all.
 
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Old 03-12-12, 05:07 PM
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A two-pole circuit-breaker can be used for a dis-connect , and they are much more compact than a saftey switch . Safety-type dis-connects are necessary for dis-connecting motors because thay are designed to be locked in the "open" with a padlock.
 
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Old 03-12-12, 06:46 PM
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The only time a fused safety switch is required is when the load current is significantly less than the available current on the branch circuit.
 
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Old 03-12-12, 09:29 PM
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For the Hot Water Heater, I like the idea of having a safety switch at the heater instead of having to go outside to flip the breaker off. It sounds like a non-fusible would be acceptable at this location.

For the well pump there is a 15 amp double pole breaker in the panel which runs inside to the existing disconnect, then to the pressure switch, and then outside to the well pump. The inside disconnect is a fusible 30amp disconnect. I'll need to research the well pump a little more but it doesn't seem like the fusible disconnect provides any value in this arrangement and would a non-fusible work for the well pump? If a fusible disconnect should be used, maybe I need to use a 15 amp fuse to protect the well pump.

Thanks,
 
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Old 03-13-12, 05:43 PM
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For the well pump there is a 15 amp double pole breaker in the panel which runs inside to the existing disconnect, then to the pressure switch, and then outside to the well pump. The inside disconnect is a fusible 30amp disconnect. I'll need to research the well pump a little more but it doesn't seem like the fusible disconnect provides any value in this arrangement and would a non-fusible work for the well pump? If a fusible disconnect should be used, maybe I need to use a 15 amp fuse to protect the well pump.
There would be no point. Your well pump is already protected by a 15 amp circuit breaker, why use a 15 amp fuse too, it's not needed. The best residential example I can think of where you need a fusible disconnect would be something like this. Let's say you have a 50 amp air conditioner circuit, but the condensing unit label says MOCP 45 amps or maximum fuse size 45 amps. Then you would use a 60 amp fusible disconnect and fuse it at 45 amps.
 
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Old 03-13-12, 05:47 PM
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For the Hot Water Heater, I like the idea of having a safety switch at the heater instead of having to go outside to flip the breaker off. It sounds like a non-fusible would be acceptable at this location.
Any 2 pole switch would also qualify as a service disconnect. You could even use a Leviton switch like this in a 1900 box with raised cover.

Leviton 30-Amp Industrial Double Pole White Switch R52-03032-2WS at The Home Depot
 
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Old 03-13-12, 06:27 PM
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Great, that makes perfect sense. Thank you!
 
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