120V Point Of Use water heater switch

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  #1  
Old 11-24-15, 06:53 PM
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120V Point Of Use water heater switch

I have a lean-to shed next to the main building. Inside I have installed a point of use mini tank hot water heater. It's a small 8 gallon unit that uses 120V electric with a 1440W heat element.

1440/120 = 12A

I have it on a 20A breaker at the panel. Now from the panel to the shed I have two 20A circuits sharing a single #12 neutral conductor. In order to be able to turn the HWH on and off like when I go on vacation or when I don't need hot water in the Miami summer months (yes I could just flip the breakers too) so I installed a 20A 120V single pole switch right next to the WH.

After doing so I am thinking may be it's a bad idea...because may be one day someone else need to service the water heater and mistakenly used the switch as an interrupt thinking power is turned off, when in fact the shared neutral conductor is still "live" on the other circuit (i.e. using it incorrectly as an interrupt). At the panel I have them on a set of 20A double pole breakers.

I am wondering if I should have that switch at all...or if I do want a switch right there, may be I should use a double pole switch and put both the hot and neutral through it?

Thoughts?
 
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  #2  
Old 11-24-15, 08:09 PM
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The shared neutral should be before that switch so that at that service switch you are opening the hot and killing the circuit. The neutral is still neutral.
 
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Old 11-24-15, 10:43 PM
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I don't see a problem as long as the breaker feeding it is either equipped with an identified handle tie, or 2-pole breaker.

You also need a line of sight disconnect or breaker lock.
 
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Old 11-25-15, 04:36 AM
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Using a single pole switch at the water heater as a disconnect is done all the time. If you only interrupt the feed to the water heater, you should not need to open the neutral conductor on a 120 volt circuit. If the switch (disconnect) is in line of sight of the water heater no lock is needed.
 
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Old 11-26-15, 04:19 PM
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Justin Smith, yes the MWBC is on double pole breakers on opposite legs so I am ok there.

Tolyn the concern is when the switch is off the neutral conductor may carry load from the other circuit that shares the neutral. If the other circuit is not turned off, and someone didn't know the two circuits share a neutral conductor, wouldn't he/she be unpleasantly surprised if they decide to service the hot water heater by flipping the switch to off?
 
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Old 11-26-15, 04:48 PM
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It doesn't make a difference. The neutral is combined before the disconnect switch. From the disconnect to the water heater should just be the water heaters neutral...... not a shared neutral.
 
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Old 11-27-15, 09:46 AM
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PJmax I am not sure I understand, the switch does not open/close the neutral, only open/close the hot. The neutral is still "continuous". If the other circuit sharing the neutral is running say a plugged in drill, that neutral is carrying the unbalanced load, no? This is why they need to be handled tied is my understanding.
 
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