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Old 12-22-16, 09:44 PM   #1
Xringer
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Default Circuit Breaker for your 240vac heat pump

When I look at the diagram below, (bottom sensor loop) and see the
overload OLR and the high pressure switch controlling the Power Relay,
(upper right). I see only one side of the 240 vac line is switched..

If the high pressure switch opens, the Power Relay opens only one side
of the 240 vac. Black, ACin1 is opened, but ACin2 is still connected.
I know that 120 volts is still on the main board (relative to chassis ground).

My question is, do we really need a pair of 240 breakers that are mechanically coupled?
I know they make it safer to work on the Outdoor unit,
but I don't think anyone is going to poke around inside an outdoor unit,
without pulling the disconnect hanging on the wall, right next to the outdoor unit..

Besides the safety aspect, is there any other reason to have a mech-coupled breaker pair?
Can't two non-coupled breakers do the job just as well?



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Old 12-22-16, 10:58 PM   #2
oil pan 4
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Electrical code demands that tandem breakers be used in all 240v circuits.

I used a 10 amp tandem square D breaker on my 9,000btu mini split.

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Old 01-04-17, 05:50 PM   #3
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And 3 phase demands a 3 pole Circuit Breaker ( 208 or 240 VAC ) . And 3 phase 480 VAC .

Functionally , 3 single pole CB's ( or 2 single pole CB's for single phase ) can be used with breaker handle ties . Best I remember , this is still code legal .

2 or 3 single pole CB's without handle ties are not code legal .

That's the way it is .

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Old 01-04-17, 06:32 PM   #4
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That is the way it is ..
But, besides the obvious safety issue (leaving one side hot),
is there any other reason for the rule? Any electrically based reason?
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Old 01-05-17, 05:23 AM   #5
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Leaving 1 side hot is the biggest thing I can think of .

Or the slight possibility of something running at 1/2 voltage ?

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Old 01-05-17, 09:09 AM   #6
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If the A/C runs 2 hots and a ground you shouldn't have anything running at half voltage.
But with out both hots connected to a tandem breaker it will fail an electrical inspection.
Did you run out of room in your breaker panel?
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Old 01-05-17, 09:45 AM   #7
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Yeah, the half voltage thing doesn't fly.. Since the 240 supplies in some other nations
aren't two 120 supplies stacked up. Just 240 and that's it.
I did hear of one electrician mistake on a US install, gave it 120 and it kinda worked.
It cooled, but would not heat.. IIRC

I am low on space in my breaker panel. I'm using those small 20A double breakers, one above the other.
But I've lost the little steel pin that connects them in tandem.
I think it fell out and went into the sump pump hole.. Have to make a new one.
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Old 01-05-17, 11:27 AM   #8
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I have seen electricians replace the steel pin with a piece of copper electrical wire in Eaton panels.

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