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Old 03-04-2012, 10:15 AM   #1
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AC wiring/breaker questions?


Hello All,

I have some confusion in regards to the wiring for our air conditioner (split system) and would like some insight. This is straight ac with a heat strip.

The air handler/heat strip is in the attic, while the condenser unit is outdoors of course.

Anyhow, there is an 80amp breaker(for ac) in the outdoor "entrance" load center that supplies power to a subpanel in the attic.

1) One breaker in the subpanel is an 80amp dp that supplies power to two 60amp built-in air handler breakers. The two 60amp breakers are double wide with single type throws. One should be for the blower whereas one should be for the heat strip, correct? However, shouldn't these two 60amp breakers be fed with adequate wiring and a 120amp subpanel breaker?

2) The other breaker in the subpanel is a 40amp dp that goes outside to the condenser disconnect. Again however, you have 80amp and 40amp subpanel breakers that are fed/protected by a single 80amp, main load center breaker? Shouldn't they be fed/protected by 120amp breaker? Maybe not 120amp, given the condenser will never run while heat is on...

In short:
80amp main load center breaker (feeds/protects AC subpanel)
AC subpanel has two breakers in it, an 80amp dp and a 40amp dp.
(The 80amp breaker feeds two 60amp built-in air handler/heat strip breakers.
The 40amp breaker feeds the outside condenser).

I would appreciate some clarification, as otherwise it would seem the wiring and/or breakers are not matched properly?

Thanks

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Old 03-04-2012, 10:42 AM   #2
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AC wiring/breaker questions?


What size heat strips are in the heater?

Depending on the actual voltage supplied to each strip they will pull about 20.8 amps per 5kw. The blower in an air handler will usually pull less than 3 amps. If you have 20 kw and a blower running you might see over 80 amps.
The installer may have dropped one strip to prevent this.

Amperage on the heat strips will increase as voltage increases. So 208VAC will pull less amps than 240. 208vac will also have a lower kw output.

You mentioned wire size but did not list it. Do you have 4awg to the supbpanel and 2 sets of 6 to the air handler and 8 gauge to the outdoor unit?
What is listed on the outdoor unit documentation and tag about wire size and max fuse and RLA? What about the air handler specs?

A heat pump would have been cheaper in the long run...

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Old 03-04-2012, 03:12 PM   #3
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AC wiring/breaker questions?


Thanks for the reply. I may have to get more details for you but was questioning the obvious.

The wire size looks adequate for what is there now in regards to breaker size. My question is why would an 80amp subpanel breaker be supplying two built-in 60amp breakers on the air handler?

I'm assuming we have either a 8kw or 10kw heat strip but again would have to check specs.

A lesser question is also why would only an 80amp breaker be supplying the subpanel, which has both an 80amp and 40amp breaker? I guess this may be mute though given the condenser and heat strip will never be "on" at the same time.

Ralph
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Old 03-04-2012, 03:47 PM   #4
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AC wiring/breaker questions?


Sounds like someone cut corners.
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Old 03-04-2012, 08:42 PM   #5
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AC wiring/breaker questions?


Ok, I took a few pics to show what I have. You can see the plastic junction box that supplies power(80amp breaker) to the attic air handler/heat strip. The discolored plastic door houses the two 60amp built-in air handler/heat strip breakers.

1) Can you make heads or tails from this setup and schematics?
2) The breakers he used in the junction box are mis-matched(should be GE types) whereas he (previous owner/builder) used one Siemens and one Bryant. I will look to replace those with compatible types.
3) The two 60amp breakers in the air handler are actually "frozen". I couldn't get those to turn off and not sure if I can, minus asserting some real pressure.

Any insight would be appreciated.

Ralph
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Last edited by Ralph III; 03-04-2012 at 08:47 PM.
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Old 03-05-2012, 04:17 AM   #6
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AC wiring/breaker questions?


You need to look inside the air handler, and see how many strip heaters are connected.

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