HVAC Install

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  #1  
Old 07-29-14, 02:35 PM
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HVAC Install

My nephew bought a foreclosure house in which the original central heat/cool self contained package unit is missing. The house was built in 1998 and looks like it was wired to 1996 code. [4 wire receptacles for the range and dryer and so forth] We have selected a new unit to install which will be 2 tons straight cooling with a 7kw heat strip; the new unit is not a heat pump. Currently, there is a 70 amp 2 pole CB in the 200 amp main panel marked heat and air. Outside, there is a 3R pullout type disconnect box with a lid that flips up. I think it's metal, but didn't check to be sure. The guts for the box are not around. The only thing inside the box are 2 large insulated hot wires and a bare aluminum ground wire all coming from the main panel which is inside the house. The hot wires look like they might be #4. At this time, I don't know if the hot wires are aluminum or copper and I don't know the insulation type. I think the old unit was probably a heat pump with backup heat strips. As you probably know, when a heat pump is in a defrost cycle, both the compressor and heat strips are energized as well as the indoor fan motor. The 70 amp CB in the main panel is why I think the old unit was a heat pump. It appears that the original electrician used the box outside as a junction box. There are no disconnects outside.

The new unit:
The MCA for the cooling section is 12.2 amps, the MOPD is 20 amps.
The MCA for the heat strips is 38 amps, the MOPD is 40 amps. The heat strips consist of a bolt in module that includes a 40 amp 2 pole circuit breaker intregal to the module.

The plan:

1. Reuse the existing box outside as a JB.
2. Install a 30 amp, 3R, 2 pole fused disconect adjacent to the JB. Run 3 #12's [2 blacks and a green] from the JB to the disconnect in Sealtite, then run 3 #12's from the disconnect to the unit in Sealtite. Install 2 20 amp DETD fuses in the disconnect.
3. Run 2 #8 blacks and a #10 green from the JB to the heating section in Sealtite.
4. Replace the 70 amp breaker in the main panel with a 40 amp breaker.

Questions:

1. Can I use the box outside as a JB?
2. Do I need to put an additional disconnect on the outside wall for the heating section? The CB that comes with the heat strips will be inside the unit.
3. Who makes connectors that can mate aluminum and copper conductors? I mean a split bolt or lug style, not wirenuts. I've seen them before- I know you have to put the anticorrosion goop on.
4. Am I missing anything?

Thanks in advance. John D.
 
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Old 07-29-14, 04:09 PM
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I would suggest changing the JB to one of these, then install a 2/40 and 2/20 breaker and then feed the equipment.[ATTACH=CONFIG]35505[/ATTACH]
 
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Old 07-29-14, 04:57 PM
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Thank you very much. That is a most excellent idea. I can't read the part # in the photo. I found a QO24L60NRNM at the Schneider website. Non-metallic, 60 amp, 3R, fixed main lugs. 2 spaces, 4 circuits. It includes a nuetral bar. Is this about what I need? Can I use the nuetral bar for the ground wires?
 
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Old 07-29-14, 05:29 PM
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Is this about what I need? Can I use the neutral bar for the ground wires?
Yes, but only if the neutral bar can be bonded to the steel case of the enclosure.

3. Who makes connectors that can mate aluminum and copper conductors? I mean a split bolt or lug style, not wirenuts. I've seen them before- I know you have to put the anticorrosion goop on.
There are lots out there. Some available at the big box like split bolts or butt lugs like this: [ATTACH=CONFIG]35513[/ATTACH]

Others are available at electrical supply houses.
 
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Old 07-29-14, 07:03 PM
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Thanks Tolyn. The enclosure is non-metallic, the nuetral bar is included so i tought is would be a convenient place to land the ground wires.
 
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Old 07-30-14, 03:59 AM
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That particular one is a QO24L70RBCP.
It'll come with a bonding screw to bond the neutral bar to the can and it's a metallic enclosure.
Pretty common at home centers and supply houses.
 
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Old 07-30-14, 03:52 PM
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Ok. Thanks wirenut. The one I looked up has a non-metallic enclosure. I got to wondering that if I used a knockout punch on it if the enclosure would crack. I think I'll stick with a metal enclosure coz that's what I'm familiar with. Thanks again.
 
  #8  
Old 07-30-14, 06:21 PM
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leave the 70 amp breaker alone................replace the outside box with a 6 or 8 circuit rain tight box
into which you can put 2 full size double pole circuit breakers
6 CIRCUIT WOULD BE FINE,SINCE YOU CAN NOT USE THIS BOX FOR 120 VOLT CIRCUIT..........YOU HAVE NO WHITE WIRE.

SQUARE "D" BRAND TYPE"QO" IS THE BEST AND HAS A COPPER BUS

SQUARE "D" BRAND TYPE HOMELINE HAS AN ALUMINUM BUS...NUFF SAID

YOU CAN NOT PUT 2 DOUBLE POLE CIRCUIT BREAKERS IN THE ANY OF THE BOXES NOTED EARLIER

YOU MAY BOND THE NEUTRAL BAR TO THE BOX AND PLACE ALL THE GROUND WIRES ON IT SINCE YOU HAVE NO NEUTRAL (WHITE WIRE) FROM THE FIRST PANEL...THIS WILL BE A 220 (aka 240) ONLY PANEL
 
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Old 07-31-14, 02:14 PM
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ok thanks T will be sure that the load center will take two 2 pole breakers.
 
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