wiring for central a/c disconnect box


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Old 06-03-09, 08:30 AM
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wiring for central a/c disconnect box

i recently noticed that that my disconnect box (23 years old) to compressor/condenser unit is rusting and the ground conductor is deteriorating. currently it is connected to the condenser unit by a piece of 6-2 XNNH AL cable (about 2 feet long) . there is no conduit.

the current breaker in the main panel is 40AMP; the feed from the main panel to the disconnect is also the same 6-2 AL cable. (2 hots, no neutral)

3 questions: 1. shouldn't the wire be in a conduit? does the code allow the wire to in the open? what the proper conduit?

2. what is the proper wire/cable? should i use 8-2 CU cable (in the conduit) or single #8 copper wires?

3. any violation of the code by the fact that the disconnect box has 6-2 AL on one side (feeder) and #8 CU going to the a/c?
 
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Old 06-03-09, 02:06 PM
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I'm assuming that the #6 cable also has a braided bare wire inside the jacket? Is that correct?

3 questions: 1. shouldn't the wire be in a conduit? does the code allow the wire to in the open? what the proper conduit?

the wire needs to be protected, it's not allowed to be out in the open. Normally you would use an outdoor flexible metal conduit like sealtite or liquidtite which are brand names. They both have a metal spiral inside the jacket for strength [not to be confused with Greenfield or MC which are both all metal spiral outer covering and not for outdoor use] and they utilize special fittings. There is also available a plastic type of flexible conduit which I think is called Carflex, which uses different fittings. I'm old school, I was using LT and ST long before the plastic stuff came out and I like it more better.

2. what is the proper wire/cable? should i use 8-2 CU cable (in the conduit) or single #8 copper wires?

You can use cable inside flexible conduit or individual conductors. Individual conductors are easier to work with.

3. any violation of the code by the fact that the disconnect box has 6-2 AL on one side (feeder) and #8 CU going to the a/c?

Aluminum wire has more resistance to the flow of electricity than copper does. So #6 AL and #8 CU have the same rating.

Look at the nameplate of the a/c unit. It will tell you several things:

Maximum overcurrent protection or MOCP- this is the largest size fuse or circuit breaker you can use. Most units will say fuse or HACR breaker. If the nameplate ONLY says fuse, then you can only use fuses, if it ONLY says HACR breaker, then you can only use a circuit breaker. Most units say fuse or breaker but you have to check to be sure. Then the nameplate will also indicate the minimum circuit ampacity and the maximum circuit ampacity. The MCA number will determine the minimum size wire you can use. The easy way to get it all fixed up is to replace the disconnect. Be sure that it is rated for CU or AL conductors and that it is rated for outdoor use. If you buy a metal one, you have to ground the box which means you'll have to install a grounding bar. If you buy one that is non-metallic, you can dispense with that problem. You will still have to connect the aluminum ground wire from the feeder to copper ground wire in your new wires going to the a/c unit. The easiest way is to use a split bolt connector that is made for CU to AL connections. Then you want to buy what is called a whip. A whip is a 6 foot piece of LT or ST that has the wires already installed in it and has a connector on each end. So you would want a #8 whip which will have black, red and green THHN wires. I almost forgot, you also have to apply a special anti-corrosion compound to the bare ends of the aluminum conductors. Make sure you clean the ends nice and bright and shiny with a wire brush before applying the compound. HD or Lowe's should have everything you need. Let us know how you make out. Thanks.
 
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Old 06-03-09, 09:26 PM
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daddyjohn...thanks a ton for answering in detail...great help.
to your questions- yes there is braided bare (ground wire) and that is one of the things not looking healthy.
i will definitely replace the disconnect. HD has EATON brand for about $12 ; it is rated at 60AMP and for CU as well as AL.

thanks for pointing out the anti-corrosion compound- i'll remember to get it with the box. i'll open the panel (on a/c) and see what it says about the OCP devices....though i am assuming the original electrician installed the right device (i.e, the current 40AMP breaker). btw, the unit is working great, i am just doing preventive maintenance.
thanks again

Originally Posted by dr.gj
i recently noticed that that my disconnect box (23 years old) to compressor/condenser unit is rusting and the ground conductor is deteriorating. currently it is connected to the condenser unit by a piece of 6-2 XNNH AL cable (about 2 feet long) . there is no conduit.

the current breaker in the main panel is 40AMP; the feed from the main panel to the disconnect is also the same 6-2 AL cable. (2 hots, no neutral)

3 questions: 1. shouldn't the wire be in a conduit? does the code allow the wire to in the open? what the proper conduit?

2. what is the proper wire/cable? should i use 8-2 CU cable (in the conduit) or single #8 copper wires?

3. any violation of the code by the fact that the disconnect box has 6-2 AL on one side (feeder) and #8 CU going to the a/c?
 
 

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