Wire Size for heat Pump

Hi;
We had a fire and are putting are building back together. I have a new heat pump that has heat strips that draw 90 amps. A new wire has to be run from the panel to the heater. The run is about 75 feet. The electrical contractor is responsible by contract to hook up all wires to the new 200 amp panel he is installing. He wants an additional 1300 to run the one wire for the heat pump. He says the wire and conduit alone will run 1000 dollars. I am debating running this wire myself. If I run the wire, he will attach it to the panel as part of the original bid to hook up all wires to the new panel. So all I have to do is put the wire in the conduit and attach it to the wall. I would like to weigh the cost. What is the correct wire size that will be needed for 90 amps?
Thanks Pat
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4ga.
s

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Ask your electrician. Since he is doing the final hookup which is is going to be inspected (I assume you had to get a permit), you will want to make sure he agrees that you choose the right gauge. Otherwise, he could refuse to hook it up.
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On 4/4/2008 7:57 AM snipped-for-privacy@hotmail.com spake thus:

Correction: he *should* refuse to hook it up.
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wrote:

What does the label say? If the actual draw of the heat strips is 90 you also have to add the motor and other load and the largest load has to be taken at 125%. Usually the installation instructions /label will do all this calculation and give you a "minimum circuit ampacity". If that is where you got 90, the answer is 3 ga copper
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komobu wrote:

It depends upon a number of factors: 1) What type of wire 2) Where did you get this 90 amp number from? Is that the actual load or is that the ampacity of the circuit? The installation manual should tell you what ampacity circuit you need. What size breaker were you planning to install? If 90Amps is your actual max load, since it is potentially a "continuous" load, the ampacity of the circuit would need to be at least 112.5 amps. (90 x 1.25). For either 75C or 90C insulated wire, I get 2ga wire and a 125 amp breaker.
If 90 amps is the ampacity of the circuit, I get 3ga for 75C wire and 4ga for 90C wire.
In any case, don't rely on what you read here. Talk to your electrician or the electrical inspector.
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wrote:

Nope. the 90c column is generally just for derating purposes. You won't find any 90c rated lugs on the breaker end or the heat pump ernd so you can't use that column for rating the ampacity of the circuit.
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snipped-for-privacy@aol.com wrote:

You can in fact buy 90C terminal blocks and install them bridged by short lengths of the larger conductors to the breaker and heat pump terminals but it would only be worth the bother on a very long run or on very large conductors.
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Not 'one' wire; surely at least two (neutral and live, or two 230 volt live, or two phase wires if wired from a 3 phase supply) plus a ground wire; each of appropriate gauge, as discussed above. And if you don't get it right it won't get approved might have to be redone and might become an insurance liability or cause another fire??????
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Was that price for copper wire? If so ask for a price using aluminum. You may be able to save a few bucks that way.
As far as wire size I would use at least #2 copper or 1/0 aluminum. Check the nameplate on the unit to see what the maximum fuse size is. It may also state minimum wire size.
Of course you realize that if anything goes wrong with the installation, the contractor could easily say it is not his fault because you installed the wiring.
Who is going to install the disconnect switch at the heater location and wire the unit from there?
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