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?
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.
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
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.
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.
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.
"This alternating current stuff is just a fad. It is much too dangerous
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
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
Who is going to install the disconnect switch at the heater location and
wire the unit from there?
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