komobu wrote:

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

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.