DIYbanter - View Single Post - What size wiring for Central A/C compressor?

The Daring Dufas[_8_]

On 3/4/2013 3:27 PM, wrote:
On Mar 4, 1:50 pm, The Daring Dufas the-daring-du...@stinky-
finger.net wrote:
On 3/4/2013 11:47 AM, wrote:

On Mar 4, 11:50 am, The Daring Dufas the-daring-du...@stinky-
finger.net wrote:
On 3/4/2013 10:27 AM, wrote:

On Mar 4, 10:50 am, The Daring Dufas the-daring-du...@stinky-
finger.net wrote:
On 3/4/2013 7:56 AM, wrote:

On Mar 4, 7:50 am, The Daring Dufas the-daring-du...@stinky-
finger.net wrote:
On 3/4/2013 6:13 AM, wrote:

On Mar 3, 11:16 pm, The Daring Dufas the-daring-du...@stinky-
finger.net wrote:
On 3/3/2013 9:46 PM, gregz wrote:

Mikepier wrote:
I'm running new electric in a friends basement and so far uncovered a
lot of bad wiring jobs, buried splice boxes, you name it. So now I
noticed that the central A/C compressor is wired with 10 guage wire.
I'm pretty sure its suppose to be 8 guage. And also the existing 10
guage wire is hooked up to a 40 A breaker, which of course is not
right, its suppose to be a 30A breaker.
So since everything is wide open now, I was wondering should I run
new 8 guage wire to the A/C? The unit is a Lennox, I beleive a 3 ton
unit, and the plate says "Min circuit ampacity 24.4 amps" and it also
says " Max fuse or ckt bkr 40A".
Even if the unit has been running fine all these years, I'm wondering
what happens down the road if it needs to be replaced with a new unit
that needs more amperage. the existing 10 guage wire will not be
sufficient I'm thinking.

I had a 3.5 ton installed. They used 10 gauge and 30 amp breaker. After
reading data plate and measuring operating current I switched to 20 amp
breaker.
It's only drawing 6.5 Amps and no problems. Never hurts to use thicker
wire.

Greg

The circuit breaker is meant to protect the wiring not necessarily the
equipment which will normally have its own secondary protective devices.
The 20 amp breaker won't harm anything but if there is a surge current
greater than 20 amps from the AC unit starting on a hot day, you may get
nuisance tripping of the breaker. O_o

TDD- Hide quoted text -

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A 20 amp breaker is less than the rated 24 amp min
circuit capacity on the eqpt label. As others have stated, the
existing 12 gauge wiring and 40 amp breaker are
correct, meet code and no change is required.

Not around here. Every electrical inspector I know would reject a 12
gauge wired circuit with a 40 amp circuit breaker.

Then they are not following the NEC and either they don't know
what they are doing or that particualr AHJ has unusual requirements.

A 40 amp circuit
uses #8 copper NM/UF 60°C cable or #8 aluminum SE/USE 75°C cable.

You're trying to apply the NEC rules for general purpose branch
circuits to motor eqpt that is on a dedicated circuit with
it's own over-current protection. As the Mike stated, the eqpt
label says the minimum circuit ampacity is 24 Amps. That translates
into 10 guage wire being fine. Actually, 12 would also meet it.
It further states that a 40 amp breaker is the max allowed, which
is what he has. Presumably any competent electrical inspector
would read the eqpt label and follow it.

An
electrical inspector may require #6 aluminum be used depending on the
jurisdiction's requirements which may be stricter than The NEC.

Theoretically any AHJ could make up anything they want. But #6
for this 3 ton AC is nuts.

This
applies to "homes" not necessarily industry which will normally use
different wiring methods and higher temperature insulated wiring. I've
wired homes, businesses and industry for a living so I know a little
about electrical wiring.

Then you should know that what Mike has is perfectly fine.
It exceeds the eqpt label, which is what governs here and it
meets NEC.

I've also worked in commercial sales of
electrical products. The circuit breaker is meant to protect the wiring
and should always be sized accordingly.

You're ignoring the fact that the eqpt has it's own over-current
protection.

There are places that have no
electrical inspection department and I suppose you can do whatever you
want. I've worked in those areas too and seen extremely dangerous wiring
that was quite scary. ^_^

TDD- Hide quoted text -

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What Mike has is not dangerous. Itfully meets or exceeds NEC in
every regard.

I'm not going to argue with you over it except to tell you it would not
pass inspection in my area.

Then maybe you can tell us what rules the inspectors
are following and where your area is, because it's entirely
consistent with NEC. And it would pass inspection here,
in NJ. Or do your inspectors just make stuff up as they
go along?

Everywhere I've worked followed the NEC even on U.S. installations
overseas where The Army Corps of Engineers took care of inspections.

Then you should be able to cite for us the section of NEC
that says the installation that Mikepier has is in violation.
Reference please.

All I know is from my own experience working on various jobs over
four decades. Perhaps you have much more experience in the field of
electrical work than I do but I can only refer to my own experience.

I'm an electrical engineer. And gfretw has weighed in on
the issue. I believe he's an electrician. And he said the
same things I did, in particular that what Mike has is code
compliant and does not need to be changed.

Perhaps you are an experienced electrician in your city/state and know
how things are done in your kingdom but from your post, it appears you
follow different standards. I must contact my relatives in New Jersey
and implore them to run, run like the wind! ^_^

TDD- Hide quoted text -

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We follow the NEC here. So show us where the NEC says
we're wrong..... And until them, stop spreading FUD.
There is absolutely nothing unsafe, dangerous or in violation of NEC
in
what Mike has. This is a common confusion. Your mistake
is applying the rules for branch circuits for lights, receptacles, etc
to HVAC eqpt. Different rules apply for obvious reasons and if you'd
just take the time to read the NEC, you'll see that.

How often do you deal with electrical and mechanical inspection
services? I've done electrical and HVAC work for a living and I
base my assertions on practical experience where I've worked. It
may be different where you did your electrical and HVAC work for
a living. Perhaps the authorities interpret the NEC differently
where you have done your professional electrical and HVAC work?

TDD- Hide quoted text -

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When you can give us the section of the NEC where you can
conclude that there is something wrong with Mikepier's
installation, under ANY interpretation, then we can discuss differing
interpretations. If an inspector is going to fail it, then he should
be
able to tell you that per NEC section X.Y, it's not allowed.

This isn't the first time this issue has come up. And the result is
usually the same. You have some people thinking that the same
rules for lights and receptacles under the NEC also apply to
motors and AC equipment. They don't. I would hope that
someone who installs that eqpt would understand the distinction.

If you'll look at NEC Table 310-16 you will see the amp rating for wire
size. It changes depending on the insulation on the wire. Every 40 amp
circuit I've ever installed in a home using 60°C NM/UF cable has been #8
copper. If I install a 40 amp circuit in conduit using 90°C THHN/THWN
insulated wire I'll use #10 copper. I don't usually run conduit in a
home. The last 4 ton AC condensing unit I installed used #14 THHN/THWN
copper in conduit. It was a 3ø unit that called for a 15 amp breaker. I
have to install what I know the inspector will pass and the inspectors
do look at the temperature rating of the wire and check if the circuit
breaker is HACR rated if it's hooked to an AC condensing unit. I don't
argue with the inspectors, you can if you wish. O_o

TDD