Electrician and AC installer disagree

[atphvac]

in general hvac guys are a brighter bunch than electricians. I saw a licenced electician wire a door bell to the humidifier transformer. And then the homeowner wondered why the doorbell only works when the furnace is on!

[cem-bsee]

1999Article110 deals with terminal & wire temp rating-- has this changed?
1999Article230 deals with services -- which has no bearing on this circuit.
This is a FEEDER circuit.

once again, if one chooses over 60C wire rating, the HO pays extra $$ EVERY time the load is on. -- for ANY circuit= service, feeder, branch. just check the I^2R losses [= voltage drop].

remember, one can provide a quality install, or just meet competition & the code which is the miminum requirements.

I sure would not install an overcurrent device at 300%, even where permitted by NEC!

but then, I needed to keep a plant running at minimum costs [ elec at ICP, Lewisburg TN cost ~ $100k per MONTH ], at least from 1984- 1994.

[jacob perkins]

..

[suemarkp]

Originally posted by rsmith46
No you have to use 60C column under 100amps.
Article 110.14 C 1a
When making terminations of 100amps or less you are limited to using conductors rated 60C.
70 amp breaker for #4
And the 125% rule doesn't apply since this isn't a continous load.

You've got to read all of the code. These are all from the 2002 code.

110.14(C)(1)(a)(3) says "Conductors with higher temperature ratings if the equipment is listed and identified for use with such conductors".

You'll find most modern breakers, large receptacles, and panel busbars to be marked "60/75C" as part of the listing labeling on the equipment. If this label is not present, then you're right you are limited to the 60C ampacity column.

As far as the 125% rule, I don't know if its continuous or not, that isn't the issue. Article 424 (Fixed electric space heating) says you have to for whatever their reasoning:

424.3(B) Branch-Circuit Sizing. The ampacity of the branch circuit conductors and the rating or setting of overcurrent protective devices supplying fixed electric space-heating equipment consisting of resistance elements with or without a motor shall not be less than 125 percent of the total load of the motors and the heaters. The rating or setting of overcurrent protective devices shall be permitted in accordance with 240.4(B). A contactor, thermostat, relay, or similar device, listed for continuous operation at 100 percent of its rating, shall be permitted to supply its full-rated load as provided in 210.19(A), Exception. The size of the branch-circuit conductors and overcurrent protective devices supplying fixed electric spaceheating equipment, including a hermetic refrigerant motor compressor with or without resistance units, shall be computed in accordance with 440.34 and 440.35. The provisions of this section shall not apply to conductors that form an integral part of approved fixed electric spaceheating equipment.

The above only applies to branch circuits and not feeders, that is why its important to determine what the electrician has actually installed.

[rsmith46]

Originally posted by suemarkp

Originally posted by rsmith46
No you have to use 60C column under 100amps.
Article 110.14 C 1a
When making terminations of 100amps or less you are limited to using conductors rated 60C.
70 amp breaker for #4
And the 125% rule doesn't apply since this isn't a continous load.

110.14(C)(1)(a)(3) says "Conductors with higher temperature ratings if the equipment is listed and identified for use with such conductors".

You'll find most modern breakers, large receptacles, and panel busbars to be marked "60/75C" as part of the listing labeling on the equipment. If this label is not present, then you're right you are limited to the 60C ampacity column.

Listed conductors are not listed busbar termiations rated 60/75C. 2 different things.

You are right about the branch circuit conductors needing to be 125% of the FLA.
#4 copper is too small for 15kw + the fan. If the FLA is 70amp you need a conductor & breaker of 87.5amps. You still have to use the 60C column unless the air handler is listed and identified for a specific 75C conductor. Doubtful and since its going to a subpanel that's not the case.
Needs to be a 4 wire #2 copper with a 90amp breaker to the subpanel.

[hvac hero]

Originally posted by atphvac
in general hvac guys are a brighter bunch than electricians. I saw a licenced electician wire a door bell to the humidifier transformer. And then the homeowner wondered why the doorbell only works when the furnace is on!

Reminds me of the time one of my installers cut into the phone line thinking it was the low voltage. Everytime we tried turning her A/C on, her phone started ringing. & wouldnt ya know it was a old lady that was hard of hearing. To this day I can still hear her yelling "HELLO" into the phone over & over

[Wild Leg]

Originally posted by atphvac
in general hvac guys are a brighter bunch than electricians. I saw a licenced electician wire a door bell to the humidifier transformer. And then the homeowner wondered why the doorbell only works when the furnace is on!

That's a pretty broad paintbrush.

You might want to visit the wall of shame.
We have our share of rookies & dimwits too!