30 amp question


Old 03-28-07, 04:17 PM
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30 amp question

I had my service panel upgraded last week from 150 to 200 amps. I need to run two circuits to an electric air handler for a new heating/cooling system. The HVAC company owner has told me I need to run both circuits to the air handler, one 60 amp (220 v) and one 30 amp (220 v).

The electrician told me to run #4 copper wire for the 60 amp. What size should I run for the 30 amp?
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Old 03-28-07, 04:36 PM
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In Canada we would run a #6 for the 60A circuit and a # 10 for the 30A. I'm not sure why the electrician would say a #4 for the 60A unless the NEC requires heavier wire guages than the Canadian Electrical Code.
I need some help and verification from the American electricians here.
Help us out guys.
Old 03-28-07, 04:40 PM
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#10-3 wg cable is sufficient for a 30 amp circuit.
Old 03-28-07, 04:57 PM
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Our Menard's (big box store) electrical dept. also has a length of wire-run chart also. The length of the run, if long, can cause you to have to drop down one gauge size number.
Old 03-28-07, 05:06 PM
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What wiring method are you using (conductors in conduit, cable assemblies such as non metallic cable ("Romex"), armored cable) or something else?

If you are running conductors in conduit, are you running both circuits in the same conduit?

Does any portion of the circuit extend out of doors?

When you say a '60A' circuit, do you mean a circuit which is required to carry 60A, or do you mean a circuit protected by a 60A breaker but carrying less current? For example, a heat pump might have a 'minimum circuit ampacity' of 25A but require a 40A circuit breaker.

To Rollie73, under the NEC it would be very common to use 6ga conductors with a 60A breaker, however there are circumstances which would push the required conductor size to 4ga. I'm pretty certain that the Canadian electric code is similar in this regard. Since we don't know the details, there may be some reason that 4ga is required.

The wire tables at the 'big box stores' never go into all of the required details, and are only a rough guide.

Old 03-28-07, 07:12 PM
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#6 is normally adequate for 60A
#10 is normally adequate for 30A

This can change for derating and voltage drop, though. If the cables are too long (80-100' or more) they frequently need to be larger, as larger cables have lower resistance and will see less voltage drop. Also, if more than 3 conductors are run together, you have to "derate" the cables and upsize them to handle the same current. If either of these apply to your 60A circuit, they may apply to your 30A, too! If so, run #8 wire.
Old 03-29-07, 08:48 AM
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The #4 copper may be required for the 60A if the HVAC unit is considered a continuous load. Perhaps with the emergency heat strips engaged the unit may run continuously which would require the circuit to be designed to supply 125% of the load.
Old 03-29-07, 02:26 PM
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Thanks winnie, the CEC is very similar in this aspect, voltage drop,number of conductors in the conduit, ambient temperature must all be considered.
Old 03-31-07, 09:56 AM
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Originally Posted by chandler View Post
#10-3 wg cable is sufficient for a 30 amp circuit.
Since no neutral is required, he only needs 10/2 w/ ground, assuming #10 is correct for this application, and he is running NM.

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