Does The RES Spec On The Side Of Contactor Refer To Resistive Amps? - HVAC - DIY Chatroom Home Improvement Forum

 DIY Chatroom Home Improvement Forum > HVAC Does The RES Spec On The Side of Contactor refer to Resistive Amps?
 Register Blogs Articles Rewards Search Today's Posts Mark Forums Read

06-29-2014, 08:59 PM   #1
Member

Join Date: Aug 2009
Location: Southwest Ohio
Posts: 1,041
Rewards Points: 1,472

## Does The RES Spec On The Side of Contactor refer to Resistive Amps?

Looking at a new contactor - single pole, 24v coil

VAC...........FLA....LRA......RES
240/277....30.....180......40

Can I assume the "40" is a resistive amps number and A/C fan, blower and compressor motors are not resistive loads?

Last edited by justplumducky; 06-29-2014 at 09:04 PM.

06-30-2014, 01:29 AM   #2

Join Date: Mar 2011
Posts: 5,884
Rewards Points: 2,270

Volt-ampere (VA) is a measurement of power in a direct current ( DC ) electrical circuit. The VA specification is also used in alternating current ( AC ) circuits, but it is less precise in this application, because it represents apparent power , which often differs from true power .
In a DC circuit, 1 VA is the equivalent of one watt (1 W). The power, P (in watts) in a DC circuit is equal to the product of the voltage V (in volt s) and the current I (in ampere s):
P = VI
In an AC circuit, power and VA mean the same thing only when there is no reactance . Reactance is introduced when a circuit contains an inductor or capacitor . Because most AC circuits contain reactance, the VA figure is greater than the actual dissipated or delivered power in watts. This can cause confusion in specifications for power supplies. For example, a supply might be rated at 600 VA. This does not mean it can deliver 600 watts, unless the equipment is reactance-free. In real life, the true wattage rating of a power supply is 1/2 to 2/3 of the VA rating.
When purchasing a power source such as an uninterruptible power supply ( UPS ) for use with electronic equipment (including computers, monitors, and other peripherals), be sure the VA specifications for the equipment are used when determining the minimum ratings for the power supply. The VA figure is nominally 1.67 times (167 percent of) the power consumption in watts. Alternatively, you can multiply the VA rating of the power supply by 0.6 (60 percent) to get a good idea of its power-delivering capability in watts.

__________________
Thanks.

06-30-2014, 07:03 AM   #3
Member

Join Date: Aug 2009
Location: Southwest Ohio
Posts: 1,041
Rewards Points: 1,472

Quote:
 Originally Posted by Doc Holliday Volt-ampere (VA) is a measurement of power in a direct current ( DC ) electrical circuit. The VA specification is also used in alternating current ( AC ) circuits, but it is less precise in this application, because it represents apparent power , which often differs from true power . In a DC circuit, 1 VA is the equivalent of one watt (1 W). The power, P (in watts) in a DC circuit is equal to the product of the voltage V (in volt s) and the current I (in ampere s): P = VI In an AC circuit, power and VA mean the same thing only when there is no reactance . Reactance is introduced when a circuit contains an inductor or capacitor . Because most AC circuits contain reactance, the VA figure is greater than the actual dissipated or delivered power in watts. This can cause confusion in specifications for power supplies. For example, a supply might be rated at 600 VA. This does not mean it can deliver 600 watts, unless the equipment is reactance-free. In real life, the true wattage rating of a power supply is 1/2 to 2/3 of the VA rating. When purchasing a power source such as an uninterruptible power supply ( UPS ) for use with electronic equipment (including computers, monitors, and other peripherals), be sure the VA specifications for the equipment are used when determining the minimum ratings for the power supply. The VA figure is nominally 1.67 times (167 percent of) the power consumption in watts. Alternatively, you can multiply the VA rating of the power supply by 0.6 (60 percent) to get a good idea of its power-delivering capability in watts.
Thx Doc. I had google and found that online also, because I was wanting to know how to calculate the current a xfmr puts out (found: VA divided by Volts). I found that same article, but don't see how it applies to my contactor question.

 06-30-2014, 09:42 AM #4 Member   Join Date: Oct 2007 Location: Manitoba, Canada Posts: 400 Rewards Points: 380 I believe the RES is the Resistive amps that the contacts are rated to handle the current load of. Some will give hp ratings at different voltages, and FLA as you described, But the RES is a higher value primarily because there is no inrush current to be worried about in a resistive load. At least that is my understanding. Perhaps a site like FURNAS may have more information.
 06-30-2014, 10:54 AM #5 Hvac Pro     Join Date: Nov 2008 Location: Winnipeg, Canada Posts: 15,241 Rewards Points: 1,122 It is resistive load. Contactors are used to turn on elements in some electric furnaces and that is a pure resistive load. __________________ "Cut it twice and it is still too short".
06-30-2014, 05:35 PM   #6
Member

Join Date: Aug 2009
Location: Southwest Ohio
Posts: 1,041
Rewards Points: 1,472

Quote:
 Originally Posted by yuri It is resistive load. Contactors are used to turn on elements in some electric furnaces and that is a pure resistive load.
So the "40" number for a resistive load, which I assume means a relatively constant load (heat strips on an electric furnace), as opposed to a variable speed (variable load) PSC Motor, means 40 Amps?

Thanks HVACDave, I'll check out that site.

 06-30-2014, 06:01 PM #7 JOATMON     Join Date: Aug 2011 Location: S. California Posts: 10,829 Rewards Points: 818 Blog Entries: 2 Most contactors can handle a higher resitive vs inductive load. __________________ Even if you are on the right track, you will still get run over if you just sit there. My 2-Story Addition Build in Progress Link ... My Garage Build Link and My Jeep Build Link
06-30-2014, 08:47 PM   #8

Join Date: Oct 2008
Location: Somewhere
Posts: 33,574
Rewards Points: 6,112

Yes, resistive is strip heaters. Motors are inductive loads.

__________________
When posting in certain forums, knowing your location will help others give better feedback/advice/solutions to your questions.

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are Off Pingbacks are Off Refbacks are Off Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post navi_jen Remodeling 0 06-16-2010 11:02 AM Hossenfeffer Building & Construction 3 04-09-2010 11:12 PM Bigfoot Electrical 13 06-02-2009 09:08 AM Piedmont Electrical 19 01-22-2008 09:39 PM Susie Q Appliances 6 08-31-2007 04:26 PM

Top of Page | View New Posts