# Thread: Motor relay vs. contactor

1. ## Motor relay vs. contactor

Guys, I have a cabinet with limited space and am trying to figure the small footprint device to energize a pool pump type motor.

I'm confused about labeling on this motor. There are two stickers. Name plate and HP sticker above it.
Based on part number on nameplate, this should be a 3/4Hp motor, however, the sticker above it lists it as 1/2HP.

I'm going to go worst case scenario and use 3/4HP numbers for my calcs.

I ran the calcs, and it looks like my max inrush current is 19.5Amp , and according to nameplate the running current of 6Amp
Here is calc: solve ((343.5*1000)=220*x*1.73),x
This is type L motor: http://powertips-elec.blogspot.com/2...rents-and.html

In this application, the motor will only start once a day and run for 8-10 hours. There is scenario where on windy days it might start multiple times (nanometer in place).

Cost between the 2 choices is not a factor (and it should never be one in properly designed solution).

I'm looking at 24.3mm width for the 782 relay base, vs 45mm for the CWC016-10-30L03 mini contactor. That's almost twice the width.

Looks like the 782 is rated for 1/2hp at 120VAC & 1hp at 277VAC. Since I'm using 220VAC, I should be comfortably somewhere around 3/4hp range.
Amperage is rated at 15A for 120VAC and 12A for 277VAC, so again 11.2Amp rated amperage is met.

http://www.automationdirect.com/stat...s/78relays.pdf

What would you guys do?2016-05-13 21.28.54.jpg2016-05-13 21.36.30.jpg2016-05-13 21.39.19.jpg

2. ## Re: Motor relay vs. contactor

I would rewire that box. Pretty messy and really hard to follow.

After that, any 1 HP starter will work. With the wiring cleaned up, you might find extra room.

3. ## Re: Motor relay vs. contactor

Also, because I'm having a brainfart -- when using 220V, the calculation for my inrush current should be cut in half, right?
If so, I should be looking at roughly 10Amp inrush and actual measured current of 5.5Amp.

4. ## Re: Motor relay vs. contactor

Originally Posted by Griswald
I would rewire that box. Pretty messy and really hard to follow.

After that, any 1 HP starter will work. With the wiring cleaned up, you might find extra room.
I'm in the process of doing just that.
Once I get some wire ducts installed, this will look all better.

5. ## Re: Motor relay vs. contactor

The main problem with what you propose is you are mixing data lines and power lines in the same box. You motor controls need to be either in a separate box or in a partitioned off area in this box.

6. ## Re: Motor relay vs. contactor

Originally Posted by gwegan
The main problem with what you propose is you are mixing data lines and power lines in the same box. You motor controls need to be either in a separate box or in a partitioned off area in this box.
Why is that a problem and what do you mean by data lines?

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