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If I do a search for a DPDT relay with 120VAC coil voltage, 30A and 220/240VAC contact rating as the parameters, I get results that look somewhat like the 2 examples listed below. What is it that sets them apart functionally? What am I looking for in the specs that tells me whether it will work for a motor/pump or otherwise?

  1. DAYTON Relay, Power, DPDT, 120VAC

  2. DAYTON Relay, DPDT, 8 Pins, 120VAC

I am working on a brewing system and the plans (diagrams but no schematics) call for three relays with the above parameters. Two are for two 110VAC pumps (3). The third is for voltage and amperage meters (4). You can find the diagrams here:

Control Panel step 7: Wire up volt and amp meters

Control Panel step 8: Wire up pumps

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    \$\begingroup\$ Too localized. Question is dealing with a specific device. Pricing from specific vendor. \$\endgroup\$ Commented Jul 2, 2013 at 1:33
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    \$\begingroup\$ The 1. has lower current ratings. \$\endgroup\$ Commented Jul 2, 2013 at 1:35
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    \$\begingroup\$ The second is rated for motor control, The HP ratings indicate this. Also the second is rated for higher voltage ratings (480VAC). I would guess the first is more for resistive loads (heaters etc) the second for motors. Motor switching is very agressive and needs a much more robust construction to function reliably. \$\endgroup\$
    – Spoon
    Commented Jul 2, 2013 at 7:49
  • \$\begingroup\$ Having looked at the question from a non-electrical engineer point of view I think looking at the datasheets for these devices would help... but I must admit the links on google seem to be swamped by consumer ....stuff ... so I couldn't find a datasheet via google .... even knowing the part number 1EJG7 \$\endgroup\$
    – Spoon
    Commented Jul 2, 2013 at 8:01
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    \$\begingroup\$ Both have HP ratings. But they are not the same. The First is 30/15 Resistive/Inductive Load capacity, the second is 40/30 Resistive/Inductive Load Capacity. Since you are driving an inductive load (a motor/pump), you want the one with the higher Inductive Capacity. \$\endgroup\$
    – Passerby
    Commented Jul 3, 2013 at 1:11

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The enclosed one is definately better for the motors. Check the spec table below the description:

 Open relay:  HP @ 240V -> 1-1/2 
 Closed relay:  HP @ 240V -> 3 

This means that the contacts are more rugged against the inductive feedback of switching a motor on and off, and therefore will last longer. The open relay, however would be better for the ammeter as it appears to be connected not to the motors, but only the boiler and would benefit from the extra resistive load capabilities, although the closed relay would do just as well, since it is above spec. Basically, use the enclosed relay for motor control, and the open one for resistive load if you are not concerned about spending almost $20 extra.

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