air compressor magnetic starter Q

[Spyider]

Ok so long story short. i got a 3ph air compressor, swapped from 10hp 3ph to 7.5hp 1ph..
wanted to know if i can re use the magnetic starter that came with it.. (siemens 16cf35a) thats the part number inside the box.. right now its still wired for 3ph. it looks like i can switch out the heater elements to a larger size E74.. motor says 34A.. so the E74 would work good..

am i overthinking this.. i just want to know if i can use this 3ph starter on my 1ph to save a little money.. or am i just better off buying one of these cheap 50$ 1ph 7.5 hp magnetic starters i see on amazon.. haha

 

[LXCam]

As long as you can get the right heater size which it appears you can, go for it.

 

[Spyider]

I see some people mention looping a wire from one side baxk around to bypass the 3ph stuff.. But if i got the right size heaters and only using 1ph.. Where their is no hookup on that last leg.. Why would i have to loop a wire.

 

[LXCam]

Some starters won't work unless they sense current through all three heaters. Unless yours is set up that way it's not needed. If you're unable to get the overloads reset, then loop it.

 

[Spyider]

Well i dont know yet.. But lets say yes it needs all 3 heaters.. Should i put all them the same e74.. Or leave that 3rd one the e69 thats in their now..

How can i tell if i need all 3 withought the obvious of it not starting.. Lol

 

[LXCam]

You do need all three heaters or you'll never get the overload mechanism to reset. Just hook up both leads and try it. If it won't close or kicks out the overloads then loop it. Oop's missed part of your question. Yes use the same size heater, that way if you do need to loop it, it won't drop out by using too small a heater. But if it does work with only two legs running through it, you can use that smaller heater for the third set of poles.

 

[wyliesdiesels]

The issue with using a 3ph starter for a single phase load has to do with the overload relay and whether its solid state or not.

Many solid state overload relay blocks have phase loss protection. What this means is that if current isnt sensed on all 3 wires then the overload relay trips to prevent a 3phase motor from single phasing and overheating due to running on only 2 legs which causes the motor to use mOre current than designed.

Since u have heaters, u most likely dont have separate phase loss protection.

Can u take a pic of the starter and post it here.

 

[Norcal]

When a 3Ø SQ D starter is used for 1Ø, a jumper kit offered by SQ D is available, which is cheaper then using 2 new heater coils & one of the old ones as a filler, as the O/L relay will not reset without all 3 positions filled with a heater and the jumper kit, or 3- heater coils.

SQ D melting alloy overload relay jumper strap kit, Class 9998 Kit type No. SO-31 for NEMA size 0,1,2, kit for size 3,& 4 is No. SO-32.

The above info applies to Square D only.

 

[matt_i]

Since u have heaters, u most likely dont have separate phase loss protection.

Unless I misunderstand, I disagree. The 3pc single element heaters are also good for phase loss protection if they are sized properly. The thermo-mechanical mechanism will release the contact if its heated unevenly, which is also to say its overheated on 2 poles with a locked rotor in a 3phase system.

 

[Norcal]

Phase loss protection is where a phase is lost, namely single phasing.

 

[wyliesdiesels]

Unless I misunderstand, I disagree. The 3pc single element heaters are also good for phase loss protection if they are sized properly. The thermo-mechanical mechanism will release the contact if its heated unevenly, which is also to say its overheated on 2 poles with a locked rotor in a 3phase system.

Solid state phase loss protection will trip almost instantly with the loss of a phase because of no current running through one CT.

Heaters on the other hand will take a little longer to trip IF theyre sized correctly as they have to heat up. If theyre sized wrong then they may never trip even with the lost phase causing the motor to use more current than designed.

So there is a difference. 2 different animals...

 

[Spyider]

ok here is what i got now.. haven't messed with any of the wires in it yet.. this is exactly how i got it.
use it or replace with a single phase unit..

ohh and thats the plate on my new motor.

 

[Norcal]

The DP contactor is rated for 7 1/2 HP single phase.

 

[dave89iroc]

The DP contactor is rated for 7 1/2 HP single phase.

agreed, that starter is rated for 7.5hp single phase use, when wired properly

 

[Spyider]

Do you know where i could find a diagram for single phase for the starter? All that it shows on my cover is 3phase. But it does say if using single phase to just not use L3.. So to me it would seem its all wires up for the pressure switch already. Just put my new wires in and hook up..
Wired my entire garage and this is the only item thats got me haha.

 

[Norcal]

Your just using 2 of the 3 poles of the starter, use L1, and whatever other pole that power for the coil is tapped from, from the looks of it seems to be L2, but verify to be sure.