30 amp lighting contactor question

I am assembling a temporary 5 hp RPC for use on a 5 hp shaper I am cleaning up. I will not be running it under load- but do need to run it to work on the oil circulation system, etc.

I have several Sq D 30 amp class 8903 type smg 3 series A lighting contactors.

http://stevenengineering.com/tech_support/PDFs/45NLTCO.pdf
indicates
"Motor Loads. These loads consist of motors having an inrush current,
or locked-rotor current, of approximately six times the
full-load current. Square D Type S lighting contactors
are fully rated for motor loads and have a horsepower
rating equal to the equivalent NEMA-Size motor
contactor."
30 AMP would be a NEMA size one - and 7.5 hp on 3 p 208-230V

For a tungsten load it indicates:
Type SM 30 Amperes
When Connected 1 Pole to Load ---------------277 Vac
When Connected 2 Poles to Load on 1PH and
3 Poles to Load on 3PH--------480 Vac


Another table on mixed motor/non-motor loads indicates the max single phase hp is 3 hp.
I assume this is per pole- and that if I use two of the poles for the single phase input to the RPC I will be OK- as the tungsten information suggests.

Can some one confirm this?

Temporary

You could parallel the contacts since you have a 4 pole contactor and a 2 pole load.I think I would just start the thing with a 60 amp safety switch.That way you have a place to put some fuses to protect things,and a visible disconnect when its off.Also avoids the need for control wiring.

It has 3 poles with a 4th attached to the side. I am not sure of the rating of that 4th pole.

I am sure a fused saftey switch would work- but would prefer to use what I already have.

J_R_Thiele said:

It has 3 poles with a 4th attached to the side. I am not sure of the rating of that 4th pole.

Click to expand...

I just looked at the auxiliary contacts on a Siemens 40-amp 3-pole contactor.

They're rated 15 amps AC, 13 amps DC.

Auxiliary contacts are designed to support control circuits and similar functions. Their current ratings are much lower than the main contacts.

- Leigh

Hmmm...

Hi JR...

I'll second what Robert said... if this is just a temporary deal, go with a rope-start/safety-switch/no balancing caps archetecture. If you're figuring on needing an RPC on a regular basis, using contactors makes perfect sense... but parallelling a bunch'a 30A contacts will likely result in burning 'em enough that if you ever try to re-use them, you'll have one or more floating around that just-ain't-right afterwards.

The safety switch... if you have an old machine that came out of an industrial environment, it'd have a 3-pole switch, or if you've done any remodeling, or torn down any old farm buildings, you'd have a fusable safety switch (box with lever) lying around. Check your local Habitat Re-Store- they often have a few of 'em that've come out of older home remodeling projects. Usually, you can insert fuses, too...

Surplus

Guess I sort of jumped to the conclusion that ayone who had contactors control transformers and pushbuttons around the house would probably have a few old safety switches.

k3vyl

I have an odd assortment of things- but a 60 amp fused disconnect is not one of them.

I do have a --- "found it" after the original post--- 30 amp fused disconnect which I will go ahead and use temporarily or infrequently --if I leave it assembled as a potentially portable phase converter.



I have at least 4 of the lighting contactors and was wanting to put them to use.

The essense of my original question is what the contact rating is per pole.

It appears it is downrated for the inrush for starting a motor- but not for a tungsten load, which has a much greater inrush current. This does not make sense to me- but I am not "into" electronics. (though I am learning...)



I am intending to assemble a 10 HP RPC for the basement. I was thinking of buying a NEMA 2 or 3 starter to wire in a remote on and off switch for the single phase input, and size the heaters to the single phase load.

I might use a lighting contactors controled by a potential relay for the starting capacitors- using one per pole. I also may use use two 50 amp potential relays and make sure each is below 550UF.



FYI I now truly do have an odd assortment of things, as the local "Toastmaster " branch closed. They did not do manufacturing- but did do some QC there. I learned about the sale late- but the prices were very good as the next step was the dumpster.. I now have about 6 120 V variacs, an assortment of mid 1970's Simpson and Weston meters for voltage, amps and watts, a capacitor tester- and two 240 volt variacs. One is rated at 20 amps with 0 to 280 V output. Not sure what I will use it for- but better me than the dumpster.