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#68127 - 07/28/06 10:24 PM Single phase motor using 3 phase starter...  
Cinner  Offline
Joined: Dec 2004
Posts: 78
Kelowna, B.C., Canada
Has anyone seen a cutler hammer 3 phase starter used with a single phase motor? The wiring was done so the 3 OLR were wired in series. Why would they wire all three in series? As well the cutler hammer starter model #ce15cns3 was marked "trip amps = 125%FLC" Does this mean that you just dial in the FLA of the motor and it takes into consideration the 125%? (ie. if FLA = 7.5 then you set at 7.5)

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#68128 - 07/28/06 11:58 PM Re: Single phase motor using 3 phase starter...  
hypress  Offline
Joined: Jul 2004
Posts: 129
Charleston WV
There is nothing wrong with using a 3PH starter in 1PH service.
There is an overload heater in each of the "T" leads on the starter. This monators each phase for overload conditions. This is running overcurrent protection.Short circuit protection is provided by fuses or circuit breaker in the starter. Set the trip for the running overcurrent from the info on the motor nameplate and the overload unit will take care of the rest. To many times I have seen people add 125% to the nameplate info this makes the overload trip at 250%.

#68129 - 07/29/06 01:52 AM Re: Single phase motor using 3 phase starter...  
andy1959  Offline
Junior Member
Joined: Jul 2006
Posts: 3
i have seen the exact setup on a city sewers lift station .where we had to set the overloads on the pump starters so they will trip saving the motor which had thermal overloads factory set.. so yes you can use a 3 ph starter{not recommended} on 1ph applications

#68130 - 07/29/06 02:43 AM Re: Single phase motor using 3 phase starter...  
Alan Belson  Offline
Joined: Mar 2005
Posts: 1,803
Mayenne N. France
The heaters are wired in series so they all get the same temperature on normal running but from the single phase supply. Wire out 2 of the heaters and the unit will eventually trip out on normal amps due to temperature differences. Ditto parallel wiring of all three, you won't get acceptable balance.
I second what hypress says about the setting; just dial in the motor amps.


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#68131 - 07/29/06 04:52 AM Re: Single phase motor using 3 phase starter...  
jraef  Offline
Joined: Jul 2004
Posts: 101
San francisco, CA, USA
In the old NEMA style OL relays with melting alloy elements it was not necessary to use all 3 elements when protecting a 1 phase motor. What changed is that when IEC (European) designed starters hit the US market years ago, they brought with them the IEC style OL relay which has what is called a "differential bar" in the trip mechanism. This was a cheap way of attaining current imbalance protection, because if any phase had more or less current running through it than the others, the differential bar would toggle partially and allow the other two phases to trip faster. While that worked OK on imbalances, a complete loss of phase current could be a nuisance if it wasn't a 3 phase system (where you WOULD want to detect a complete loss of phase). In Europe they don't use a lot of 1 phase motors outside of household appliances, so the IEC manufacturers didn't bother to make 1 phase OL relays. Their answer was to just loop one phase back through the 3rd unused OL element so that they all saw the same current under normal circumstances. Cutler-Hammer, in an attempt to try and market their product world wide, went to the IEC OL relay style years ago after they discontinued the old Citation starter line, so now you MUST loop through C-H OLRs to make them work on 1 phase applications.

[This message has been edited by jraef (edited 07-29-2006).]


#68132 - 07/29/06 09:25 PM Re: Single phase motor using 3 phase starter...  
marke  Offline
Junior Member
Joined: Sep 2005
Posts: 4
Christchurch,cant,New Zealand
The differential bar acts to amplify the measured current if there is a curent dfferential between the three phases. It increases the sensitivity of the thermal overload relay, so it is important to wire all three phases in series for a single phse load.

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