Three phase moto rstarter used for single phase

[Sierrasparky]

Is there anything wrong with using a 3phase starter for a single phase motor? The faculity purchased a single phase replacement by error.

 

[ActionDave]

As long as your conductors, overcurrent devices and heaters are correct then the answer would be no. Depending on the starter you may need to series one line through T2 back up to L3 to fake it out.

What HP is the motor?

 

[Sierrasparky]

Both are were 1 hp
looking at the table on the cover I need the next size up overload by amps . Would that table on the cover be correct for single phase.

 

[ActionDave]

I don't know what "table on the cover" means. You will draw more amps using the single phase motor.

For a 1 HP motor it won't be much more so the conductors are probably ok. Heaters will probably be ok also.

 

[Sierrasparky]

I don't know what "table on the cover" means. You will draw more amps using the single phase motor.

For a 1 HP motor it won't be much more so the conductors are probably ok. Heaters will probably be ok also.

There is a chart on the inside of the starter cover.
says wha thermal to use by full amps. But the table is for three phase.

 

[masterinbama]

There is a chart on the inside of the starter cover.
says wha thermal to use by full amps. But the table is for three phase.

Your heaters are sized by FLC, single or three phase makes no difference.

 

[kwired]

Your heaters are sized by FLC, single or three phase makes no difference.

Single or three phase makes no difference, but the number of thermal elements inside the enclosue to contribute heat to the enclosure does. The table on the cover (if properly applied the first time around) is for that enclosure with three thermal elements inside. If you end up reducing to two or even one (which is all that is needed for the single phase motor) then a different table likely applies.

Other thing you must watch out for is if the current rating of the contactor is in the range of the replacement motor. Single phase motor will have higher current rating than an equal HP rated three phase motor with same input voltage. Most of them will have both single and three phase HP rating marked on them.

It has been mentioned to use all three poles - you must do this if the overload unit senses phase loss.

 

[Sierrasparky]

Your heaters are sized by FLC, single or three phase makes no difference.

That is what I would think but the SqD charts shows the single phase Thermal having a greater amp limit for the same unit.

ie 2 trip units 6.x amps
3 trip units 5.1 amps

 

[petersonra]

sometimes you have to rewire the starter so all three thermals see the current or they won't work correctly.

the only way to know for sure is to look up the instructions for that starter. it will tell you how to wire it up for single phase use.

 

[kwired]

sometimes you have to rewire the starter so all three thermals see the current or they won't work correctly.

the only way to know for sure is to look up the instructions for that starter. it will tell you how to wire it up for single phase use.

The contactor will not care, the overload will if it is a type that senses phase loss.

 

[Besoeker]

The contactor will not care, the overload will if it is a type that senses phase loss.

Or possibly unbalance.
We used to use thermal overload protection for single phase motors using OL units designed for three phase. We wired all three elements in series. In practical terms, this was the simplest arrangement. The current is the same in both legs so monitoring just one was fine. Mostly this was for enclosure fans and cooling fans for heatsinks.
Nowadays these mostly have built in impedance protection so external overload protection has become redundant. The fan will shut itself down. A different issue arises. A fan that stops by itself is a potential problem at puts at risk the kit it is supposed to be cooling. So we now fit air flow sensors.

 

[topgone]

Or possibly unbalance.
We used to use thermal overload protection for single phase motors using OL units designed for three phase. We wired all three elements in series. In practical terms, this was the simplest arrangement. The current is the same in both legs so monitoring just one was fine. Mostly this was for enclosure fans and cooling fans for heatsinks.
Nowadays these mostly have built in impedance protection so external overload protection has become redundant. The fan will shut itself down. A different issue arises. A fan that stops by itself is a potential problem at puts at risk the kit it is supposed to be cooling. So we now fit air flow sensors.

What you said: three-phase OLs when used on single phase applications need to have the current pass through all the heaters in each leg of the OL to work out. One heater left out could mean an earlier, perhaps a nuissance trip due to the differential trip lever in most electro-mechanical type OLs (except on some earlier types where each OL heater (and trip contact) is individually sensing the current passing thru their respective heaters).

But on a criticallly needed fan aspect, I guess you don't need to trip the fan in the first place. You just need to sound an alarm, right?

 

[jim dungar]

... the differential trip lever in most electro-mechanical type OLs (except on some earlier types where each OL heater (and trip contact) is individually sensing the current passing thru their respective heaters)

Very few NEMA starters, and especially those with replaceable 'heaters', have this phase unbalance sensitivity. On the other hand, very few of the contained bi-metallic ones, like those on IEC devices, do not have this function.

I am not aware of anyone that markets this 'sensitivity' as actual phase loss protection.

 

[Jraef]

Very few NEMA starters, and especially those with replaceable 'heaters', have this phase unbalance sensitivity. On the other hand, very few of the contained bi-metallic ones, like those on IEC devices, do not have this function.

I am not aware of anyone that markets this 'sensitivity' as actual phase loss protection.

They used to, but I think someone got caught on that and now it seems nobody says it in writing any longer. Still though, I have heard several salesmen say it point blank. I correct them and it makes me unpopular, but I don't care, I can't stand people spewing blatantly false information.

You are dead right about the NEMA starters with replaceable heaters too, none of them have that issue so a single phase OL block is a 3 phase block without the heater in one pole (or two if 115V).

 

[Jraef]

That is what I would think but the SqD charts shows the single phase Thermal having a greater amp limit for the same unit.

ie 2 trip units 6.x amps
3 trip units 5.1 amps

Most likely that's because they know that if you have 3 heaters side by side, there is more heat, especially on the center pole. it's not uncommon for them to be de-rated like that. You also have different ratings for the same heaters if the starters are enclosed or open style.

 

[Besoeker]

But on a criticallly needed fan aspect, I guess you don't need to trip the fan in the first place. You just need to sound an alarm, right?

Mostly, these fans were on variable speed drive systems. If the fan stops, you have to shut down the drive fairly quickly.

 

[kwired]

Most likely that's because they know that if you have 3 heaters side by side, there is more heat, especially on the center pole. it's not uncommon for them to be de-rated like that. You also have different ratings for the same heaters if the starters are enclosed or open style.

Even though you don't have to use all three poles to make it function, I guess by doing so you make the element selection table accurate again by running current through all three.

The starters that are assembled for use as a single phase unit that have three pole devices but only one heater do not have the same table included with them, as only one heater will introduce different heat levels into the enclosure.

 

[Sierrasparky]

Thanks for all your help.