Sierrasparky
Senior Member
- Location
- USA
- Occupation
- Electrician ,contractor
Is there anything wrong with using a 3phase starter for a single phase motor? The faculity purchased a single phase replacement by error.
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.
Your heaters are sized by FLC, single or three phase makes no difference.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.
Your heaters are sized by FLC, single or three phase makes no difference.
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.
Or possibly unbalance.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.
... 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)
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.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.
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.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
Mostly, these fans were on variable speed drive systems. If the fan stops, you have to shut down the drive fairly quickly.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?
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.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.