Correct contactors for a transformer

[jim dungar]

The Orange box uses lighting contactors extensively to turn large transformers off and on loaded, but its not a motor load, but then the OP is not starting the motor until after the transformer is turned on. They have a couple thousand stores like this, and don't appear to have a problem with it, some stores are over 20 years old and use this system. When I first saw this set up, I thought they would be issues, but I never had to change one due to contact failure, it's always a coil failure.

Are you sure they are "lighting" contactors? Past 30A, the primary difference between contactor types, is the composition of their contacts. Some of the hardest loads to switch (from a contact perspective) are tungsten filaments.

For the OP's application, it is all about inrush current ratings, not full load ratings.

 

[conmgt]

templdl suggested lighting contactors, for this application, about a year ago in another posting of mine when I started looking into this project.
Would you say that lighting contactors have the toughest material on their contacts?

 

[jim dungar]

Would you say that lighting contactors have the toughest material on their contacts?

No.

Contact material selection involves among other criteria; the make current, the continuous current, the break current, contact bounce, frequency of switching, and operations per hour.
From memory, lighting contacts are relatively large and moderately soft.

I find many people using the term 'lighting contactor' as a marketing term rather than a reference to specific device. Kind of along the lines of: Definitive purpose = general duty, lighting contactor = intermediate duty, and NEMA rated contactor = heavy duty

 

[hillbilly1]

No.

Contact material selection involves among other criteria; the make current, the continuous current, the break current, contact bounce, frequency of switching, and operations per hour.
From memory, lighting contacts are relatively large and moderately soft.

I find many people using the term 'lighting contactor' as a marketing term rather than a reference to specific device. Kind of along the lines of: Definitive purpose = general duty, lighting contactor = intermediate duty, and NEMA rated contactor = heavy duty

Square D calls them lighting contactors, you can get them up to 600 amp, they use 100 and 200 amp ones for transformers supplying displays, 200 amp ones controlling lighting. All of them latching type.

 

[jim dungar]

Square D calls them lighting contactors, you can get them up to 600 amp, they use 100 and 200 amp ones for transformers supplying displays, 200 amp ones controlling lighting. All of them latching type.

Latching, is definitely a standard option for lighting contactors.
The primary difference between Square D's Class 8502 'motor' contactor and their Class 8903 lighting contactor is the contact material.

 

[hillbilly1]

Latching, is definitely a standard option for lighting contactors.
The primary difference between Square D's Class 8502 'motor' contactor and their Class 8903 lighting contactor is the contact material.

And the 8903 is what they use..........

 

[conmgt]

I just heard from the manufacturer of the transformer:
At 0 impedance, the inrush would be 1221A.
But the "practical max amps" would be 407A
I'm not sure what exactly to do with that info.

 

[jim dungar]

I just heard from the manufacturer of the transformer:
At 0 impedance, the inrush would be 1221A.
But the "practical max amps" would be 407A
I'm not sure what exactly to do with that info.

For the theoretical (design) inrush currents, small transformers like this are often modeled as air core inductors. If everything in the world is against you (e.g. closing into a saturated coil) you might see 1221A in which case your protective device might trip. In real world normal operating conditions would be 407A or about 4.9X, which seems to be a reasonable number based on the earlier nameplate. in this case you might be able to use a 30HP rated contactor.

 

[conmgt]

So it looks like a 90 definite purpose or NEMA3 contactor would work.
A definite purpose contactor rated for 90A has a locked rotor rating of 540A at 230V.

 

[John120/240]

Hello,
I need contactors for the primary side of a 30kVA transformer that is dedicated to an infrequently used motor (once a week-ish). I need to cut off the transformer to save on standby losses.

For once a week use why not just turn off the breaker or disconnect that feeds this transformer ? Educate me please.

 

[hillbilly1]

For once a week use why not just turn off the breaker or disconnect that feeds this transformer ? Educate me please.

This being in Philly, it's probably Union, so they would be required to have an electrician to turn the disconnect off and on, a pushbutton would not. Probably help with 70E too.

 

[jim dungar]

... has a locked rotor rating of 540A at 230V.

That is the rating I would care about.

Whether it is NEMA, IEC, or definite purpose construction is immaterial.