All i know is there are 3 distinctions, motor start, lighting & definite purpose Jay

each being listed for the particulars they serve

~CS~

 

Inductive loads have inrush and voltage spikes. Those contactors tend to be tougher where resistives are less so. But like CS says they are listed for what application is best for them.

 

Like meadow said, the inrush / lock rotor currents when a motor starts. The contacts are heavier duty.

For a motor with a full load amps of 10a, the starting current can be 100 amps.

 

All of the above. Also, when looking at the contactor, it will have a HP rating if designed for motor start.

 

Load types will differ in inrush current and arching.

Inductive loads that use solenoids or transformers will have a higher arch when turned off/on.

Resistive loads like heaters and motor loads have similar arching, but motor loads will have an inrush of 6x the current.

Lamp loads fall into several categories: tungsten, fluorescent, electronic, HIDs, and more, but tungsten in general has an inrush like motors do. Usually 10-15x the current inrush.

 

Lamp loads fall into several categories: tungsten, fluorescent, electronic, HIDs, and more, but tungsten in general has an inrush like motors do. Usually 10-15x the current inrush.

hmmm, i always tend to think the other way 'round on lights Ablyss.....:001_huh:~CS~

 

While a cold resistive heating load will have a high inrush, once the temperature stabilizes it will have a relatively low interrupting current when the contactor attempts to open the load.

An inductive load will hit the contactor at both ends: There's a high initial inrush, and there's also a significant amount of energy that has to be dealt with when the circuit opens and the magnetic field collapses, so there's a good sized arc when turning the load off, too.

Just did a troubleshooting call for exactly this problem on an electromagnet: They were burning through manual disconnects that were in theory rated to handle the current, but they weren't designed to open an inductive coil that size and it was caused serious contact erosion.

 

While a cold resistive heating load will have a high inrush, once the temperature stabilizes it will have a relatively low interrupting current when the contactor attempts to open the load.

Just a little confused by this statement. Other than incandescent lighting, what resistive heating loads have a high inrush?

 

Just a little confused by this statement. Other than incandescent lighting, what resistive heating loads have a high inrush?

I would think any load that has a very low cold resistance and then tapers off to a resistance in mid-range once it's up to normal temp. This resistance can only be calculated, not measured directly with a meter.

Similar to a motor starting to turn and one at normal RPM and developing counter-emf.

 

I would think any load that has a very low cold resistance and then tapers off to a resistance in mid-range once it's up to normal temp. This resistance can only be calculated, not measured directly with a meter. Similar to a motor starting to turn and one at normal RPM and developing counter-emf.

Like I asked! other than light bulbs, I can't think of any other resistive heating loads that fall into this category. I'm not saying that there is not, just it can't think of any.

 

Most of them actually. It's called having a Positive Temperature Coefficient of Resistivity, meaning that as the temperature rises, the resistance rises as well. So when cold (off for a certain time), the resistance is low and current is high for a fraction of a second until the element heats up. NiChrome, the most common heating element material, has a relatively high PTC of Resistance, about 60x that of silver or copper. Tungsten is a lot lower than NiChrome, but still 4-5x that of silver or copper. So quartz and quartz halogen lamps, because the element inside is still tungsten, is high as well.

Are all these heating loads for lighting? I guess I wasn't thinking about lighting as being a heating load.

 

Incandescent lamps typically convert only 20% of their energy as visible light, 80% is given off as heat.

The high inrush current prompted the switch rating "T" for large tungsten loads.