Electronics gurus - Tell me where I went wrong with this relay

[David0858]

I needed a relay to switch a 1000W, 120VAC resistive load (heating element) and a 120V control voltage. I went through the relays on Amazon until I hit this one, https://www.amazon.com/gp/product/B0030G8SC8/ref=oh_aui_detailpage_o00_s01?ie=UTF8&psc=1. 30A, I only needed to switch 8.33A and will fit where I needed to put it so in the cart it went.

It just came and everybody's data sheet for it says for a resistive load, max switched power of 840W. This is Zettler's, https://www.azettler.com/pdfs/az2280.pdf. The N.O. contact is rated at 30A at 277VAC. 840W is a long way from 30A at 277V. What am I missing?

This relay is supposed to do 30A at 277VAC, so 8310W. 840W is barely over one tenth. I just replaced the compressor relay on the controller board in a 15,000 BTU AC. It's probably a third the size of this relay, is rated at 20A and is actually probably switching 10A or more..

 

[wyliesdiesels]

Youre mixing up the ratings.

For resistive loads, the rating is lower.

For general use the rating is higher.

This difference of ratings is found on almost every relay.

 

[Lamakocklee]

I am thinking that there is an error in the datasheet. That same line states

Max. switched power: 840W or 11,080VA

that is a big difference.. even with a .8 PF that should be at least 8000 W.. the number work out to a 0.076 PF about...????

If you were to contact the manufacturer, I bet they would give you the right answer.

 

[bjcouche]

To me "General Use" IS a resistive load. Being the relay is rated for 28 or 40A for general use, I would feel fine using it at 10A and 120V. Actually, you will find these similar relays in much higher current and voltage ratings inside household appliances like ovens. Having a "power" rating is a new one to me and I've seen a lot of datasheets. When you need to be concerned about a relays rating is when you are switching more than 50VDC, or you have highly capacitive or inductive load, or are trying to start an electric motor with high starting current. Under those circumstances, the relay will have lower ratings as seen in the datasheet because those things cause challenges for arcing at the contacts...
Also note that there are lifespan ratings too.... that sometimes come into concern, like if you have the relay on a PID controller, turning on and off 10 times per minute trying to regulate temperature of a kiln, etc.

 

[wyliesdiesels]

I am thinking that there is an error in the datasheet. That same line states

Max. switched power: 840W or 11,080VA

that is a big difference.. even with a .8 PF that should be at least 8000 W.. the number work out to a 0.076 PF about...????

If you were to contact the manufacturer, I bet they would give you the right answer.

yes i did notice the apparent power rating being way off from the rest of the ratings.

 

[David0858]

yes i did notice the apparent power rating being way off from the rest of the ratings.

That's my thought that there's an error there somewhere. It's going to blow or not as it's getting built in my temp controller. It's already mounted and I just need to finish the wiring. I've got a pork roast that needs smoked.