Need TD relay

[Bugman1400]

I'm controlling a 208V AC contractor coil.

Some of the cheaper timedelay relays can only handle 2 or 3 amps AC. Not sure how big your contactor is or how many on same circuit but, perhaps you should do a cursory review of the expected AC amp draw.

 

[Jraef]

Some of the cheaper timedelay relays can only handle 2 or 3 amps AC. Not sure how big your contactor is or how many on same circuit but, perhaps you should do a cursory review of the expected AC amp draw.

Excellent point. In your contactor specs, you will find values of "Inrush" (or "Pull-In") and "Holding" (or "Sealed) VA. The Inrush value is what you need to be most concerned with, because if your TD relay contacts are not rated for that, they could weld shut. On your timing relay, the contacts will have a "Make" and a "Break" rating. Your contact Make rating must be more than the contactor coil Inrush current (convert from VA by dividing by 208V), the Break rating must be more than the contactor Holding current too, but that's rarely an issue.


Contact ratings: Make = 15A, Break = 1.5A

Example:
100A NEMA Size 3 contactor, coil inrush = 660VA / 208V = 3.17A, no problem for this timer (but would be for one rated only 3A)
600A NEMA Size 6 contactor, coil inrush = 4860VA / 208V = 21.44A, big problem

 

[kwired]

Excellent point. In your contactor specs, you will find values of "Inrush" (or "Pull-In") and "Holding" (or "Sealed) VA. The Inrush value is what you need to be most concerned with, because if your TD relay contacts are not rated for that, they could weld shut. On your timing relay, the contacts will have a "Make" and a "Break" rating. Your contact Make rating must be more than the contactor coil Inrush current (convert from VA by dividing by 208V), the Break rating must be more than the contactor Holding current too, but that's rarely an issue.

View attachment 13341
Contact ratings: Make = 15A, Break = 1.5A

Example:
100A NEMA Size 3 contactor, coil inrush = 660VA / 208V = 3.17A, no problem for this timer (but would be for one rated only 3A)
600A NEMA Size 6 contactor, coil inrush = 4860VA / 208V = 21.44A, big problem

So for the NEMA size 6 you may need to drive a small contactor with the timer which then drives the large contator, or be prepared to change timer's frequently as they burn out contacts.

 

[ptonsparky]

That's why we use little bitty relay contacts to energize the coil of another relay which in turn pulls in another etc.

A few years ago we worked on a couple old starters for 300 hp motors. I could stand in the enclosures and I hazard a guess the last relay to pull in controlling the starter was rated 10 hp itself. Maybe a little exaggeration, but not much. Two stage and auto transformer start IIRC.

 

[kwired]

Do you need "off delay" function?

Grainger has Omron timers - some that will operate @ up to 240 volts, but I only found one that has an off delay function that also can operate at 240 volts - Grainger #1A983. Their "comparable" Dayton product that came up on same page only operates @ 120 volts.

 

[chris kennedy]

Do you need "off delay" function?

Yes, need contactor to open in 6 to 10 mins.

 

[don_resqcapt19]

Yes, need contactor to open in 6 to 10 mins.

The TDRU does about any timing function you can think of based on the switch setting on the relay. That is why I used it....only one device to keep on hand.

 

[victor.cherkashi]

Grainger.com

Sent from my Nexus 5 using Tapatalk

 

[ATSman]

Personally I prefer the Omron H3CA-A timer. 24 to 240 VAC, 12 to 240 VDC. Most any time delay between 0.1 seconds and 9990 hours. On delay, off delay, recycle, etc.

Usually available on eBay for around $35.00. I have bought over a dozen over the years, have several with over 10 years of continuous usage, no failures.

I am also a big fan of Omron products. In fact Zenith Controls back in the 70's private labeled their TD relays and used them in their ATS control circuits. The most common part # we use is
the H3CR-A8. 8 pin octal base plug in. very reliable.
The Agastat timer is also an industry standard but very pricey. Check ebay for new surplus to get the price down. I rarely buy from large elect supply houses, too pricey for the same part :thumbsup: