Convert dual circuit manual Intermatic to photocell relay

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Old 08-19-09, 12:21 PM
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Convert dual circuit manual Intermatic to photocell relay

I have two groups of 120v decorative street lamps each on their own 20A circuit that are controlled by a single manual Intermatic timer. I want to replace the manual timer with a photocell control relay. What confuses me is the two 20A circuits, making this a 40A timer I guess. I could just put a photo control on each circuit but I'm trying to figure out how to control both circuits with one photo control. 12 lights, 6 per circuit, each with 40w CFL on 120v line. It almost seems like I need an intermediate relay between the line and the load that is controlled by the photo control. Thanks Rick
 
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Old 08-19-09, 12:39 PM
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Originally Posted by 911_Wannabe View Post
What confuses me is the two 20A circuits, making this a 40A timer I guess.
No, it is (or should be) a double-pole timer rated for at least 20A.

It almost seems like I need an intermediate relay between the line and the load that is controlled by the photo control.
That is the correct solution. The intermatic timer is actually just a relay where the coil is energized by the flippers on the mechanical clock. If you don't want the timer anymore, a little dissection and you should be able to replace the clock mechanism with a photocell and leave everything else as-is.
 
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Old 08-19-09, 01:08 PM
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Thank you for the reply, so dual-pole 20A is less confusing for me. Without dissecting the timer I'm pretty certain it is controlled by a motor inside the timer and the motor mechanically switches the load. I don't see an obvious route to adding a photocell to the mechanical (analog) timer. I'll investigate further but would rather replace the timer entirely. How about a stand-alone dual-pole 20A relay that can be controlled by the photocell? Surely there is such a product?
 
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Old 08-19-09, 02:19 PM
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Originally Posted by 911_Wannabe View Post
How about a stand-alone dual-pole 20A relay that can be controlled by the photocell? Surely there is such a product?

Yes, very readily available. You can google 2 pole contactor and find what you need. Locally, most electrical or HVAC supply.

I would just use the timer enclosure to mount the contactor. Remove the timer of course, .

Since you have 2 circuits with neutrals available, you can get a contactor with 120 volt or 240 volt coils and a matching photo-cell.

You can get a 20 amp or 30 amp for about $10-$15. I usually use a higher rating than the circuit 30 amp contactor for a 20 amp circuit but, that's just me no real reason for it, but a 20 will be fine.
 
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Old 08-19-09, 04:31 PM
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Why are the lamps on two separate circuits? Twelve 40 watt lamps total 480 watts. A 20 ampere 120 volt circuit, even derated to 80% (for continuous usage) is 1,920 watts.

Even if there is some unknown (by me) reason for having two separate circuits the cost of the relay would likely exceed the cost of the second photocell.
 
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Old 08-19-09, 05:49 PM
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I have heard of people having issues with cfl's and photocells (poet and don't know it...lol) not that I have had any problems but I've heard of them dimming and flashing as if it's on a dimmer.

Wondering if this is an issue?
 
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Old 08-19-09, 06:54 PM
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The problems with photocells and CFL lamps are usually from using a two-wire photocell in series with the lamps. I have three CFL fixtures running on a three-wire photocell with absolutely no problems.
 
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Old 08-21-09, 01:31 PM
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Originally Posted by furd View Post
Why are the lamps on two separate circuits? Twelve 40 watt lamps total 480 watts. A 20 ampere 120 volt circuit, even derated to 80% (for continuous usage) is 1,920 watts.

Even if there is some unknown (by me) reason for having two separate circuits the cost of the relay would likely exceed the cost of the second photocell.

I have a couple of these arrangements, they are two separate circuits because when originally installed they used 150w & 200w incandescent bulbs. That's my guess as to why. I've since replaced with 40w/150w CFL which reduces the load.

Thanks
Rick
 
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Old 08-21-09, 01:36 PM
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Originally Posted by wirenut1110 View Post
I have heard of people having issues with cfl's and photocells (poet and don't know it...lol) not that I have had any problems but I've heard of them dimming and flashing as if it's on a dimmer.

Wondering if this is an issue?
I was also concerned about that, I have 3-wire 25amp photo cells but thought the relay would eliminate the potential for this and keep me from having two sensors side by side on the outside wall. I've also been told by one electrician that CFL's on a photocell will not last as long as a direct switch. No proof, just heresay.

Thanks to all for the information- extremely helpful. I'm off to try the relay.
 
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Old 08-21-09, 01:41 PM
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Originally Posted by furd View Post
Why are the lamps on two separate circuits? Twelve 40 watt lamps total 480 watts. A 20 ampere 120 volt circuit, even derated to 80% (for continuous usage) is 1,920 watts.

BTW - I did consider running all 12 posts on a single 20A circuit and just capping off the other circuity. For the mathematical reason you mentioned plus the fact that the timers are always right above the breaker box. I just didn't trust my reasoning.....
 
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Old 08-21-09, 02:15 PM
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I've also been told by one electrician that CFL's on a photocell will not last as long as a direct switch.
I had to replace one of my CFLs the other day, it had been in for three years and three months.

I get my CFLs from a local hardware store that uses coupons issued by a local utility. Final cost for the lamps is $1.00 each. Thirty-plus cents a year for lamps that run from dusk to dawn is pretty cheap, I think.
 
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Old 09-03-09, 08:21 AM
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After Action - I consolidated the wiring for the 12 light post to a single 20A circuit and installed a single 25A photocell. Works just fine and has since last posting. Will be moving on to the other posts next week. Thanks to all of you for the insightful assistance.
 
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