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rjbaiad 09-21-2008 11:11 PM

Delay on Break timers
I am working on installing a generator for a friend of mine. This house currently has four window units and I'd like to set them up to stagger their startups with something like a delay on break timer. There are four window units and I'd like to start one after say 5 minutes, the next 6 minutes, and so on and so forth. Do they make any kind of delay on break timers for window air conditioners?

TazinCR 09-22-2008 06:19 AM

They do make timers you can use but it will be a very expensive project. You need time delay contact relays. I believe Granger sell them. What size gen. are you installing?
Does it have an automatic transfer switch?

rjbaiad 09-22-2008 09:22 AM

I am installing a 16 kw generator. I have one 240 volt unit (17500 btu) and 3 120 volt units (ranges from 8-12000 btus). The generator is rated for 28080 watts surge or 117 amps. I also would have the fridge/freezer and stand alone freezer starting up as well, which I'm afraid would be too much for it to handle. If I could somehow stagger the startup of these units it wouldn't be so hard on the generator. If this isn't feasible, do you have any other suggestions?

micromind 09-22-2008 10:58 PM

If these units are on separate circuits, it really wouldn't be any too difficult.

You'd need to set a box somewhere near the panel, and get a conduit (1" will do) from the panel to this box. The size of the box would be determined by the number of relays installed in it. For your set-up, I'd recommend a 12"X12"X4". If it's outside, it needs to be weatherproof, commonly known as 3R.

If you're doing 4 A/C units, you'll need 4 time-delay relays. Since this type of relay usually has contacts rated for low current, it's best if you have the time-delay relays power the coils of high-current relays. I know, this is a lot of relays, (8 total), but time-delay relays are not made to control high power loads.

I've designed and built quite a few of these systems on commercial/industrial buildings, the only difference is these generators are several hundred to several thousand KW, and the A/C's are sometimes more than 500HP. The timing relays are all the same, and operate on the same principal. The system I have in mind will keep the A/C power hot always, until a power failure. Then, upon restoration of power (either from the generator, or from the utility), each load will be energized in a sequence. This sequence can be a few seconds to a few minutes, I recommend about a 2 minute delay for the first one (to allow the generator to warm up), then each additional load comes on in 30 second intervals. Then they stay on until the next power failure.

If you want to go ahead with this, figure around $60-80 per A/C unit + the box and fittings + 1 more 15 amp breaker in the panel.


TazinCR 09-23-2008 06:40 AM

Micromind can you give us a link to these relays large and small. That is a very good idea. I was thinking of large time delay contactors with time delay.

micromind 09-23-2008 11:22 PM

I'd sure like to be able to post a link, but I just don't have the computer skills. Wiring a control house for a power plant, consisting of noticing and correcting about 40 mistakes on the drawings, and landing about 3000 control wires, and getting it right the first time is easy for me. Computers.....I'm half surprised I can even get to this site sometimes! lol.

To answer the question though, go to, and in the little search box, type in 5Z538. This is an inexpensive power relay that will handle just about any load that's cord and plug. It's even horsepower rated, so it'll handle motors as well. They're easy to install, and pretty much bullet-proof, but they have exposed live parts, and must be installed in a box with a cover. This (or something similar) is the power relay I'd use to control your A/C units.

The time delays I usually use are Allen-Bradley 700-HNC. These are multi-function timers, and must be set up for a specific application. I wouldn't recommend them for a DIYer. They're somewhat similar to the Grainger #4KN15. I've never used them, but the 1EJN1 looks pretty simple, and it has a very wide timing range. You'll need a socket to mount this relay into, 2A584 will work, and it's not too spendy. As is normal with relays, there are 14 terminals on this socket, you'll be using 4 of them.

You'll need 1 time delay relay, and 1 power relay for each load, you can have as many as you want, provided they'll all fit in the box.


DRFREON 09-24-2008 05:17 AM

I agree with "Micromind". An alternate would be a sequencer- multiple loads triggered (via control circuit as he outlined) with adjustable delays. By the way, you are describing a delay on make timer.

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