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Old 01-31-2010, 03:13 PM   #1
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Understanding this wiring schematic


I recently ran a 240v subpannel to my garage on a 50A breaker.

I want to run an electic heater in there, but am having a hard time understanding this diagram someone drew up for me.

here it is



I have a 50amp plug/cord that runs to a 30A fuse disconnect.
I want to wire a thermostat to it and run the heater, via a 30A 240v contactor because the thermostat draws 8amps at 240v.

I am going to use #10 THWN wire for this and he never drew in any grounds on the schematic.

im also wondering if i should wire in a 5amp fuse/holder to the contactor incase something shorts out, so it doesnt melt my wiring or start a fire.

the schematic just seems odd to me. it doesnt really click for me i guess. if someone could explain it to me i think i will be fine. i have basic knowlege about this stuff, but never really went off a schematic. normally i was shown how to do things.

this is how i interpreted his schematic. feel free to steer me in the right direction. thank you very much!

Understanding this wiring schematic-schematic-4.jpg

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Last edited by 3500lt; 01-31-2010 at 03:19 PM.
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Old 01-31-2010, 03:48 PM   #2
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Understanding this wiring schematic


first, you already have a fuse in the drawing. It won't protect the coil on the contactor but it will protect the wiring in general.

I'm not real sure how to make it any clearer that what you have. Simple connect each device just how it shows.
You have 1 leg of the power; that goes to the thermostat and a set of normally open contacts in the contactor.

from the t-stat you go to one side of the high limit switch and from the other side of the high limit switch you then go to one terminal on the coil of the contactor. On the other side of the contactor, you have the other power leg.


from the contact in the contactor you attached to, from the other side of that contact you go to the heating element. Then, from the other end of the heating element, you go to one side of the other contact in the contactor. then from the other side of that same contact, you have the other power leg.


Of course, I didn't say anything about the disconnect and fuses at the top so:

power from your panel, 1 leg to either terminal in the disco, this will then go through the fuses and you then go from their to your control circuitry.
edit to add:

any metal that is not actually part of the power or control systems gets bonded with a ground wire. If 2 pieces of metal are screwed together, you would not need a wire to each of them as the screwed joint will bond them generally.

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Last edited by nap; 01-31-2010 at 03:51 PM.
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Old 01-31-2010, 03:48 PM   #3
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Understanding this wiring schematic


What kind of heater do you have, my first though would have been to go from the breaker to the thermostat to the heater. I don't understand the contactor in between.

If it only draws 5A why don't you put it on a 15A breaker with #14 wire or is there other heaters on this circuit.
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Old 01-31-2010, 04:46 PM   #4
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Understanding this wiring schematic


Ladder Logic
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Old 01-31-2010, 07:55 PM   #5
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Understanding this wiring schematic


At the top are two wires coming down. These wires are 240 volts.

Next are switches and below that are "S". The "S" is a fuse in drawings. In this case the combined switch/S is showing the 30 amp circuit breaker/disconnect.

Then next is a switch going across, a limit switch which is closed, and a coil. When the switch is activated, it sends 240 volts to the coil. In this case the switch is a thermostat. The limit switch is a safety device which will open probably if something gets to be too hot, but is normally closed. The coil in this case is part of a contactor and operates the switches on the next line...

Insert comment -> A contactor is a relay. How relays work...
http://www.google.com/search?hl=en&s...h&aq=f&aqi=&oq=

The last line has a switch, a heating element, and another switch. In this case both switches are part of the above contactor and "close" (make a connection) when the above coil is energized.
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Old 01-31-2010, 08:04 PM   #6
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Understanding this wiring schematic


I don't know what type of heater you have or want, but I recently bought a heater for my shop for less than $100 from Northern Tool - includes thermostatic control, automatic fan, and has a 30a 240v plug. I ran #10 to a 30a 240v recept, plugged in the heater, turned it on - and have been warm and snuggy ever since. Seems a lot simpler that what you are working to do.
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Old 01-31-2010, 09:17 PM   #7
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Understanding this wiring schematic


Quote:
Originally Posted by Billy_Bob View Post
At the top are two wires coming down. These wires are 240 volts.

Next are switches and below that are "S". The "S" is a fuse in drawings. In this case the combined switch/S is showing the 30 amp circuit breaker/disconnect.

Then next is a switch going across, a limit switch which is closed, and a coil. When the switch is activated, it sends 240 volts to the coil. In this case the switch is a thermostat. The limit switch is a safety device which will open probably if something gets to be too hot, but is normally closed. The coil in this case is part of a contactor and operates the switches on the next line...

Insert comment -> A contactor is a relay. How relays work...
http://www.google.com/search?hl=en&s...h&aq=f&aqi=&oq=

The last line has a switch, a heating element, and another switch. In this case both switches are part of the above contactor and "close" (make a connection) when the above coil is energized.
But a relay/contactor has Two critical elements which are not related to each other. The Coil operating voltage and current draw. And the voltage and current rating of the Contacts. Those can be on different Voltages. In this particular case, however, both operate @ 240v. The (Line Voltage) thermostat is in Series with one leg of the Coil!!
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Old 01-31-2010, 09:26 PM   #8
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Understanding this wiring schematic


Thanks alot. i can make sense of this now. just needed a little help thats all.

BTW. i am using a digital thermostat, and the heater doesnt have a thermostat so thats why i am doing this. i already have all the stuff, just need to wire it up. wanted to make double sure of what i am doing before it gets pluged in. Plus i have a Welder outlet on the 240v pannel so i made a plug and cord to match for the 30A disconnect so i can unplug it and run the welder when need be. Might be a little more complicated than need be, but thats what projects are for. plus it gives me a reason to stay in the garage longer, while supper is cookin!
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Old 01-31-2010, 09:30 PM   #9
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Understanding this wiring schematic


WWHHHOOOOAAAAA!!!


digital thermostat?


you do not show any power for a t-stat and the t-stat would have to be rated to be able to handle 240 volts on it's controlled circuit and whatever current the contactor draws.


make sure before hooking anything up.
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Old 01-31-2010, 09:41 PM   #10
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Understanding this wiring schematic


Quote:
Originally Posted by nap View Post
WWHHHOOOOAAAAA!!!


digital thermostat?


you do not show any power for a t-stat and the t-stat would have to be rated to be able to handle 240 volts on it's controlled circuit and whatever current the contactor draws.


make sure before hooking anything up.
I don't think they (J. controls and W. Rodg.) manufacture Digital Line voltage Thermostats that operate @ 240V. $80..+ could burn up!!
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Old 01-31-2010, 10:19 PM   #11
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Understanding this wiring schematic


Quote:
Originally Posted by spark plug View Post
I don't think they (J. controls and W. Rodg.) manufacture Digital Line voltage Thermostats that operate @ 240V. $80..+ could burn up!!
well, in his drawing he provides no power for a digital t-stat, which is what he said he has. So, he at least needs to provide a power circuit for a digital t-stat.

my bigger question is, can whatever t-stat he has handle the voltage and current through it's control contacts. I'm not an HVAC guy so I do not know a huge amount about t-stat but I know a bit about smoking things accidentally
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Old 01-31-2010, 10:41 PM   #12
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Understanding this wiring schematic


Quote:
Originally Posted by nap View Post
well, in his drawing he provides no power for a digital t-stat, which is what he said he has. So, he at least needs to provide a power circuit for a digital t-stat.

my bigger question is, can whatever t-stat he has handle the voltage and current through it's control contacts. I'm not an HVAC guy so I do not know a huge amount about t-stat but I know a bit about smoking things accidentally
But at least you could go back and trace the problem to know where you went wrong. I once connected a paint heater/mixer in a Furniture refinishing factory. Made sure all the connections are per instructions. Not to speak of voltage and other requirements. When I hit the 240v., 30 Amp. Toggle Switch, I heard the loudest BOOOM ever. My only mistake. I tested it DRY. Learned my lesson. Anything to do with HEATING/Cooking, Do Not Test DRY!!
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Old 02-01-2010, 01:46 AM   #13
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Understanding this wiring schematic


http://www.rancoetc.com/ranco-etc111...ller-p-86.html

this is the thermostat and yes it can be hooked up to the 240. I understand the schematic now. thanks guys. but my dog is pissing me off so i might use her to ground this out!!! jk
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Old 02-01-2010, 02:02 PM   #14
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Understanding this wiring schematic


just realize you do have to add another rung in the ladder for a power circuit to the t-stat. Your friend did not include that and without that, your t-stat will not operate.
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Old 02-02-2010, 01:10 PM   #15
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Understanding this wiring schematic


yea he didnt put in a common or ground in the schematic

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