controlling 3 heater circuits with one thermo - contactor method

hi folks,

would love input on my thinking.

planning on running 5 radiant heaters on three 240V 20A circuits for a detached yurt. (off of a subpanel.)

would prefer to have single thermostat. the thought is to get a low-voltage 24V thermostat, connected to a single 3-pole contactor. is the following link the kind of contactor i need? 220-240V Coil Motor Controler AC Contactor 3P 3 Pole NO 660V 5.5KW CJX2-0910

or this? IEC Mini Contactor 3 Pole 20A w 16A Aux 24 V DC Coil | eBay

i'm wanting to make sure that each pole (which will be connected to separate circuits) is able to handle the full 20A (in practice, 15A). also that it can be controlled by a 24v thermostat.

i think the 24v thermostat is pretty straightforward, but curious also about the 240v-24v transformer: are there any factors to consider around idle power usage, etc? would something like this be fine: TCT40-05E07AB Triad Magnetics | Power Transformers TCT40 05E07AB | Onlinecomponents.com

as you can see, price is a major factor for us, but also want to be as energy-efficient as possible.

finally, my plan is to include on/off switches for each of the heaters independently, so that we can choose to run just some of them. fine to use 20A 240v normal leviton switches? Commercial-Industrial : Leviton Commercial Double Pole Toggle Switch

thanks everyone!
.brush

 

Welcome to the forums!

The first three pole contactor you have listed would work the best for you depending on the load per circuit which you didn't post. Each contact is only rated 9 amps per pole so I suspect that is not large enough.

I would not bother with a 24 volt thermostat/relay(contactor) because you would need to buy a transformer, and located it someplace, when you could just use a line voltage thermostat. Line voltage thermostats are only about $20.

The double pole switches you listed would be fine for disconnects.

If you post the heater watts, and quantity, I'm sure we can find you a relay that will fit the application.

 

thanks for the welcome, and the response!

sorry for not explaining myself adequately.

i'm running 5 1500W heaters, on three 240V circuits. so 12.5A on two of the circuits and 6.25A on the other.

if the first contactor i listed can only handle 9A per pole, that would not be enough. on the specs it said "20A thermal ampacity" or something -- i guess that's something else? what do i look for to ensure it can handle a full 20A?

i agree i could just use a line thermostat, if there are contactors or relays that can receive 240V as control? i didn't realize that...

[doing a bit of research]

or maybe actually the contactors i was looking at actually WERE using line voltage as control! what about this model:
GE 4 Pole Contactor 20A CR124 Overload OS 92A Heaters | eBay
when it says "110v coil" is that the voltage for the control circuit? so i would put the thermostat on a 120v circuit?

thanks!
.b

 

That is correct. I would get one with a 240 volt coil, that way you can use the circuit that is only running one heater to also run the thermostat/control.

You do not need a contactor/relay that handles 20 amps, it only needs to handle at least the full load amps of the heaters, which is 12.5 amps. Look closely at the specs of the relay as the contact ratings can vary whether the load is inductive or resistive. (heaters are resistive)

The relay you are looking for should have the following:
at least 3 poles
Coil voltage of 208-240 volts
contact rating of at least 12.5 amps resistive.

Here is one that would work for you: DAYTON ELECTRIC MANUFACTURING CO./DAYTON Relay,Ice Cube,3PDT,240VAC,Coil Volts - Relays - 1EHW3|1EHW3 - Grainger Industrial Supply
And you would need this socket: DAYTON ELECTRIC MANUFACTURING CO./DAYTON Socket,11 Pin,16 Amp - Relay Sockets - 1FC14|1FC14 - Grainger Industrial Supply
You might need a DIN rail to mount it too.

You will need an enclosure for the relay and all the wiring, so just keep that in mind.

 

Rather than a motor starting contactor, I'd use a definite purpose contactor, something like this.

SCHNEIDER ELECTRIC/SQUARE D Contactor,24VAC,20A,3P,Open - Definite Purpose Magnetic Contactors - 5KAG9|8910DPA13V14 - Grainger Industrial Supply

 

But that is a 24 volt coil and it has been suggested to use a 240 volt coil.

 

Same contactor with higher voltage coil.
SCHNEIDER ELECTRIC/SQUARE D Contactor,208/240VAC,20A,3P,Open - Grainger Industrial Supply

 

i'm so confused. on the GE 4-pole it's a 24v coil? where does it say that? i see this on the description page (which to me implies 110V coil):

good used ge 4 pole contactor at 240v: fla 20, 1 pole 68a, 1ph 2 pole 120a individual 20a, at 600v fla 10a, 1 pole 34a, 3ph 3 pole 60a, individual 20A with cr124 overload and three os-92a heaters, 110v coil

---

and pjmax, thanks for the suggestion. am i right that the following -- which is 1/7th the price!! -- is basically equivalent? SCHNEIDER ELECTRIC/SQUARE D DP Contactor,208/240VAC,20A,Open,3P - Definite Purpose Magnetic Contactors - 2CF90|8910DPA13V09 - Grainger Industrial Supply

 

I do like definite purpose contactors as they are the workhorse of contactor world, but the cost is about 10x of the ice cube relay I posted.

Brush, the last one you posted would work just fine and a great price. No extra stuff needed like sockets or mounting rails.

 

Definite purpose contactors can be purchased with nearly any voltage coil the OP would want to use.

 

Brush.....keep in mind that these contactors are noisy when they close. They will make a distinctly noticeable sound in your yurt.

 

thanks, everyone. great advice and help! i think somehow a couple of the early responses were "missing" when i looked the first time, so my previous confused response re: 110v was misunderstanding.

pjmax -- regarding the sound the contactors make, is it noisy like "crap! what was that! is something wrong?" or noisy like "ah yes, i notice that something just switched on!" i'm thinking of locating the contactors underneath the floor -- would they still be noisy down there?

most importantly, are there any alternatives?

thanks!

 

bump. for example, it would cost a bit more, but would getting something like the following solid state relay work (and address the noise issue)?

Silicon Power Cube 240D45 10sp 50R2D Solid State Relay 240V 50A | eBay

obviously, i'd have to get a) a dc thermostat, and transformer, and b) 3 of the relays. but at least in principle, is something rated adequate amps (in this case 50!!) on the 240VAC side going to work?

thanks again!

 

I think using the solid state relay like that would be more of a hassle then it is worth given you would need all the extra equipment. A definite purpose contactor does make a good "thunk" when it pulls in, but not so loud it would startle you. An Ice cube relay on the other hand makes a small "click" when it pulls in similar to what your thermostat would make. If you're worried about the noise, I would suggest an ice cube relay I posted earlier.

If you choose to put it in the floor you must have an access panel as all splices are required to be accessible.

 

hmmmm, understood. (re: the floor, it's a yurt so there's crawlspace underneath.)

with the ice cube relay, i'll need two of them, right, one for each of the other circuits? that's 2 relays and 2 sockets?

and it's not a concern that the 15A load on the circuit may be a continuous load? no need to derate like NEC requires with wire sizing? (ie. no more than 16A on a 20A breaker.)

tnx!

 

thanks for the help everyone. here's a new thread with more context and info on the overall project, and request for feedback. thanks!

http://www.doityourself.com/forum/el...arts-list.html

and for those that are curious, i figured out that the "3PDN" means "three pole dual throw" (not sure exactly what dual throw means), so only need the one relay (i think). assuming that 100% of amp rating on switches, etc., can be used for continuous load (unlike wire).