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**Walker** · 02-01-2011, 04:50 PM

Quote:

Originally Posted by thelorax121

I figured that was the case with the neutral running through the contactor, but I was not sure if both poles HAD to have a line running through them. In this version, I ran the neutral line directly to the power block, then ran a line from that to the contactor, is that correct?

Yes. That will work fine.

Quote:

Originally Posted by thelorax121

The key switch has a NO contact that the line will run through, which when engaged will allow it to flow through the e-stop contact (NC) and then to the contactor coil, providing power to the panel.

I understand that the key is NO and the e-stop is NC, but how does the action of them work? When you press the e-stop in, does it stay in, or does it spring back up?

Likewise with the key.... when you turn it on, does it stay in that position or does it spring back like the key in your car does?

Quote:

Originally Posted by thelorax121

I was also planning on running the 120V line from the power block for the 240V contactor through a second NC block on the E-stop switch before it goes downstream to the on/off switch and the contactor, that way the E-stop will kill both the 120V and 240V power. Does this sound accurate?

Not necessary.

When you press the e-stop, it will cut off the 120V power via the top contactor. With no 120V power flowing through, the contactor that is passing the 240V through will switch off (it's coil signal was just terminated).

thelorax121 · 02-01-2011, 05:33 PM

Sorry for the confusion there, the key is maintained, and the e-stop is a twist-release once it is pushed down. Does this change the way I need to wire anything?

Totally missed that connection on the 240V e-stop too, thanks for clarifying, that makes perfect sense.

**Walker** · 02-01-2011, 05:38 PM

Quote:

Originally Posted by thelorax121

Sorry for the confusion there, the key is maintained, and the e-stop is a twist-release once it is pushed down. Does this change the way I need to wire anything?

Nope. If that's the way the e-stop works, then it's looking good to me.

One comment regarding your lights. SSRs leak a little bit of current, even when they are off. I installed a very small 120V bulb in my panel with the intention of having it tell me when power was flowing through the SSR and contactor and was causing my element to heat up.

However, the small amount of current that leaks through the SSR is enough to cause that light to illuminate all the time, so it doesn't behave like I want it to.

thelorax121 · 02-02-2011, 02:49 PM

Ok one more quick question, I am getting ready to order a 2P mini circuit breaker for the 240V line in, and if the element is 5500W, should I get a 25A or 30A breaker? When calculated 5500/240= 23A, but 5500/220= 25A, and I was not sure if the current would vary in that range at all, resulting in nuisance trips. Also, I want a standard trip breaker, not a delayed trip because the element does not have an inrush current, correct?

**Walker** · 02-02-2011, 03:04 PM

)heater elements are not a fixed wattage. They are advertised as a certain wattage if you run them at the advertised voltage.

SO, a 5500W/240V element means just that... it will produce 5500W of heat if you run them at 240V. If, instead, you run them at 220V, then you will not get 5500W of power out of them, so your amp calculation for the 220V supply is not correct.

The proper way to figure it is to determine the resistance of the heater element, because that is the thing that will remain constant.

Power = Voltage * Current

So, 5500W/240V = 22.9A

And

Voltage = Current * Resistance

So, 240V/22.9A = 10.4 Ohm

That element is a 10.4 Ohm resistor, and it will always be a 10.4 Ohm resistor, regardless of what voltage you drive it with.

So, if you were to run it at 120V, for example, you can figure out the current it would draw with that Voltage = Current * Resistance equation again, solved for Current

120V/10.4Ohm = 11.5 Amps

And then to the power equation again

120V * 11.5A = 1375 Watts

So, dropping the voltage in half causes the power to drop to one quarter and the current to drop to one half.

Doing this again for 220V instead of the advertised 240V (and the element is STILL a 10.4 Ohm resistor):

220V/10.4Ohm = 21.2 Amps

220V * 21.2 Amps = 4653 Watts.

So, if you run it on 220V, you will get 4653 watts and draw 21.2 Amps.

Now.... having going through all of that, you are supposed to have breakers that are rated higher than the load you are running through them. I bought 25A breakers for my 5500W element and it has worked out fine for me, but I probably SHOULD HAVE bought 30A breakers, because I really do have a full 240V at my house.

If you have 220V, then 25A breakers should be OK since you are only going to pull 21A through them.

thelorax121 · 02-03-2011, 01:58 AM

Thank you as always Walker, great info, much obliged!