Power/E-stop Wiring for 2 inputs (120V & 220V)

Since my only 220V access is a 3-pole outlet, I have to run one 120V line in as well as a 220V line for my 5500W heatstick element. However, I am having some trouble figuring out how to wire both of these into my control box in a logical, cohesive manner, and was hoping some some of the enlightened amongst us could give me a helping hand. Here is the VERY crude diagram I have so far:



So my first few questions are:

1. Is the neutral leg run into the box and the power in contactor correctly?
2. Where would I wire the load line from the 120V? I want to run it through a second NC contact on the E-stop, but then where, an additional bus bar? Since I already have the two lines from the 240V, I don't know where a third would safely reside

I am sure that more questions will crop up as I go, but we'll start here for now. Thanks for the help, and sorry for the crude nature of my diagram!

i can't see the picture.

nevermind. I know why I can't see it. It's on a file sharing site and my laptop (which belongs to my employer) has the firewall set up so that I cannot go to file sharing sites.

Hm, I would love your input, is there a better way to post the picture so that it is accessible?

I managed to get the picture via my blackberry (not controlled by my employer's IT department).

What you have isn't going to work. You cannot use the neutral from the 120V input and one of the hots from the 240V input to activate the coil on your contactor. That will cause the GFI circuitry (which you ARE using, correct?) to trip on both the 240V and 120V sources. The whole system would shut down as soon as you tried to turn it on.

If you have things that need to be controlled by 120V they are going to have to be drawing completely from the 120V feed. Your 240V will simply pass through the contactor and to your heater element and will not connect to anything else.

What is the "shunt"?

I can draw this up, but I need to know how your key start and e-stop buttons work.

Are they "momentary" switches?

Walker said:

I managed to get the picture via my blackberry (not controlled by my employer's IT department).

What you have isn't going to work. You cannot use the neutral from the 120V input and one of the hots from the 240V input to activate the coil on your contactor. That will cause the GFI circuitry (which you ARE using, correct?) to trip on both the 240V and 120V sources. The whole system would shut down as soon as you tried to turn it on.

If you have things that need to be controlled by 120V they are going to have to be drawing completely from the 120V feed. Your 240V will simply pass through the contactor and to your heater element and will not connect to anything else.

What is the "shunt"?

Click to expand...

First, yes I will be using GFCI, I have two inline cords, one for 120v 20A, and another for 240V 30A. The shunt is for the AMP meters, similar to the ones that KAL used on his build. I am posting a pic of my latest diagram (and a link to the google doc if that is easier to see), the 240VC will be run through the contactor and SSR and the 120V devices (not shown) will be fed from the power distribution block. The wiring of the SSRs and Contactors still has me a bit confused, so any and all help is appreciated!



https://docs.google.com/document/d/1oyfJ4hmn0FBKoxhYkJJ3wqi_JoKm9vA9xEaBCCLjzyA/edit?hl=en#

Yeah, I can see stuff on google docs just fine.

This is looking better, except that your shunt needs to go on one of the the 240V lines if you are in fact interested in monitoring the current to your heater element.

Also, it's not necessary to pass the 120V neutral through the contactor, but you can if you want to.

The specifics of how your e-stop button and key switch are still not known to me, so I can't comment on whether that portion of the circuitry is or is not correct.

Walker said:

Also, it's not necessary to pass the 120V neutral through the contactor, but you can if you want to.

Click to expand...

Actually.... the neutral connected to the 120V source's contactor coil must come directly from the 120V feed and not from the "post contactor" side. You wouldn't be able to start this thing up with it wired like you currently have it wired.

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?

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 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?

As for the shunt, totally mussed that up, here is current rendition with it wired into one of the 240V legs. Thanks so much for your help here man, you're a lifesaver!

https://docs.google.com/document/d/1d6ayZXOobTlkRJSxzhhie0BVEZeHLt7ML-yWsvAidTo/edit?hl=en

thelorax121 said:

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?

Click to expand...

Yes. That will work fine.

thelorax121 said:

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.

Click to expand...

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?

thelorax121 said:

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?

Click to expand...

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).

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.

thelorax121 said:

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?

Click to expand...

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.

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?

)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.

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