Help Needed wiring FW-x240 Transformer

n1st
n1st Solar Expert Posts: 77 ✭✭✭✭
in Solar Beginners Corner #1
My application for the Outback X240 transformer is to step 120AC up to 240AC for use of a 240v pump, and has nothing to do with inverters. The step up diagram that OB provides involves inverters.

Please review my wiring diagram along with the diagram that OB provides. My diagram shows 120AC coming in at the top. For clarity, I've left out ground wiring.

If I've translated the OB diagram correctly to my simple application, the only difference should be the "A" vs. "B" wiring. "A" is how outback suggests. "B" is what I came up with to avoid a double tap at the top of the left top breaker - but I don't know if there's any ramification of this change that I'm not seeing.

So, what I'm asking:
1) Is my diagram a correct interpretation of the OB diagram?
2) Is my use of "B" instead of "A" proper?
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Help Needed wiring FW-x240 Transformer

    I can't see diagrams on my netbook (too small) but try this:

    Both white leads tied to AC neutral.
    Black lead goes to AC hot 120 Volt.
    Red lead should provide 240 VAC against black lead.

    Put your meter on it from black to red and see if you don't get 240 VAC. Remember the power available at the output will be roughly 1/2 the input (i.e. 20 Amps in @ 120 VAC = 10 Amps out @ 240 VAC).
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #3
    Re: Help Needed wiring FW-x240 Transformer

    If you need some bus bars for parallel wiring, take a look at these:

    http://www.solar-electric.com/mnsbb.html

    Although, just using wire nuts should be fine too (assuming breaker/wire sizes are all correct).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • GreenerPower
    GreenerPower Solar Expert Posts: 264 ✭✭✭✭✭✭
    #4
    Re: Help Needed wiring FW-x240 Transformer
    n1st wrote: »
    So, what I'm asking:
    1) Is my diagram a correct interpretation of the OB diagram?
    2) Is my use of "B" instead of "A" proper?
    Either "A" or "B" is OK if you use 2 sets of double breakers. You can use "B" and just the upper double breaker though i.e. remove the lower double breaker. The x-240 and the pump is still protected by the upper double breaker.

    GP
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  • n1st
    n1st Solar Expert Posts: 77 ✭✭✭✭
    #5
    Re: Help Needed wiring FW-x240 Transformer
    Cariboocoot wrote: »
    I can't see diagrams on my netbook (too small) but try this:

    Both white leads tied to AC neutral.
    Black lead goes to AC hot 120 Volt.
    Red lead should provide 240 VAC against black lead.

    Put your meter on it from black to red and see if you don't get 240 VAC. Remember the power available at the output will be roughly 1/2 the input (i.e. 20 Amps in @ 120 VAC = 10 Amps out @ 240 VAC).

    Basically, that's what my diagram is doing. But...
    In words, I have 120 hot coming in the top left half of tandem breaker and the xformer #4 black lead coming out the bottom. Right half of CB has #1 red lead coming in the top, and bottom goes to the 240 load. OB has another lead coming from the source (top of left breaker) and going to the 240 load, but I would like to tap the bottom of the left half instead since the bottom screw is made to handle 2 lines, and it would seem to offer the additional protection of shutting off this feed to the load if the CB flips.
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  • n1st
    n1st Solar Expert Posts: 77 ✭✭✭✭
    #6
    Re: Help Needed wiring FW-x240 Transformer
    GreenerPower wrote: »
    Either "A" or "B" is OK if you use 2 sets of double breakers. You can use "B" and just the upper double breaker though i.e. remove the lower double breaker. The x-240 and the pump is still protected by the upper double breaker.

    GP

    Interesting! So the double breaker on the bottom serves no purpose if I use the bottom of the left half of the top breaker (i.e. pass the source through the left half of top breaker) for the 240v load?

    If there was a short at the pump, the left half would flip the CB before the transformer would heat up as a result of the short?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: Help Needed wiring FW-x240 Transformer

    The current will always be higher on the low Voltage "input" than on the high Voltage "output".
    The only time you'd need double pole breakers on the 240 Volt side would be if you were running multiple devices from it and needed to protect the 240 VAC supply against a possible failure in one of them.

    If possible, put the pump control switch on the 120 VAC side, turning the transformer on and off as it will consume some power on its own even without a load.
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  • n1st
    n1st Solar Expert Posts: 77 ✭✭✭✭
    #8
    Re: Help Needed wiring FW-x240 Transformer
    BB. wrote: »
    If you need some bus bars for parallel wiring, take a look at these:

    http://www.solar-electric.com/mnsbb.html

    Although, just using wire nuts should be fine too (assuming breaker/wire sizes are all correct).

    -Bill

    Thanks Bill, that looks like a good value.
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  • n1st
    n1st Solar Expert Posts: 77 ✭✭✭✭
    #9
    Re: Help Needed wiring FW-x240 Transformer

    Ok, just one more question about this (I hope)...

    I've wired it up and tested the resistance of the two 240v lines (without any power applied of course). There appears to be a short across them (.3 ohms). Should this be expected? I see that the other end of #1 is #2, and the other end of #4 is #3, and #2 is connected to #3. So it would follow that #1 is the other end of #4 (the two 240 leads). Disconcerting, but all is well?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #10
    Re: Help Needed wiring FW-x240 Transformer

    You are probably just measuring the DC resistance of the transformer/branch circuit wiring. They are designed to have AC Impedance to prevent excessive/improper current flow.

    Disconnect one (or more) of the transformer leads and you should see very high resistance between the two hot leads. Note, if you have a neutral/grounded neutral, you may see low resistance between the power leads and earth ground (unless the transformer/ground bond is lifted for testing).

    Also note, it is very possible to get a 100-300 volt (more or less) shock from any transformer when using a DC ohm meter set to low resistance scales. The meter causes DC current to flow in the transformer and when you disconnect one of the meter leads, the magnetic field will collapse and can give you a nice/surprising shock (no danger, just uncomfortable).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • n1st
    n1st Solar Expert Posts: 77 ✭✭✭✭
    #11
    Re: Help Needed wiring FW-x240 Transformer

    Bill,

    Thank you much for the reply. I powered it up and got a healthy 246v under no load.
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