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Old 11-30-2012, 04:08 PM   #1
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Default Two Power Sources in One Control Panel

I haven't been able to find a definitive answer to this question yet.

I would like to run a 120v element for my HLT and a 240v element for my boil kettle at the same time. To accomplish this, my plan is to run a 120v supply and a 240v supply into one control panel, though keep them completely separate, except for the grounding.

Has anyone else done this? Would this cause any problems? Should both power systems be grounded together? I'm concerned that if the grounds and hooked togther and a 30amp fault occurs on the panel, that the current could run down the 14AWG ground. Or would a fault run simultaneously down both the 10AWG and 14AWG grounds?

Any electrical engineers or electricians care to bite?

Thanks.

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Old 11-30-2012, 04:16 PM   #2
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Don't bother, just run the 240v and split the neutral and one hot leg off to FORM a 120v line in the box. This works, it's "normal", just did it recently so my 240v power box also has a 120v fan plug on it for my vent fan. Works a treat, no more extra extension cords

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Old 11-30-2012, 04:19 PM   #3
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Quote:
Originally Posted by Psych View Post
Don't bother, just run the 240v and split the neutral and one hot leg off to FORM a 120v line in the box. This works, it's "normal", just did it recently so my 240v power box also has a 120v fan plug on it for my vent fan. Works a treat, no more extra extension cords
This will work fine.. You just need to make sure the Amperage is correct size to support both.
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Old 11-30-2012, 04:26 PM   #4
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This will work fine.. You just need to make sure the Amperage is correct size to support both.
Good to keep in mind yes, just because your big fat 240v cable can handle everything you need doesn't mean the 20gauge wire you just put in for your 120v line will handle the 120v device.

Use switches/plugs/wiring rated for more than your anticipated load on the 120v line. Remember, watts divided by volts = amps, add an extra 20% to the amps for safety padding.
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Old 11-30-2012, 04:33 PM   #5
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The issue at hand though is that the 240v plug is only rated for 30amps. I'm bringing in the 120v power source not to have 120v service but to add an additional 15amps to run the second burner.

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Old 11-30-2012, 04:51 PM   #6
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If a line to ground fault occurs, and both ground wires are connected in parallel, the fault current will flow in both grounds. But that's not really an issue; it will likely tend to favor the 10ga because it would theoretically have less impedance than the 14ga.

You wouldn't have a '30amp fault occur' though; a short is going to draw whatever short circuit current is available, and that might be a couple thousand amperes theoretically, until the breaker trips (which should be pretty fast since that will definitely be in the instantaneous/magnetic trip range).

Usually it would be good to put a label on the panel such as 'energized from multiple sources' just as a note to self that unplugging one plug isn't enough.

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Old 11-30-2012, 04:56 PM   #7
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The 240v 30amp service is good enough for Cal's high end setup.
I would keep it simple and design a 240V 4-wire panel, perhaps using internal wiring and components rated for 50 Amp service. Add a secondary 120v panel if/when you decide it is necessary for large batches or back to back batches. Even if you have to alternate between power to HLT and Boil, you will be heating the water twice as fast with 240V 5500 Watts vs a 120V element.

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Old 12-02-2012, 06:30 AM   #8
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You can run the two power sources together into you control panel, yes tie all the equiptment grounding wires together. Don't worry about the size of the smaller ground wire. On a line to ground fault that tiny wire will in reality carry several hundred amps (mind you for a very short amount of time) until the breaker trips. I recommend getting a 3 pole contactor and wiring into your on/off, kill, e-stop, oh s&!t... switch. That way you can turn off the power to your entire system with one switch. You can find 3 pole contactors on ebay just as inexpensive as the 2 pole contactors others are using.

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Old 12-02-2012, 02:14 PM   #9
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I'm sorta thinking that in this scenario all equipment grounding wires are supposed to be sized according to the largest OCP that serves a device. IOW, if you have a 30A breaker feeding one part and a 15A breaker feeding another, all grounding wires would have to be min of 10ga.

I think the reason may be that if we assume a dead short and low enough resistance/impedance to ground to drive high enough fault current to trip the breaker everything from a practical standpoint probably will work out fine. However, what if the ideal situation doesn't occur...that for what ever reason 29 amps of fault current from the 30A system tries to use your 14ga grounding wire from that 15A circuit?

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Old 12-03-2012, 02:32 PM   #10
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While it would be cleaner to simply have one 50A outlet/power cable to power everything, as long as you keep them completely separate and don't hardwire anything into house power I think you'd be fine.

It's not uncommon to see high end powerful home theater amplifiers that come with 2 power cords to meet the rated specs (example). You must of course plug them into separate circuits.

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