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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => AC Power and Grounding => Topic started by: Kevin Smith on May 01, 2014, 02:46:38 PM
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For running power for my live rig, I have a range/stove plug (220V 50a) wired into a power distro which has 6x 20a breakers (110v). How does this work? How can I have 6 20a breakers which would run 120a from my 50a range outlet?
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For running power for my live rig, I have a range/stove plug (220V 50a) wired into a power distro which has 6x 20a breakers (110v). How does this work? How can I have 6 20a breakers which would run 120a from my 50a range outlet?
Qratt, you need to go back to your profile and enter your full name for this forum. Then we'll be able to help you.
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Qratt, you need to go back to your profile and enter your full name for this forum. Then we'll be able to help you.
Updated.
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For running power for my live rig, I have a range/stove plug (220V 50a) wired into a power distro which has 6x 20a breakers (110v). How does this work? How can I have 6 20a breakers which would run 120a from my 50a range outlet?
The assumption is that you won't be using all 20 amps on all circuits at the same time. If for some reason you do (which would be pretty tough unless you're running lighting loads right to the edge), no issues, as the receptacle you are plugging your distro into has a breaker that will trip at the appropriate value.
The term for this is over-subscription. If you look in your house breaker panel, you will see the same thing. If you have a 100A main breaker, you will likely have many more than 10 20A breakers. My house has a 200A service, and between two panels, I have about 60 breakers.
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For running power for my live rig, I have a range/stove plug (220V 50a) wired into a power distro which has 6x 20a breakers (110v). How does this work? How can I have 6 20a breakers which would run 120a from my 50a range outlet?
You actually have 100A total capacity (not 120, the sum of the breakers) at 120V on a 50A 240V circuit. This is because a 240V circuit is actually two 120V circuits comprised of two hot legs and a neutral. Between each hot leg and neutral it is 120V; between the two hot legs it is 240V. At no time can more than 50A of current flow on either of the two hot legs because it is limited by the upstream breaker in the service panel. However, you can have 50A at 120V flowing on one hot leg, while you have 50A 120V flowing on the other hot leg, to give a total of 100A at 120V.
Now you may be thinking, "does that mean that 100A is flowing on the neutral wire?" No. A 240V circuit is a kind of balanced circuit (by means of analogy, like a balanced audio cable). That means that under ideal conditions, the load and therefore the current flow on the two hot legs is balanced, and no current flows on the neutral. The neutral wire only carries the difference between the two hot legs.
If you open up your distro, you will notice that three of the breakers connect to one hot leg, and three connect to the other hot leg. Three 20A breakers sums to 60A, but you will be limited to 50A for each bank of breakers connected to each leg. It is considered good practice to try and distribute your loads on your distro in such a way that the loads on the hot legs will be balanced as much as possible so as to reduce the currents in the neutral. By balancing your loads, you maximize the available power not only from your distro, but also from the electrical distribution system in the facility. If you are way out of balance, you can end up tripping a main breaker if the facility's other electrical loads bring the electrical system near capacity. And that will ruin not only your day, but also for every other person in that facility that is using electrical power.
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Now you may be thinking, "does that mean that 100A is flowing on the neutral wire?" No. A 240V circuit is a kind of balanced circuit (by means of analogy, like a balanced audio cable). That means that under ideal conditions, the load and therefore the current flow on the two hot legs is balanced, and no current flows on the neutral. The neutral wire only carries the difference between the two hot legs.
This is and is not true. It depends. If your loads are purely resistive (conventional lighting) and you are using two out of phase hots from a single phase source, then yes the neutral currents will cancel.
If your load has a reactive component, commonly found in switch mode power supplies in amps, or you are using 2 legs of a 3 phase system. Your neutral currents will not cancel and could even add.
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This is and is not true. It depends. If your loads are purely resistive (conventional lighting) and you are using two out of phase hots from a single phase source, then yes the neutral currents will cancel.
If your load has a reactive component, commonly found in switch mode power supplies in amps, or you are using 2 legs of a 3 phase system. Your neutral currents will not cancel and could even add.
The OP was specifically concerned with single-phase. And considering the question, adding considerations of reactance, power factor, and multiphase systems may be too much information to digest at once.
Presently the NEC does not permit interrupting devices in the neutral line. (Well, it might permit a common-trip breaker that interrupts both the neutral and hot simultaneously, but I don't remember for sure.) However, considering the proliferation of switched-mode power supplies in consumer and professional electronics, it may be time to begin implementing common-trip breakers that protect both legs and the neutral of multiphase and split phase circuits.
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The OP was specifically concerned with single-phase. And considering the question, adding considerations of reactance, power factor, and multiphase systems may be too much information to digest at once.
Actually the op has a single/split phase distro. There is no garuntee he doesn't go to a facility with 3 phase power that simply has a 2 pole breaker to provide for his distro. I think a discussion of three phase power with a single phase distro is valid and good information for the OP to have.
Resistive/reactive may be a bit much, but sometimes it's enough for someone to simply have an awareness that there is more going on than they understand...
Regardless, I'm not trying to be a dick about it, I just think it's important information for the OP to know.
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The OP was specifically concerned with single-phase. And considering the question, adding considerations of reactance, power factor, and multiphase systems may be too much information to digest at once.
Presently the NEC does not permit interrupting devices in the neutral line. (Well, it might permit a common-trip breaker that interrupts both the neutral and hot simultaneously, but I don't remember for sure.) However, considering the proliferation of switched-mode power supplies in consumer and professional electronics, it may be time to begin implementing common-trip breakers that protect both legs and the neutral of multiphase and split phase circuits.
Yep,
There are switched neutral breakers that have a neutral pigtail and load neutral terminal on a 'side-car' that uses another pole space but does not connect to the power buss. Normally I only see requests for gas stations (required for the pump circuit in the dispensers).
Jeff Robinson
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Yep,
There are switched neutral breakers that have a neutral pigtail and load neutral terminal on a 'side-car' that uses another pole space but does not connect to the power buss. Normally I only see requests for gas stations (required for the pump circuit in the dispensers).
Jeff Robinson
Would this also be true for the Generators ? 2 phase or 3 phase? Better protection of the amp switch mode power supply on generator.
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I would recommend picking up this book: http://www.amazon.com/Wiring-Simplified-Based-National-Electrical/dp/0971977976 (http://www.amazon.com/Wiring-Simplified-Based-National-Electrical/dp/0971977976),
and reading it. It is good basic, fairly comprehensive, easy to understand book. Even though it is not directly geared to temporary/entertainment power distribution, it will give you a good basic understanding of electrical wiring that I feel anyone who turns on a light switch should have.
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Breakers and ELCB/GFCIs that cut both the live and neutral line are mandatory for construction site wiring in Australia. The "shows and carnivals" electrical standard lags behind a bit, but using products that comply with the construction standards is an easy way to get IP44 or IP66 ratings for outdoor use too. The downside is nobody makes this type of gear in black.
Cutting both live and neutral makes sense in environments where live and neutral might be swapped somewhere.
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Breakers and ELCB/GFCIs that cut both the live and neutral line are mandatory for construction site wiring in Australia. The "shows and carnivals" electrical standard lags behind a bit, but using products that comply with the construction standards is an easy way to get IP44 or IP66 ratings for outdoor use too. The downside is nobody makes this type of gear in black.
Cutting both live and neutral makes sense in environments where live and neutral might be swapped somewhere.
Multiple sources for CEEform plugs in black, also distribution gear. http://www.showtechnix.co.nz/3-phase-connectors-1/ , the Midnight series is all black. Cheers