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[Stephen Swaffer]

Breakers trip on current flowing through them-so a phase to phase fault will create an overcurrent that tips the breaker.

The reason for the G-N bond is to create a path for current to flow back to the neutral when there is a fault to anything that should not be energized.  So, if staging or a piece of gear can conceivably come into contact with  a phase conductor, either though a failed component or pinched wire, etc it should be connected to ground.  The current then flows through whatever "equipment grounding conductors" it needs to until it gets back to the Ground-Neutral bond where it completes the circuit tripping the breaker.

So, if you draw out the circuit, you will see that the Ground and Neutral wires would need to be bonded at both ends of a "4-core" cable.  As Jonathan pointed out this will function just fine-unless there are other metallic paths (and possibly even wet ground" between the two points.  If that is the case, safety and function will be improved by added a 5th wire dedicated "safety ground" and bonding at one location.   

For the casual reader, note that the "double" G-N bond is a special circumstance due to the OP being located in India and it requires extra diligence.. I doubt any AHJ in the States would allow it-and from a liability standpoint it would not be wise.

[Jonathan Johnson]

Also, in 3phase systems, what happens if 2 live phase cables were to come into direct contact ? Will a 4pole circuit breaker trip ? Or does it rely on current flowing through the phase and Neutral wires only ?

Typically, breakers only monitor and protect the phase conductors. (Only AFCI and GFCI monitor the neutral; neutral and ground are never interrupted/switched.)

With a multipole breaker, an over current condition on any pole will interrupt all poles in the circuit. So a breaker on a 3-phase circuit will disconnect all three phases if one experiences a fault. If a neutral is overloaded, such as might occur with triplen harmonics introduced by switched-mode power supplies, there is no protection for the neutral.

To monitor and protect the neutral would require a multiple breaker that interrupts all phases in the event of a neutral overload, as interrupting only the neutral could result in a voltage imbalance on single phase, single pole (120V) devices.

[Nitin Sidhu]

Typically, breakers only monitor and protect the phase conductors. (Only AFCI and GFCI monitor the neutral; neutral and ground are never interrupted/switched.)

With a multipole breaker, an over current condition on any pole will interrupt all poles in the circuit. So a breaker on a 3-phase circuit will disconnect all three phases if one experiences a fault. If a neutral is overloaded, such as might occur with triplen harmonics introduced by switched-mode power supplies, there is no protection for the neutral.

To monitor and protect the neutral would require a multiple breaker that interrupts all phases in the event of a neutral overload, as interrupting only the neutral could result in a voltage imbalance on single phase, single pole (120V) devices.

Thank you Jonathan! I more or less grasp it.

So what im aiming at is an insolator at the generator terminal, Circuit breakers at the main distro, Over Voltage protection devices after that (to protect against neutral faults), RCBO's at the sub distro's... This all gets very expensive very fast... haha...

A neutral breaking would only cause an overvoltage in a 3phase system, and not a single phase system. If i understand correctly. India is at 440/220v

[Jonathan Johnson]

A neutral breaking would only cause an overvoltage in a 3phase system, and not a single phase system. If i understand correctly. India is at 440/220v

As I was rereading my post, yes, I can see that a broken neutral could cause an overvoltage condition in a 3-phase system.

Differences between North America and the rest of the world...

I don't know enough details about your systems in India. Here in the US, in addition to 3-phase, we also have split single-phase which is installed in every home, office, and factory to serve small portable tools, appliances, and lighting. (Homes never have three-phase; they all have split single-phase. Except for a few oddball install that *someone* is sure to mention. :-) )

In the split single-phase system, the secondary of the transformer is center-tapped, with the center tap going to the grounded neutral. That gives 120V between each "end" of the transformer and the center tap; and 240V between the "ends" of the transformer. In a 120/240V single-phase distro, the loss of a neutral could result in over/undervoltage conditions on the 120V circuits. Small portable tools, appliances, and lighting use 120V, while larger fixed tools and appliances use 240V (unless it's 3-phase in a commercial install).

[Nitin Sidhu]

As I was rereading my post, yes, I can see that a broken neutral could cause an overvoltage condition in a 3-phase system.

Differences between North America and the rest of the world...

I don't know enough details about your systems in India. Here in the US, in addition to 3-phase, we also have split single-phase which is installed in every home, office, and factory to serve small portable tools, appliances, and lighting. (Homes never have three-phase; they all have split single-phase. Except for a few oddball install that *someone* is sure to mention. :-) )

In the split single-phase system, the secondary of the transformer is center-tapped, with the center tap going to the grounded neutral. That gives 120V between each "end" of the transformer and the center tap; and 240V between the "ends" of the transformer. In a 120/240V single-phase distro, the loss of a neutral could result in over/undervoltage conditions on the 120V circuits. Small portable tools, appliances, and lighting use 120V, while larger fixed tools and appliances use 240V (unless it's 3-phase in a commercial install).

Hey Jonathan,

During my first and only visit to the US a few years ago, I discovered that you had both 120v and 240v available at some venues. It kinda freaked me out. Now why would you have that ? Here, its 220/240, single or 3 phase.

I also managed to smoke a JCM900 (120v) head plugged into a 240v receptacle. I think this was at a D.C. club. Wasn't our head or crew,  Bummer....

[Ray Aberle]

During my first and only visit to the US a few years ago, I discovered that you had both 120v and 240v available at some venues. It kinda freaked me out. Now why would you have that ? Here, its 220/240, single or 3 phase.

Sorry, I'm not Jonathan... lol.

So many times for larger rigs, the amp racks have RackPacks of varying kinds; the Furman ACD-100 and the Peavey Distro are both good examples of introductory units that will serve their users well. I don't know for sure about the Peavey Distro, but the Furman can be wired either 1Ø or 3Ø, and accepts a 50A inbound connection. The distro then breaks that down into multiple 20A/120V circuits for amplifiers or whatever.

Larger rigs will use LEx Products or Motion Labs RackPacks; see attached for a JBL VerTec amp rack with a Motion Labs unit. That takes a 30A/3Ø L21-30 input and provides 4-20A breakers, one for each amplifier.

Large venues will usually just have CamLock disconnects.

Small to medium sized venues (the smart ones, who realise that their wall outlets might not be enough, and don't want production providers to have to run extension cords all over tarnation) will have both wall outlets and 1-2 30A to 50A/220V connections- the NEMA 14-50 "Range Plug" being the most common. Then, a provider can use that to power their amps in a much more efficient manner, and if a 20A breaker is tripped, it's local and therefore easy to reset. (Ever try to find a breaker panel at a school? And then find someone with a key to get in that room?!?)

Having both 120V standard 20A outlets for smaller rigs/stage power/backline, and 220V 30A-50A outlets for amps/monitors can make life easier for a production provider.
-Ray

[Jonathan Johnson]

During my first and only visit to the US a few years ago, I discovered that you had both 120v and 240v available at some venues. It kinda freaked me out. Now why would you have that ? Here, its 220/240, single or 3 phase.

Legacy. You see, we invented this thing called "Electricity." Or, at least we like to think we did. In the beginning, Edison created light. (Please pardon my sacrilege!) He decreed that it should be 110V, and that it should be direct current. And he called it good. The disadvantage was that the generator had to produce 110V, and you couldn't push it very far before voltage drop made it worthless. That meant that every neighborhood needed a generator, and out in the country, every farm needed one.

Then along came Westinghouse (AKA "the evil one" if you were to listen to Edison), who touted the benefits of alternating current, chiefly because you could boost the voltage at the generator, send it long distances on wires, step it back down, and use it. Voltage drop became an insignificant factor. But since a light bulb didn't care if it was fed DC or AC, Westinghouse conveniently specified 110V AC. Edison's light bulbs would work just fine on Westinghouse's system. Generating plants could be large and centralized.

It didn't take very long for industry to progress beyond the light bulb. With motors and heating appliances, it was quickly discovered that 220V provided a more cost effective, yet still reasonably safe means of powering things. So we added 220V circuits, which could deliver twice the power across the same size wire. (And eventually, 3-phase and other voltages were developed.) But because we still had a huge installed base of 110V light bulbs and small appliances, we had to devise a system that would support the legacy 110V things. So we came up with the 110/220V split single phase system.

But since it isn't easy to dump that installed base ("I have 110V outlets, why do I have to buy a 220V toaster and rewire my house?") we've got so many "standards."

As someone once told me, "the nice thing about standards is that there are so many to choose from."

"But wait," you say, "why are you talking about 110/220V when it's supposed to be 120/240V?" That's because I was talking about the old days and over the years, the nominal voltage has gradually increased from 110V to 115V to 117V to 120V to 125V (and, correspondingly, 220V to 230V to 240V to 250V. No idea what happened to 234V.). [Not to mention the "130V long life" light bulbs you used to be able to buy.] Current NEMA standards specify 125 and 250V for wiring devices. Utilities generally aim to deliver 120/240V at the service entrance, though anything between 110-125/220-250V is considered to be within acceptable range. So anything within that voltage range is considered to be nominally the same voltage.

(Interestingly, the 208V found on three-phase wiring seems to always have been called 208V. But then I haven't done much historical research on three-phase voltages in North America.)

[Mark Cadwallader]

(Deleted. I did not recall correctly. My apologies.) Mark C.

[Nitin Sidhu]

Hello All!

Attached along is a simple diagram of our main 3-phase distro. A couple of questions.

>Does the neutral-ground bond have to be before the TPN or After the TPN ? Im confused considering that a TPN does not have protection on the Neutral pole, only isolation i think.

>Is it correct to use a TPN (three phase + neutral) MCB in this circuit, or should we be using a 4-pole MCB ?


To rephrase the thread, as we are only supplied a 4 core cable from the DG, we have to bond ground at our distro.

Thank you all for your time.

[Steve M Smith]

Legacy. You see, we invented this thing called "Electricity." Or, at least we like to think we did.

Silly Americans... thinking they invented the world!!

Luigi Galvani and Alessandro Volta (Italian) put in most of the ground work, André-Marie Ampère (French) worked on electro-magnetism, Michael Faraday (English) invented the electric motor and worked on induction used to generate power.

Of course, Nikola Tesla (Serbian) showed the rest of the world what we should do with it.

As for Edison... http://theoatmeal.com/comics/tesla


Steve.

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