Tie Breaker MCCB

LOL... well said!

Possibly, but it depends on the application and system, and not by itself.

Thank you for your reply.

The application is the following:

I have a building that needs to be supplied with Low voltage partial emergency generator backup.

I should install a 320AT circuit breaker and tie the bus that is fed by the low voltage "normal" side to the bus bar that is fed by the low voltage "emergency" side. Can this tie breaker be a Molded Case circuit breaker (MCCB)? Noting that the short circuit value that we calculated doesn't exceed the short circuit current to be handled by the MCCB...

Now why didn't you post this information in the first place?

You would have saved yourself a lot of abuse.

Haven't you noticed that when Anonymous Poster #1 asks a short, incomplete question, he only gets picked on and called silly names?

Remember, details help to produce answers, incomplete questions only produce more questions, Anonymous questions produce sarcasm.

Should be ok as long as the MCCB normal and short circuit currents aren't exceeded and you don't mind an outage while you manually operate the MCCB to switch supply sources.

HOWEVER a few things to note. The MCCB is still only a small part of a larger transfer switch control system, you will have to consult your local electrical codes and standards which should offer more guidance on what is required and isn't allowed. For example.

http://en.wikipedia.org/wiki/Transfer_switch

It would be best if you talked with a qualified electrician and/or contacted a local company that can offer you a complete source transfer solution product. It may even be cheaper than trying to do it yourself, and remember - an improperly designed or installed transfer switch may void your building insurance.

How much current will each horse experience at the finish line?

Actually, in all honesty, you should actually deal with an electrical engineer, and pay the man his worth for his time. To simply say it is OK, to "plug and play" electrical components in special applications they were not specifically designed for, is usually asking for trouble, or proving that all electricity is made of sparks and smoke, as in all instances of big failures, one either lets the sparks out, or the smoke out, or both.

Why MCCB isn't supposed to be used as tie breaker? It's not a plug and play issue but I am seeking to know the technical issue behind this. If it's technically feasible or not, I need please the technical valid reason.

Thank you

It's technically feasible to travel to the Moon in a washing machine. The question one must ask is, "why, if there are enough satisfactory solutions for this particular application, would one choose something that has not been tried?".

What you have is the situation where you want the electrical panel equivalent of a NOR (not or), or a NAND (NOT AND) circuit. What you want is to isolate your standby generator from the grid, and still supply your local building needs, and also to isolate the grid supply from the standby generator (so that it is not motorized???), and to have both these active at the same time is tantamount to a fire soon breaking out, since you have no way of guaranteeing that the grid supply and the generator supply are phased in lock. They only way your idea could ever possibly work (and I doubt it even then), would be to have your building on DC power, rectify the AC from the grid, use a DC breaker on this, with a relay to open this breaker on loss of upstream DC (you will need to include a diode reverse biased from the breaker back to the DC rectifier, with a resistor off the upstream side of the diode to assist the reverse-bias potential to remain stable.). Then also, you standby generator will have to be converted to DC as well, once this is done the remaining requirement is voltage regulation to match each supply side, but you still should utilize loss of voltage relay with breaker to open circuit, and prevent any overheating that could result in fire.

As I have told you once already, electricity is composed of smoke, sparks, and also fire. You do not want to release any of these sub-particles of electricity.

Yeah, I was looking at a similar problem with a unit that was going to 'leach power' from it's neighbor in the control chain. The power is 24VDC, each 'powered' unit supplies its own 24VDC upstream and downstream to 'read' the control bits of its neighbors (control bits are dry contacts), power feeds do not mix, Supply A and Supply B never energize the same power bus. The 'Leeching unit' could be hooked up to a 'powered' unit on the upstream, the downstream, both, or it could be working in standalone mode, not hooked up to anything. The 'leeching unit' has its own 120VAC supply, but no 24VDC supply, the 24VDC is used only to run control relays that pass on the control bit information.

By solution there, was to have a pair of DPDT relays, when energized they would connect the upstream 24DVC to the internal power, when de-energized they would connect the downstream 24vdc to the internal bus, the relays were energized by the upstream power feed. Changes to the power connections were not expected while the equipment was running, and any such changes were likely die to a fault in the machinery.

If memory serves, Tie-Breakers also work like this: acting as a switch, connecting power to the Primary Feed as long as the Primary is good, switching to the Secondary feed if the Primary fails. Trying to build a 'low cost' mock-up for high power systems is an exercise in madness and legal liabilities.

I only hope we either solved this guy's homework for him, or convinced him to not committ career hari kari this way.

Then again, if he's from one of the areas that have a strong belief in reincarnation, they may not take safety too seriously, since the worst that can happen, in their opinion is "Whoops, time to get a new body."

(With sincere and humble apologies to those offended by my light take on Hinduism. However, if you look at my posts, you will see that I treat ALL religions lightly, even the one that I was raised in. I personally believe that any and all deities worth the title are strong enough to shrug off whatever foolishness that comes out of my mouth. I would tend to question the strength of faith of someone who believes that their god (or their interpretation of god) is so weak that I, a mere mortal, could hurt the Divine Being with mere mockery. I'm an imperfect mortal, and I can take (and make) jokes at my own expense, how could I do something that a Perfect Being could not?)

Adreasler: careful, my friend. It might not be the compassionate deity you should be concerned with, but the always and already ticked off followers of said deity. But even then, do not be afraid. The Alpha and Omega has the keys of life and death in his hand, and he rests for now seated at the right hand of the Eternal One.

I think the Hindi are far more forgiving than others, so you are most likely in the clear.

Back on the subject: IMHO there is nothing more dangerous than a desperate engineer (or wanna be engineer), who is expected to produce a "rabbit in a hat" type result, right now, or 30 minutes ago, with very little materials, parts, or choices to go on.

As far as making people angry with me, I seem to have polished that to a fine edge, a perfectly smooth sphere of influence, or an axe to rival that of Paul Bunyan's. I have a knack for getting under the hides of people with opposing opinions, viewpoints, or agendas. Then I burrow down, until they are rabid with hate, foaming at the mouth, dancing around from side-to-side like a mangy dog, etc., etc. I just can't help myself. I should be the next U.S. Ambassador to the U.N. (except I hate what the U.N. has become so much I would take a dump in the middle of the floor), even putting John Bolton to shame (as if that could ever be possible, as he is indeed a Great One). I would be so bad, I would make Nikita Sergeyevich Khrushchev's "shoe pounding" incident look very mild by comparison. You almost have to admire men like Nikita Sergeyevich Khrushchev, because at least with him, you pretty much knew what you have in front of you, and he was at least predictable in that regard. some of the other things about him, I obviously do not approve of, including his complicity with the Stalin purges in the Ukraine before Germany invaded under Hitler. (oops there goes the thread).

Advice to the anonmymous poster: It is most likely well boding for you that you remain anonymous, because you are most definitely playing with co-worker's safety. Safety always must come first, as there will be no product, or production, when there is nothing and no one left there to produce it.