MPCB, MCCB and Optical Fiber

1. The need for BOTH an MPCB and an MCCB is suspect to begin with, indicating that maybe you are in over your head.
2. If for some unknown reason your MPCB requires further protection by an MCCB, it would probably be UP STREAM, not down stream of the MPCB.
3. "Optical fiber" (fiber optics) just describes the medium, but what is the network? Or is there even a network involved? If not, what do you want to transmit via fiber optic cable, and why?
   

ABB have a nice range (and likely application notes to go with them). I haven't used them personally thou.

Try their website for more information.

The OP's question is not clear.

If you use a MCCB with a motor protection release (but make sure it is phase unbalance sensitive as it is not always the case even if there's a short-circuit and motor overload protection function, it depends on the used trip unit) there is no need for a further downstream protection (you may just need a safety switch in some cases unless you handle the safety disconnection indirectly in which case very specific rules, which are often not followed strictly, apply).

But depending on the MCCB rating you'll need a backup protection (or a fully selective protection in some cases) upstream for economical reasons (i.e. you can get a 200 kA rated breaker for a very small motor but it will be less expensive to opt for multistage backup scheme, the tradeoff being a less perfect selectivity).

Don't know why you want optical fiber. Do you only need contact signals or do you want to communicate with electronic releases? Those communication accessories are very expensive.

And BTW even for advanced electrically controlled zone selectivity schemes between several LV breakers you don't need fiber links, shielded twisted pairs are sufficient (i.e. systems where a breaker send a locking signal to another breaker to ensure selective tripping). That said I'm not sure that such complex protection schemes are a good idea in LV as there's an increased risk or wiring and commissioning error.

(I'm always referring to the IEC/EN pratice, I don't know the North American practice well where I believe that fuses are still required in some cases, while in Europe you can design fully fuseless if you want, with the notable exception of semiconductor protection.)

Hi,

We will have 18 such 8 kW motors. I want to have remote controlling through control building situated at nearly 25 metres from the nearest ones. Some sort of central monitoring computer shall also be kept. (Kind of Scada, and PLCs shall also be used).

But control through local control panel should also be possible.

Hopefully, DoL starting shall be used, giving 1 minute after every successive start so as to give time to subside for surge currents. I intend to start one by one, ie not 2 or 3 motors in a sequence. I intend to keep local starting panels near to the load. But is it possible? Or shall I keep local starting panel at the control building only?

I was of the opinion that only electronics (ie) remote controlling panel shall be kept near to the load forming what is called local control unit in Scada architecture.

Regs,

1. You do not need both MPCB and MCCB. One will do. Maybe even fuses (see below)

2. There has to be a starter, you say DOL. This consists of a Contactor (which is meant for motor switching, that too millions of times) and an overload relay, which can be thermal bimetallic or electronic. Since you want SCADA and local control, you can use an electronic relay with all necessary protection features, and with communication facilty for SCADA. If you do this, you do not need an MCCB upstream with electronic release. Short-circuit protection can even be a set of fuses.

sorry friends, we have to adhere to IEC norms as far as possible. If IEC norms are not available, then next relevant norms.

Regs,

IEC? Of course whatever i have said conforms to IEC. Whay do say that it is not? i am curious to know.

Er, i normally do not respond to Anonymous Posters, this is an exception.

(i posted this a while ago, but it has disappeared ! So, posting again)

Don't you have any designers there, Mildred? You know, someone who knows how to do electrical design? You could hire someone to do it. You would then absolve any liability for its not being right because you're going to screw up doing it on your own, by all indications.

I've some doubts about the competence of the anonymous OP.

To switch remotely on/off a small motor you only need what's called a "manual motor starter" and a contactor. The manual motor starter is indeed a motor protection circuit breaker which provides short-circuit and overload protection and also allows manual on/off switching if required, very often it's not used to switch on/off the motor manually but simply protects it. The contactor can be mounted just below, usually for small powers there are accessories which allow you a direct assembly so there are no additional wires required. The are also compact assemblies of motor protection circuit breaker and contactor.

For any remote-controlled motor I'd highly recommend to install a safety switch next to each motor which switches all phases directly regardless of the power of the motor (ideally even with medium voltage but in most cases it's not done for larger motors), that one, if not required to be used as emergency off switch (red/yellow, only lockable in OFF position), can be lockable both in ON and OFF position (must NOT be red/yellow, will typically be black/grey).

Personally I always design fuseless unless the client or local rules require fuses, or if it's about semiconductor protection for power electronics (which still requires expensive special fuses).

If someone has a good knowledge of the IEC practice there's no need to read the standards, even a very old obsolete German VDE 0113 (on which en EN 60204 was based) together with experience and common sense will be mostly sufficient (but you can get the latest EN 61439 series if you've time and money to waste). Unless you manufacture devices you don't really have to read the EN papercrap in detail. I've designed quite large complex systems and didn't have to read much of the standards as for most details you've company internal practice rules which are typically more stringent that the standards and other legal requirements. If your design is based on typicals a relatively small collections of diagrams is required for power switching circuits (see also how MCCs are engineered, here I mean the full-fledged draw-out types).

BTW Some computation requirements of EN 61439 are pure crap and represent just a waste of time. Maybe it has been made for idiots who have no idea about switchgear design but I don't see any reason to waste time with useless computations just to mathematically prove something you already know that it will meet all requirements. Just more paper for the bureaucrats, which increases costs and reduces our competitivity.

But if I use an optical fiber, I am not sure, which network to use as specified by JRaef.

Things are confined to 500 metres area. Local area networking should be used, as there is no need to use wide area networking.

Regs,

Please read again JRae's reply above. You didn't explain why you want to use optical fiber.

For 500 m and normal conditions you can use copper pairs (if required together with surge protectors and optocoupling) or optical fiber, in latter case you can use electrical <-> optical fiber converters for fieldbuses or transmit through Ethernet. There are lots of options burt once more, as we don't know exactly what you want really to do it's impossible to give you very useful advice.