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3 Pole vs 4 Pole Circuit Breaker Usage

3 Pole vs 4 Pole Circuit Breaker Usage

3 Pole vs 4 Pole Circuit Breaker Usage

(OP)
Hi Mates,

kindly illustrate the difference between 3 pole circuit breakers with 4 pole.

one quite significant difference i aware is on the price between 3pole  vs 4 pole based on same rating.Because 3pole cheaper, so we always facing recommendation to use 3 pole rather than 4 pole.

Therefore need your help to understand more on the difference in application between 3 pole with 4 pole.

thanks.

RE: 3 Pole vs 4 Pole Circuit Breaker Usage

Use 4-pole when you need to open the neutral along with the three phases. Application is usually based on local electrical code requirements and/or system grounding and protection design.

RE: 3 Pole vs 4 Pole Circuit Breaker Usage

4 pole seems to be an IEC thing.  I have never found myself looking for a four pole breaker.  If readily available and not much more expense than a 3 pole breaker they could have simplified a few grounding schemes over the years, but given the base cost of a 2000A or larger low voltage power breaker (or any medium voltage breaker) a premium of only 33% for the fourth pole for three or four breakers means it is less expensive to arrange the system such that all required neutral-ground bonds happen at the same location.  4 pole breakers would seem to be effective if they could be had for less than a 5% premium and I doubt that will ever happen.

RE: 3 Pole vs 4 Pole Circuit Breaker Usage

They are needed in TN-S systems, where all current-carrying lines (that includes the Neutral) need to be switched. In such systems, it is not a question of a certain cost limit if they shall be used or not.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: 3 Pole vs 4 Pole Circuit Breaker Usage

(OP)
Thanks guys.

But Skogsgurra, why is TN-S systems must switch the neutral pole at the same time? Kindly elaborate more on the technical side?

RE: 3 Pole vs 4 Pole Circuit Breaker Usage

There are several reasons.

One is that the N conductor often has a smaller area than the L1-L3 conductors and that means that the N conductor can be overloaded if it is not protected and can be opened in case of an overload.

Another reason is that the N conductor usually has some residual voltage on it. If you want to make sure that an installation is completely "dead" (=no potential at all), then you need to break also the N conductor. This is often the case in hospitals.

This Schneider link has more information. http://www.schneider-electric.com.my/selink/my/Schinternetnew.nsf/($All)/B2F87BB8059DB9D248256F860022B379/$file/Schneider_Tech_Vol04.pdf

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: 3 Pole vs 4 Pole Circuit Breaker Usage

Gunnar, what is a TN-S system?  If what is shown in figures 9 and 10 of your referenced Schneider paper is an example of a TN-S system, it looks dangerously improperly grounded, violating the basic requirement that systems be grounded exactly once.  With both source breakers closed all of the problems of multiple grounds are present and it is only after one breaker opens, opening the neutral and reducing the number of neutral grounds to one that the ground relaying could accurately determine what is going on and where the fault might be.  Looks to me like there are better ways of designing the system than what is shown in those two figures.

RE: 3 Pole vs 4 Pole Circuit Breaker Usage

Hi David.
TN-S system, that mean : Neutral conductor (N) and protective conductor (PE) are separated.
BTW, additional systems:
TN-C : N and PE are combinated , now is PEN.
TN-C-S, you have combination of both of system
And, what I remambare: N-is blue color and PE is yellow/green color. And additional systems are TT and IT ( isolated system or HI sytems)
Regards.
Slava

RE: 3 Pole vs 4 Pole Circuit Breaker Usage

I'm also understand, whay you ask about Fig9 and Fig10,
it's some very schematic drw. I try found my old papers with "better" drw.
Regards.
Slava

RE: 3 Pole vs 4 Pole Circuit Breaker Usage

The neutral would be switched if there is considerable
amount of Triplen Harmonics. This would be a result from
a Delta-Wye transformer connection. The triplens are not
cansuled in the neutral as other currents,but they add
as much as 1.73 X phase current. Single phase computer
systems are well known for this (non-linear loads).

RE: 3 Pole vs 4 Pole Circuit Breaker Usage

davidbeach,

There is more to grounding than you think. What is the ultimate truth in the US may not be the truth in Europe. And, without being overly partial, I dare say that we have analysed these problems a lot more thoroughly than you have on your side of the pool. Read and learn!

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: 3 Pole vs 4 Pole Circuit Breaker Usage

Sorry to be a little rude, davidbeach. But it is really as I say. I looked at the Mike Holt site. He is 100 % American, I would say. And this pdf says a lot:  http://www.mikeholt.com/files/PDF/ect172.pdf  A lot of information there.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: 3 Pole vs 4 Pole Circuit Breaker Usage

Gunnar,

I hope you are hiding in a bunker!

Slava,

Thanks for that IEE download. I have seen it but lost my copy. - I want to send it to a few guys at work.
 

----------------------------------
  
If we learn from our mistakes I'm getting a great education!

RE: 3 Pole vs 4 Pole Circuit Breaker Usage

No Scotty! I have nothing to hide.  smile

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: 3 Pole vs 4 Pole Circuit Breaker Usage

Gunnar, I know the IEC world does things differently, some of which seem pretty strange.  I'm not sure how if >6mA is considered lethal here it would take 30mA there to become a hazard; I sure someone can provide all sorts of studies to support both numbers.

I'm not convinced that switching neutrals is a viable means of getting around the problems created by having two neutral-ground bonds when one is trying to detect ground faults using a residual connection.

I don't know which side of the pond may have done the most research on the topic, but regardless both sides of the pond seem to be comfortable with what they do and rather uncomfortable some of the practices on the other side of the pond.

In the example of the figures cited, I would leave the wye points ungrounded and bring in four wires, landing the neutral on the switchgear neutral bus and then forming a single neutral-ground bond in the gear.  That way there is only one return path for ground faults and they can be readily detected and cleared.

But if you are satisfied with the safety and efficacy of the protection for your system designs then I won't argue with you.

RE: 3 Pole vs 4 Pole Circuit Breaker Usage

Yes, what you are not used to does always seem strange. But strange doesn't mean wrong. There are horror stories about your open delta, sometimes corner grounded, being told in Europe. And I am sure there are similar stories being told over there about our seemingly silly "two grounds".

The big conceptual problem seems to be that we make a very definitive difference between Neutral and Ground in TN-S installations. During my visit this October to some drive installations in Elizabeth, NJ, I was told by the foreman that everything had been done wrong in those cranes. Mainly because of the way the Neutral and Ground were connected and used.

It takes some exposure to a system to fully understand it. The TN-S system is not just another way of doing it. It is a way of keeping installations safe in a lot of fault situations. But, surely, it can be a can of worms for those that are not used to think "outside the NEC".

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: 3 Pole vs 4 Pole Circuit Breaker Usage

I'm in favour of four pole breakers in circumstances where multiple sources can feed one load, e.g. in a source transfer arrangement, especially where the transformers are physically separated. Earthing around source transfer systems gets much more complicated if there are multiple sources which can operate in parallel.

As David alluded to, residual connected earth fault detection becomes unpredictable with multiple neutral-earth bonds, but multiple neutral-earth bonds are not permitted under UK regulations except in a PME installation. PME installations are explicitly prohibited in the UK except for utility distribution systems so for most people the problem of multiple neutral earthing does not arise if a four-pole breaker is used to open the neutral when disconnecting the source, thus removing the neutral-earth bond at the origin of that supply. A three pole breaker would leave an additional neutral-earth bond connected which would potentially upset any residually connected earth fault detection relay such as those commonly fitted within ACBs, in addition to being a code violation. I guess the US solution would be to use an isolation transformer for each supply and locally earth the transformer secondary neutral point on the switchgear?
 

----------------------------------
  
If we learn from our mistakes I'm getting a great education!

RE: 3 Pole vs 4 Pole Circuit Breaker Usage

I agree with Scotty. Isolation (service)transformers with sec neutral grounded solves the "one-ground at source" code stipulation.
David, in his post could have been wary of correcting problems related with too many ground paths for residual-connected earth fault protections!

Also, newer systems configurations on the other side of the pond require newer electrical protection equipment! Makes millions!

I prefer more simple and cheaper systems!

RE: 3 Pole vs 4 Pole Circuit Breaker Usage

Hi.
What is system in US, like to TT?
Regards.
Slava

RE: 3 Pole vs 4 Pole Circuit Breaker Usage

The usual system in the US is TN-C-S.  The utility service has a combined neutral/ground conductor that is grounded at the utility transformer secondary and at the service disconnect.  From the service, there is a protective ground (equipment ground in NEC terms) run along with the phase conductors.  If there is phase-to-ground connected load, there is a separate neutral (grounded conductor in NEC terms) that is not grounded except at the service disconnect.

If there is another ground source, such as a delta-wye transformer or a generator, it is a "separately derived source" and it's neutral is grounded at the source.  NEC prohibits grounding the neutral at more than one point in each separately derived system.  If you have two separately derives sources connected to a transfer switch, then you need a four-pole transfer switch to switch the neutral so that it is only grounded at one point in each separately derived system.  If there are breakers connecting two separately derived system, then they need to be four-pole breakers for the same reason.

This doesn't seem too different from what the common European practice is, based on references in previous posts.

You can have a generator connected to a three-pole transfer switch, but the neutral cannot be grounded both at the generator and at the service disconnect.  The problem with this is that if the neutral is grounded only at the service and the system is running on the generator, ground fault current would have to flow through the protective ground to the service and then flow through the neutral to the generator source.  This increases the impedance and can increase fault clearing times.

RE: 3 Pole vs 4 Pole Circuit Breaker Usage

And so in an uncharacteristically "catty" discussion we unequivocally determine that there certainly are applications where using a 4-pole breaker to disconnect what the US "NEC" officially calls "the grounded conductor" is appropriate.

Where is the installation to be?  What with pond-sides and all, that may well be the dominant factor.  Right guys?!  A 4-pole breaker may be used in other instances where 4 phase conductors are to be disconnected simultaneously.

Thanks to some of our regular contributors for continuing to share some of their expertise and insights (and links!!!) with us.  (bunkers notwithstanding)  
smile

I know I've learned a bit from this thread!

RE: 3 Pole vs 4 Pole Circuit Breaker Usage

TN-C-S and TN-S is not so big difference.
More or les both of systems have same advantages and disadvantages.
We use both of system, but deciding is case by case.
Regards.
Slava

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