Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

When do I use a 4 pole breaker or disconnect?

When do I use a 4 pole breaker or disconnect?

When do I use a 4 pole breaker or disconnect?

I am trying to find documentation that talks about when to use a 4 pole circuit breaker.  Is there a source that specifies the countries that still use a 5 wire power system(i.e.  3 phases, N, PE) that switches the neutral?

I would appreciate any help in this matter.

RE: When do I use a 4 pole breaker or disconnect?

Yes, its a practice here to use 4pole breakers at service provider incoming.

RE: When do I use a 4 pole breaker or disconnect?

Power distribution with neutral conductors in TT requires the use of 5 Pole Earth Leakage Circuit Breakers on final DB's.

RE: When do I use a 4 pole breaker or disconnect?

I don’t know any code or standard that recognizes more than 3 pole circuit breaker in the USA. However, in the IEC marketplace it is very common to use of 4-pole circuit breaker mainly used to isolate the neutral during ground fault event.

Earth leakage circuit breakers can be used in TN-S, TN-C, TT and IT network systems or with others words in all places where neutral and protective conductor are separated (See Earthing Classification below).

The enclose catalog and the thread for additional detail for multipole circuit breakers.



Erathing System Classification:
The first letter indicates the type of supply earthing.
T  - indicates that one or more points of the Supply are directly earthed (for example, the earthed neutral at the transformer).
I - indicates either that the supply system is not earthed at all, or that the earthing includes a deliberately-inserted impedance, the purpose of which is to limit fault current. This method is not used for public supplies in the UK.

The second letter indicates the earthing arrangement in the installation.
T - all exposed conductive metalwork is connected directly to earth.
N - all exposed conductive metalwork is connected directly to an earthed supply conductor provided by the Electricity Supply Company.

The third and fourth letters indicate the arrangement of the earthed supply conductor system.
S - neutral and earth conductor systems are quite separate.
C - neutral and earth are combined into a single conductor.

RE: When do I use a 4 pole breaker or disconnect?

cuky - 4-pole breakers are recognized in the US, but not often required.  One notable exception is where multiple 4-wire generators back up multiple 4-wire service entrances; 4-pole breakers or transfer switches are often required in such installations depending on exact configuration and conductor length between sources.

RE: When do I use a 4 pole breaker or disconnect?

A 4-pole breaker or disconnect is required for 3-phase ungrounded systems in Europe where they are allowed to have a neutral conductor. A neutral conductor is not allowed in the U.S., therefore, there would not be a reason for using a 4-pole breaker.
The 4th pole is necessary when using a neutral in an ungrounded system. This is necessary since a single phase-to-ground fault will cause the neutral to rise to, say, 277V in a 480V system. Without the 4th pole, this becomes a real safety issue!

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close