3-Phase 4-Wires System

Many many thanks North60. That was a fantastic answer which cleared most of my doubt. As 4 wires are referring to the live three phases +neutral (i.e. The ground does not count), I understood from your answer that the fourth wire (neutral) shall be extended to the entery equupment and grounded somoeewhere there if the loads are 4 wires ( i.e the nwutral bus bar is not provided inside the switchgear). Kr Am I right? Shall I use the ground bus, provided inside the busway,for extending the forth conductor inside the switchgear? Deeply appreciating your answer. Mark

You need to understand how the switchgear you have is configured. If it is 3p 4w switchgear, you should have 3 busbars for the phases and a neutral bus and you may also have a bonding bus.

Evaluate the switchgear you have to see if it is suitable for your use under the codes and standards in effect in your jurisdiction and then proceed as required by those documents.

As I can not "see" the switchgear from here, it would be reckless on my part to say "yes" or "no" to what you are asking.

You may want to get someone to do this for you if you cannot do so yourself.

We always run an Equipment Grounding Conductor (EGC) from the switchgear to the load, along with the Load Conductors. (I have encountered SO many damaged or loose conduits and EMT).

This EGC may or may not be required to be bonded to neutral in the main switchgear. However, such bonding is a Most common practice, and is the default unless the electrical engineer has compelling reasons.

If the load is designed to not use a neutral load conductor (delta-configured), it may be possible to omit neutral on the branch circuit, but first check your local Code requirements. Finally, consider whether the load may be replaced at a later date with one that does require neutral.

Correction, as North of Sixty said, you may omit neutral on feeders and branch circuits that do not have neutral load currents. And I emphasize his other point: there are great advantages to bonding the source's neutral conductor to Equipment Ground, even though no load uses neutral.

Measure your voltages. If the 4 wire system is 3 phases + neutral (Y), you should have the same voltage reading between each of the three phases and the neutral. The phase to phase voltage should be 1.732 times the phase to neutral voltage.

If the fourth wire is a centertap between two phases, the voltage between it and these two phases would be 1/2 the phase-to-phase voltage. The voltage to the remaining phase would be about 1.07 times the phase-to-phase voltage.

Excellent answer.

I'm surprised, considering where your location is, that you've seen 3 phase voltages. Isn't that single phase only territory up there?

Is that 600V way up there like the areas south of you? I'm designing/building a control system for that part of Canada, and have found some major companies rate their equipment to 600V but only test it to 480V. Had to change some of my stocked components to a different brand.

Please tell me you are joking...

Of course I'm joking.

However, not about the 600V AC. You got that way up there? That makes life difficult for 480VAC panel designers/builders when you realize your stock products are only recommended for 480VAC service.

Phew... you had me worried.

Most 3 phase installations here are 208Y/120 volt installations. Some of our new larger buildings do have 600Y/347 volt systems in them or in the process of being installed, such as a few of the larger schools, Qikitanni General Hospital, new airport, new Iqaluit Aquatic Center and new Canadian High Arctic Research Center.

As to 480Y/277 volt systems, there are very few of them (I can think of only a handful) and those are limited to specific utilization equipment and not building services (the utility will not supply a 480V consumer service). So... step up transformers are needed to get the 480 volt source for the equipment in question.

Ya... ya have to watch this issue. If you are making and selling stuff meant for use in Canada on 600 volt systems, it is advisable to get it certifed to the proper Part II standard or we reject it upon inspection. The 480 volt standards do not cut it.

I agree fully. I decided not to include that info as I am not quite sure if the OP is looking at a ground rail or a bond rail.

I truly wish that the industry would retire the term "ground bus" from use. After the neutral to ground connection point, any conductor or busbar (other than the actual neutral bus or a neutral conductor) that extends from that point any further should be considered a "bonding bus" or a "bonding conductor" that serves to "bond" something to the neutral/ground connection point.

Since we still have ungrounded or high impedance grounded systems, the terminology requires more complexity. I prefer to say "Equipment Ground Bus", since that works all ways.

In fact, this discussion thread is based on the question of whether that bonding is necessary. Some system designs emphasize fault tolerance over every other consideration and, thus, are "ungrounded".

Agreed... it is very common for systems that require "up time" be not gounded, such as sewage transfer staions. But... they require ground fault indication equipment and skilled resources to deal with any issues that crop up.

Often... the 1st line to ground fault is ignored, and a subsequent fault will be at the elevated fault currents present during a line to line fault event.

In ungrounded systems, one ground fault can be detected by ANSI 64. VAMP265 (SCHNEIDER) will be working nicely for this.