220V Ac 1Ph + N Power Supply To Control Cabinet

If your 2 Phase legs come out of a delta (triangle) 3 X 220 VAC net, there is no neutral.

You should not connect one phase to a neutral when your neutral is at ground potential.

Grounding the metal parts of the cabinet is a possibility, but your 2 phases have to be isolated from it.

I just don't get it well since in a 220/380 you have a star configuration, meaning between one phase and the commons of the other ends you get 220 Volts and the star point is your neutral.

Where do you get your 2 phases with 220 volts? Is there already a transformer between?

The internals of the cabinet need re-work. If the panel has been designed for L1+N, then there will be no overcurrent protective device in the N conductor inside the panel. If the panel is to be fed from L1+L2 instead, then overcurrent protection needs to be provided in both the L1 and the L2 conductor as well.

Get the panel over to a local panel builder, and explain the problem to them. The insulation colour on the N inside the panel may well be incorrect for an L1+L2 supply. Get them to change that too so that the panel is compliant with local standards.They might turn it round within a day, perhaps?

Next time, issue the full wiring spec to the original panel builder, and carry out a Factory Acceptance Test to that standard before the next panel leaves their works.

Tsk, tsk. That will take money.

An old saying from my days working on government spacecraft was, " there's never enough time to do the job right, but there's always enough time to re-work it".

OP, get it fixed, properly. Remember this next time.

Hire an electrician licensed for your region! This is not a difficult problem to solve but it must meet your local power distribution codes. Different regions have slightly different rules for solving this problem. Some regions will allow a rewiring of your feed. Some regions will require an isolation transformer. Installing a fix that does not meet your local code standards can be anything from a benign violation to the root cause of a death one day.

What is your supply distribution system.

eg North America, or Asia or ?

3+n 4wires; and you are using 2 phases?

And why 2 ph without N ?

Think about the points of #1 and reply in detail

If, as you say, the supply is single phase and floating, I presume it is from either a local generator/inverter or an isolation transformer.

What is the control cabinet doing? An isolated supply will perform essentially the same as mains active and neutral except that there will be no earth reference and no first fault detection, which means that you should only use class 2 devices from it

You should be able to earth either leg of this supply to form a neutral, which will then enable RCDs to be operative, which they will not be on an isolated supply.

This connection should be done at the supply point and an earth wire then connected to the other system earths and the cabinet.

An earth stake is generally not recommended for small isolated installations, but this will be dependent on your usage of the supply, which won't be very heavy at just 1400 watts. Local regulations may require or preclude the installation of a stake, and you will need to check that out.

if you dont know the details of source (upstream) better to use a transformer, since the voltage is 220, how can u provide 380/220V, u can use 220/220V 1ph control transformer with ur required VA, then u can earth secondary

Apparently there is equipment inside the cabinet that requires an earth/ground neutral for equipment "noise" protection and/or personnel protection.

Most likely some of the equipment requires 110V which would be provided by one of the 220V 1PH conductors referenced to neutral ground.

You can use the 1PH 220 (no neutral) power to supply a 1 PH (with neutral) transformer and bond the neutral to earth/ground in the cabinet.

You can also use the 3PH 380V/220V 1PH transformer to feed your cabinet and bond the neutral earth/ground in the cabinet.

Both are acceptable as far as providing the cabinet wiring neutral earthing/grounding requirements however you must check your local electrical code requirements and follow/verify the installation is in compliance with all aspects of the applicable code section(s) as you may have to earth/ground the neutral immediately at the transformer.

If you do not know how to do this seek a qualified electrical person that is competent and capable of performing the installation safely and correctly.

To this question almost 2 days has gone and some 6-7 replies are there.

Do we not expect that the poster should respond to within a reasonable time and should add to his post further information asked for.

In a last post the poster just went out as he got his/ her problem solved by Google / grandchild without telling the group how.

This site is not for passing time and put ambiguous questions and let the others to look and assume what his inquiry may be and suggesting and searching ....

I suggest our reply to this type of inquiries be " Search Google" "Ask Yahoo"

Vinsue,

Knowing your location would have helped, but the voltages you mention suggest that it is not North America. I worked for a panel builder for years, and we had to ship panels wired for supply and control voltages normal for the country the panel went to. I suggest that you make no modifications to the panel itself. Instead, mount a 1500VA or larger transformer onto the side or top of it (or some other nearby location, with a disconnect switch and proper overcurrent protection. This transformer should have a primary 220 (two wire) or 220/440 (four wire) or 220/110 (3 or 4 wire) and a secondary 220/110 (3 or 4 wire). Wire the primary for 220V 2-wire input without any neutral (floating is no problem). Wire the secondary for 220/110 3-wire output with the midpoint of this output grounded. This midpoint becomes your neutral; and the output is what you then wire into the panel. You have now supplied the panel with the power it is specified to need and have made no modifications to it.

--JMM

Please correct me if I'm reading this response incorrectly, but I see the result of the above instructions providing a 110 volt active and neutral, whereas the OP requires a 220 volt one.

I agree with you but obviously we agree on only one interpretation of the situation. The OP obviously is neither a licensed electrician or very knowledgeable of the appropriate local electrical codes because he asked an international forum to answer a site specific question. I find these types of questions even more worrisome than the people to lazy too do their own web searches.

Bwilko,

If the secondary of the transformer has two windings, each producing 110V, and they are connected in parallel, you would have only a 110V output which I believe is the concern in your question. If the two windings are connected in series, with the midpoint and ends of these windings then made available to the panel, you would have what I described. Grounding this midpoint gives you a choice of 110V from it to either of the "hot" leads, and 220V between the two "hot" leads. All secondary voltages would be constrained to be no more than 110V away from ground, as opposed to the floating condition you would have if the midpoint were not grounded. Of course, a person could ground one end and then have 110V to ground and 220V to ground, but this is generally less-desirable.

--JMM

Sorry, I still don't see it.

Grounding is what produces the neutral.

If you ground the mid point of a 2 winding transformer then the active to neutral voltages are what is across each winding with respect to that earth point.

In your example, it will only be 110v, which is not what was required.

If you ground one end as you suggest in the last sentence of your reply, what have you achieved with the transformer?

You already had an isolated supply which could simply have had one leg grounded in the first instance to provide the required 220v active to grounded neutral without the extra transformer and its associated losses.

Friend,

I could be wrong in my use of the words. Perhaps we are only debating the meanings of words here. To me, the neutral is the current-carrying conductor that is at the midpoint between other current-carrying conductors in a 3 or 4-wire circuit. By extension, if a 2-wire tap is made from that circuit and one is connected to the feeder's neutral, then that wire is also referred to as the neutral.

You can have an ungrounded or a grounded neutral. However, I would be very reluctant to convert an ungrounded system into a grounded one by connecting a "hot" wire to the ground if a neutral is also present.

Back to the original question. I assumed that the requirement of a neutral in the panel was because some portion of the total load was to be connected at 110V (hot to neutral), while other portion(s) were to be connected at 220V. For this reason, a 3-wire supply to the panel was required, with two hot conductors separated by 220V and a neutral in between.

In areas subject to the NEC, the normal requirement is to ground a conductor in the system if by doing so the maximum voltage to ground can be kept below 300V. Thus, a single-phase 3-wire 120/240V system, a 4-wire 208/120V wye system, and a 4-wire 480/277V system would all have their neutral (midpoint) grounded. With a "high-leg" or "red-leg" or "wild-leg" 4-wire 120/208/240V delta system, the grounded wire would be the neutral wire at the midpoint between the 3 phase conductors with the additional requirement to clearly mark the hot conductor that was at 208V to the neutral so accidental connection of 120V loads to it was less likely (orange is the required color for it). In addition, a 3-wirea 240V delta system would also have one of its three hot leads grounded.

Thanks--JMM

Not wishing to get into a prolonged debate over this, and not being in the US, but does not the US National Electrical Code itself refer to the neutral conductor as "that conductor which is grounded". I believe that it also states that "the neutral conductor shall be grounded at the source of the Separately derived system".

Therefore by extrapolation, to be classed as a neutral conductor, it must be grounded.

Wikipedia states that "the neutral is a circuit conductor that carries current in normal operation, which is connected to ground or earth".

The US Websters dictionary defines the neutral wire as "the wire in a three wire distribution system required to be connected to ground for safety purposes".

A neutral conductor is required to have its potential tied to that of ground

The ungrounded centre tap of a two winding transformer is simply a common active, not a neutral, its potential is not at that of ground, and it could be dangerous treating or referring to it as such, as there is no first fault detection built into such a setup.

If I could get the hyperlink insertion setup to work here, I would post a link to the NEC definitions for you. Seems odd that you can't cut, copy or paste on these threads.

Seems we will have to agree to disagree. cheers

Friend,

I apparently have my latest code book in my work van or at work, so cannot check its definitions. I did check the older ones (back to 1971), and did not find any definition of "neutral" other than a reference to de-rating tables and notes thereto in Article 310. The latest code does make a number of definition changes, so I will defer that topic.

Regarding your comments on the "centre tap of a two-winding transformer", I assume you are considering the transformer to be one with a single primary winding and a separate single secondary winding from which its center is tapped as a separate conductor brought to the transformer's terminals. Each of the two windings is electrically insulated from the other. Therefore all three terminals of the secondary winding (the two end-points and the center-point) have no pre-determined reference voltage vis-a-vis ground; and as such constitute an ungrounded secondary. If you were to read the voltages from each conductor to ground, you would find that they do not equal the voltage between the conductors. You can ground any one of the conductors without worry about safety or injury. Indeed, it is only when you ground one of these three conductors that the voltage-to-ground for the others will equal the secondary voltage(s) of the transformer's output. Now, which conductor to ground? We agree that it should be the one connected to the center tap. If this conductor is used as a current-carrying circuit conductor, then it is also the Neutral. "First fault detection" is not needed on the grounded neutral conductor because grounding it does not create a fault. Overcurrent protection (fault detection) is only needed on the other circuit conductors.

This characteristic of being able, with an ungrounded system, to ground any one conductor without harm or injury is used in supervised industrial settings to provide a measure of electrical safety and continuity. The service equipment is provided with a group of lights that will illuminate equally if no grounds exist; but if one of the circuit conductors becomes grounded then its light will extinguish and the others become bright. This alerts the maintenance electricians to a problem without causing any equipment to fail, and gives time for the unintended ground to be found and fixed. The avoidance of a short circuit allows a plant to continue running with minimal disruptions. Such an approach gives you "first fault detection".

--JMM

The neutral of a transformer must be grounded and bonded to become neutral. It is a NESC (National Electric Safety Code) definition. There are even requirements for a new grounding and bonding with long transmission lengths. Having the neutral attached to the middle of a transformer makes this phase a split phase. The OP here has not clearly identified if this is a split phase system with four connections (hot, hot, neu, gnd) or three connection (hot, neu, gnd). Both wiring configurations are a standard on this planet.

Sir,

It is confusing at times when working on different systems even within a very limited area of a few km or mi, let alone a blog site such as CR4 with world-wide reach. Your comments as well as those from Bwilko are worthwhile. I had not looked at the NESC definitions, but will do so now (since I have a copy and am studying it).

--JMM

Hi get a qualified electrician to do the job for you...then you dont have to battle so much

Greetings M & L