Ammeter Used for Measuring One-Phase Current

So what was your question?

Can you elaborate. You have made a statement.What do you expect ?

Why yellow phase is selected not Red or Blue?

The 3 phases should be nearly the same.

if you have any significent difference, there is probably a bad winding.

No, there is significance for using yellow phase.Will wait for some more view.

Traditionally, extensions to a distribution board where three phases come in and single phases go out usually place a greater load upon the red phase, as the electrician making the connections will habitually start in the top-left and end at the bottom-right. It just so happens that most UK distribution boards have been arranged with the red phase at the top, the yellow in the middle and the blue at the bottom. So the red phase traditionally carries more current and therefore will be at a slightly lower voltage than the yellow or blue. Would this have any bearing upon the matter, perhaps?

The significance must mean something in your locality. It means nothing here, in fact "yellow phase" means nothing here in the US. I can think of no specific engineering reason to put a 1 phase CT on any particular phase of a 3 phase motor circuit. In any case it gives you a nearly useless representation of what is happening in the motor.

JRaef,

Thank you for your view. But in many countries in Asia and Gulf, for 3 ph FHP motor one ammeter used in series of contactor to measure current and thus save cost of 3CTs & A/S or 3 ammeter. The reason is the yellow phase is gets affected if there is disturbance in other two phase. Say yellow phase is the winded in central core of upstream transformer. Remember magnetic balance test etc. This can be better explained by manufacturer.

I am of the opinion is yellow phase gets affected if there is disturbance in other two phase. The yellow phase also the central winding of upstream trafo core.once there is some problem in red or blue, it will surely affect the flux density in central limb even if its small, than other limb. We can think more over it and if possible adopt mathemetical justification.

There is a "disturbance" with another phase any time a phase has a problem. Often the other phase(s), when a single phase is lost show a current somewhat similar to starting current, which can happily cause HRC fuses to blow and stop any further damage for example......

But picking out a particular (yellow) phase as being the "one to monitor" shows little understanding of the way 3 phase systems really work.The colors are usually arbitrary anyway, though not always.....

To really check things out in a correct and fundamental manner, all three phases need to be monitored at the same time.....nothing more, nothing less......

We know how 3 phase system works. There are protections, monitoring devices etc. But, for an operator for a quick observation the ammeter will be useful. The yellow phase is a better choice than arbitrarily selecting red or blue.

Well tell me what's the norml choice of control voltage for MCC 240V AC or 110V Ac and which will be a better choice?

Why is yellow better?

Are you color prejudiced?

There is simply no reason that any phase is "better" than any other, unless you just believe in luck of course!!!

It may be convention. Why is the phase color yellow? It could be something as simple as that is the phase that is always used for this particular purpose.

Here we use

Brown

Orange

Yellow

in panels

drop cords are generally

Black

White

Red

Green=ground

The white is hot & can be confusing, having 277v on the neutral is not a good thing.

If there is a difference between the 3 phases (current reading] there is a problem. There is no master winding on a 3 phase motor.

Certain industries, localites or regulatory bodies may have a convention they would require, but operationally there is no difference on a 480 3 phase set up.

There are some older 240volt 3 phase where there is a "stinger" Leg with a higher voltage, I can't quite remember the details? 205 to ground, 120 on the other 2?

So I guess I should ask, what is the voltage measurement between the phases & also the measurements to ground, neutral?

Anyone who believes as he seems to, that a particular phase is "different" or "better" does not understand electricity at all......

But you and the other posters seem to understand that better than he does.....thank God!!

That's already justified with reasoning. Well, let me give you another example, if you do magnetic balance test of transformer putting a low voltage on say, R phase, you will see little less voltage in yellow ph and much less on blue. Just think over how it will affect in case of disturbance.

I requested a suggestion with reasoning on selection of 240vAC or 110V AC for control voltage in MCC. I got some reasoning if you have, can please forward.

Thank you for communication.

Regards

Depends on the situation.

In the US small power tools & computers run on 110vac, so that is the natural chioce.

If 240 is the norm, that would be the best choice.

Boilers & HVAC many times use 24vac, which is a good choice for safety reasons.

Having all equipment use the same control voltage, helps keep the inventory of spares low & reduces the confusion in regards to troubleshooting to a minimum.

The other question is for control signals is source or sink for switches & proximity devices. Again consistency helps keep inventory & confusion to a minimum.

· NEC National Electrical Code

· UL 508A Standard for safety for Industrial Control Panels

gives color coding of cables. Pleaserefer.

I was refering to what you actually find in common use.

I've seen plenty of panels where all the power is black & all the controls red.

If you're lucky there may be numbers.

For your query the current in one phase can be measured using the clamp on meter. In the panel there will be current terminal for each pahse from the CT secondary. Let usconsider a case of 2000/1 A CT. The secondary current in one phase will be measured with the neutral being connected to the earth terminal.

This can be seen in the practical application in which we canmeasure the single phase current in the Control & Realy anel orthe CT Junction Box itself or in the Marshalling Kiosk provided in the outdoor yard.

Regards,

N.Suresh

I wrote for fhp motors only. Any way, we had good discussion on this topic. thanks to everyone who shared their view and knowledge.

Regards,