Neutral Pole

[jdsouza]

Good day.

This has always got me confounded.
Witha 4-pole 63A breaker, can someone please confirm/advise what the current carrying capacity of the component is?
Does the 63A current stamped on the product mean
1. 63A per pole?
2. A total of 63A but limited to 63A in any one pole?

If #1 is correct, then if each pole drew 63A, what amount of current would flow through the neutral pole. (RYB 220V to Neutral).

And could you please clarify further with this scenario?
I have a 20 kW load distributed to some 380-415 3-phase appliances and some 220V 1-Phase appliances.
What should the stamp of the Mains breaker read for current?

 

[timhoward]

Does the 63A current stamped on the product mean
1. 63A per pole?

Yes

If #1 is correct, then if each pole drew 63A, what amount of current would flow through the neutral pole. (RYB 220V to Neutral).

If all 3 phases are carrying 63amps, and connected in a star configuration, N current is zero.
Otherwise if the 3 phases are not balanced the N current is square root of ( L1^2 + L2^2 + L3^2 - L1L2 - L1L3 - L2L3)

And could you please clarify further with this scenario?
I have a 20 kW load distributed to some 380-415 3-phase appliances and some 220V 1-Phase appliances.

You would need to describe your calculations to get to 20 Kw

 

[jdsouza]

Yes

If all 3 phases are carrying 63amps, and connected in a star configuration, N current is zero.
Otherwise if the 3 phases are not balanced the N current is square root of ( L1^2 + L2^2 + L3^2 - L1L2 - L1L3 - L2*L3)

You would need to describe your calculations to get to 20

Yes

If all 3 phases are carrying 63amps, and connected in a star configuration, N current is zero.
Otherwise if the 3 phases are not balanced the N current is square root of ( L1^2 + L2^2 + L3^2 - L1L2 - L1L3 - L2*L3)

You would need to describe your calculations to get to 20 Kw

Yes

If all 3 phases are carrying 63amps, and connected in a star configuration, N current is zero.
Otherwise if the 3 phases are not balanced the N current is square root of ( L1^2 + L2^2 + L3^2 - L1L2 - L1L3 - L2L3)

You would need to describe your calculations to get to 20 Kw

Thank you.
I meant in a domestic scenario where the house is supplied with a 3-phase connection via 4-pole 63A breaker. The voltages from RYB to the neutral would be 220V each. RN, YN and BN would have different loads, with an attempt to make them as equal to each other as possible. In this case. What does the 63A stamped on the breaker mean?

Does it mean that the sum of current of the three phases should not exceed 63A while any one phase not exceeding 63A or is it permissible to load the house with 63A in each branch? If the latter is true, what is the current in the neutral pole?

For the second part of the question, Say I have a heat pump driven by 380-415V 3-phase and some other equipment driven by 1-phase 220V and the total power for these is 20 kW. What rating 4-pole breaker should I purchase? That is the question.

 

[James]

if you have 63A on any one phase and zero A on the other 2 phases, the N current will be 63A

that is the highest N current you can get (equal to a single phase load with no other phases under load)

Any load you put on either of the other phases will REDUCE the N current, with the exception of a load across the other 2 phases that has no connection to N (in this case it would neither increase or decrease the N current.

 

[Julie.]

Thank you.
I meant in a domestic scenario where the house is supplied with a 3-phase connection via 4-pole 63A breaker. The voltages from RYB to the neutral would be 220V each. RN, YN and BN would have different loads, with an attempt to make them as equal to each other as possible. In this case. What does the 63A stamped on the breaker mean?

Does it mean that the sum of current of the three phases should not exceed 63A while any one phase not exceeding 63A or is it permissible to load the house with 63A in each branch? If the latter is true, what is the current in the neutral pole?

For the second part of the question, Say I have a heat pump driven by 380-415V 3-phase and some other equipment driven by 1-phase 220V and the total power for these is 20 kW. What rating 4-pole breaker should I purchase? That is the question.

As said above the maximum normal current in each pole (phase and neutral) is 63A

If you have balanced correctly across the three phases the current in the neutral will be zero.

As for your kW question, there isn't enough information, it could be that 19.9999kW of the 20kW is in the 3 phase part - giving a balanced load of around 37A with the single phase load being negligible; or it could be the 3 phase load is negligible and 19.9999kW of the 20kW being on the single phase, which could be over 90A on that one phase (and neutral). Obviously in practice, the real figure will be something sensible between these values.

Equipment, such as a heat pump will have a rating specifying the current, the instructions will also specify what size and type of protection (breaker) is required.

 

[jdsouza]

if you have 63A on any one phase and zero A on the other 2 phases, the N current will be 63A

that is the highest N current you can get (equal to a single phase load with no other phases under load)

Any load you put on either of the other phases will REDUCE the N current, with the exception of a load across the other 2 phases that has no connection to N (in this case it would neither increase or decrease the N current.

In other words, to answer my question. If a 3-phase 4-pole breaker is stamped at 63A, it means that the sum of the currents should not exceed 63A with any one pole not exceeding 63A. (for example : RN 20a, YN 20A, then BN can carry 23A).?

The confusion persists because, different forums / platforms including CoPilot and Gemini respond with both. 1. A 20A breaker means the breaker can handle 20A per pole or 60A in total and others respond with 2. A 20A stamp on the breaker means that the sum of the 3 phases must not exceed 20A.

 

[James]

If you are on a forum that has anyone telling you that a multipole switch or breaker is rated at say 20A to be split across the poles (i.e. 4 pole device =5A per pole)

LEAVE THE FORUM IMEDIATLEY. it has not got a professional amongst them and if it has they are too weak to speak up.

I also think you need to improve your knowledge a little about how 3 phase systems work and in particular note that live currents from different phases do not add up to become one large N current but cancel each other out to reduce it.

 

[MDJ]

If you are on a forum that has anyone telling you that a multipole switch or breaker is rated at say 20A to be split across the poles (i.e. 4 pole device =5A per pole)

LEAVE THE FORUM IMEDIATLEY. it has not got a professional amongst them and if it has they are too weak to speak up.

I also think you need to improve your knowledge a little about how 3 phase systems work and in particular note that live currents from different phases do not add up to become one large N current but cancel each other out to reduce it.

Here Here, good reply mate

 

[Risteard]

that is the highest N current you can get

Subject to harmonic distortion...

 

[jdsouza]

If you are on a forum that has anyone telling you that a multipole switch or breaker is rated at say 20A to be split across the poles (i.e. 4 pole device =5A per pole)

LEAVE THE FORUM IMEDIATLEY. it has not got a professional amongst them and if it has they are too weak to speak up.

I also think you need to improve your knowledge a little about how 3 phase systems work and in particular note that live currents from different phases do not add up to become one large N current but cancel each other out to reduce it.

You assume I am referring to a single load like a star or delta motor. No. That is not the case in question. It is, for example, the mains breaker for a distributed domestic load. Say, the sanctioned load for the apartment is 18 kW. A 4-core cable will bring the power to the meter. From there it will go to a breaker. From the breaker, the RN, YN, BN branches will be used to distribute as equally as possible the incoming power. To make it simple. Let us say, RN gives 220V to Room 1, YN gives 220V to Room 2 and BN gives 220V to Room 3. Where all three rooms have about the same appliances. In this case, what is the current flow in the neutral pole of the breaker when appliances in all three rooms are in use? What size breaker would be necessary for this apartment? And Ah. yes. I do no need to improve my knowledge about many things. For now. The question is explicit. Could anyone give an explicit answer?

The electricity supplier would have calculated the total load in the apartment and provided the sanctioned load of 18 kW (in this example instance).

Let's make the question even more explicit. You have 3 rooms with identical appliances (220V 1-Ph) with a total load of 18 kW. Your apartment is supplied with a sanctioned power load of 18 kW via a 4-core cable. Please advise the current rating of the 4-pole breaker needed in this case? What will be the current in the neutral pole if all the appliances (in all the 3 rooms) are running/switched on?

 

[timhoward]

Let us say, RN gives 220V to Room 1, YN gives 220V to Room 2 and BN gives 220V to Room 3. Where all three rooms have about the same appliances. In this case, what is the current flow in the neutral pole of the breaker when appliances in all three rooms are in use? What size breaker would be necessary for this apartment? question is explicit. Could anyone give an explicit answer?

This has been answered at least 3 times above. Please read the replies again.

 

[James]

You assume I am referring to a single load like a star or delta motor. No. That is not the case in question. It is, for example, the mains breaker for a distributed domestic load. Say, the sanctioned load for the apartment is 18 kW. A 4-core cable will bring the power to the meter. From there it will go to a breaker. From the breaker, the RN, YN, BN branches will be used to distribute as equally as possible the incoming power. To make it simple. Let us say, RN gives 220V to Room 1, YN gives 220V to Room 2 and BN gives 220V to Room 3. Where all three rooms have about the same appliances. In this case, what is the current flow in the neutral pole of the breaker when appliances in all three rooms are in use? What size breaker would be necessary for this apartment? And Ah. yes. I do no need to improve my knowledge about many things. For now. The question is explicit. Could anyone give an explicit answer?

The electricity supplier would have calculated the total load in the apartment and provided the sanctioned load of 18 kW (in this example instance).

Let's make the question even more explicit. You have 3 rooms with identical appliances (220V 1-Ph) with a total load of 18 kW. Your apartment is supplied with a sanctioned power load of 18 kW via a 4-core cable. Please advise the current rating of the 4-pole breaker needed in this case? What will be the current in the neutral pole if all the appliances (in all the 3 rooms) are running/switched on?

Electricity doesn’t care if the load is a single star connected device or 3 separate loads connected in a star configuration (as you have described here.)

Simply put AGAIN.
the N current will always be less than or equal to the largest phase current, depending on the other phase loadings.

 

[timhoward]

I don't know if this helps or confuses more, but sometimes seeing it visually can help.
If you consider a 5 amp load on each phase, with a scale of 1 amp = 10mm, and the phases 120 degrees apart you get a vector graph like this:

If you arrange the vectors after each other in phase sequence, you end you back at zero:

The key point is that as the phase angles stay the same, you can't ever get further away from the middle (0v) than the magnitude of the longest vector, so the greatest possible N current is that of the largest phase current.

Or to say another way, if you take any three distances A B and C, and walk each in turn, turning 120 degrees in the same direction after each one, you cannot end up more than the largest of A, B or C away from where you started.

 

[jdsouza]

I don't know if this helps or confuses more, but sometimes seeing it visually can help.
If you consider a 5 amp load on each phase, with a scale of 1 amp = 10mm, and the phases 120 degrees apart you get a vector graph like this:

View attachment 116461

If you arrange the vectors after each other in phase sequence, you end you back at zero:

View attachment 116462

The key point is that as the phase angles stay the same, you can't ever get further away from the middle (0v) than the magnitude of the longest vector, so the greatest possible N current is that of the largest phase current.

Or to say another way, if you take any three distances A B and C, and walk each in turn, turning 120 degrees in the same direction after each one, you cannot end up more than the largest of A, B or C away from where you started.

Thank you. I gather that for a 63A breaker connected to a distributed domestic load (220V to neutral per phase), the current in the neutral line will never be more the maximum rating value of 63A (assuming that the loads in each branch are limited to this value of 63A). A 4-pole 63A breaker can thus handle 63A in each of the 3 distributed domestic branches with the current in the neutral pole never going over 63A.

 

[jdsouza]

Electricity doesn’t care if the load is a single star connected device or 3 separate loads connected in a star configuration (as you have described here.)

Simply put AGAIN.
the N current will always be less than or equal to the largest phase current, depending on the other phase loadings.

Noted. Thank you. Out of phase summation being the answer to the question.