Current demand & load per phase Q

[cavemonster]

Hi all,

This is my first post on this forum. I'm currently doing my C&G 2365 and I've found myself completely stumped on a problem that's probably quite simple, but which I've had a lot of conflicting answers for from various people, which has left me a little confused.

I'm working on a design assignment and I'm calculating my maximum demand for a sub-board and distributing it across phases so that I can select a fuse and an armored cable to feed it from the main board. Two of my circuits on the sub-board are 3-phase.

Anyway, the thing that had me stumped was this. One of my three phase loads is described as "pool & sauna equipment that requires a 32A 400V 3-phase and neutral supply."

A classmate of mine has told me that this means 32A per phase, whereas someone I know in the industry has read it as meaning 32A across phases.

From what I understand, from a star-wound configuration IL=IP, so there is 32A in each phase and this does not change between lines (only voltage). So in my head, they're both correct. However, my classmate has tripled this value to add to his demand (a figure later to be divided into three phases) to a a big old 96A. Others that have chimed in have divided 32A into 3 to get 10.66A. I'm assuming that the rule IL=IP still applies even though the feed is technically not coming from a star-wound transformer, so wouldn't both these approaches be incorrect? Shouldn't we just be adding the 32A to max demand and be done with it?

I really appreciate any clarification I can get on this.

Happy Saturday!

 

[Top Cat]

I would give the answer to both scenarios and then say that the question is ambiguous (or a heap of sh*i!)

 

[buzzlightyear]

Kilowatts to amps (A) conversion calculator - https://www.rapidtables.com/calc/electric/kW_to_Amp_Calculator.html their you go .

 

[snowhead]

"pool & sauna equipment that requires a 32A 400V 3-phase and neutral supply."
A classmate of mine has told me that this means 32A per phase,

How many amps per phase is a 32amp 3 phase MCB?

 

[cavemonster]

Can it be both? Ambiguous and a heap of ----, in all: an ambiguous heap of ----? I will accept that my question is also the same, given that I've been linked to a calculator (which to be fair is still useful, thanks).

 

[cavemonster]

Wouldn't it be 32A per phase on a 32A MCB?

 

[cavemonster]

Let me rephrase my question.

If I was to assume 100% demand on a 32A 3-phase power circuit, would I add 32A to my max demand or would I multiply the 32A per phase to get 96A to add to my max demand?

My guess is the former.

Honest (stupid/ignorant) question.

 

[westward10]

You are over thinking this. The pool requires a 32A triple pole supply, that is 32A per phase. The maximum demand cannot exceed 32A per phase and yes you could take 96A in total if each phase supplied 32A single phase loads but it is distributed across the three phases. For example you could have three 32A single phase sockets one on each phase at full load equates to 96A but each phase is only loaded to 32A.

 

[cavemonster]

Thanks for unsticking me, mate.

 

[Lucien Nunes]

When describing a supply, load, or circuit rating, the current stated is always taken to mean the line current regardless of the number of conductors or phases. As per Westward, about the only situation in which one would take an interest in IL x 3 is when specifying the total rating of single-phase loads that can be served by a 3-phase supply.

 

[davesparks]

Let me rephrase my question.

If I was to assume 100% demand on a 32A 3-phase power circuit, would I add 32A to my max demand or would I multiply the 32A per phase to get 96A to add to my max demand?

My guess is the former.

Honest (stupid/ignorant) question.

If you are trying a to add up all of the single phase loads and divide by 3 to get max demand then yes you would have to use 96A for this circuit.