3 Phase + Single phase load balancing (got myself confused)

[Kiwi-Turret]

Hi All,

Just after a small bit of clarification (have electricians coming next week so will re-confer with them also) as owners of property asked my advice on some equipment they want to install which lead me down a rabbit hole and i forgot how things work (have a brain injury so when i get overwhelmed it turns into a mess unless i get a clear answer)
Current setup - x3 240v Single phase connection (rated @ 60amp) - Mains line to house only supports 40amp per phase (but have been told multiple different stories by contractors and lines men)
Changing to 400v 3 Phase 40amp connection (wanted 60amps but electrician wouldn't approve, so will seek written confirmation when they are onsite to do work, as if i intend to stay onsite i might have to pay for an upgrade i wanted to do years ago but got conflicting stories...So brought a 40kva gen that worked until i let someone use it and they overheated the engine)

Two questions:
1. Does a 3 phase motor rated at 15amps pull this per phase (i was told it was Divided by 3 due to the 3 phases, but i was under assumption it is 15amps across the 3 phases as the 3 phase supply only made it more efficient)
2. If above answer is 15amps across the supply(3 phases) and not say 5amps per phase, Then considering the house oven/garage/heat pump/hot water etc are still on single phase that even when it is balanced i have to take into consideration the total amount of load per phase... Example 15amps (3 phase motor on lathe) + Single phase 15amp heatpump. Would that be 30amps on one phase + 15 amps per the other two.

I am going to look into options to reduce start-up current like VFD's etc if required.

Hopefully someone can answer this in simple terms (like i said i will have electricians give written responses so owners have a copy) - Sadly if i had done the conversion few years back i could of had mains + 3 phase conversion done for less than the price of just the conversion.

Thanks

 

[BT Fabrication]

Amperage rating is per leg. Can also be specified in KVA which is easier, as loads can become imbalanced on 3PH.
input amps from service are usually rated at 60% constant so 100A will allow 60A constantly without overheating and 150% over a short time to get the full 100A

 

[rons]

Two questions:
1. Does a 3 phase motor rated at 15amps pull this per phase (i was told it was Divided by 3 due to the 3 phases, but i was under assumption it is 15amps across the 3 phases as the 3 phase supply only made it more efficient)
2. If above answer is 15amps across the supply(3 phases) and not say 5amps per phase, Then considering the house oven/garage/heat pump/hot water etc are still on single phase that even when it is balanced i have to take into consideration the total amount of load per phase... Example 15amps (3 phase motor on lathe) + Single phase 15amp heatpump. Would that be 30amps on one phase + 15 amps per the other two.

1. Kept me awake at night until I realized that you have to consider an exact moment in time.
Not all three phases are at the same voltage/current or even the same polarity. All three are 15 amp peak at different times.

2. Ordinary residential single phase uses two wires at 115VAC that are 180 degrees out of phase. Thus your 230VAC.
Your heatpump needs two wires. Which two wires? The first wire is one incoming 3 phase line. What is the second wire?

 

[steve-l]

1. Kept me awake at night until I realized that you have to consider an exact moment in time.
Not all three phases are at the same voltage/current or even the same polarity. All three are 15 amp peak at different times.

2. Ordinary residential single phase uses two wires at 115VAC that are 180 degrees out of phase. Thus your 230VAC.
Your heatpump needs two wires. Which two wires? The first wire is one incoming 3 phase line. What is the second wire?

Your queries leads me to believe you are a bit confused. I'm sorry if I got this wrong. Just in case. So just for clarity, yes, you are correct single phase power is created at the service transformer by a center tapped secondary where the center tap is neutral and each end of the secondary winding is 115V from each end to the center tap. End to end voltage would be 230V because each end of the secondary is 180 degrees out of phase with the opposite end.
3 Phase power can be used WYE or Delta depending on how you wire up the load, but each of the power legs each have a 120 degree phase angle from each other. Leg voltage can be 115V/120V or 230/240V. AC voltage is not usually stated as peak to peak, but usually stated as RMS (root mean square)( .707 x peak). Service is delivered from the distribution transformer(s) to your service box with 4 wires L1, L2, L3 and ground. These legs can be 120, 240 or even higher depending on your request, but because of the 120 degree phase angle, the leg to leg voltage will be less than double as in single phase. Typically 208 or 380. If the leg voltage is higher, so will be the leg to leg voltage. This is where we sometimes see 400V, 440V or even 460V, but the relationship between leg voltage and leg to leg voltage is the same. If you wish to power Wye or Delta loads, you can by simply creating a neutral bus bar at the entrance box. Here the rule is simple, ground must not carry return current that is what neutral is used for, not ground. The ground to neutral connection must only be made at the entrance point, no where else..
On edit max current is always per leg, not total of all 3 legs. If you state power in watts or KVA, it is a total of all 3 legs.

 

[rabler]

Note the OP is in New Zealand.

 

[rons]

Your queries leads me to believe you are a bit confused. I'm sorry if I got this wrong. Just in case. So just for clarity, yes, you are correct single phase power is created at the service transformer by a center tapped secondary where the center tap is neutral and each end of the secondary winding is 115V from each end to the center tap. End to end voltage would be 230V because each end of the secondary is 180 degrees out of phase with the opposite end.
3 Phase power can be used WYE or Delta depending on how you wire up the load, but each of the power legs each have a 120 degree phase angle from each other. Leg voltage can be 115V/120V or 230/240V. AC voltage is not usually stated as peak to peak, but usually stated as RMS (root mean square)( .707 x peak). Service is delivered from the distribution transformer(s) to your service box with 4 wires L1, L2, L3 and ground. These legs can be 120, 240 or even higher depending on your request, but because of the 120 degree phase angle, the leg to leg voltage will be less than double as in single phase. Typically 208 or 380. If the leg voltage is higher, so will be the leg to leg voltage. This is where we sometimes see 400V, 440V or even 460V, but the relationship between leg voltage and leg to leg voltage is the same. If you wish to power Wye or Delta loads, you can by simply creating a neutral bus bar at the entrance box. Here the rule is simple, ground must not carry return current that is what neutral is used for, not ground. The ground to neutral connection must only be made at the entrance point, no where else..
On edit max current is always per leg, not total of all 3 legs. If you state power in watts or KVA, it is a total of all 3 legs.

I know all of that. Thank you for the refresher course. Maybe somebody less educated is a little more educated now.

I would like to hear what the facts are from the OP. I wanted to see if he knows what neutral is.
And I don't know where the OP is from.

 

[Kiwi-Turret]

I know all of that. Thank you for the refresher course. Maybe somebody less educated is a little more educated now.

I would like to hear what the facts are from the OP. I wanted to see if he knows what neutral is.
And I don't know where the OP is from.

Firstly, Thanks for everyone that replied

The information above has been helpful to clarify things and give me a refresher course as information overload didn't help me, I clearly have lots to learn and re-learn and will leave the fiddling for the professionals and stick with the basics.

I can confirm i am from NZ so we have 240v (single phase) & 400v (3phase)

Also i am aware of Neutral in an AC system but get confused when the word Ground comes up as i think DC not AC (which above from Steve-L helped clarify that in terms of AC)

I think i need to do some more research on balancing loads, as obviously that is the electricians job when they do our upgrade but feel like will be a juggling act considering our current setup on single phase is a mess that i probably know most about (mostly due to dodgy contractors splicing into lines they shouldn't and me finding out later. Ex - Heatpump had its own fuse, we replaced the heatpump and the guy spliced into my certified 15A garage only supply cause he clearly didn't want to run a new line, and only worked this out after 2 years of problems with my welder and it cant be changed without being re-certified and at extra cost for a new fuse+line)

Thanks all, any questions at me let me know

 

[rons]

I think your first assessment is correct. I might ask the power company about unbalanced 3 phase and if that affects billing, etc.
Maybe I'm wrong. But I don't think it matters. Even if you had only your heat pump on. That is unbalancing the system.
I would be interested if you have conflicting data.
(Thoughts from a 3 phase conjurer who has no choice)

 

[steve-l]

I think the OP is using the term load balancing incorrectly.. Generically, load balancing in a 3 phase system means to load each Leg (phase) equally as much as possible current wise. I suspect the OP is talking about overloading individual fused circuits.. Unfortunately when 3 phase power is delivered to a property as most domestic loads are single phase, it is often the case that all or most of these single phase loads are driven by only one leg and the other 2 legs are very lightly used. That of course is imbalanced. You folks in the USA do not suffer this issue as you don't have 3 phase power in residential areas. In Europe, Australia and New Zealand most everybody else gets delivered 3 phase and this can be an issue. I think the OP though has a situation where an electrician has tapped into his garage circuit because it was convenient, not necessarily incorrect, especially if the garage loads were not explicitly stated to the electrician before hand.