# 3 phase to single phase

#### hvavra

Joined Jun 29, 2021
3
I have a 3 phase system (machine) that will be connected to a dust collector. The dust collector is a single phase 230V system. I'm looking at transformers to step down voltage. My question is if I buy a single phase transformer to step down the voltage, how safe is it to connect as a single phase from the 3 phase line voltage? And would it just be 2 legs connected, there is no neutral? Dust collector is 230V, 16A, so around 4-5kVA.

#### SamR

Joined Mar 19, 2019
5,019
I have a 3 phase system (machine)
What voltage? Used to split single phase from 3 phase 480V all the time.

Joined Jan 15, 2015
7,453
You don't mention if your 3 phase power is WYE or DELTA configured?
You don't mention what the 3 phase voltage is?

Just as an example if your 3 phase power is 480 VAC 60 Hz. Delta and you want 220 VAC 60 Hz your transformer would be wired phase to phase (any two phases). If your power is 3 phase WYE your transformer primary would be wired Phase (any phase) to neutral. You want what is commonly called a "control transformer" with a 230 VAC secondary.

Ah, Sam beat me.

Ron

#### hvavra

Joined Jun 29, 2021
3
What voltage? Used to split single phase from 3 phase 480V all the time.
Input voltage i
You don't mention if your 3 phase power is WYE or DELTA configured?
You don't mention what the 3 phase voltage is?

Just as an example if your 3 phase power is 480 VAC 60 Hz. Delta and you want 220 VAC 60 Hz your transformer would be wired phase to phase (any two phases). If your power is 3 phase WYE your transformer primary would be wired Phase (any phase) to neutral. You want what is commonly called a "control transformer" with a 230 VAC secondary.

Ah, Sam beat me.

Ron
Input voltage is 480, sorry thought I put that in there. Its a machine build that was specified 480 - 3 phase, but the dust collector was ordered by someone else and is 230V single phase. Incoming power to initial machine would be supplied by company, so whatever is standard, I'm not entirely sure on that. I do know that we do not have a neutral from the machine control panel. The collector is to be ran from the machine, hence the need for a transformer. I was thinking that we would wire phase to phase on the primary side of the transformer. My concern is unbalanced load and how that will affect the performance of the collector. The collector will be the only load on the transformer.

Joined Jan 15, 2015
7,453
Less a neutral if we assume 480 Volts phase to phase then you have 480 Volt Delta configuration. You want a 480 Volt to 240 Volt transformer. However you need to consider the current for the dust collector to select a transformer. The dust collector motor name plate data should give Voltage and Current. Assuming DELTA your transformer primary would connect phase to phase (any two of three). Transformers like this are common but make sure the transformer can easily handle the dust collector current. Transformers like this are rated in KVA (Voltage X Current). Don't worry about phase imbalance, it is not an issue as long as the supplied power is adequate. Whoever ordered the dust collector should have known the available machine power. Then a transformer would not be required and the overall cost much lower.

Ron

#### SamR

Joined Mar 19, 2019
5,019
It's not the load on the equipment you need to worry about being unbalanced but the substation feeding it. Too many splits from the same phase can cause unbalance problems, not a single feed split. So look at the substation and what it feeds. If it's fed directly from the "High" line by a single feed transformer it's not a problem usually. Your 3 phase 480V breaker will have more load on 2 phases so plan accordingly.

EDIT: Or use a stepdown XFMR for the 230V if needed.

#### GetDeviceInfo

Joined Jun 7, 2009
2,190
I have a 3 phase system (machine) that will be connected to a dust collector. The dust collector is a single phase 230V system. I'm looking at transformers to step down voltage. My question is if I buy a single phase transformer to step down the voltage, how safe is it to connect as a single phase from the 3 phase line voltage? And would it just be 2 legs connected, there is no neutral? Dust collector is 230V, 16A, so around 4-5kVA.
Won’t be a problem as long as you are not exceeding the rating of the source. Which phases you use will be determined by existing loads, aiming for the best balance. Delta or wye supply has little to do with it, other than an extra option.

Joined Jan 15, 2015
7,453
Delta or wye supply has little to do with it, other than an extra option.
Yes, my bad on that. 480 volt be it DELTA or WYE is 480 Volt phase to phase. The only difference is 480 Volt WYE is 277 Volt any phase to neutral.

Ron

#### hvavra

Joined Jun 29, 2021
3
Less a neutral if we assume 480 Volts phase to phase then you have 480 Volt Delta configuration. You want a 480 Volt to 240 Volt transformer. However you need to consider the current for the dust collector to select a transformer. The dust collector motor name plate data should give Voltage and Current. Assuming DELTA your transformer primary would connect phase to phase (any two of three). Transformers like this are common but make sure the transformer can easily handle the dust collector current. Transformers like this are rated in KVA (Voltage X Current). Don't worry about phase imbalance, it is not an issue as long as the supplied power is adequate. Whoever ordered the dust collector should have known the available machine power. Then a transformer would not be required and the overall cost much lower.

Ron

That makes sense, the collector is 230V, 16A, so 3680 + allowance for loss should be 4.6kVA, I've spec'd out a 5kVA transformer. And yes, I'm aware that it should've been ordered correctly, but we can't always control what other people hear or do and subsequently order. lol

#### GetDeviceInfo

Joined Jun 7, 2009
2,190
That makes sense, the collector is 230V, 16A, so 3680 + allowance for loss should be 4.6kVA, I've spec'd out a 5kVA transformer. And yes, I'm aware that it should've been ordered correctly, but we can't always control what other people hear or do and subsequently order. lol
Motor starts typically demand more current than FLA. Starting a motor on an undersized transformer can lead to long start times, generating excessive heat in the motor and transformer. I often size 3x FLA, and larger for hard starts. A smaller blower isn’t considered a hard start, but you want to avoid a trip, restart scenario, which happens if you can’t get the motor up to speed promptly.

#### SamR

Joined Mar 19, 2019
5,019
I speced out a 400HP 480VAC induced draft blower motor for a large package boiler that got started up with the draft inlet shutters closed (big project startup mistake) and browned out half the plant! It didn't trip the 9600VAC substations feeder breaker surprisingly but sagged the entire 9600VAC distribution system. Don't remember what its breaker amps were but FLA ~600A and the feeder breaker held for a very short time while until the breaker's thermal overloads tripped it. Blowers have a HUGE inrush, especially when their airflow is blocked!

#### GetDeviceInfo

Joined Jun 7, 2009
2,190
I speced out a 400HP 480VAC induced draft blower motor for a large package boiler that got started up with the draft inlet shutters closed (big project startup mistake) and browned out half the plant! It didn't trip the 9600VAC substations feeder breaker surprisingly but sagged the entire 9600VAC distribution system. Don't remember what its breaker amps were but FLA ~600A and the feeder breaker held for a very short time while until the breaker's thermal overloads tripped it. Blowers have a HUGE inrush, especially when their airflow is blocked!
Hate when that happens
I watched a crew struggling with starting a 150hp blower over a few days. I finally dropped in, and after querying their troubles, discovered they had jumped out the start transformer, misunderstanding its function. Rewired and set timers with a couple of open start sequences. Off and running. A couple of HV compressor motors in one site can only be started by coordinating with down line customers.

Joined Jul 18, 2013
28,522
. My question is if I buy a single phase transformer to step down the voltage, how safe is it to connect as a single phase from the 3 phase line voltage? And would it just be 2 legs connected, there is no neutral? Dust collector is 230V, 16A, so around 4-5kVA.
This is how N.A. residential supplies are obtained.
A single phase transformer across two phases, or same thing, from phase to neutral.
Think of a 3ph transformer as three single phase transformers in one.
When using a transformer to drop the voltage to 230v/240v you lose the grounded neutral, so you would need to select one of the secondary's to connect to earth ground in order to re-reference it and produce the neutral..
,

Joined Jan 15, 2015
7,453
That makes sense, the collector is 230V, 16A, so 3680 + allowance for loss should be 4.6kVA, I've spec'd out a 5kVA transformer. And yes, I'm aware that it should've been ordered correctly, but we can't always control what other people hear or do and subsequently order. lol
Such is true and a large part of my early career was fixing problems which never should have been. Yes, a 5.0 KVA should power it fine.

Ron

#### Janis59

Joined Aug 21, 2017
1,822
Probably Your vacuum cleaner is collector motor it means it demands for shape of voltage is not very critical, thus You may use the SCR for diminishing the output and then full wave three phase rectifier to compose one nice DC output. Those motors ought work from DC however it would be wise to check it experimentally beforehand

#### Msarikaya

Joined Jul 1, 2021
1
I have a 3 phase system (machine) that will be connected to a dust collector. The dust collector is a single phase 230V system. I'm looking at transformers to step down voltage. My question is if I buy a single phase transformer to step down the voltage, how safe is it to connect as a single phase from the 3 phase line voltage? And would it just be 2 legs connected, there is no neutral? Dust collector is 230V, 16A, so around 4-5kVA.
To convert 3-phase to single-phase power, you can use a phase converter. This device can be wired to the motor you plan to run that requires single-phase power. Note that this will impact only the device wired to it, not an entire outlet because it is not hardwired into your electrical system