How would I do this...

[1793]

I have a situation where I have an air compressor, Cord & Plug, 240v, 15amp. The electric service is 208Y/120. What is the best way to get to the 240 for this compressor.

Buck-Boost Transformer?

Edit: to add Transformer information

 

[raider1]

Check with the manufacture to see if the compressor can be run on 208 volts. Most of the compressors that I have installed are rated for 208/240 volt, but this one may not.

If you must have 240 volts then you will need to install a buck-boost transformer.

JMHO, Chris

 

[tshea]

Yup!
Check the motor. Is it 208-230Volt? If so, you don't need the buck-boost.

 

[1793]

Motor Nameplate 230v -- 15amp.

 

[growler]

1793 1 don't know how you handle a situation like this but I can tell you how I handle it. I install a 15 Amp Receptacle on a 15 Amp breaker then I mark the receptacle as 208 V. Whatever they plug into it is none of my concern. If the customer is worried that the equipment will not work properly I inform them it's probably cheaper to by a compressor that will work on the 208 volts that to by a buck/bust transformer ( materials & installation ). Most motors listed for 230 volts will work just fine at 208 volts. They have a built in thermal overload. If this were a commercial rated compressor it would already be list as 208/230 V.

 

[1793]

As I understand this, I would need to use two transformers to achieve the 230-240 volts needed. I would like to know if someone would be able to point me in the right direction to see how to wire this.

Another thouhgt I have is do I have to protect the secondary side, 240, before I get to the receptacle?

 

[scott thompson]

1793,

This may be of assistance:

1: Schematics for Voltage Boosting setup - 1 Phase

and

Located at:
Voltage Boosting Setup - 1 Phase

2: Schematics for Voltage Boosting setup - 3 Phase Open Delta

and

Located at:
Voltage Boosting Setup - 3 Phase open Delta

All items located at the Technical Reference area of Electrical Contractors Network (ECN)

Scott35

 

[Pierre C Belarge]

Thanks Scott, gooooooooooooooooood job!

 

[1793]

I too appreciate your reply.

Thank you again

 

[scott thompson]

Thanks for the pleasing replies guys! (Pierre and "1793").

Glad the drawings were of help.

As far as the ratings for the Isolated Transformers goes, the Secondary Voltage may be either 12/24 VAC or 16/32 VAC.
If the choice of Input Voltage to the Motor is in the 230 VAC range, the 12/24 VAC Secondary Voltage type Transformer(s) may be used.
With the Secondary Windings connected in series (as shown in the 1? drawings), an input of 208 VAC will yield an output of apx. 232 VAC.

If the choice is more in the 240 VAC range, go for the 16/32 VAC Secondary Voltage type Transformer(s).
Again, the Secondary Windings are connected in series - like the 1? drawings show; and with an input of 208 VAC, the output will be apx. 240 VAC.

As to the arrangement and KVA Size of the Transformers, I am unsure if this Motor is Single Phase or 3 Phase.

If The Motor Is Single Phase:

Use one Transformer - connected as described in the "Single Phase Voltage Boosting Transformer Setup" drawing. (Primary Windings connected in series adding, Secondary Windings connected in series adding).

For an output of apx. 232 Volts, use a Transformer with these ratings:
* Primary Voltage: 120/240 VAC
* Secondary Voltage: 12/24 VAC
* Minimum Volt-Amps Rating: 500 VA (0.5 KVA)

This will be sufficient for a load Current value of 20.83 Amps maximum, which equates to around 4,832 Volt-Amps (4.8 KVA).
------------------------------------------------------------------------------------------------------
------------------------------------------------------------------------------------------------------
For an output of apx. 240 Volts, use a Transformer with these ratings:
* Primary Voltage: 120/240 VAC
* Secondary Voltage: 16/32 VAC
* Minimum Volt-Amps Rating: 750 VA (0.75 KVA)

This will be sufficient for a load Current value of 23.40 Amps maximum, which equates to around 5,616 Volt-Amps (5.6 KVA).

-------------------------------------------------------------------------------------------------------
-------------------------------------------------------------------------------------------------------

These ratings should be sufficient for a 230 VAC 1? 2.0 HP Motor (FLA = 12.0 Amps), or a 3.0 HP 1? 230 VAC Motor (FLA = 17.0 Amps).


If The Motor Is Three Phase:


Use two Transformers - connected in an Open Delta configuration, as described in the "Three Phase Open Delta Voltage Boosting Transformer Setup" drawing. (Primary Windings connected in series adding, Secondary Windings connected in series adding).

For an output of apx. 232 Volts, use 2 Transformers with these ratings:
* Primary Voltage: 120/240 VAC
* Secondary Voltage: 12/24 VAC
* Minimum Volt-Amps Rating: 500 VA (0.5 KVA)

This will be sufficient for a load Current value of 20.83 Amps maximum, which equates to around 8,369 Volt-Amps (8.35 KVA).
------------------------------------------------------------------------------------------------------
------------------------------------------------------------------------------------------------------
For an output of apx. 240 Volts, use 2 Transformers with these ratings:
* Primary Voltage: 120/240 VAC
* Secondary Voltage: 16/32 VAC
* Minimum Volt-Amps Rating: 750 VA (0.75 KVA)

This will be sufficient for a load Current value of 23.40 Amps maximum, which equates to around 9,727 Volt-Amps (9.7 KVA).

-------------------------------------------------------------------------------------------------------
-------------------------------------------------------------------------------------------------------

These ratings should be sufficient for a 230 VAC 3? 5.0 HP Motor (FLA = 15.2 Amps).


Good luck!

Let us know what the outcome is

Don't let the Smoke out of the Motor or Transformers! :lol: :wink:

Scott35

 

[engy]

Quote: "If the choice of Input Voltage to the Motor is in the 230 VAC range, the 12/24 VAC Secondary Voltage type Transformer(s) may be used. With the Secondary Windings connected in series (as shown in the 1? drawings), an input of 208 VAC will yield an output of apx. 232 VAC."

Yes, but more like 229V (240Vpri=24Vsec, 208Vpri=21Vsec)

 

[1793]

I have a follow up question: the situation, recap, 30 amp three phase (208y/120) to a non fused disconnect currently to power a fork lift battery charger. This battery charger will be disconnected. Customer would like to come off of disconnect set a buck-boost transformer to bring the 208 to 230 volt to power a single phase air compressor motor. Motor is 15 amp. I have looked at Article 450 and I'm sure about the placement of OCP. I will be setting the receptacle about three feet from the disconnect / transformer.

If I change the 30 amp breaker to 20 amp at the source, do I also need to protect the circuit after the transformer?

I hope this can be followed.

 

[bcorbin]

Why would you change to a 20A/3 circuit breaker? Are you trying to get below a maximum OCP rating? If you are, there seems to be something incorrect (or I am reading it incorrectly) here. If the motor draws 15 full-load amps at 230V, at 208V it will draw 16.59 amps (even without considering start-up inrush), which will definitely trip out a 20A breaker. I would keep the 30A breaker, provided it doesn't exceed your maximum OCP rating. (I don't know your motor data.)

The real issue is: the conductors feeding the motor are not considered to be protected by the primary OCP unless you use a delta-delta, 3-wire secondary transformer. (per Section 240.)

 

[1793]

First of all, thanks to all who took the time to reply to this topic. We found that this motor would run just fine with the current current (208).

Thanks again.

 

[izak]

its kinda surprising that nobody really said that it probably would be just fine at 208

happens All the time

 

[raider1]

its kinda surprising that nobody really said that it probably would be just fine at 208

happens All the time

I thought that I did.

I have seen a few motors that need 240 volts and won't run on 208, but most motors that I have installed will work on either 208 or 240.

Chris