230v cabinet shop equipment on 208v service

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James L

James L

Senior Member
Location
Kansas Cty, Mo, USA
Occupation
Electrician
I'm going to be wiring a small cabinet shop, with new 120/208 service. All of the big equipment is rated 230v....

CNC machine 3ph 30a + 1ph 20a
Edge bander 3ph 30a
Table saw 1 ph 30a
Shaper 3ph 20a
Belt sander 3ph 30a
Dust collector 3ph 30a
Vacuum pump 1ph 30a
Air compressor 1ph 30a

The CNC manufacturer has suggested buck boost transformer. They said their machine doesn't really like 208 volts. I know motors don't like under voltage, so my question is about all of the other equipment. Think it's best to run all of it at 230-240 volts?

Then that got me thinking. Rather than sprinkling 14 buck/boost transformers throughout the place, it would probably be better to just set a 50 kVA transformer on the floor and feed up to a separate panel for all of that equipment.

Buck/boost transformers look like about $400 each, which would total about $6,000

The 50 KVA transformer is about $7,500 but probably a lot less work and definitely a lot less clutter.

I feel like I may have written out the obvious answer. But what do you think?
 
For the most cost effective solution, is running the service transformer a bit hot by adjusting the tap an option? E.g. to obtain 230/132.7v. You could put a couple small buck boost transformers on the general use 120v receptacle circuits that way, though any modern equipment like switch mode power supplies, LED drivers or single phase VFDs will completely tolerate this.

Or, if it's not too late to specify the service, it may be possible to tap a 277v transformer much lower to get closer to 250v. The overall benefit for this second option is contingent on the three phase equipment being able to be wired that way.
 
James L said:
I'm going to be wiring a small cabinet shop, with new 120/208 service. All of the big equipment is rated 230v....

CNC machine 3ph 30a + 1ph 20a
Edge bander 3ph 30a
Table saw 1 ph 30a
Shaper 3ph 20a
Belt sander 3ph 30a
Dust collector 3ph 30a
Vacuum pump 1ph 30a
Air compressor 1ph 30a

The CNC manufacturer has suggested buck boost transformer. They said their machine doesn't really like 208 volts. I know motors don't like under voltage, so my question is about all of the other equipment. Think it's best to run all of it at 230-240 volts?

Then that got me thinking. Rather than sprinkling 14 buck/boost transformers throughout the place, it would probably be better to just set a 50 kVA transformer on the floor and feed up to a separate panel for all of that equipment.

Buck/boost transformers look like about $400 each, which would total about $6,000

The 50 KVA transformer is about $7,500 but probably a lot less work and definitely a lot less clutter.

I feel like I may have written out the obvious answer. But what do you think?
Click to expand...
From my calculations you would need a 75kVA transformer to support all the loads that you described. That's the way I would do it. Seems much simpler of an install to me if you have the space for the equipment.
 
What are the HP ratings of the motors and are they really only rated for 230? Will everything operate at once?

There will be times when it's better to replace the motor than adjust the voltage; don't know if this is one of them.
 
Knightryder12 said:
From my calculations you would need a 75kVA transformer to support all the loads that you described.
Click to expand...
You could be right, but I'll have to calculate that after I see all the real specs. Those are the breaker ratings, and I think the 30 amp circuit for the CNC machine has 21.75 amps in the data sheet

Knightryder12 said:
That's the way I would do it. Seems much simpler of an install to me if you have the space for the equipment.
Click to expand...
I think I have the space. It's a small place, but I can probably tell them to carve out a couple of extra feet for me in the corner where the panel is.
 
zbang said:
What are the HP ratings of the motors and are they really only rated for 230? Will everything operate at once?

There will be times when it's better to replace the motor than adjust the voltage; don't know if this is one of them.
Click to expand...
I don't have any of the full specs, right now just going by the info the cabinet shop owner is giving me. So far, from what he's said, the CNC machine and the vacuum pump are the only ones that show 208-240v and everything else shows 230v.

But he also said the CNC sales rep told him that they recommend not running it at 208v
 
James L said:
I'm going to be wiring a small cabinet shop, with new 120/208 service. All of the big equipment is rated 230v....

CNC machine 3ph 30a + 1ph 20a
Edge bander 3ph 30a
Table saw 1 ph 30a
Shaper 3ph 20a
Belt sander 3ph 30a
Dust collector 3ph 30a
Vacuum pump 1ph 30a
Air compressor 1ph 30a

The CNC manufacturer has suggested buck boost transformer. They said their machine doesn't really like 208 volts. I know motors don't like under voltage, so my question is about all of the other equipment. Think it's best to run all of it at 230-240 volts?

Then that got me thinking. Rather than sprinkling 14 buck/boost transformers throughout the place, it would probably be better to just set a 50 kVA transformer on the floor and feed up to a separate panel for all of that equipment.

Buck/boost transformers look like about $400 each, which would total about $6,000

The 50 KVA transformer is about $7,500 but probably a lot less work and definitely a lot less clutter.

I feel like I may have written out the obvious answer. But what do you think?
Click to expand...
Sounds like about same equipment in a cabinet shop I sometimes do work in other than dust collector and vacuum pump are definitely larger circuits. IIRC the vacuum pump was 25 hp. The dust collector I never wired but guessing at least 15 hp or more.

I will say most the equipment in the one I've worked in is all European made and rated 240 volts, though is possible could be ordered to run @208? That shop has a 240 volt with high leg service supplying it.
 
IMHO the plan of a single 'buck-boost' transformer (post 4) is probably your best bet.

A 'buck-boost' transformer for 3 phase could be a single 3 phase unit. But the most common approach is to bank a set of 2 or 3 single phase step down transformers in an 'autotransformer' configuration so that the stepped down voltage gets _added_ to the supply voltage. The transformers only have to supply the change in voltage, and so the power rating of the autotransformer configuration is much greater than the sum of the transformer ratings.

As an example, three of these 3 kVA transformers, connected for 120V primary, 16V secondary in a wye boost configuration would take your 208/120V system and boost it up to a 236/136V wye, with 186A current rating and 76kVA system capacity.

I prefer wye symmetry, but a similar result could be had using two 240V:24V transformers in an 'open delta autotransformer' configuration.

-Jon
 
James L said:
You could be right, but I'll have to calculate that after I see all the real specs. Those are the breaker ratings, and I think the 30 amp circuit for the CNC machine has 21.75 amps in the data sheet


I think I have the space. It's a small place, but I can probably tell them to carve out a couple of extra feet for me in the corner where the panel is.
Click to expand...
I basically used 80% of the breakers that you listed and counted it all as motor load as well. But I think you will want a 75Kva xfrmr at a minimum due to the possible inrush of the motors.
 
Ok so I got my materials quote from supply house, and they said the lead time for a transformer would be 6-8 months, and the salesperson suggested reverse wiring a 240v delta - 208 wye transformer.

I'm curious (worried?) about having a delta secondary, because I will have single phase loads (several 2-pole circuits). I'm thinking about unbalanced loads 🤔

Thoughts?
 
Don't use a transformer in reverse.

It screws up your grounding, it screws up your voltage regulation, and you can have problems with inrush current.

It is a workable solution when you have something on the shelf and a job that needs to be done yesterday.

Just go the buck/boost route.
 
winnie said:
Don't use a transformer in reverse.

It screws up your grounding, it screws up your voltage regulation, and you can have problems with inrush current.

It is a workable solution when you have something on the shelf and a job that needs to be done yesterday.

Just go the buck/boost route.
Click to expand...
Thanks. That's what my gut was telling me
 
James L said:
I'm curious (worried?) about having a delta secondary, because I will have single phase loads (several 2-pole circuits). I'm thinking about unbalanced loads 🤔

Thoughts?
Click to expand...
For L-L 240 single phase on a (full) delta just balance as best as you can;
A-B, B-C, C-A
I try to make up a panel schedule ahead of time.
You'll also need straight rated '240V' breakers

EDIT: I guess with a autotransfromer you'll still be on a wye not a delta, but I think the same thing applies with the breakers at 240y/139
 
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