3-phase 250V feed?

[apelkner]

Hi,

I have a client with 3-phase 250V 50A refrigerated truck trailers with locking type california style plugs who wants receptacles at the loading dock.

The building has 120/208V and 277/480V panels. I'm not familiar with 250V. Is there a way they can get this from existing panels or is there a different type of panel that will need to be installed?

Thanks,
Amy

 

[iwire]

I doubt these units are 250, in my experience these units will be 230 volt. We deal with at least a 1 or 2 dozen of these each year. The receptacles used for these are 250 volt rated.

It is a crap shoot if they will run non 208, sometimes they do fine on 208 other times they trip the overloads at 208.

Because of that we usually install buck/boost transformers to kick the 208 up to 236 which works out very well.

 

[apelkner]

Thanks iwire. Right, the units are 230V.

I checked out the Buck/Boost Transformer in a SQD catalog and found that I would need a set of (3) for each of the (9) receptacles in addition to the transformer and 120/208 panel already needed.

What about a 240V 3-phase panel? I'm just trying to understand what options there are since for now they're wanting this for pricing.

Amy

 

[charlie b]

I wouldn't feed each receptacle separately through a set of three buck/boost transformers. I would look for a single transformer, three phase, or a set of three buck/boost transformers, to step up the 208 to 240. Then I would feed a three phase panel rated for at least the 240 volts. Finally, I would feed each receptacle from a separate three phase breaker in this panel.

 

[iwire]

I checked out the Buck/Boost Transformer in a SQD catalog and found that I would need a set of (3) for each of the (9) receptacles in addition to the transformer and 120/208 panel already needed.

Actually you should only need two transformers for each branch circuit.

Or two larger transformers to power an entire panel to do as Charlie suggests.

This assumes the panel will only be expected to supply straight three phase loads with out neutrals.

 

[iwire]

I would look for a single transformer, three phase,

That would work without a doubt but is a more expensive option with no added value (In my opinion)

or a set of three buck/boost transformers, to step up the 208 to 240.

Buck boosts will get you to 236 from 208 which is fine for the 230 volt motors.

You would only need two fairly small buck boost transformer to supply a panel.

 

[charlie b]

That would work without a doubt but is a more expensive option with no added value (In my opinion). Buck boosts will get you to 236 from 208 which is fine for the 230 volt motors. You would only need two fairly small buck boost transformer to supply a panel.

Thanks, Bob. I have only encountered the notion of buck/boost twice. The first time was in a college course so long ago that I am not sure I ever attended the class. The second time was an existing installation that was so badly configured that I wound up recommending that they tear it all out and start over. I never did figure out how the transformer was able to do its boosting job, and carry full load current, with a wire that was many sizes smaller than the wires leading to, and away from the buck/boost.

 

[iwire]

As an apprentice I helped with instilling a pair to boost 3 phase 480 to 575 for a printing machine. I remember how confusing they seemed at the time.

Now we do a lot of them, but we are only supplying one machine per location so we do it at the branch circuit level. I have never supplied a panel with buck boosts but I think your suggestion to do that makes great sense.

 

[jim dungar]

I never did figure out how the transformer was able to do its boosting job, and carry full load current, with a wire that was many sizes smaller than the wires leading to, and away from the buck/boost.

Actually, the wires in the transformer are fairly large. For example: a 1kVA buck boost to go from 208V to 236V would have a primary winding of 240V and a secondary of 32V which means the secondary is rated to carry 31.25A maximum.

So, with rounding, the effective boost transformer is 208V+28V= 236V @ 31.25A maximum = 7.4kVA

 

[LarryFine]

I'm thinking (uh-oh!) that a 480-240 3p transformer might be better than adding this load to the existing 208v supply, which is likely to be closer to being maxed out than the 480 service.

 

[Electric-Light]

460 is a motor meant for 480v
575 is a motor meant for 600Y/347 in Canada and some parts of US.
They're actually different.

250 is receptacle name plate for 230 delta, just as your average household outlet is 125 rated.

For 50A,
208Y/120v 50A receptacle would be NEMA L21-50R (5 pins 3 poles + N + G. This is most likely what you find at event power and spider boxes, so that 120v power can be derived if needed for service outlets and such)

3ph 230v (without neutral) would have L15-50R (4 pins 3 poles + G) where 120v is absolutely not needed. There is no harm in not utilizing the neutral from such receptacle.

Motors are usually rated 208-230v. Check nameplate on refer unit.

It might be wise to keep a L15-50R female to L21-50P male adapter cord on the truck, so the trailer can plug into other sites having L21-50R receptacles.

 

[iwire]

460 is a motor meant for 480v
575 is a motor meant for 600Y/347 in Canada and some parts of US.
They're actually different.

No kidding.

250 is receptacle name plate for 230 delta, just as your average household outlet is 125 rated.

No Kidding again.

For 50A,
208Y/120v 50A receptacle would be NEMA L21-50R (5 pins 3 poles + N + G. This is most likely what you find at event power and spider boxes, so that 120v power can be derived if needed for service outlets and such)

It could be many things but it will not be an L21-50 ...... refer trailers have no neutral. We happen to use non-MEMA 60 amp devices.

Motors are usually rated 208-230v. Check nameplate on refer unit.

I have never seen a refer unit with anything but a straight 230 motor and I have easily wired more than a 100 of them ....... of course I have not seen them all.

It might be wise to keep a L15-50R female to L21-50P male adapter cord on the truck, so the trailer can plug into other sites having L21-50R receptacles.

At least in this area NEMA L-50s are a rare thing, for 50 amps many people use non-NEMA receptacles, pin and sleeve types or the 'California style' 50.

I suspect a NEMA L*-50 is just to fragile to put up with heavy duty use. The California style is much more rugged just like pin and sleeve types are.

We happen to use Meltric type as they are heavy duty, rated as motor disconnecting means and have a '3R' rating which is handy for outdoor use.

 

[iwire]

I'm thinking (uh-oh!) that a 480-240 3p transformer might be better than adding this load to the existing 208v supply, which is likely to be closer to being maxed out than the 480 service.

As the OP is dealing with 9 of these units that may be the way to go.

 

[apelkner]

The plug model is Hubbell CS-8364C non-NEMA. I'm liking the idea of transforming 480V to 240V 3-phase and providing a panel for only these receptacles. Now the next issue is if (9) 42A loads will even fit on the spare service ampacity.... yay for adding new equipment to the project every five minutes!

Thanks everyone.

 

[Electric-Light]

The plug model is Hubbell CS-8364C non-NEMA. I'm liking the idea of transforming 480V to 240V 3-phase and providing a panel for only these receptacles. Now the next issue is if (9) 42A loads will even fit on the spare service ampacity.... yay for adding new equipment to the project every five minutes!

Thanks everyone.

A 208 to 230 or 240 auto-transformer will be much cheaper and smaller for the given requirements. The auto-transformer won't have to handle the full kVA where regular transformers do.

For 50A 230v, a 208 to 230 will only have to handle 22v * 50 * sqrt3 = 1.9kVA.

 

[LarryFine]

For 50A 230v, a 208 to 230 will only have to handle 22v * 50 * sqrt3 = 1.9kVA.

Now, multiply that by nine and see if you reach the same conclusion.