Lyophilizer 480/3/60 25A 4 Wire

[Dolemite]

Gents,

We just purchased a lyophilzer (freeze dryer) that operates on 480/3/60 4 wire. Twelve weeks until it arrives on site. It is a machine with a cascade refrigeration system (2 refrigeration systems with individual compressors). The refrigeration compressors are 3 phase. It has an electric heater that operates 480/1 phase. It also has a 277 to 230 transformer for other stuff. We want to install the power circuit before the machine arrives, however, I have read about the neutral sizing on 'non linear' loads. Should I be concerned or do I just size the neutral conductor the same size and the phase conductors? Would the manufacturer be able to provide up front info on expected neutral current/conductor sizing?

Thank you

 

[btrueblood]

" Would the manufacturer be able to provide up front info on expected neutral current/conductor sizing?"

They'd better, if this unit has UL or CE certifications, since that is a requirement of same.

 

[Dolemite]

Btrueblood,

Great point. Yes, it will have UL certification.

Thank you

 

[jraef]

Just size it the same as the phase conductors. The issue has been that you COULD size the neutral conductor SMALLER, now it is not recommended. Besides, it's unlikely that the amount of single phase non-linear loads are significant compared to the 3 phase loads.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[itsmoked]

I agree with Jeff. Same size. If you had a bunch of non-linear loads like a truck-load of LED lights or a large office filled with computers then you might want a bigger neutral.

Jeff; At your daughter's university they recently built a new college dorm and all the neutrals were one size larger than the phase conductors because of all the rectifier based loads.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Dolemite]

Many thanks for all the great input!

 

[jraef]

Keith,
I did some contract work with Boeing Computer Services back in the late 80s as they were converting from rooms full of draftsmen with mechanical pencils and slide rules to rooms full of IBM Catia CAD workstations (mini-computers). The buildings were WWII vintage with MWBCs throughout (Multi Wire Branch Circuits for those unfamiliar) so shared neutrals on several circuits, plus because of copper shortages during war time, neutrals were under sized by one gauge. After a few months we could trace the neutral wire routing inside the walls because the heat was turning the white paint brown from the inside out! They had several pole mounted transformer meltdowns as well before someone decided to investigate. That was the first time I had ever heard someone mention “harmonics” and “non-linear loads” outside of the classroom. It was a rude awakening for all involved... A lot of the Boeing facilities people there were high-up members of IEEE and eventually influenced the drive toward issuing the major rework of IEEE Standard 519 that became THE standard for harmonics issues in 1993. Prior to that, I think that hardly anybody was reading it. I certainly hadn’t and when the fires happened, nobody else involved (at first) had either.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden