3 Phase 3 Wire panel feed 3 phase 4 wire lab equipment

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David Christian

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Fremont, CA, USA
Hi Guys,

I have one project that I find some lab equipment are fed by 3 phase 3 wire panel. Please see the picture below. I checked the old wiring diagram of each lab equipment. It shows that the equipment needs neutral. Therefore, I just want to double check whether it is fine to use 3 phase 3 wire panels to feed 3 phase equipment that has balanced load.

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Well, it’s right there in your data sheets: there is no Neutral bus in the panels, so if you have loads that need a neutral, it isn’t going to work. You would have to feed a transformer that gives you a 4 wire system, then set up a new panel board for that system.

But is your lab equipment Really 480/277V? The 277V would be unusual for anything other than lighting. If it’s 240V (or 208V), you need a transformer anyway...
 
Jraef said:
Well, it’s right there in your data sheets: there is no Neutral bus in the panels, so if you have loads that need a neutral, it isn’t going to work. You would have to feed a transformer that gives you a 4 wire system, then set up a new panel board for that system.

But is your lab equipment Really 480/277V? The 277V would be unusual for anything other than lighting. If it’s 240V (or 208V), you need a transformer anyway...
Click to expand...

There are several 480V 3P lab equipment for this lab TI project. Yes, you are right. It would be better to install a new 3 phase 4 wire panel to feed these lab equipment.
 
But again, are you SURE that the lab equipment needs 4 wires? It’s entirely possible, especially if it has any power electronics (now that I think about it). Power electronics typically need a solidly referenced ground point and with the panels you show, there might not be one. That may leave the transformer as the only option.

But...

If that’s the only issue (meaning the lab equipment is not actually using neutral connected loads) then check your SERVICE connection. If it is 4 wire, but they just used 3 wire panels because they had no neutral connected loads, then the fact that the service is solidly grounded is all you need. You could use a meter to see if you get 277 to ground, that’s a good indicator, but still check the service to be sure. Meters can be fooled.
 
When only 480/3 loads are supplied from a particular panel it is fairly common for the neutral not to be pulled from the MDP to the panel. As Jraef said, check the service to determine its specifications then look at the nameplates on the equipment to determine if you actually need a neutral to feed that equipment.
 
Jraef said:
But again, are you SURE that the lab equipment needs 4 wires? It’s entirely possible, especially if it has any power electronics (now that I think about it). Power electronics typically need a solidly referenced ground point and with the panels you show, there might not be one. That may leave the transformer as the only option.

But...

If that’s the only issue (meaning the lab equipment is not actually using neutral connected loads) then check your SERVICE connection. If it is 4 wire, but they just used 3 wire panels because they had no neutral connected loads, then the fact that the service is solidly grounded is all you need. You could use a meter to see if you get 277 to ground, that’s a good indicator, but still check the service to be sure. Meters can be fooled.
Click to expand...
Thanks a lot for your suggestion!
 
Beaches EE said:
When only 480/3 loads are supplied from a particular panel it is fairly common for the neutral not to be pulled from the MDP to the panel. As Jraef said, check the service to determine its specifications then look at the nameplates on the equipment to determine if you actually need a neutral to feed that equipment.
Click to expand...
Yeah, I will double check whether these lab equipment really need neutral.
 
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