120/208Y - 208 3?

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mn_voyageur

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I have a 120/208Y 3? 800 Amp Load Center with a spare 200 amp breaker.
1. May I run three 3/0 cables to a 240 volt 3? Main Lug panel?
2. I know that I can run a 240 3? motor on 208, but is there a problem with doing this? (According to the NEC.)

I understand that the motor will draw more current, build up heat, etc...

But is it legal?

[ February 11, 2005, 09:02 PM: Message edited by: mn_voyageur ]
 
Re: 120/208Y - 208 3?

I assume the motor involved is 3-phase. If so you may well find its nameplate says 230V not 240V.
It cannot necessarily be said that it will over heat, etc.
It depends on the driven load & the characteristics of that load.
Generally speaking, if other electrical parameters are within tolerance, then 90% of the motor rating would be okay. (207V. for 230V. rated motor).

This is not the preferred situation. But in the real world, there are many, many standard 230/460V. motors, connected for 230V., doing fine on nominal 208V. systems.

For new applications - 208V. & 200V. 3-phase motors are readily available & should be used.

This is not really an NEC issue. NEC has fine print notes about voltage below rated. But no hard, fast rules - if the various requirments of Art.430 are met, then there's not really an NEC issue.

It is legal. Whether practical, efficient, or the right thing is a different question.
 
Re: 120/208Y - 208 3?

Check the motor nameplate older motors say 208/240 newer motors usually say only 208 or only 240. the way they build motors 240V motors are not made to run to run on 208V. This could reduce the life of the motor. check with the motor manufacturer
 
Re: 120/208Y - 208 3?

Originally posted by laidman:
Check the motor nameplate older motors say 208/240 newer motors usually say only 208 or only 240. the way they build motors 240V motors are not made to run to run on 208V. This could reduce the life of the motor. check with the motor manufacturer
Click to expand...
I have to agree, I've have seen this happy oh to many times...
 
Re: 120/208Y - 208 3?

Just so I understand, one can take two ungrounded conductors and an EGC (three-3/0 conductors from original post) from the load center and run them to a 240 Volt rated 3 phase MLO panel and it will function properly and only output 208 V? I haven't heard of doing this before, but I guess it would work. And just to be clear, there is a lot I have not heard of yet. :)
 
Re: 120/208Y - 208 3?

wirenut - re-read the original post. I took it as meaning (3) 3/0 insulated "hots" without a "neutral" from an existing 208Y/120V. panelboard bkr. to feed a new 3-phase 3-wire panelboard rated 240V. max.

Nothing wrong with that. It's fundamental.
 
Re: 120/208Y - 208 3?

2. I know that I can run a 240 3? motor on 208, but is there a problem with doing this? (According to the NEC.)
Click to expand...
I thought 110.3(B) and 110.4 require equipment to be installed IAW nameplate.
 
Re: 120/208Y - 208 3?

I got ya kiloamp. How else am I going to power a 3 phase motor :eek: . I guess I am getting confused because I thought that an EGC had to be run from the load center to the 240 V "subpanel" so one would have to run 4 conductors, 3 hots and an EGC. Am I way off?
 
Re: 120/208Y - 208 3?

No, you are not way off, wirenut.
It kinda goes without saying that, of course, there must be an EGC of some type.
But the EGC does not have to be a wire. It can be the metallic raceway system. Generally I prefer to use a green or bare wire in parallel with the metallic raceway system.
 
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