Single Phase 480V - Single Phase 120V Xfmr & Distribution Question

[kvramesh]

Your transformer data you gave us said it was 30kVA.

To be able to use full capacity of the transformer @ 120 volts you will need 250 amp gear, 250 amp secondary conductors.

To be able to use full capacity of the tranformer @ 120/240 volts you will only need 125 amp gear, 125 amp secondary conductors. You will need to balance the load so each 120 volt leg is evenly loaded - especially when using near full capacity. Plus 240 volts is available should you come up with a need for it.

That is correct. I checked the panel and it says, max of 225 Amps. So, we are planning to change the main breaker from 175A to 225A so we can run close to the FLA if at all required. It seems this panel was initially designed for 120/240V and then changed for 120V only but forgot to increase the breaker amps.

We are not intending to change any other equipment, otherwise we will need to change both xfmr and distr pnl which is not a viable option at this time for us especially when there is no need of 240V requirement. But, I understand your suggestion and we will most likely design 120/240 in all future jobs. This seems to be one odd design

 

[kwired]

This seems to be one odd design

Nobody thinks that:happyyes:

 

[kvramesh]

Nobody thinks that:happyyes:

I meant the 120V only design that I have on this job seems not so common

 

[hurk27]

I meant the 120V only design that I have on this job seems not so common

Its only odd that it adds cost for larger conductors and removes some of the capacity of the transformer being available because of the limit of the main breaker, and doesn't give you the option of not being able to use MWBC that can save on voltage drop issues, but other then that I have seen many 120 volt only panel over time and used for various reasons, so not really odd, just not a very good choice of design when 240/120 was available.

 

[Besoeker]

smaller conductors, equipment, plus voltage drop advantages.

I meant this:

120/240 gives you advantages of both

I can't see a lot of advantages of having two voltages in a house for example when one voltage such as we have in UK serves us perfectly well. And you don't have the problem of a loose neutral subjecting equipment to overvoltages. Just my thoughts.

The 240 you use in Europe is typically one phase to ground of a 415 volt wye system IIRC.

Actually, it's phase to neutral, not ground. That's an important distinction. The neutral is usually grounded at the distribution transformer star point.And is now 400/230V. Nominally, at least. Just another crock from the wonderful EU.

But on a 120/240 not using the grounded neutral does not present voltage drop issues from neutral to ground, the leader in stray voltage types of issues. I do work for a lot of agricultural installations, and where livestock is present I prefer to use line to line loads over line to neutral loads as much as possible when I have a choice, for all the reasons mentioned above.

Fair enough.

 

[kwired]

I meant this:

I can't see a lot of advantages of having two voltages in a house for example when one voltage such as we have in UK serves us perfectly well. And you don't have the problem of a loose neutral subjecting equipment to overvoltages. Just my thoughts.


Actually, it's phase to neutral, not ground. That's an important distinction. The neutral is usually grounded at the distribution transformer star point.And is now 400/230V. Nominally, at least. Just another crock from the wonderful EU.


Fair enough.

When I said phase to ground I was using the term ground rather loosley -

As far as equipment goes there is no good reason to not make everything 240 volt and do away with 120 as far as I am concerned.

As far as shock hazard for people, 120 volts to ground is better, but not necessarily by enough to say this system is any safer, finding ways to limit users to exposure is still very important.

 

[Besoeker]

When I said phase to ground I was using the term ground rather loosley

And I'm a pedant.

As far as equipment goes there is no good reason to not make everything 240 volt and do away with 120 as far as I am concerned.
As far as shock hazard for people, 120 volts to ground is better, but not necessarily by enough to say this system is any safer, finding ways to limit users to exposure is still very important.

I agree with both points.
Wonder if there are any statistics comparing the two.......

 

[weressl]

Hi Jraef, This is being installed inside a e-house for mining facility. The mining plant is in South America but we are asked to follow NEC anyways. If you see the specs of the panel I posted above, it says 120V, 2 wire and it is supplied in USA.

You can certainly connect the ungrounded secondary conductor to BOTH buses and the grounded conductor to the neutral bar. Using single pole breakers only will give you a 120V panel.