Transformer tap setting primary over current

[hhsting]

If a transformer has tap settings which can compensate for voltage drop at secondary side then how one sizes overcurrent protection size primary? Primary voltage depends on tap settings no and can change if tap settings of transformer is change? Anything in code regarding above situation.

 

[augie47]

The primary voltage is going to fluctuate anyway and it would be rare that the minimal tap changes are going to effect the OCP rating. Art 100 gives you the nominal voltages used by the Code and I would use those.

 

[hhsting]

If tap changer voltage goes up for example assuming secondary side 240V to 252V would not panelboard rating that’s nearest see252V have to be higher than 252V for 240/120V single phase panelboard right now it’s at 240V? What about secondary panelboard voltage rating? Does code have nominal voltage for those? Similar for 208/120V, 277/480V three phase panelboards

 

[bwat]

If tap changer voltage goes up for example assuming secondary side 240V to 252V would not panelboard rating that’s nearest see252V have to be higher than 252V for 240/120V single phase panelboard right now it’s at 240V? What about secondary panelboard voltage rating? Does code have nominal voltage for those? Similar for 208/120V, 277/480V three phase panelboards

Yes, and they probably do have ratings that make that kind of increase in voltage OK. But of course you’d have to check it. For example, if you have 240V panel, you wouldn’t expect it to all of the sudden have a problem if your voltage was 241V would you? A good bit of equipment has 10% variance and is ok. You have to check the specs...

And I’m with Augie on the slight voltage changes not really impacting settings with what we’re talking about it. We’re talking low percentage voltage changes. Probably much smaller than any margin of error accounted for when sizing or setting OCP.

 

[hhsting]

Yes, and they probably do have ratings that make that kind of increase in voltage OK. But of course you’d have to check it. For example, if you have 240V panel, you wouldn’t expect it to all of the sudden have a problem if your voltage was 241V would you? A good bit of equipment has 10% variance and is ok. You have to check the specs...

And I’m with Augie on the slight voltage changes not really impacting settings with what we’re talking about it. We’re talking low percentage voltage changes. Probably much smaller than any margin of error accounted for when sizing or setting OCP.

You mean any regular panelboard would be ok or panelboard that is made for tap changer ok? I don’t follow. I don’t recall any manufacturer data sheet listing variation or any code. By the way 10% is 264V not 241V.

 

[augie47]

The Code is based on nominal voltage, NEMA Standards recommend equipment operate + or -10% and utility voltages are normally +or- 5%. (short duration figures are -13, +6%
Bottom line, use the Code nominal voltages for calculations, etc. The variations are taken into account.

 

[bwat]

You mean any regular panelboard would be ok or panelboard that is made for tap changer ok? I don’t follow. I don’t recall any manufacturer data sheet listing variation or any code. By the way 10% is 264V not 241V.

I did not say 10% is 241V. I asked you if you expected the panelboard to have a problem with 1V over nominal 240V. Of course not. There is always a tolerance. So what is it? Check the specs. Possibly 10%. If you don’t see it listed and you are concerned about it, call the manufacturer.

 

[hhsting]

As contracted reviewer we enforce NEC 2014 and I don’t see NEC 2014 allowing any tolerances for panelboards should tap changer change the voltage higher than panel rating. NEC 2014 says to provide panelboard rating equal to or greater than system voltage. It would not comply with NEC 2014 . I also don’t see manufacturer or listing that say panelboard, receptacles, equipment voltage tolerances. How can all this comply with MEC 2014?

 

[augie47]

You are wasting time reinventing the wheel.
There is a whole world of documentation beyond the NEC concerning ratings of equipment.

If the nominal voltage is 240v, use that number and move on.
As bwat states, it really will work fine a t 241v

 

[ptonsparky]

I’ve seen 240v rated ice cube relays switching 480 and had been successfully for a number of years. I’m thinking the spacing on a 240v panel board or loadcenter will tolerate a few extra volts.

 

[roger]

The question has been answered and the OP might need to ask another reviewer in his office for more help, this is just spinning wheels.

Roger