Overhead/Pole-Mounted Transformer Sizing for dwelling units.

[Frank A]

Hi everybody.


I want to know what's the procedure or steps for calculating overhead transformers for 3 or 4 dwelling units. I assume that it won't be just adding the 3-4 dwelling units' VA; it will have I think some demand factors, etc.



This image below is an example.

 

[electrofelon]

First, are the transformers under the nec rules?

 

[Fnewman]

Probably not - his profile says Venezuela! However, given that he is asking in a US forum, we can assume he wants to know what our code and practice would say.

 

[Frank A]

First, are the transformers under the nec rules?

Yes, they're. We use a code almost similar to US's code.

I need just an approximation to know the framework. Because I was looking for some info on the web; to buy some vids or handbooks to size them but nothing yet.

Have you sized transformer before?

 

[Frank A]

Probably not - his profile says Venezuela! However, given that he is asking in a US forum, we can assume he wants to know what our code and practice would say.

Calm down, lil' brother. Our grid and codes are almost identical to US's. In fact, it's pretty much the translation of your code.

What applies to the US's electrical grid applies here too.

So, if you're not going to help, better not reply;

 

[electrofelon]

Calm down, lil' brother. Our grid and codes are almost identical to US's. In fact, it's pretty much the translation of your code.

What applies to the US's electrical grid applies here too.

So, if you're not going to help, better not reply;

Well understand that here, the nec would not apply to a pole transformer 99.9% of the time - the utility would size it.

But if you were sizing it per the nec, IMO the nec doesn't have any direct guidance for transformer sizing. There is no specific reference to using an article 220 calculation. However your required transformer protection and secondary conductor protection would have to meet article 220.

 

[Frank A]

Well understand that here, the nec would not apply to a pole transformer 99.9% of the time - the utility would size it.

But if you were sizing it per the nec, IMO the nec doesn't have any direct guidance for transformer sizing. There is no specific reference to using an article 220 calculation. However your required transformer protection and secondary conductor protection would have to meet article 220.

I see. That's pretty much the framework I was looking for.

Thanks you very much for your input, Mr.

Regards.

 

[kwired]

If you were to size this per NEC you would probably do it like you would a common service or feeder to a multifamily dwelling and need to know how many ranges, clothes dryers, etc. and other details of what may allow certain demand factors to be used.

 

[don_resqcapt19]

Around here the utility would probably hang a 25 KVA for those 4 loads.

 

[Fnewman]

Calm down, lil' brother. Our grid and codes are almost identical to US's. In fact, it's pretty much the translation of your code.

What applies to the US's electrical grid applies here too.

So, if you're not going to help, better not reply;

No calming necessary - I was trying to help and only replying because the first reply asked about NEC. Until you clarified, I doubt that few posters in The US were aware of the similarity.

 

[Frank A]

No calming necessary - I was trying to help and only replying because the first reply asked about NEC. Until you clarified, I doubt that few posters in The US were aware of the similarity.

I understand. Well, I think this is a lesson for you to learn: don't make assumptions without data.

I apologize. Thanks for trying to help.

 

[Frank A]

If you were to size this per NEC you would probably do it like you would a common service or feeder to a multifamily dwelling and need to know how many ranges, clothes dryers, etc. and other details of what may allow certain demand factors to be used.

Thanks for the input.

 

[kwired]

Thanks for the input.

That method likely results in larger transformer being used then what most POCO's in the US would typically install to supply the same load though. They don't use NEC to size their equipment.