residential isolation xfmr

[jeremysterling]

transformer nameplate

transformer nameplate

Here is the transformer nameplate. If we assume the attic ambient temperature = 140*F, what does that tell me with the rise indicated on the nameplate? What is the danger? Conductor insulation damage?

 

[Rampage_Rick]

the end objective of this install is to reduce power line noise.

This smacks of a $200k home theater for someone who SWEARS they can hear the difference between brand XXXY oxygen-free speaker/slash/jumper-cables and your average coat hanger

 

[jim dungar]

Here is the transformer nameplate. If we assume the attic ambient temperature = 140*F, what does that tell me with the rise indicated on the nameplate? What is the danger? Conductor insulation damage?

Transformer life is reduced due to insulation degradation. There is no good formula to determine by how much unless you have a true loading and ambient temperature profile. A lightly loaded transformer can usually tolerate a high ambient without significant issues, especially if it has a chance to cool down.

Your transformer has 155?C insulation so it is rated for maximum life at full load, running 24/7 in an ambient of 40?C plus an design internal hot spot of 30?C for a total temperature of 225?C. Exceed this temperature profile and your transformer will fail early, stay under this profile and your transformer will last longer.

 

[steelersman]

This smacks of a $200k home theater for someone who SWEARS they can hear the difference between brand XXXY oxygen-free speaker/slash/jumper-cables and your average coat hanger

very interesting! That's funny! All of these audio afficionados getting fooled by coathangers!! Brilliant I say!!!!!

 

[don_resqcapt19]

Gar,
You cannot use any impedance that would have an effect on the code required effective fault clearing path. The primary EGC has to be bonded to the frame and the case to protect from a primary winding to frame fault and the secondary EGC has to be connected to the frame and case to protect from secondary side faults.
If I was an inspector I would reject any fault clearing path that has a higher impedance that the a code sized EGC.

 

[don_resqcapt19]

If you read my OP, you see I am asking for guidance on tying the secondary's Grounding Electrode Conductor (not the EGC, I know where that goes) back to the structure's grounding electrode (at the service).

It is my opinion that you are required to use the metal water pipe or building steel if they are available at the building. If neither of those are available then you can use other electrodes. In this case you have a metal underground water pipe and are required to bond the SDS to the water pipe. As Pierre pointed out this connection must be made within 5' of where the water pipe enters the building.

 

[wwhitney]

It is my opinion that you are required to use the metal water pipe or building steel if they are available at the building. If neither of those are available then you can use other electrodes. In this case you have a metal underground water pipe and are required to bond the SDS to the water pipe. As Pierre pointed out this connection must be made within 5' of where the water pipe enters the building.

Basic transformer question: if the primary and secondary EGCs are bonded via the transformer case, and the primary EGC is aleady connected to the grounding electrode system, what is the purpose of directly connecting the secondary EGC to the grounding electrode system? Redundancy?

Thanks, Wayne

 

[don_resqcapt19]

Basic transformer question: if the primary and secondary EGCs are bonded via the transformer case, and the primary EGC is aleady connected to the grounding electrode system, what is the purpose of directly connecting the secondary EGC to the grounding electrode system? Redundancy?

Thanks, Wayne

Wayne,
For a transformer that is located within the same building as the primary OCPD, I see no electrical reason to provide a grounding electrode for the secondary of the transformer...I only see a code reason.