Transfo Transformer Output

[powerplay]

an 100KVA 600volt step down to 120/240 Transformer has 400amp output. We installed an 400amp Splitter as usual with 2 200amp panels out of it, but an Electrician asked why didn't we just put the 2 200amp Panels with Main shutoffs direct out of the Transformer... On an expansion and maintenance standpoint it makes sense to me, but is it permitted to install two 200amp Panels directly out of the Transformer, or is that making it an junction box?

 

[Smart $]

It's permitted as long as each panel has its own overcurrent device and secondary conductors.

 

[Smart $]

In fact, the 400A splitter route may be a violation. See 240.21(C).

Exactly what is this splitter you refer to?

 

[powerplay]

We're in Canada, so do not have reference to the Code Rule you are referring to. The Transformer is fused on the Primary side, and each Panel represents different areas.

 

[powerplay]

In fact, the 400A splitter route may be a violation. See 240.21(C).

Exactly what is this splitter you refer to?

The Splitter I was referring to has Pads with Terminal screws up to 3/0 for branch conductors for separate Phases. An less expensive option yo an Busbar Splitter.

 

[Smart $]

We're in Canada, so do not have reference to the Code Rule you are referring to. The Transformer is fused on the Primary side, and each Panel represents different areas.

Not at all familiar with the CEC, so I cannot advise.

 

[Smart $]

The Splitter I was referring to has Pads with Terminal screws up to 3/0 for branch conductors for separate Phases. An less expensive option yo an Busbar Splitter.

I believe the industry calls those power distribution blocks.

 

[Sahib]

I think without splitter, there would be more than one cable at each transformer terminal and unless the latter is rated for such termination, it may be a violation.

 

[Smart $]

I think without splitter, there would be more than one cable at each transformer terminal and unless the latter is rated for such termination, it may be a violation.

Under the NEC, for the most part, transformer secondary conductors must land on a single OCPD. We can split it after the OCPD. Many here describe splitting a secondary conductor as tapping a tap, which is disallowed.

 

[Sahib]

Under the NEC, for the most part, transformer secondary conductors must land on a single OCPD. We can split it after the OCPD. Many here describe splitting a secondary conductor as tapping a tap, which is disallowed.

Is it not the 10ft tap rule allowing many sets of conductors tapped off from secondary of a transformer with primary side protection only?

 

[Smart $]

Is it not the 10ft tap rule allowing many sets of conductors tapped off from secondary of a transformer with primary side protection only?

No, it is not. Primary side only protection is permitted in the same section [240.21(C)], but only where you have no neutral on the secondary, e.g. a 3Ø three-wire delta output, no center tap; 1Ø two-wire output. 240.21(C) does not limit the number of secondary conductors... but each set or parallel sets must terminate in a single OCPD.

 

[Sahib]

Smart$: The NEC handbook I have clearly shows it applies to transformer with star connected secondary also. OP is correct......

 

[ActionDave]

Smart$: The NEC handbook I have clearly shows it applies to transformer with star connected secondary also. OP is correct......

Primary side only protection is not allowed with star secondary.

Smart$ already confirmed you can come off the transformer secondary lugs to more than one panel, each set has to end it's own overcurrent device.

 

[Sahib]

Primary side only protection is not allowed with star secondary.

I think there is a misunderstanding. By 'Primary side only protection', I meant there is no OCPD immediately after the transformer star secondary but there is one OCPD at load end of each set of secondary conductors.

 

[ActionDave]

I think there is a misunderstanding. By 'Primary side only protection', I meant there is no OCPD immediately after the transformer star secondary but there is one OCPD at load end of each set of secondary conductors.

What would you call it where there is only overcurrent protection on the primary conductors and none on the secondary?

 

[retirede]

What would you call it where there is only overcurrent protection on the primary conductors and none on the secondary?

Noncompliant?

 

[Sahib]

What would you call it where there is only overcurrent protection on the primary conductors and none on the secondary?

What about "None on the secondary" and "None on the secondary side"? Any difference?

 

[ActionDave]

What about "None on the secondary" and "None on the secondary side"? Any difference?

There is no nec code language like that.

 

[Sahib]

Summarizing,

Either a 400amp Splitter (or power distribution block) may be installed at the transformer secondary (with primary side protection) with 2 200amp panels out of it, provided each panel has main OCPD or the two 200amp Panels directly out of the Transformer, provided the transformer terminals are rated for more than one cable termination.

 

[david luchini]

Summarizing,

Either a 400amp Splitter (or power distribution block) may be installed at the transformer secondary (with primary side protection) with 2 200amp panels out of it, provided each panel has main OCPD

This is not NEC compliant.

or the two 200amp Panels directly out of the Transformer, provided the transformer terminals are rated for more than one cable termination.

This is NEC compliant, provided each panel has main OCPD.