Medium Voltage (13.8kV) and Low Voltage (480V or 208V) in same Pullbox

[dwhensley]

I have two existing transformers one goes from 13.8kV primary to 480V secondary the other goes from 13.8kV primary to 208V secondary. The customer wants to start putting all electrical equipment on platforms to get out of the flood plain. We are using the existing pad mounted xfmrs which have the space in the bottom to stub up conduits. When these are elevated the transformers will be open on the bottom so we want to put a galvanized box on the bottom that we can connect the conduit to. With that said when this is done the medium voltage and low voltage cables will be in the same box as the wires to up to the lugs on the transformer.

Is this alowed since will technically be two different voltages in the same box?

 

[Dennis Alwon]

You may put 2 different voltages in the same box however they must be marked according to the plaque at the service equipment. 230.2(E)

 

[Smart $]

...

Is this alowed since will technically be two different voltages in the same box?

No.

(2) Over 600 Volts, Nominal. Conductors of circuits rated
over 600 volts, nominal, shall not occupy the same equipment
wiring enclosure, cable, or raceway with conductors
of circuits rated 600 volts, nominal, or less unless otherwise
permitted in (C)(2)(a) through (C)(2)(e).
...
(a) through (e) do not apply.
...
Conductors having nonshielded insulation and operating
at different voltage levels shall not occupy the same
enclosure, cable, or raceway.

 

[Dennis Alwon]

No.

480V is over 600V????

 

[Smart $]

480V is over 600V????

No... but you might want to re-read the subsection I posted.

 

[Dennis Alwon]

No... but you might want to re-read the subsection I posted.

I did read it and it seems that all applies to 600v or more- hence the heading.

 

[Hv&Lv]

I have to say I agree with smart money...
Padmount transformers have really never been NEC compliant. Utilities use them and don't have to worry about the NEC.

Many electrical contractors that buy regular padmounted single phase transformers fail to realize that they aren't NEC compliant IMO.

The primary and the secondary are supposed to cross each other in the front of the XF. Adding some type of seperation is almost impossible in these transformers.

edit to add.

Conductors of circuits rated over 600 volts, nominal, shall not occupy the same equipment
wiring enclosure, cable, or raceway with conductors of circuits rated 600 volts, nominal, or less
13.8 is over, 480 is less


edit to add more.
Check out page 9 &10 for this counties position.

http://charmeck.org/mecklenburg/county/CodeEnforcement/Electrical/Documents/CAECAReport.pdf

 

[Dennis Alwon]

Conductors of circuits rated over 600 volts, nominal, shall not occupy the same equipment
wiring enclosure, cable, or raceway with conductors of circuits rated 600 volts, nominal, or less
13.8 is over, 480 is less

Correct so where are the conductors that are rated over 600v in the OP's post. We are talking about circuits under 600V-- what am I missing???

 

[Hv&Lv]

Correct so where are the conductors that are rated over 600v in the OP's post. We are talking about circuits under 600V-- what am I missing???

The title of the thread is Medium Voltage (13.8kV) and Low Voltage (480V or 208V) in same Pullbox
The conductors over 600 volts are the 13.8 kV primary lines.

I am assuming this is what he is talking about:

http://www.aps.com/aps_services/construction/construction_33.html

By the way, that guy operating the Bay-o-Net needs gloves and sleeves on. The picture is a liability IMO.

 

[Smart $]

...
Padmount transformers have really never been NEC compliant. Utilities use them and don't have to worry about the NEC.

Many electrical contractors that buy regular padmounted single phase transformers fail to realize that they aren't NEC compliant IMO.

The primary and the secondary are supposed to cross each other in the front of the XF. Adding some type of seperation is almost impossible in these transformers.

I have never worked on an MV to LV padmount that didn't have separated wire compartments...???

 

[Hv&Lv]

I have never worked on an MV to LV padmount that didn't have separated wire compartments...???

Look at the pic in the link above

 

[Dennis Alwon]

I saw the 480 and 208-- doh....:slaphead:

 

[Smart $]

Look at the pic in the link above

I did... but I can't tell the particulars just from looking at the pic... never seen an MV to LV padmount that looks like that, and I've seen and worked on plenty... not saying they don't exist... my day to learn something new, something old...

 

[Hv&Lv]

I have never worked on an MV to LV padmount that didn't have separated wire compartments...???

The three phase XF have the seperartor, the single phase do not.

For the three phase XF padmount, I don't see why he cant set the padmount on a vault with a sheet of metal for the bottom of the padmount and mount his conduits to the sheet of steel or aluminum plate.

I went the single phase way by mistake. We had a discussion about this very thing last Monday regarding padmounts installed by EC's.

That is a single phase padmount. Used all over.

 

[Hv&Lv]

Allow me to start over.:slaphead:

What the OP is suggesting, no.
Extend the conduits through the box the padmount will be setting on, at least to the plate that is in the middle, and I see no reason why it shouldn't be compliant.

 

[Smart $]

Allow me to start over.:slaphead:

What the OP is suggesting, no.
Extend the conduits through the box the padmount will be setting on, at least to the plate that is in the middle, and I see no reason why it shouldn't be compliant.

I'm wondering why the box in the first place? I'd prefer sheet steel on the bottom of the trannies.

 

[Haji]

Originally Posted by 300.3(C)
(2) Over 600 Volts, Nominal. Conductors of circuits rated
over 600 volts, nominal, shall not occupy the same equipment
wiring enclosure, cable, or raceway with conductors
of circuits rated 600 volts, nominal, or less unless otherwise
permitted in (C)(2)(a) through (C)(2)(e).
...
(a) through (e) do not apply.
...
Conductors having nonshielded insulation and operating
at different voltage levels shall not occupy the same
enclosure, cable, or raceway.

Perhaps, if the cables are of shielded type, it may be permissible.

 

[dwhensley]

So it looks like from section 300.3.C.2 there will need to be a divider since one of the sets of conductors will be 13.8kV.

Thanks for all the information!

 

[Smart $]

Perhaps, if the cables are of shielded type, it may be permissible.

That's only if all are over 600V.

 

[Hv&Lv]

I'm wondering why the box in the first place? I'd prefer sheet steel on the bottom of the trannies.

I'm assuming somewhere to splice the conductors.