# Secondary wiring method



## paulengr (Oct 8, 2017)

Is it a utility or not? You said service but then you said feeders. The rules are different.

Also have you looked at ring main units (RMUs)? Common in some countries and may solve your issue. They are inexpensive.


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## Panda (5 mo ago)

Not sure how much it matters for the scenarios in question but from the main switch gear we are feeding a CRU. This equipment is in the CRU stepping the main incoming supply from 600V to 120/208V. 
The ‘single service’ im referring to is the two tubs on the 120/208 side of the transformer. Two tubs that are joined together physically and electrically to make one single ‘service’ / ‘panel’ .

Perhaps panel is a better word to use here but i didnt want to confuse the fact that there is two tubs making up one panel. 

Also Im not looking for a piece of equipment to fix any problem, just opinions on the best practices of installing parallel feeders into two tubs.


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## SWDweller (Dec 9, 2020)

No offense but my "tubs" have water in them for bathing.

Using slang terms in any trade can back fire.

Your wording is clear as mud for me.


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## frankendodge (Oct 25, 2019)

We call them tubs up here. You call them cans down there. Clear picture in my head.

Your double tub should have feed through lugs on the bottom of one side of the guts. Ie lugs top and bottom.
If none of the guts have lugs rated for 2 wires you will have to change them.
Feed both parallel sets into the first tub, landed together on the same lugs(Probably the top lugs)
Take parallel cuts of the same wire between the two tubs(bottom feed through lugs).
You would never feed each bus separately and jump them together with a single conductor. The jumper between the panels needs to be rated for the same full ampacity as the incoming feeders. You are essentially extending the bus from the first tub to the second.

Hope that was clearer than mud. I need a coffee.


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## Panda (5 mo ago)

frankendodge said:


> We call them tubs up here. You call them cans down there. Clear picture in my head.
> 
> Your double tub should have feed through lugs on the bottom of one side of the guts. Ie lugs top and bottom.
> If none of the guts have lugs rated for 2 wires you will have to change them.
> ...


Thank you frankendodge, great response! 

i was starting to lose hope in the community for my first post, comments over terminology lead to toxic threads.


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## wcord (Jan 23, 2011)

Frankendodge's explanation is dead on.
You may not have the room to change the lugs to stacking 4 barrel if that is the way you want to proceed. In one end and out the other is the easiest way.
Also if I remember (somewhere in the code) you are not allowed to feed branch circuits thru one tub to the other. The only wiring allowed is the feeder.


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## CMP (Oct 30, 2019)

What happened to the transformer secondary protection in that scenario ?


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## frankendodge (Oct 25, 2019)

There would be none. Ocpd on the primary is considered to protect the secondary.
Pretty common setup in a shop or office.. with a 75kva 600-120/208 delta/wye transformer, fused at 90 on the primary, you would have a 225a main lug only panel unfused off the secondary.


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## hornetd (Oct 30, 2014)

frankendodge said:


> If none of the guts have lugs rated for 2 wires you will have to change them.


You can mount lug sets on insulated stand offs and run suitably sized conductors to the single lugs on each panel. Short copper jumpers to extend parallel Aluminum conductors sets might work just fine. I suggest that because the multi barrel lugs which are listed for that panel may not be available on a timely basis or the cost calculation might show a marked difference in price between the 2 approaches. 

Tom Horne


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