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Joined: Oct 2012
Posts: 13
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Hello all,

I'm upgrading a building for a machine shop with three new 225 amp 208/120 volt three phase 42 space panels.

I have over 50 machines to wire up and I'm running out of breaker space in the panels.In one section I have 29
machines that pull 16 amps under full load.I plan on putting them on 20 amp three pole breakers(They are being fed with #12 wire currently with a 30 amp fused disconnect(Allready exisiting on the machines)

I want every machine to have it's own breaker

Since I can only get 14 breakers per panel I'm thinking about adding a secondary panel or extension panel that will feed off of the bus bars from the 225 amp panels to create more space(not a sub).The feeder panel will have a 225 amp mainbreaker in it.While the secondary will be just busbars.I plan on using 3/0 as the jumpers from the main panel to the secondary panel.

All of the machines are not going to be used at one time so there's really no chance of an overload.

I'm pretty sure this is legal.

Any and all advice is appreciated.

Thanks




Joined: Apr 2002
Posts: 7,283
Likes: 3
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What you need, and I hope you already have is a 'main panel' with feed thru lugs, you will be OK.

Based on your OP above, is that how you are going from panel to panel?



John
Joined: Oct 2012
Posts: 13
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I'm feeding two 225 amp panels through the exisiting 400 amp switchgear from one 225kva transformer that allready exsists.Each panel will have a 225amp main protecting it at the switchgear.

I'm adding another 225kva transformer and adding two more 225 amp panels directly tapped from the transformer which will have mains built in the panels.

Three of the panels will have feed through lugs that will feed the secondary panels.

Thanks for the input

Joined: Apr 2002
Posts: 7,283
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Sounds like a plan!

BTW, Welcome to ECN!!


John
Joined: Oct 2012
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Thanks John for your input

Joined: Jun 2004
Posts: 1,273
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With motor control the NEC has permitted panels beyond 42 spaces for the longest time.

You might get quotes going both ways -- since there's some labor economy to using fewer parts.

Sometimes space, itself, is a hassel.



Tesla
Joined: Oct 2012
Posts: 13
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Where exactly does it state in the code that it permits more than 42 spaces in a panel when dealing with motor controls?

Thanks

Joined: Jul 2004
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The recent code has actually lifted all restrictions on breaker count (2008 I think)

I have not compared the pricing tho. Until they get into the supply chain in quantity, 2 panels may be cheaper of one is MLO.


Greg Fretwell
Joined: Jun 2004
Posts: 1,273
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Way, way back in the olden days...

There was a 42 circuit limit on LIGHTING PANELS. (Only)

In a footnote, it was mentioned that if there were no lighting (and appliance-- eg 1-phase recepticals and such) loads, the panel was not deemed a LIGHTING PANEL.

That little detail skipped by most of us commercial electricians because we almost never touched a panel that would not be deemed a LIGHTING panel.

If you dig out your ancient Square D catalogs -- and peruse their I Line offerings it will be quickly apparent that 54 circuit panels were an industrial option from... forever.

The ancient panels would often termed 'controlling' because the industrial firm would turn the big motor(s) on and off back at the panel.

This practice pre-dates modern notions of motor control.

In the beginning, even switches were expensive, and so reduced to the bare minimum.

This practice dates into the 19th Century. You can see such devices in museums, or old photos. It's hard to believe that knife switches were used to control high horsepower switches -- but they certainly did in the field of electric traction motors! (railroads)

BTW, the guys throwing those switches looked like Dr. Frankenstien -- of moviedom -- with his googles and massive insulating gloves, as he threw his 'monster' switch.

That practice is exactly where the movie crew got the whole idea.

=========

The actual wording never stated that it was permitted to exceed 42 spaces -- the wording was that LIGHTING panels were RESTRICTED to 42 spaces. It then went on to describe our common variety breaker panels as being just such restricted panels.

That restriction has been lifted because of the AFCI. It's now hopeless to construct a McMansion with only 42 spaces -- while meeting the code -- and using but one panel.

So, NEMA threw the limit away, and had the NEC agree.

BTW, there was a period when fuse boxes were restricted to just six fuses. Again, that limit was eliminated when it proved inconvenient. But, you will find simply no end of antique fuse boxes limited to just six.

With them, the residence could technically eliminate a MAINS cut-off. That's just how cheesy things were. (Think retrofit shacks.)

France, BTW, is still big into fuses, not circuit breakers. It's a sweet deal for fuse sales -- and fuse makers. Naturally, only French fuses will do.

Last edited by Tesla; 12/22/12 11:28 PM.

Tesla
Joined: Oct 2012
Posts: 13
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Thanks for the history lesson smile

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